A large-section loess tunnel support system and support construction method

Abstract

The invention discloses a large-section loess tunnel support system and a support construction method. The support system includes a tunnel advance support structure, a tunnel initial support structure and a tunnel secondary lining. The upper surface of the secondary lining of the tunnel invert is a horizontal plane and an invert backfill layer is arranged thereon. The method includes the following steps: 1. tunnel excavation and initial support; 2. secondary lining construction and invert backfill. The invention has reasonable design, simple construction, high construction efficiency and good use effect. The tunnel advance support structure, the tunnel initial support structure and the tunnel secondary lining form a joint support system, which provides stable and reliable support for large-section loess tunnels, and adjusts the upper surface of the secondary lining invert to a horizontal plane, which can effectively simplify the tunnel invert construction process, greatly improve the overall rigidity of the tunnel invert, improve the construction efficiency of the tunnel secondary lining, shorten the sealing time of the tunnel secondary lining, make the integrity of the tunnel secondary lining stronger, and have a better overall force effect.

Description

Technical Field

[0001] The invention belongs to the technical field of tunnel construction, and in particular relates to a large-section loess tunnel support system and a support construction method. Background Art

[0002] Loess refers to yellow silty soil sediments transported by wind during the Quaternary period in the geological era. The loess collapsibility coefficient (also called the collapsibility coefficient) is a mechanical parameter for evaluating the collapsibility of loess. It refers to the ratio of the difference in height before and after the soil sample is soaked in water to the original height of the soil sample under a certain pressure. The loess collapsibility coefficient is an important indicator for evaluating the collapsibility of loess and can be directly measured by experiments. According to the different loess collapsibility coefficients, loess is divided into collapsible loess and non-collapsed loess. Among them, non-collapsed loess refers to loess that does not collapse at all after being soaked in water under the action of its own weight and external load, or the loess collapsibility coefficient is less than 0.015. Non-collapsed loess is a special type of loess formed under arid climatic conditions. It is generally light yellow, grayish yellow or yellowish brown, with visible large pores and vertical joints. Collapsible loess refers to soil that undergoes significant additional deformation due to structural destruction of the soil after being soaked in water under the action of the self-weight stress of the overlying soil layer, or under the combined action of self-weight stress and additional stress. It is a special soil. Some miscellaneous fill soils are also collapsible. Loess widely distributed in Northeast, Northwest, Central my country and parts of East China is mostly collapsible. Through geological surveys, it was found that there are many types of loess in the loess strata, which can be divided into sandy loess (also called sandy loess), clay loess (also called clay loess or clay loess), etc. according to the material. Sandy loess refers to loess with a high content of fine sand particles, generally greater than 30%, and its essence is loess-like soil. Clay loess refers to loess with a fine sand content of less than 15% and a clay content of more than 25%, and its essence is loess-like soil. According to the geological age, it can be divided into new loess and old loess. Old loess is loess belonging to the Early and Middle Pleistocene in geological age and generally does not have collapsible properties. New loess refers to loess that is later than old loess. The new loess has a loose structure and generally has collapsible properties. New loess is mostly distributed on old loess.

[0003] Loess strata have geological characteristics such as porosity, vertical joint development, strong permeability and subsidence. When constructing a deep buried tunnel in a loess stratum where the upper covering layer of the tunnel is greater than 2.5 times the tunnel span (i.e. tunnel excavation width), the soil layer around the tunnel body will deform greatly due to the deep buried tunnel. This is especially true for tunnel excavation sections greater than 100m. 2 For large-section tunnels, the deformation of the soil layer around the tunnel is very large, and the excavation construction is very difficult.

[0004] When excavating a large-section loess tunnel, the step method is used for excavation. The step method refers to a construction method in which the upper section of the tunnel (upper step) is excavated first, and the lower section (lower step, also known as the upper tunnel body) is excavated after the upper step advances a certain distance, and the upper and lower steps are advanced simultaneously. Among them, the three-step excavation method (also known as the three-step method) refers to dividing the excavated tunnel into three steps: upper, middle, and lower for excavation. When the three-step method is used to excavate a large-section loess tunnel, due to the large deformation of the soil layer around the tunnel body, the construction is difficult and the construction risk is high. It is necessary to set up a reasonable support structure in time to prevent the collapse of the subsequent excavation area on the one hand, and to effectively support the excavated and formed tunnel body on the other hand to ensure construction safety. Nowadays, in the construction process of deep loess tunnels at home and abroad, due to the soft and porous loess geology, developed vertical joints, and creep effect, especially in the water-rich section, the surrounding rock is easily deformed after excavation due to the long exposure time. There are problems such as difficulty in deformation control and restricted construction progress. When using the traditional three-step method, three-step temporary invert method, three-step large arch foot temporary invert method, double side wall pilot method, CD method and other excavation construction methods, there are the following three problems: First, the invert is not closed into a ring in time, the surrounding rock is greatly deformed, and collapse accidents are prone to occur; second, the spatial section is divided, the narrow working space is not conducive to large-scale mechanical construction, and it cannot meet the needs of large-scale mechanized construction. There is a lot of interference between the various processes, and the various working surfaces cannot work synchronously, the efficiency is low, and the construction speed is slow; third, the use of temporary inverts has high engineering costs and there are great safety risks during the removal process. In addition, when the three-step method is used to excavate a large-section loess tunnel, due to the large number of excavation sections, the large-section tunnel section is divided into several small sections (divisions) for construction. During the excavation construction, a large number of temporary supports need to be erected and removed, the construction process is large, the process requirements for the connection of the support structures of each small section are high, the support is difficult, and the construction efficiency is low. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a large-section loess tunnel support system in view of the deficiencies in the above-mentioned prior art, which has a reasonable structural design, is easy to construct and has good use effect. The tunnel advance support structure, the tunnel initial support structure and the tunnel secondary lining form a joint support system to provide stable and reliable support for the large-section loess tunnel, and the upper surface of the secondary lining invert is adjusted to a horizontal plane, and the interface between the invert secondary lining and the invert filling layer is adjusted to a horizontal plane, which can effectively simplify the tunnel invert construction process and greatly improve the overall stiffness of the tunnel invert structure, further improve the construction efficiency of the tunnel secondary lining, shorten the sealing time of the tunnel secondary lining, make the tunnel secondary lining more integrated, and have a better overall force effect.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a large-section loess tunnel support system, characterized in that it includes a tunnel advance support structure for advanced support of the tunnel arch of the constructed loess tunnel, a tunnel initial support structure for initial support of the tunnel hole and a tunnel secondary lining arranged on the inner side of the tunnel initial support structure, the tunnel advance support structure is located above the tunnel initial support structure, the tunnel initial support structure and the tunnel secondary lining are both full-section support structures for full-section support of the tunnel hole of the constructed loess tunnel, the tunnel secondary lining is a reinforced concrete lining; the cross-sectional area of ​​the tunnel hole is greater than 100m 2 The tunnel is divided into an upper cave body, a middle cave body and a lower cave body from top to bottom; the upper cave body is a cave body formed by excavating the upper step of the loess tunnel from back to front, the middle cave body is a cave body formed by excavating the middle step of the loess tunnel from back to front, and the lower cave body is a cave body formed by excavating the lower step of the loess tunnel from back to front;

[0007] The initial support structure of the tunnel is divided into an arch wall initial support structure for initially supporting the arch wall of the tunnel hole and an initial support invert for initially supporting the bottom of the tunnel hole, and the secondary lining of the tunnel is divided into an arch wall secondary lining for supporting the arch wall of the tunnel hole and an invert secondary lining for supporting the bottom of the tunnel hole; the invert secondary lining is located above the initial support invert, an invert backfill layer is arranged on the invert secondary lining, the upper surface of the invert secondary lining is a horizontal plane, the bottoms of the left and right sides of the arch wall secondary lining are both horizontal planes, the arch wall secondary lining is supported on the invert secondary lining and the two are cast as one, and the invert backfill layer is a concrete filling layer;

[0008] The tunnel initial support structure includes a full-section support structure for full-section support of the tunnel, an arch wall mesh spraying support structure for initial support of the arch wall of the tunnel, and an inverted arch initial support structure for initial support of the bottom of the tunnel; the full-section support structure includes multiple full-section support frames arranged from back to front along the longitudinal extension direction of the tunnel, and the front and rear adjacent full-section support frames are fastened together by multiple longitudinal connecting steel bars, and the longitudinal connecting steel bars are arranged horizontally and along the longitudinal extension direction of the tunnel. The longitudinal connecting steel bars are arranged along the contour line of the full-section support frame; the shape of the full-section support frame is the same as the cross-sectional shape of the tunnel hole, and each of the full-section support frames is spliced ​​by an arch wall support arch frame for supporting the arch wall of the tunnel hole and a tunnel inverted arch support for supporting the bottom of the tunnel hole, the tunnel inverted arch support is located directly below the arch wall support arch frame and the two are located on the same tunnel cross section, and the tunnel inverted arch support and the arch wall support arch frame form a closed full-section support;

[0009] The arch wall mesh spraying support structure and the arch wall steel arch frame in the full-section support structure form an arch wall initial support structure, and the inverted arch initial support structure and the tunnel inverted arch support in the full-section support structure form an initial support inverted arch; the inverted arch initial support structure is a layer of inverted arch concrete spraying layer sprayed on the bottom of the tunnel hole, and the tunnel inverted arch support is fixed in the inverted arch concrete spraying layer;

[0010] The arch wall supporting arch frame is composed of an upper arch frame located in the upper cave body, two middle side supports symmetrically arranged below the left and right sides of the upper arch frame and both located in the middle cave body, and two lower side supports symmetrically arranged below the left and right sides of the upper arch frame and both located in the lower cave body. The tunnel inverted arch support is located in the lower cave body; each of the middle side supports is connected between the upper end of a lower side support and the upper arch frame; the left end of the tunnel inverted arch support is fastened to the bottom of one of the lower side supports, and the right end of the tunnel inverted arch support is fastened to the bottom of another lower side support;

[0011] An anchoring system is arranged outside the full-section support structure, and the anchoring system includes a plurality of anchoring groups arranged from back to front along the longitudinal extension direction of the tunnel, and one anchoring group is arranged outside each full-section support frame, and each full-section support frame and the anchoring group arranged thereon are arranged on the same cross section of the tunnel;

[0012] Each of the anchoring groups includes two groups of upper locking foot anchor pipes symmetrically arranged on the outer sides of the bottom of the left and right sides of the upper arch frame, two groups of middle locking foot anchor pipes symmetrically arranged on the left and right sides, and two groups of lower locking foot anchor pipes symmetrically arranged on the left and right sides. The two groups of upper locking foot anchor pipes, the two groups of middle locking foot anchor pipes and the two groups of lower locking foot anchor pipes are all arranged on the same cross section of the tunnel; a group of middle locking foot anchor pipes is arranged on the outer side of the bottom of each middle side bracket, and a group of lower locking foot anchor pipes is arranged on the outer side of the bottom of each lower side bracket; each group of upper locking foot anchor pipes includes two upper and lower upper locking foot anchor pipes arranged in parallel, each group of middle locking foot anchor pipes includes two upper and lower middle locking foot anchor pipes arranged in parallel, and each group of lower locking foot anchor pipes includes two upper and lower lower locking foot anchor pipes arranged in parallel; the upper locking foot anchor pipes, the middle locking foot anchor pipes and the lower locking foot anchor pipes are all locking foot anchor pipes that enter the soil layer around the tunnel from the inside to the outside, and the three gradually tilt downward from the inside to the outside.

[0013] The above-mentioned large-section loess tunnel support system is characterized in that: the excavation heights of the upper tunnel body and the middle tunnel body are both 3.5m to 4.5m, a tunnel bottom backfill layer is arranged behind the excavation surface of the lower tunnel body, the tunnel bottom backfill layer is located in the lower tunnel body, and the tunnel bottom backfill layer is located on the initial support invert; the tunnel bottom backfill layer is a temporary mobile platform for the wet spraying manipulator to move forward and backward.

[0014] The above-mentioned large-section loess tunnel support system is characterized in that: the tunnel advance support structure includes a plurality of advance small-duct grouting support structures for advance support of the tunnel arch from back to front along the longitudinal extension direction of the tunnel; the structures of the plurality of advance small-duct grouting support structures are the same, and the overlap length between two adjacent advance small-duct grouting support structures is not less than 0.5m;

[0015] Each of the advanced small-duct grouting support structures includes a plurality of small grouting ducts drilled from back to front into the soil in front of the tunnel face and a small-duct guide frame for guiding the plurality of small grouting ducts, and the plurality of small grouting ducts are arranged from left to right on the same tunnel section along the arch contour line of the upper tunnel body; the structures and sizes of all the small grouting ducts in each of the advanced small-duct grouting support structures are the same; the small-duct guide frame is an upper arch frame, and the small-duct guide frame is provided with a plurality of guide holes for guiding the small grouting ducts, and the plurality of guide holes are arranged from left to right along the arch contour line of the upper tunnel body.

[0016] At the same time, the present invention also discloses a large-section loess tunnel support construction method with simple steps, reasonable design, simple construction and good use effect, characterized in that the method comprises the following steps:

[0017] Step 1: Tunnel excavation and initial support: excavate the constructed loess tunnel from back to front along the longitudinal extension direction of the tunnel, and simultaneously perform initial support on the excavated tunnel hole from back to front during the excavation process to obtain the initial support structure of the tunnel formed by construction;

[0018] Step 2, secondary lining construction and backfilling of the invert: During the initial support of the excavated tunnel from back to front in step 1, the secondary lining of the tunnel is constructed from back to front along the longitudinal extension direction of the tunnel on the inner side of the completed initial support structure of the tunnel;

[0019] When constructing the secondary lining of the tunnel from back to front, the secondary lining of the inverted arch is constructed from back to front on the completed initial support inverted arch, so as to obtain the completed secondary lining of the inverted arch; when constructing the secondary lining of the inverted arch from back to front, the secondary lining of the arch wall is constructed from back to front on the completed secondary lining of the inverted arch, and the constructed secondary lining of the arch wall is connected with the secondary lining of the inverted arch located therebelow as a whole, so as to obtain the completed secondary lining of the tunnel;

[0020] In this step, during the construction of the secondary lining of the invert arch from back to front, the backfill layer of the invert arch is constructed on the completed secondary lining of the invert arch from back to front along the longitudinal extension direction of the tunnel.

[0021] The above construction method is characterized in that: when performing tunnel excavation and initial support in step 1, the following steps are included:

[0022] Step B1, excavation of the upper tunnel and initial support: excavating the upper tunnel of the constructed loess tunnel from back to front along the longitudinal extension direction of the tunnel;

[0023] During the excavation of the upper cave, the upper cave arch is supported by spraying from back to front, and the upper arch frame is installed from back to front in the excavated upper cave, completing the excavation and initial support construction process of the upper cave;

[0024] Step B2, excavation of the middle cavern and initial support: During the process of excavation of the upper cavern and initial support in step B1, the middle cavern is excavated from the back to the front along the longitudinal extension direction of the tunnel below the excavated upper cavern;

[0025] During the excavation of the middle cave, mesh spraying support is performed on the left and right sides of the excavated middle cave from back to front, and at the same time, middle side supports are installed on the left and right sides of the excavated middle cave from back to front, and each of the middle side supports is fastened and connected to the upper arch frame in step B1 as a whole, completing the excavation and initial support construction process of the middle cave;

[0026] In this step, the excavation surface of the middle cave body is located behind the excavation surface of the upper cave body and the horizontal distance between the two is 4m to 6m;

[0027] Step B3, excavation of the lower cave and initial support: During the excavation of the middle cave and initial support in step B2, the lower cave is excavated from the back to the front along the longitudinal extension direction of the tunnel below the excavated middle cave;

[0028] During the excavation of the lower cave body, mesh spraying support is performed on the left and right sides of the excavated lower cave body from back to front, and during the mesh spraying support process, lower side supports are installed on the left and right sides of the excavated lower cave body from back to front, and each of the lower side supports is fastened and connected to the middle side support in step B2 as a whole; at the same time, a tunnel invert support is installed at the bottom of the lower cave body from back to front, and the installed tunnel invert support is fastened and connected to the lower side supports installed on the left and right sides of the lower cave body as a whole; during the installation of the tunnel invert support, a layer of concrete is sprayed on the bottom of the tunnel from back to front to form an invert concrete spraying layer, and the tunnel invert support is fixed in the invert concrete spraying layer, thereby completing the excavation and initial support construction process of the lower cave body;

[0029] In this step, the excavation surface of the lower cave body is located behind the excavation surface of the middle cave body and the horizontal distance between the two is 4m to 6m;

[0030] In this step, during the process of excavating the lower cave body from back to front, an excavated tunnel hole is obtained; after mesh spraying support is performed on the left and right sides of the excavated lower cave body from back to front, the constructed arch wall mesh spraying support structure is obtained; the arch wall mesh spraying support structure is connected to the invert arch concrete spraying layer.

[0031] The above construction method is characterized in that: the multiple full-section support frames in the full-section support structure are evenly arranged, and the spacing between the two adjacent full-section support frames is L, wherein the value range of L is 0.5m to 1m;

[0032] When the upper cave is excavated and initially supported in step B1, the excavation footage of the upper cave is 2L to 3L;

[0033] When the middle cave is excavated and initially supported in step B2, the excavation footage of the middle cave is 2L to 3L;

[0034] When the lower cave is excavated and initially supported in step B3, the excavation depth of the lower cave is 2L to 3L.

[0035] The above construction method is characterized in that: the arch wall mesh spraying support structure comprises an arch wall steel mesh mounted on the tunnel arch wall and an arch wall concrete spraying layer sprayed on the tunnel arch wall, the arch wall steel mesh is fixed on the arch wall steel arch frame, and the arch wall steel mesh and the arch wall steel arch frame are both fixed in the arch wall concrete spraying layer;

[0036] When the mesh spraying support is performed on the upper cave arch from back to front in step B1, the arch steel mesh is first mounted on the upper cave arch from back to front, and the upper arch frame is installed in the upper cave from back to front, and the mounted arch steel mesh is fastened to the installed upper arch frame; then a layer of concrete is sprayed on the inner wall of the excavated upper cave from back to front to form an arch concrete spraying layer, and the mounted arch steel mesh and the installed upper arch frame are both fixed in the arch concrete spraying layer, thus completing the excavation and initial support construction process of the upper cave;

[0037] When mesh spraying support is performed on the left and right sides of the middle cave body from back to front in step B2, firstly, the middle steel mesh is mounted on the left and right sides of the middle cave body from back to front, and the middle side brackets are installed on the left and right sides of the middle cave body from back to front, and the mounted middle steel mesh is fastened to the installed middle side brackets, and the mounted middle steel mesh is fastened to the arch steel mesh described in step B1; then, a layer of concrete is sprayed on the inner walls of the left and right sides of the middle cave body from back to front to form a middle concrete spraying layer, and the middle concrete spraying layer is connected to the arch concrete spraying layer described in step B1, and the mounted middle steel mesh and the installed middle side brackets are fixed in the middle concrete spraying layer, and the excavation and initial support construction process of the middle cave body is completed;

[0038] When mesh spraying support is performed on the left and right sides of the lower cave body from back to front in step B3, firstly, the lower steel mesh is respectively mounted on the left and right sides of the lower cave body from back to front, and the lower side brackets are respectively installed on the left and right sides of the lower cave body from back to front, and the mounted lower steel mesh is fastened and connected with the installed lower side brackets, and the mounted lower steel mesh is fastened and connected with the middle steel mesh described in step B2; then, a layer of concrete is sprayed on the inner walls of the left and right sides of the lower cave body from back to front to form a lower concrete spraying layer, and the lower concrete spraying layer is connected with the middle concrete spraying layer described in step B2, and the mounted lower steel mesh and the installed lower side brackets are both fixed in the lower concrete spraying layer, completing the mesh spraying support process on the left and right sides of the lower cave body, and obtaining the constructed and formed arch wall mesh spraying support structure;

[0039] The arch steel mesh described in step B1, the middle steel mesh described in step B2 and the lower steel mesh described in step B3 are connected from top to bottom to form the arch wall steel mesh, and the arch concrete spraying layer described in step B1, the middle concrete spraying layer described in step B2 and the lower concrete spraying layer described in step B3 are connected from top to bottom to form the arch wall concrete spraying layer;

[0040] The arch wall concrete spraying layer and the invert arch concrete spraying layer are both concrete layers sprayed by a wet spraying manipulator.

[0041] The above construction method is characterized in that: the excavation footage of the upper cave body in step B1, the excavation footage of the middle cave body in step B2 and the excavation footage of the lower cave body in step B3 are all the same;

[0042] During tunnel excavation and initial support in step 1, the wet spraying manipulator moves forward in multiple steps along the longitudinal extension direction of the tunnel through the backfill soil layer at the bottom of the tunnel, and each forward movement distance is the same as the excavation footage of the lower cave body;

[0043] Each time the wet spraying manipulator moves forward to a position, the length of the excavated lower cave body in front of the backfill soil layer at the bottom of the tunnel is the same as the excavation footage of the lower cave body. At this time, the excavated lower cave body in front of the backfill soil layer at the bottom of the tunnel is the currently excavated lower cave body.

[0044] After the wet spraying manipulator moves forward to its position each time, the wet spraying manipulator is first used to spray the lower concrete spraying layer and the invert concrete spraying layer in the currently excavated lower cave body from back to front, and the excavation and initial support construction process of the currently excavated lower cave body is completed at the same time; after the excavation and initial support construction process of the currently excavated lower cave body is completed, a tunnel bottom backfill soil layer is constructed on the initial support invert that has been constructed and formed in the currently excavated lower cave body. At this time, the tunnel bottom backfill soil layer constructed is a mobile platform for the wet spraying manipulator to move forward next time;

[0045] After the lower concrete spraying layer and the invert concrete spraying layer in the currently excavated lower cave body are sprayed, the wet spraying manipulator is used to spray concrete from back to front on the upper cave body and the middle cave body that are located in front of the currently excavated lower cave body and have been excavated and formed at this time, and the excavation and initial support construction process of the upper cave body and the middle cave body located in front of the currently excavated lower cave body is completed at the same time;

[0046] After the concrete spraying in the upper and middle caverns that are located in front of the currently excavated lower cavern and have been excavated and formed at this time is completed, the wet spraying manipulator moves forward for the next time.

[0047] The above construction method is characterized in that: the left and right short side walls of the tunnel secondary lining are lining segments at the bottom of the left and right sides of the arch wall secondary lining;

[0048] When the secondary lining of the arch wall is constructed in step 2, the secondary lining trolley is used to construct the secondary lining of the arch wall from the back to the front along the longitudinal extension direction of the tunnel;

[0049] When the secondary lining construction and the backfilling of the invert are carried out in step 2, the construction progress of the secondary lining of the invert is faster than the construction progress of the secondary lining of the arch wall.

[0050] The above construction method is characterized in that: when the secondary lining construction and invert backfilling are carried out in step 2, the construction progress of the invert backfill layer is the same as the construction progress of the secondary lining of the invert;

[0051] The constructed loess tunnel is divided into multiple tunnel segments from back to front along the longitudinal extension direction of the tunnel;

[0052] The invert backfill layer and the invert secondary lining form a tunnel invert and backfill structure. When the secondary lining construction and invert backfill are carried out in step 2, a movable invert trestle is used to construct the tunnel invert and backfill structure from back to front;

[0053] When the movable invert trestle is used to construct the tunnel invert and backfill structure from back to front, the tunnel invert and backfill construction are respectively carried out from back to front on the multiple tunnel sections of the constructed loess tunnel; the tunnel invert and backfill construction methods of the multiple tunnel sections are the same;

[0054] When performing tunnel invert and backfill construction on any of the tunnel sections of the constructed loess tunnel, the process is as follows:

[0055] Step A1: Horizontally moving the trestle forward: along the longitudinal extension direction of the tunnel, the movable inverted arch trestle is horizontally moved forward to the construction position of the tunnel segment currently under construction;

[0056] Step A2, pouring of secondary lining of the invert: using the movable invert trestle moved into place in step A1, concrete is poured from bottom to top for the secondary lining of the invert of the tunnel segment currently under construction;

[0057] Step A3, backfilling the invert: after the secondary lining pouring of the invert is completed in step A2, the movable invert trestle moved into place in step A1 is used to pour concrete on the backfill layer of the invert of the tunnel segment currently under construction from bottom to top;

[0058] After the concrete poured in step A2 and step A3 has finally set, the tunnel invert and backfill construction process of the tunnel section currently under construction is completed;

[0059] Step A4, returning to step A1, performing tunnel invert and backfill construction on one of the tunnel segments.

[0060] Compared with the prior art, the present invention has the following advantages:

[0061] 1. The support system has a reasonable structural design, simple construction and low investment cost. It consists of a tunnel advance support structure for advanced support of the tunnel arch of the constructed loess tunnel, a tunnel initial support structure for full-section support of the tunnel, and a tunnel secondary lining to form a joint support system, which can provide stable and reliable support for large-section loess tunnels.

[0062] 2. The full-section support frame used can provide full-section support for the tunnel, and the support is stable and reliable. The full-section support frame is assembled from an arch wall support arch frame and a tunnel invert arch support. The arch wall support arch frame is assembled from an upper arch frame, two middle side supports and two lower side supports. It can be easily assembled during actual tunnel excavation to meet the block support requirements of the tunnel section, so that the initial support of the upper cave body is not affected by the initial support construction in the middle cave body and the lower cave body, and the initial support of the middle cave body is not affected by the initial support construction in the lower cave body. The initial support of the upper cave body and the middle cave body is constructed immediately after the excavation is completed, so the support is timely and stable. In addition, the tunnel has not been fully excavated at this time, so the supporting stability of the initial support structure in the upper cave body and the middle cave body of the tunnel is further guaranteed, and the initial support process in the upper cave body and the middle cave body of the tunnel is easier to carry out, and the support is more powerful, which is more conducive to the safety of tunnel construction.

[0063] 3. The anchoring system is used to fix the tunnel surrounding rock in full section, further improving the initial support stability. In addition, the anchoring system is connected to the full section support frame as a whole, further improving the overall stability and making the construction simple.

[0064] 4. The advance support adopts an advance small-duct grouting support structure, which is simple to construct and has high construction efficiency. It can effectively ensure the advance support strength and support effect of large-section loess tunnels and effectively limit the deformation of the arch of the loess tunnel.

[0065] 5. The upper surface of the secondary lining invert is adjusted to a horizontal plane, and the interface between the secondary lining of the invert and the invert filling layer is adjusted to a horizontal plane. The construction is simple and efficient. The invert filling layer and the secondary lining of the invert can be poured at the same time, which can greatly simplify the construction process of the secondary lining of the invert and the filling layer of the invert. The concrete of the secondary lining of the invert and the filling layer of the invert will not be mixed together, which can effectively ensure the construction quality of the secondary lining of the invert and the filling layer of the invert, and avoid the problems such as the inability to ensure the construction quality of the secondary lining of the invert and the filling layer of the invert due to different concrete grades. At the same time, the upper surface of the secondary lining of the invert is a horizontal plane. During the concrete pouring process, it is not necessary to ensure the arc shape of the secondary lining of the invert, and it is not necessary to use an arc formwork. The pouring is convenient and simple, and the pouring is simple, and the construction quality of the secondary lining of the invert is easy to ensure.

[0066] 6. The secondary lining structure of the tunnel is reasonable. The secondary lining of the tunnel is connected by the secondary lining of the inverted arch and the secondary lining of the arch wall. The middle arc-shaped part inside the secondary lining of the inverted arch is optimized to a horizontal plane. The optimized secondary lining of the inverted arch greatly improves the overall rigidity of the tunnel inverted arch structure, and there is no need to install arc-shaped templates during construction. The concrete vibration is simple and the vibration quality is easy to control. The appearance size and construction quality of the secondary lining of the inverted arch are easier to control, and the construction efficiency of the tunnel inverted arch can be greatly improved. The closure time of the secondary lining of the tunnel is greatly shortened, and the inverted arch concrete is easy to vibrate without the interference of the arc-shaped template, and the concrete quality is greatly improved. At the same time, the existing secondary lining arch wall lining is connected with two short side walls to form an integral lining (i.e., arch wall secondary lining) for construction, and a secondary lining trolley is used to construct the arch wall secondary lining. The one-time construction can further improve the construction efficiency of the tunnel secondary lining, speed up the closing time of the tunnel secondary lining, shorten the sealing time of the tunnel secondary lining, further improve the structural stability of the constructed loess tunnel, and effectively reduce the construction joints in the tunnel secondary lining, so that the integrity of the tunnel secondary lining is stronger and the overall stress effect is better.

[0067] 7. The adopted advanced small-duct grouting support structure is reasonably designed, easy to construct and has good use effect. It can effectively reinforce the tunnel arch and form a stable arch wall bearing ring, which can effectively improve the self-stabilizing ability of the rock formation around the tunnel body, effectively save construction costs and construction period, and at the same time, the construction equipment is simple, and the initial support construction is carried out in time after the tunnel construction, and the process is closely connected. In addition, the disturbance to the surrounding soil layer during the support process is small, the construction cost is low, and it can effectively solve the problems of compressive deformation and settlement of the tunnel arch caused by the horizontal pressure generated after the tunnel excavation, and can provide stable support for the tunnel arch.

[0068] 8. The adopted support method has simple steps, reasonable design, simple construction and good use effect. A three-step excavation method is adopted and the distances between the middle tunnel excavation surface and the upper tunnel excavation surface and the lower tunnel excavation surface are limited to realize short step or micro step excavation of large-section tunnels and ensure the stability of the excavated tunnel. In addition, a full-section support frame structure tunnel is used for layered support, and an anchoring system is used to reinforce the outer side of the tunnel as a whole to ensure the structural stability of the large-section loess tunnel and ensure construction safety. At the same time, the backfill soil layer at the bottom of the tunnel behind the lower tunnel excavation surface is used as a temporary mobile platform for the wet spraying manipulator to move forward and backward, and the excavation height of the upper tunnel and the middle tunnel is limited to achieve the purpose of concrete spraying by the wet spraying manipulator during the excavation process, which can effectively speed up the construction progress and enable the initial support to be quickly closed into a ring, further ensuring the stability of the tunnel structure. The construction is simple, the construction speed is fast, and the construction process is safe and reliable. At the same time, the secondary lining structure of the tunnel is reasonably designed, the construction method is simple, and the construction quality is easy to control, which can greatly reduce the construction cost, save the construction period, and ensure the construction safety. From the above content, it can be seen that the adopted support method has the characteristics of safety and reliability, high degree of mechanization, fast construction speed, low labor intensity, early construction period, and cost saving through the three-step construction method. According to the geological characteristics of the loess tunnel, the lower step and the initial support of the invert are constructed at the same time, which can ensure that the ring is closed in the shortest time, prevent the surrounding rock from deforming too much, and ensure the safety of construction; and simplify the construction method to prevent interference between the various processes, which can maximize the satisfaction of mechanized construction and reduce labor intensity. The use of spatial full-section flow construction can improve construction efficiency and reduce engineering costs. In addition, the cancellation of the temporary invert reduces the engineering cost and avoids the safety risks in the process of removing the temporary invert.

[0069] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Figure 1 It is a schematic diagram of the cross-sectional structure of the support system of the present invention.

[0071] Figure 2 It is a schematic diagram of the longitudinal section structure of the support system of the present invention.

[0072] Figure 3 It is a schematic diagram of the construction status of the wet spraying robot of the present invention.

[0073] Figure 4 It is a schematic diagram of the cross-sectional structure of the lower inner part of the tunnel of the present invention.

[0074] Figure 5 The present invention is a flowchart of a method for supporting and constructing a loess tunnel using the present invention.

[0075] Figure 6 It is a structural schematic diagram of the front template of the present invention.

[0076] Description of reference numerals:

[0077] 1—tunnel hole; 1-1—upper cave body; 1-2—middle cave body;

[0078] 1-3—lower cavern; 2—tunnel invert support; 2-1—upper arch support;

[0079] 5—middle side support; 6—lower side support; 7—backfill soil layer at the bottom of the tunnel;

[0080] 8—upper locking foot anchor pipe; 9—middle locking foot anchor pipe; 10—lower locking foot anchor pipe;

[0081] 12—primary supporting structure of arch wall; 13—primary supporting invert; 14—secondary lining of arch wall;

[0082] 15—inverted arch secondary lining; 16—inverted arch backfill layer; 17—movable inverted arch trestle;

[0083] 18—low side wall; 19—arch wall concrete spraying layer;

[0084] 20—inverted arch concrete spraying layer; 21—wet spraying manipulator; 22—grouting small conduit;

[0085] 23—water ditch and cable trough; 24—side formwork; 25—front formwork. DETAILED DESCRIPTION

[0086] like Figure 1 , Figure 2 The large-section loess tunnel support system shown in the figure comprises a tunnel advance support structure for providing advance support to the arch of the tunnel hole 1 of the constructed loess tunnel, a tunnel initial support structure for providing initial support to the tunnel hole 1, and a tunnel secondary lining arranged inside the tunnel initial support structure, wherein the tunnel advance support structure is located above the tunnel initial support structure, the tunnel initial support structure and the tunnel secondary lining are both full-section support structures for providing full-section support to the tunnel hole of the constructed loess tunnel 1, and the tunnel secondary lining is a reinforced concrete lining; the cross-sectional area of ​​the tunnel hole 1 is greater than 100m 2The tunnel 1 is divided into an upper cavern 1-1, a middle cavern 1-2 and a lower cavern 1-3 from top to bottom; the upper cavern 1-1 is a cavern formed by excavating the upper step of the loess tunnel from back to front, the middle cavern 1-2 is a cavern formed by excavating the middle step of the loess tunnel from back to front, and the lower cavern 1-3 is a cavern formed by excavating the lower step of the loess tunnel from back to front;

[0087] The tunnel initial support structure is divided into an arch wall initial support structure 12 for initial support of the arch wall of the tunnel hole 1 and an initial support invert 13 for initial support of the bottom of the tunnel hole 1. The tunnel secondary lining is divided into an arch wall secondary lining 14 for supporting the arch wall of the tunnel hole 1 and an invert secondary lining 15 for supporting the bottom of the tunnel hole 1; the invert secondary lining 15 is located above the initial support invert 13, and an invert backfill layer 16 is arranged on the invert secondary lining 15. The upper surface of the invert secondary lining 15 is a horizontal plane, and the bottoms of the left and right sides of the arch wall secondary lining 14 are both horizontal planes. The arch wall secondary lining 14 is supported on the invert secondary lining 15 and the two are cast as one body. The invert backfill layer 16 is a concrete filling layer, see Figure 4 ;

[0088] The tunnel initial support structure includes a full-section support structure for full-section support of the tunnel hole 1, an arch wall mesh spraying support structure for initial support of the arch wall of the tunnel hole 1, and a An initial support structure for an inverted arch for initial support at the bottom; the full-section support structure includes a plurality of full-section support frames arranged from back to front along the longitudinal extension direction of the tunnel, and the front and rear adjacent full-section support frames are fastened together by a plurality of longitudinal connecting steel bars, the longitudinal connecting steel bars are arranged horizontally and along the longitudinal extension direction of the tunnel, and the plurality of longitudinal connecting steel bars are arranged along the contour line of the full-section support frame; the shape of the full-section support frame is the same as the cross-sectional shape of the tunnel hole 1, and each of the full-section support frames is spliced ​​by an arch wall supporting arch frame for supporting the arch wall of the tunnel hole 1 and a tunnel inverted arch support 2 for supporting the bottom of the tunnel hole 1, the tunnel inverted arch support 2 is located directly below the arch wall supporting arch frame and the two are located on the same tunnel cross section, and the tunnel inverted arch support 2 and the arch wall supporting arch frame form a closed full-section support;

[0089] The arch wall mesh spraying support structure and the arch wall steel arch frame in the full-section support structure form an arch wall initial support structure 12, and the inverted arch initial support structure and the tunnel inverted arch support 2 in the full-section support structure form an initial support inverted arch 13; the inverted arch initial support structure is a layer of inverted arch concrete spraying layer 20 sprayed at the bottom of the tunnel hole 1, and the tunnel inverted arch support 2 is fixed in the inverted arch concrete spraying layer 20;

[0090] The arch wall supporting arch frame is composed of an upper arch frame 2-1 located in the upper cave body 1-1, two middle side brackets 5 symmetrically arranged below the left and right sides of the upper arch frame 2-1 and both located in the middle cave body 1-2, and two lower side brackets 6 symmetrically arranged below the left and right sides of the upper arch frame 2-1 and both located in the lower cave body 1-3. The tunnel inverted arch support 2 is located in the lower cave body 1-3; each of the middle side brackets 5 is connected between the upper end of one of the lower side brackets 6 and the upper arch frame 2-1; the left end of the tunnel inverted arch support 2 is fastened to the bottom of one of the lower side brackets 6, and the right end of the tunnel inverted arch support 2 is fastened to the bottom of another of the lower side brackets 6;

[0091] An anchoring system is arranged outside the full-section support structure, and the anchoring system includes a plurality of anchoring groups arranged from back to front along the longitudinal extension direction of the tunnel, and one anchoring group is arranged outside each full-section support frame, and each full-section support frame and the anchoring group arranged thereon are arranged on the same cross section of the tunnel hole 1;

[0092] Each of the anchoring groups includes two groups of upper locking foot anchor pipes 8 symmetrically arranged on the outer sides of the bottom of the left and right sides of the upper arch frame 2-1, two groups of middle locking foot anchor pipes 9 symmetrically arranged on the left and right sides, and two groups of lower locking foot anchor pipes 10 symmetrically arranged on the left and right sides. The two groups of upper locking foot anchor pipes 8, the two groups of middle locking foot anchor pipes 9 and the two groups of lower locking foot anchor pipes 10 are all arranged on the same cross section of the tunnel hole 1; a group of middle locking foot anchor pipes 9 is arranged on the outer side of the bottom of each of the middle side brackets 5, and a group of lower locking foot anchor pipes 10 is arranged on the outer side of the bottom of each of the lower side brackets 6; each group of upper locking foot anchor pipes 8 includes two upper and lower upper locking foot anchor pipes 8 arranged in parallel, and each group of middle locking foot anchor pipes 9 Each of the above-mentioned lower locking foot anchor pipes 10 includes two parallel middle locking foot anchor pipes 9 arranged in upper and lower directions. Each group of the above-mentioned lower locking foot anchor pipes 10 includes two parallel lower locking foot anchor pipes 10 arranged in upper and lower directions. The upper locking foot anchor pipe 8, the middle locking foot anchor pipe 9 and the lower locking foot anchor pipe 10 are all locking foot anchor pipes that enter the soil layer around the tunnel hole 1 from the inside to the outside and the three of them gradually tilt downward from the inside to the outside.

[0093] The excavation heights of the upper cave body 1-1 and the middle cave body 1-2 are both 3.5m to 4.5m. A tunnel bottom backfill soil layer 7 is arranged behind the excavation surface of the lower cave body 1-3. The tunnel bottom backfill soil layer 7 is located in the lower cave body 1-3. Figure 3 The backfill soil layer 7 at the bottom of the tunnel is a temporary mobile platform for the wet spraying manipulator 21 to move forward and backward. At the same time, the backfill soil layer 7 at the bottom of the tunnel can also further improve the structural stability of the bottom of the tunnel hole 1.

[0094] In this embodiment, the upper surface of the tunnel bottom backfill soil layer 7 is a horizontal plane, and the upper surface of the tunnel bottom backfill soil layer 7 is flush with the upper surface of the invert backfill layer 16 .

[0095] In this embodiment, the upper arch frame 2-1 and the middle side bracket 5, the middle side bracket 5 and the lower side bracket 6, and the lower side bracket 6 and the tunnel inverted arch bracket 2 are all fixedly connected by connecting bolts. Both ends of the upper arch frame 2-1, both ends of the middle side bracket 5, both ends of the lower side bracket 6, and both ends of the tunnel inverted arch bracket 2 are provided with connecting steel plates for installing the connecting bolts.

[0096] In order to ensure processing quality and improve on-site construction efficiency, the full-section support frame is centrally processed and distributed in a factory, and meets the requirement of being delivered to all work surfaces within half an hour.

[0097] During actual construction, the excavation height of the tunnel hole 1 is 11m to 15m, and the excavation width of the tunnel hole 1 is 10m to 15m. In addition, the constructed tunnel is a deep buried tunnel with a burial depth greater than 50m.

[0098] In this embodiment, the excavation height of the tunnel hole 1 is 12m, the height of the upper cave body 1-1 (i.e., the upper step height) is 4m, and the height of the middle cave body 1-2 (i.e., the middle step height) is 3.5m. In the actual construction process, the excavation height of the tunnel hole 1, the height of the upper cave body 1-1, and the height of the middle cave body 1-2 can be adjusted accordingly according to specific needs.

[0099] To ensure excavation safety, the upper cave 1-1 is excavated by reserving core soil in the middle, and the top clearance height of the core soil in the upper cave 1-1 is 1.5m to 1.8m. Whether to reserve core soil during the excavation of the middle cave 1-2 and the lower cave 1-3 depends on the stability of the tunnel face.

[0100] The arch wall mesh spraying support structure includes an arch wall steel mesh hung on the arch wall of the tunnel hole 1 and an arch wall concrete spraying layer 19 sprayed on the arch wall of the tunnel hole 1. The arch wall steel mesh is fixed on the arch wall steel arch frame, and the arch wall steel mesh and the arch wall steel arch frame are both fixed in the arch wall concrete spraying layer 19.

[0101] In this embodiment, the arch wall concrete spraying layer 19 and the invert arch concrete spraying layer 20 are both concrete layers sprayed by a wet spraying manipulator 21 .

[0102] During actual construction, the horizontal distance between the rear end of the tunnel bottom backfill soil layer 7 and the excavation surface of the upper cave body 1-1 is no more than 45m.

[0103] During the actual excavation of the lower cave body 1-3, the excavated lower cave body 1-3 is promptly supported initially, and an initial support invert 13 is obtained; after the initial support of the lower cave body 1-3 is completed, the tunnel bottom backfill soil layer 7 is promptly backfilled on the initial support invert 13. When backfilling the tunnel bottom backfill soil layer 7, the tunnel slag (i.e., slag) in the lower cave body 1-3 is used to backfill the tunnel bottom backfill soil layer 7.

[0104] During the excavation of the upper cave body 1-1, the middle cave body 1-2 and the lower cave body 1-3, an excavator is used to load the cave slag formed by the excavation into a dump truck, and then the dump truck is used to transport the cave slag. When the cave slag formed by the excavation is transported, it is also necessary to reserve the cave slag for backfilling the backfill soil layer 7 at the bottom of the tunnel, and the reserved cave slag is placed on the inner side of the lower cave body 1-3 so as to backfill the backfill soil layer 7 at the bottom of the tunnel in time.

[0105] In this embodiment, the plurality of full-section support frames in the full-section support structure are evenly arranged, and the distance between two adjacent full-section support frames is L, where the value range of L is 0.5m to 1m.

[0106] During actual construction, the spacing between the two adjacent full-section support frames (i.e., the value of L) can be adjusted accordingly according to specific needs.

[0107] To ensure the anchoring effect, in this embodiment, the angles between the middle locking foot anchor tube 9 and the lower locking foot anchor tube 10 and the vertical plane are both 45°.

[0108] The upper arch frame 2-1 is in an arc shape, and the angle between each of the upper locking foot anchor tubes 8 and the arch frame section of the upper arch frame 2-1 at the position where it is connected is 45°; the arch frame section is a plane that is perpendicular to the outer contour line of the upper arch frame 2-1. Among them, the arch frame section of the upper arch frame 2-1 at the position where each of the upper locking foot anchor tubes 8 is connected is a plane that is perpendicular to the outer contour line of the upper arch frame 2-1 at the position where the upper locking foot anchor tube 8 is connected.

[0109] In this embodiment, the arch wall support arch frame and the tunnel invert arch support 2 are both grid steel frames.

[0110] In addition, a foam aluminum pad or a concrete pad is installed at the bottom of each lower side bracket 6 to control displacement and settlement.

[0111] like Figure 5 As shown, the constructed loess tunnel is excavated from back to front along the longitudinal extension direction of the tunnel, and during the excavation process, the excavated tunnel hole 1 is initially supported from back to front to obtain the constructed initial support structure of the tunnel; during the initial support of the excavated tunnel hole 1 from back to front, the secondary lining of the tunnel is constructed from back to front in the completed initial support structure of the tunnel.

[0112] like Figure 1-Figure 6 A construction method for supporting a loess tunnel using a large-section loess tunnel support system is shown, comprising the following steps:

[0113] Step 1, tunnel excavation and initial support: excavate the constructed loess tunnel from back to front along the longitudinal extension direction of the tunnel, and during the excavation process, initially support the excavated tunnel hole 1 from back to front to obtain the initial support structure of the tunnel;

[0114] Step 2, secondary lining construction and backfilling of the invert: During the initial support of the excavated tunnel 1 from back to front in step 1, the secondary lining of the tunnel is constructed from back to front along the longitudinal extension direction of the tunnel on the inner side of the completed initial support structure of the tunnel;

[0115] When constructing the secondary lining of the tunnel from back to front, the secondary lining 15 of the inverted arch is constructed from back to front on the completed initial support inverted arch 13, so as to obtain the formed secondary lining 15 of the inverted arch; when constructing the secondary lining 15 of the inverted arch from back to front, the secondary lining 14 of the arch wall is constructed from back to front on the completed secondary lining 15 of the inverted arch, and the constructed secondary lining 14 of the arch wall is connected with the secondary lining 15 of the inverted arch located therebelow as a whole, so as to obtain the formed secondary lining of the tunnel;

[0116] In this step, during the construction of the inverted arch secondary lining 15 from the back to the front, the inverted arch backfill layer 16 is constructed on the completed inverted arch secondary lining 15 from the back to the front along the longitudinal extension direction of the tunnel.

[0117] In this embodiment, when performing tunnel excavation and initial support in step 1, the following steps are included:

[0118] Step B1, excavation of the upper tunnel body and initial support: excavating the upper tunnel body 1-1 of the constructed loess tunnel from back to front along the longitudinal extension direction of the tunnel;

[0119] During the excavation of the upper cave body 1-1, the arch of the excavated upper cave body 1-1 is supported by mesh spraying from back to front, and the upper arch frame 2-1 is installed in the excavated upper cave body 1-1 from back to front, completing the excavation and initial support construction process of the upper cave body 1-1;

[0120] Step B2, excavation of the middle cavern and initial support: During the excavation of the upper cavern and initial support in step B1, the middle cavern 1-2 is excavated from the back to the front below the excavated upper cavern 1-1 along the longitudinal extension direction of the tunnel;

[0121] During the excavation of the middle cave 1-2, mesh spraying support is performed on the left and right sides of the excavated middle cave 1-2 from back to front, and at the same time, middle side brackets 5 are installed on the left and right sides of the excavated middle cave 1-2 from back to front, and each of the middle side brackets 5 is fastened and connected to the upper arch frame 2-1 in step B1 as a whole, completing the excavation and initial support construction process of the middle cave 1-2;

[0122] In this step, the excavation surface of the middle cave body 1-2 is located behind the excavation surface of the upper cave body 1-1 and the horizontal distance between the two is 4m to 6m;

[0123] Step B3, excavation of the lower cavern and initial support: During the excavation of the middle cavern and initial support in step B2, the lower cavern 1-3 is excavated from the back to the front along the longitudinal extension direction of the tunnel below the excavated middle cavern 1-2;

[0124] During the excavation of the lower cave body 1-3, mesh spraying support is performed on the left and right sides of the excavated lower cave body 1-3 from back to front, and during the mesh spraying support, lower side brackets 6 are installed on the left and right sides of the excavated lower cave body 1-3 from back to front, and each of the lower side brackets 6 is fastened and connected to the middle side bracket 5 described in step B2 as a whole; at the same time, a tunnel inverted arch support 2 is installed at the bottom of the lower cave body 1-3 from back to front, and the installed tunnel inverted arch support 2 is fastened and connected to the lower side brackets 6 installed on the left and right sides of the lower cave body 1-3 as a whole; during the installation of the tunnel inverted arch support 2, a layer of concrete is sprayed on the bottom of the tunnel hole 1 from back to front to form an inverted arch concrete spraying layer 20, and the tunnel inverted arch support 2 is fixed in the inverted arch concrete spraying layer 20, completing the excavation and initial support construction process of the lower cave body 1-3;

[0125] In this step, the excavation surface of the lower cave body 1-3 is located behind the excavation surface of the middle cave body 1-2 and the horizontal distance between the two is 4m to 6m;

[0126] In this step, during the process of excavating the lower cave body 1-3 from back to front, the excavated tunnel hole 1 is obtained; after the left and right sides of the excavated lower cave body 1-3 are respectively supported by mesh spraying from back to front, the constructed arch wall mesh spraying support structure is obtained; the arch wall mesh spraying support structure is connected to the invert arch concrete spraying layer 20.

[0127] In this embodiment, when excavating the upper cave body 1-1 in step B1, an excavator with a tiller is used for excavation, and a soil layer with a thickness of 30 cm to 50 cm is reserved on all sides of the upper cave body 1-1 as an artificial finishing layer. The artificial finishing layer is excavated manually using a tool to ensure excavation accuracy. It is strictly forbidden for the excavator to touch the full-section support frame to ensure safety and prevent over-excavation. If necessary, core soil is reserved to ensure the stability of the face.

[0128] In the process of installing the upper arch frame 2-1 in the excavated upper cave body 1-1 from back to front in step B1, foam aluminum pads or concrete pads are respectively set at the bottom of the left and right sides of each installed upper arch frame 2-1 to control displacement and settlement, and locking foot anchor pipes 8 are respectively driven on the left and right sides of each installed upper arch frame 2-1; at the same time, a layer of sand cushion is respectively laid at the bottom of the left and right sides of each installed upper arch frame 2-1 to facilitate the bolt connection between the upper arch frame 2-1 and the middle side bracket 5.

[0129] When excavating the middle cave body 1-2 in step B2, an excavator with a tiller is used for excavation, and a soil layer with a thickness of 30cm to 50cm is reserved on the left and right sides and the bottom of the middle cave body 1-2 as an artificial finishing layer. It is strictly forbidden to excavate to the edge by machinery at one time. The artificial finishing layer is excavated manually using a tool to ensure excavation accuracy. It is strictly forbidden for the excavator to touch the full-section support frame to ensure safety and prevent over-excavation. If necessary, core soil is reserved to ensure the stability of the heading face.

[0130] In step B2, during the process of installing the middle side supports 5 on the left and right sides of the excavated middle cave body 1-2 from back to front, a foam aluminum pad or a concrete pad is set at the bottom of each installed middle side support 5 to control displacement and settlement, and a middle locking foot anchor pipe 9 is driven on the outside of each installed middle side support 5; at the same time, a layer of sand cushion is laid at the bottom of each installed middle side support 5 to facilitate the bolt connection between the middle side support 5 and the lower side support 6.

[0131] When excavating the lower cave body 1-3 in step B3, an excavator with a tiller is used for excavation, and a soil layer with a thickness of 30cm to 50cm is reserved on the left and right sides and the bottom of the lower cave body 1-3 as an artificial finishing layer. It is strictly forbidden to excavate to the edge by machinery at one time. The artificial finishing layer is excavated manually using a tool to ensure excavation accuracy. It is strictly forbidden for the excavator to touch the full-section support frame to ensure safety and prevent over-excavation. If necessary, core soil is reserved to ensure the stability of the heading face.

[0132] In step B3, during the process of installing the lower side supports 6 on the left and right sides of the excavated lower cave body 1-3 from back to front, a foam aluminum pad or a concrete pad is set at the bottom of each installed lower side support 6 to control displacement and settlement, and a lower locking foot anchor pipe 10 is driven on the outer side of each installed lower side support 6.

[0133] Since the loess tunnel under construction is excavated by the step method, during the excavation of the loess tunnel under construction, the full-section support frame is installed in steps and cannot be temporarily closed into a ring, which causes the initial support to be easily deformed. The present invention uses the upper locking foot anchor pipe 8, the middle locking foot anchor pipe 9 and the lower locking foot anchor pipe 10 to respectively constrain the arch feet of the upper arch frame 2-1, the middle side support 5 and the lower side support 6, which can effectively prevent the arch feet of the upper arch frame 2-1, the middle side support 5 and the lower side support 6 from rotating and moving, improve the overall stability of the steel frame, and prevent the initial support from being greatly deformed.

[0134] In this embodiment, the upper locking foot anchor pipe 8, the middle locking foot anchor pipe 9 and the lower locking foot anchor pipe 10 are all seamless steel pipes with a wall thickness of 5mm, a length of 4m and a diameter of Φ42mm. The inner ends of the upper locking foot anchor pipe 8, the middle locking foot anchor pipe 9 and the lower locking foot anchor pipe 10 are all fixed to the full-section support frame by connecting steel bars through welding. The length and driving angle of the upper locking foot anchor pipe 8, the middle locking foot anchor pipe 9 and the lower locking foot anchor pipe 10 are reasonably designed, which is not only conducive to limiting the deformation of the surrounding rock, but also helps to exert the bearing capacity of the support structure. In addition, the number of the upper locking foot anchor pipe 8, the middle locking foot anchor pipe 9 and the lower locking foot anchor pipe 10 at each anchoring position is two, which can further improve the anchoring effect.

[0135] The upper locking foot anchor pipe 8, the middle locking foot anchor pipe 9 and the lower locking foot anchor pipe 10 are inclined anchor pipes. When installing the inclined anchor pipes, the boreholes where the inclined anchor pipes are installed are first drilled. Due to limited working space, in order to effectively ensure the drilling depth and angle of the locking foot anchor pipes, the "three-time drilling method" is used for drilling. Drill rods with lengths of 2m, 3m and 4m are selected in turn, and the drilling depths are gradually drilled to the designed depths in the order of 1.5m, 2.5m and 4m. After the drilling is completed, the inclined anchor pipes are installed. During installation, the inclined anchor pipes are directly driven into the boreholes using a rock drill pipe delivery device.

[0136] In this embodiment, when the upper cave body is excavated and initially supported in step B1, the excavation footage of the upper cave body 1-1 is 2L to 3L;

[0137] When the middle cave body is excavated and initially supported in step B2, the excavation footage of the middle cave body 1-2 is 2L to 3L;

[0138] When the lower cave body is excavated and initially supported in step B3, the excavation footage of the lower cave body 1-3 is 2L to 3L.

[0139] In this embodiment, when the mesh spraying support is performed on the arch of the upper cave body 1-1 from back to front in step B1, the arch steel mesh is first mounted on the arch of the upper cave body 1-1 from back to front, and the upper arch frame 2-1 is installed in the upper cave body 1-1 from back to front, and the mounted arch steel mesh is fastened to the installed upper arch frame 2-1; then, a layer of concrete is sprayed on the inner wall of the excavated upper cave body 1-1 from back to front to form an arch concrete spraying layer, and the mounted arch steel mesh and the installed upper arch frame 2-1 are both fixed in the arch concrete spraying layer, completing the excavation and initial support construction process of the upper cave body 1-1;

[0140] When mesh spraying support is performed on the left and right sides of the middle cave body 1-2 from back to front in step B2, firstly, the middle steel mesh is mounted on the left and right sides of the middle cave body 1-2 from back to front, and the middle side brackets 5 are installed on the left and right sides of the middle cave body 1-2 from back to front, and the mounted middle steel mesh is fastened to the installed middle side brackets 5, and the mounted middle steel mesh is fastened to the arch steel mesh described in step B1; then, a layer of concrete is sprayed on the inner walls of the left and right sides of the middle cave body 1-2 from back to front to form a middle concrete spraying layer, and the middle concrete spraying layer is connected to the arch concrete spraying layer described in step B1, and the mounted middle steel mesh and the installed middle side brackets 5 are fixed in the middle concrete spraying layer, and the excavation and initial support construction process of the middle cave body 1-2 is completed;

[0141] When the mesh spraying support is performed on the left and right sides of the lower cave body 1-3 from back to front in step B3, the lower steel mesh is first hung on the left and right sides of the lower cave body 1-3 from back to front, and the lower side brackets 6 are installed on the left and right sides of the lower cave body 1-3 from back to front, and the hung lower steel mesh is fastened to the installed lower side brackets 6, and the hung lower steel mesh is fastened to the middle steel mesh described in step B2; then, a layer of concrete is sprayed on the inner walls of the left and right sides of the lower cave body 1-3 from back to front to form a lower concrete spraying layer, and the lower concrete spraying layer is connected to the middle concrete spraying layer described in step B2, and the hung lower steel mesh and the installed lower side brackets 6 are fixed in the lower concrete spraying layer, completing the mesh spraying support process on the left and right sides of the lower cave body 1-3, and obtaining the constructed arch wall mesh spraying support structure;

[0142] The arch steel mesh described in step B1, the middle steel mesh described in step B2 and the lower steel mesh described in step B3 are connected from top to bottom to form the arch wall steel mesh, and the arch concrete spraying layer in step B1, the middle concrete spraying layer in step B2 and the lower concrete spraying layer in step B3 are connected from top to bottom to form the arch wall concrete spraying layer 19.

[0143] like Figure 2 As shown, in this embodiment, the excavation footage of the upper cave body 1-1 in step B1, the excavation footage of the middle cave body 1-2 in step B2, and the excavation footage of the lower cave body 1-3 in step B3 are all the same;

[0144] During tunnel excavation and initial support in step 1, the wet spraying manipulator 21 moves forward in multiple times along the longitudinal extension direction of the tunnel through the backfill soil layer 7 at the bottom of the tunnel, and each forward movement distance is the same as the excavation footage of the lower cave body 1-3;

[0145] Each time the wet spraying manipulator 21 moves forward to a position, the length of the excavated lower cave 1-3 in front of the backfill soil layer 7 at the bottom of the tunnel is the same as the excavation footage of the lower cave 1-3. At this time, the excavated lower cave 1-3 in front of the backfill soil layer 7 at the bottom of the tunnel is the currently excavated lower cave.

[0146] After the wet spraying manipulator 21 moves forward to its position each time, the wet spraying manipulator 21 is first used to spray the lower concrete spraying layer and the invert concrete spraying layer 20 in the currently excavated lower cave body from back to front, and the excavation and initial support construction process of the currently excavated lower cave body is completed at the same time; after the excavation and initial support construction process of the currently excavated lower cave body is completed, the tunnel bottom backfill soil layer 7 is constructed on the initial support invert 13 that has been constructed and formed in the currently excavated lower cave body, and the tunnel bottom backfill soil layer 7 constructed at this time is a mobile platform for the wet spraying manipulator 21 to move forward next time;

[0147] After the lower concrete spraying layer and the invert concrete spraying layer 20 in the currently excavated lower cave body are sprayed, the wet spraying manipulator 21 is used to spray concrete from the back to the front on the upper cave body 1-1 and the middle cave body 1-2 which are located in front of the currently excavated lower cave body and have been excavated and formed at this time, respectively, and the excavation and initial support construction process of the upper cave body 1-1 and the middle cave body 1-2 located in front of the currently excavated lower cave body is completed at the same time;

[0148] After the concrete spraying is completed in the upper cavern 1-1 and the middle cavern 1-2 which are located in front of the currently excavated lower cavern and have been excavated and formed, the wet spraying manipulator 21 is moved forward for the next time.

[0149] From the above content, it can be known that the construction process of the initial support invert 13 is carried out synchronously with the excavation process of the lower cave body 1-3. Therefore, the excavation of the lower cave body 1-3 and the construction of the initial support invert 13 are carried out synchronously, which can ensure that the initial support is closed into a ring in time and that the initial support is closed into a ring in the shortest time, prevent excessive deformation of the surrounding rock, and ensure construction safety. In addition, after the initial support is closed into a ring, it is more convenient for large machinery to move in the cave, thereby meeting the needs of large-scale mechanized construction to the greatest extent, reducing labor intensity, achieving synchronous operation of the upper, middle and lower steps, and achieving full-section flow construction, which can effectively improve construction efficiency, reduce project costs, and achieve safe, economical and efficient construction goals.

[0150] During actual construction, the horizontal distance between the excavation surface of the upper tunnel body 1-1 and the excavation surface of the lower tunnel body 1-3 is 8m to 10m. Therefore, the horizontal distance between the progress of the initial support invert 13 closing into a ring (i.e., the initial support closing into a ring) and the excavation surface of the upper tunnel body 1-1 is 8m to 10m, which can ensure the safe, reliable and smooth tunnel excavation process and the stability of the large-section loess tunnel.

[0151] Moreover, since the horizontal distance between the progress of the initial support arch 13 being closed into a ring (i.e., the initial support being closed into a ring) and the excavation surface of the upper cave body 1-1 is 8m to 10m, it can ensure that the working length of the wet spraying manipulator 21 meets the construction requirements and ensure that the wet spraying manipulator 21 can spray concrete on the upper cave body 1-1 in front.

[0152] In this embodiment, the thickness of the arch wall concrete spraying layer 19 and the invert arch concrete spraying layer 20 are both 30 cm and both are made of C25 concrete.

[0153] The wet spraying manipulator 21 is a mobile concrete spraying manipulator. In this embodiment, the wet spraying manipulator 21 is an HPS3016S wet spraying manipulator (also known as an HPS3016 tire-type concrete spraying trolley) produced by China Railway Construction Heavy Industry Group Co., Ltd. or a TKJ-20 wet spraying manipulator (also known as a TKJ-20 concrete spraying manipulator) produced by China Railway Yanfeng Chengdu Technology Co., Ltd.

[0154] In this embodiment, the excavation heights of the upper cave body 1 - 1 and the middle cave body 1 - 2 can both meet the operating space of the wet spraying robot 21 .

[0155] When excavating the steps for reserving the core soil, the steps are excavated or partially trimmed before spraying the concrete to ensure that the wet spraying manipulator 21 has enough normal working space.

[0156] When spraying the arch wall concrete spraying layer 19 and the invert arch concrete spraying layer 20, the initial spraying is performed first, and then the re-spraying is performed. In the actual initial spraying, the spraying starts from the arch foot on one side along the tunnel excavation section, passes through the arch part and ends at the arch foot on the other side; the spraying thickness during the first spraying should be controlled at 10cm to 15cm for the side wall and 5cm to 10cm for the arch part.

[0157] After the initial spraying concrete sets, re-spraying shall be carried out in the order from bottom to top. When spraying the inverted arch, the middle shall be sprayed first and then the two sides, and the thickness of the middle spraying shall be greater than the thickness of the two sides.

[0158] When re-spraying the side wall, spray directly to the designed thickness based on the first initial spraying. The thickness of each spraying of the arch should be controlled at 4cm~5cm, and the interval between each spraying is 5~10min, which can greatly reduce the rebound amount. During the spraying process, the distance between the nozzle and the sprayed surface should be 1.0cm~1.5m, and the nozzle should move continuously and slowly horizontally or circumferentially during the spraying process. If the sprayed surface is blocked by a steel frame or a steel mesh, change the spraying angle of the nozzle and the distance from the sprayed surface according to the specific situation, and spray the back of the steel frame and the steel mesh to make it dense. During the spraying process, if there is water leakage from cracks on the sprayed surface, spray the water-free area first, and gradually spray to cover the water seepage area. When spraying the water seepage area, the amount of accelerator used can be increased by 0.5%~2.0% on the basis of the standard amount, and the total amount shall not exceed 6.0% of the cement amount.

[0159] After spraying concrete, moisture curing should be carried out immediately, and generally the curing period should not be less than 14 days. The ambient temperature for spraying concrete operation should not be lower than 5℃.

[0160] In order to further improve the stability of the bottom of the constructed loess tunnel, the two adjacent tunnel arch supports 2 in the initial tunnel support structure are fastened together by multiple longitudinal connectors arranged from left to right. The multiple longitudinal connectors are arranged horizontally and along the contour line of the tunnel arch support.

[0161] In this embodiment, the longitudinal connecting member is a channel steel.

[0162] During actual construction, the longitudinal connectors may also be made of other types of steel.

[0163] In this embodiment, when the arch wall secondary lining 14 is constructed in step 2, a secondary lining trolley is used to construct the arch wall secondary lining 14 from the back to the front along the longitudinal extension direction of the tunnel. Therefore, the actual construction is simple, the construction efficiency is high, and the construction quality is easy to ensure.

[0164] The two left and right short side walls 18 of the secondary lining of the tunnel are lining sections at the bottom of the left and right sides of the secondary lining 14 of the arch wall.

[0165] When the arch wall secondary lining 14 is constructed in step 2, the construction process of the two short side walls 18 is completed simultaneously, and the left and right short side walls 18 are also constructed using a secondary lining trolley. The secondary lining trolley is a conventional lining trolley, and the forming template of the lining trolley only needs to be processed according to the cross-sectional shape of the arch wall secondary lining 14. Therefore, the forming template installed on the secondary lining trolley is the forming template of the arch wall secondary lining 14, specifically, the arc-shaped template for forming the inner wall of the arch wall secondary lining 14, which has a simple structure and is easy to construct. In addition, since the upper surface of the inverted arch secondary lining 15 is a horizontal plane, the forming template can be stably supported on the inverted arch secondary lining 15, the support is stable and reliable, and can effectively ensure the construction quality of the secondary lining of the constructed tunnel.

[0166] Therefore, when the secondary lining construction and invert backfilling are carried out in step 2, the construction progress of the invert secondary lining 15 is faster than the construction progress of the arch wall secondary lining 14, thereby further ensuring the stability of the bottom of the constructed loess tunnel and effectively accelerating the closing ring time of the tunnel secondary lining.

[0167] According to the common knowledge in the art, the secondary lining of a tunnel (referred to as secondary lining or second lining) is a cast concrete or reinforced concrete lining applied inside the initial support structure of a tunnel (referred to as initial support or primary support) during tunnel construction, and together with the initial support structure of the tunnel, it forms a composite lining. The secondary lining of the tunnel includes two left and right short side walls 18, and the two short side walls 18 are symmetrically arranged above the left and right sides of the secondary lining invert. The short side wall 18 is a term in the secondary lining of a railway tunnel, also known as a small side wall. The secondary lining of the tunnel is formed by connecting the tunnel bottom lining and the secondary lining arch wall lining arranged just above the tunnel invert. The tunnel bottom lining is formed by connecting the secondary lining invert and the two short side walls 18. The tunnel bottom lining is also called a tunnel invert, so the two short side walls 18 are part of the tunnel invert. The tunnel invert is a reverse arch structure arranged at the bottom of the tunnel to improve the stress conditions of the upper support structure, and is one of the main components of the tunnel structure. The two short side walls 18 are symmetrically arranged above the left and right sides of the second lining arch. The left and right bottoms of the second lining arch wall lining are connected to the second lining arch through a short side wall 18. The tunnel bottom lining and the second lining arch wall lining are both reinforced concrete linings and the cross sections of the two are arched.

[0168] At present, when constructing the composite tunnel lining, the method of constructing the primary support together with the secondary lining inverted arch is generally adopted, and a short side wall 18 of a certain height is constructed on the secondary lining inverted arch, and then the inverted arch is filled, which has the problems of many construction processes and low efficiency. At the same time, since the inverted arch filling should be poured after the concrete of the secondary lining inverted arch is finally set, and the arc shape of the secondary lining inverted arch must be ensured, this requires that the construction of the secondary lining inverted arch and the short side wall 18 must be formed with the help of a template, otherwise the inverted arch construction will have the following problems: first, it cannot be well formed; secondly, it is difficult to vibrate, because once the concrete is vibrated, it will slide to the bottom. In addition, the inverted arch template is rarely used in tunnel construction at present, and the short side wall side template is often installed only at the top surface of the inverted arch filling, and the inverted arch filling and the secondary lining inverted arch are poured at the same time. After the inverted arch is filled in place, the worker shovels the concrete into the short side wall template, slightly inserts and tamps, and dares not vibrate. In this way, the quality of the short side wall 18 is greatly reduced, and the concrete grade of the secondary lining invert is different from that of the invert. The concrete of the secondary lining invert is often poured into the tunnel bottom first, and then the concrete of the invert is poured, and the two are mixed together. Since the short side wall 18 belongs to the tunnel invert, but it uses filling concrete, and it is not vibrated, the strength of the short side wall 18 is actually quite low. Moreover, after the demolding, it can be seen that the honeycomb surface is serious, and the appearance quality is also embarrassing, so it has to be covered with the prepared cement slurry. There are also problems such as the template being reused and uneven, without repair, and without applying a release agent. The step line shape of the short side wall 18 formed by the construction is extremely poor, resulting in the second lining trolley template not being in close contact with it, and serious misalignment and leakage. Therefore, appropriately optimizing the secondary lining structure can effectively improve the construction efficiency and make the project more economical and reasonable while ensuring the safety of the tunnel structure.

[0169] In this embodiment, the two short side walls 18 are lining segments at the bottom of the left and right sides of the arch wall secondary lining 14 , and thus the two short side walls 18 are part of the arch wall secondary lining 7 .

[0170] In order to ensure the construction quality of the inverted arch secondary lining 15 and the short side wall 18 and effectively improve the construction efficiency, the interface between the inverted arch secondary lining 15 and the inverted arch filling layer 16 is adjusted, and the interface between the inverted arch secondary lining 15 and the inverted arch filling layer 16 is adjusted to a plane, and the inverted arch filling layer 16 and the inverted arch secondary lining 15 can be cast at the same time, which can greatly simplify the construction process of the inverted arch secondary lining 15 and the inverted arch filling layer 16, and the concrete of the inverted arch secondary lining 15 and the inverted arch filling layer 16 will not be mixed together, which can effectively ensure the construction quality of the inverted arch secondary lining 15 and the inverted arch filling layer 16, and avoid the problem that the construction quality of the inverted arch secondary lining 15 and the inverted arch filling layer 16 cannot be guaranteed due to different concrete grades. At the same time, the upper surface of the inverted arch secondary lining 15 is a horizontal plane. During the concrete pouring process, there is no need to ensure the arc shape of the inverted arch secondary lining 15, and there is no need to use an arc formwork. The pouring is convenient and easy, and the construction quality of the inverted arch secondary lining 15 is easy to ensure.

[0171] The tunnel secondary lining is symmetrically provided with a ditch cable trough 23 on both sides. The ditch cable trough 23 is a pre-designed ditch for drainage and cable laying in the constructed loess tunnel 1. In this embodiment, the inverted arch filling layer 16 is arranged between the two ditch cable troughs 23. The two ditch cable troughs 23 are symmetrically supported above the left and right sides of the inverted arch secondary lining 15, and the two ditch cable troughs 23 are symmetrically arranged on the left and right sides of the inverted arch filling layer 16.

[0172] The upper surface of the inverted arch secondary lining 15 is cast into a plane, and when determining the upper surface height of the inverted arch secondary lining 15, it is determined according to the intersection between the pre-designed inner contour line of the tunnel inverted arch (i.e., the designed inner contour line of the tunnel inverted arch, which is an arc contour line) and the pre-designed bottom of the ditch cable trough 23, and the upper surface of the inverted arch secondary lining 15 and the intersection between the designed inner contour line of the tunnel inverted arch and the pre-designed bottom of the ditch cable trough 23 are arranged on the same horizontal plane. In this embodiment, the inverted arch secondary lining 15 is cast once with concrete of the same grade as the pre-designed tunnel inverted arch, and the inverted arch filling layer 16 is cast once with concrete of the same grade as the pre-designed inverted arch filling. In this embodiment, the inverted arch filling layer 16 is cast with C20 concrete. In addition, the inverted arch secondary lining 15 and the inverted arch filling layer 16 are cast separately. During the concrete pouring process of the secondary lining 15 and the filling layer 16 of the inverted arch, the mass concrete is strictly vibrated in layers.

[0173] In this embodiment, when pouring the inverted arch secondary lining 15, a movable inverted arch trestle 17 is used for the entire pouring, and the middle arc-shaped portion inside the inverted arch secondary lining 15 is optimized to be a horizontal plane.

[0174] The optimized inverted arch secondary lining 15 greatly improves the rigidity of the tunnel inverted arch structure as a whole, and there is no need to install an arc formwork during construction, the concrete is easy to vibrate and the vibration quality is easy to control, the appearance size and construction quality of the inverted arch secondary lining 15 are easier to control, and the construction efficiency of the tunnel inverted arch can be greatly improved, the closure time of the tunnel secondary lining is greatly shortened, and there is no interference from the arc formwork, which makes the inverted arch concrete easy to vibrate, and the concrete quality is greatly improved. In this embodiment, since the upper surface of the inverted arch secondary lining 15 is a horizontal plane, when the inverted arch secondary lining 15 is poured with concrete, there is no need to use a forming formwork, and it is only necessary to monitor the upper surface height of the poured concrete. When the upper surface height of the poured concrete is the same as the upper surface height of the inverted arch secondary lining 15, the concrete pouring construction process of the inverted arch secondary lining 15 is completed, thereby greatly simplifying the construction process of the inverted arch secondary lining 15.

[0175] In addition, it should be noted that: the present invention does not simply cast the concrete of the inverted arch secondary lining 15 into a plane, but also sets the upper surface of the inverted arch steel cage in the inverted arch secondary lining 15 to a horizontal plane, ensuring that the steel cage is provided in the entire cross-section of the inverted arch secondary lining 15, and the upper surface of the inverted arch steel cage is a horizontal plane, which can effectively simplify the binding process of the inverted arch steel cage.

[0176] In this embodiment, the existing secondary lining arch wall lining and the two short side walls 18 are connected to form the arch wall secondary lining 14, so the existing secondary lining arch wall lining and the two short side walls 18 are constructed as an integral lining, and a secondary lining trolley is used to construct the arch wall secondary lining 14. Therefore, the existing secondary lining arch wall lining and the two short side walls 18 are formed in one construction by the secondary lining trolley, which can further improve the construction efficiency of the tunnel secondary lining, speed up the closing time of the tunnel secondary lining, shorten the closing time of the tunnel secondary lining, and further improve the structural stability of the constructed loess tunnel.

[0177] Moreover, the existing secondary lining arch wall lining and the two short side walls 18 are cast as one, which can effectively reduce the construction joints in the secondary lining of the tunnel, make the secondary lining of the tunnel more integrated, and have a better overall force effect. At the same time, it can effectively solve the following problems existing in the existing tunnel secondary lining construction method when the invert is first constructed in advance and then the short side wall is constructed using the combined steel formwork: first, it can avoid the damage that the short side wall 18 construction process may cause to the completed secondary lining invert when the short side wall 18 is constructed using the combined steel formwork after the invert is constructed in advance; second, it can avoid the damage that the short side wall 18 construction process may cause to the completed secondary lining invert 8, and it is necessary to wait until the second lining invert is finally set before constructing the short side wall 18, so the construction efficiency is greatly improved and the construction period is effectively shortened; third, the construction quality and connection strength of the connection between the short side wall 18 and the secondary lining invert can be guaranteed, which can effectively save construction costs, and can further improve construction efficiency and reduce the construction costs and construction period of later strengthening measures.

[0178] The one-time pouring length of the inverted arch secondary lining 15 is determined according to the length of the secondary lining trolley for constructing the arch wall secondary lining 14, and the one-time pouring length of the inverted arch secondary lining 15 is 2 times or 3 times the length of the secondary lining trolley (i.e. the longitudinal length of the one-ring arch wall secondary lining 14), which can greatly improve the construction efficiency of the tunnel inverted arch and further ensure the stability of the constructed loess tunnel 1. In this embodiment, the one-time pouring length of the inverted arch secondary lining 15 is 2 times the length of the secondary lining trolley (i.e. the longitudinal length of the one-ring arch wall secondary lining 14), the length of the secondary lining trolley is 12m, and the one-time maximum pouring length of the inverted arch secondary lining 15 is 24m.

[0179] During the excavation of the loess tunnel 1, when pouring the secondary lining 15 of the inverted arch, the excavation is performed once, the bottom is cleaned once, and the pouring is performed in batches, which reduces the construction interference between the processes, reduces the construction joints, and ensures the construction quality. In addition, when constructing the secondary lining 15 of the inverted arch, the bottom is cleaned first, then the steel bars are tied, and finally the concrete is poured.

[0180] In this embodiment, the inverted arch secondary lining 15 and the arch wall secondary lining 14 are both reinforced concrete linings;

[0181] When the inverted arch secondary lining 15 is constructed from back to front in step 2, the steel cage in the inverted arch secondary lining 15 is tied from back to front on the completed initial support inverted arch 13, and the tied steel cage is the inverted arch steel cage; in the process of tying the inverted arch steel cage from back to front, the inverted arch secondary lining 15 is poured with concrete from back to front, and the inverted arch steel cage that has been tied is poured in the inverted arch secondary lining 15, and the constructed inverted arch secondary lining 15 is fastened and connected to the initial support inverted arch 13 located therebelow as one;

[0182] When the arch wall secondary lining 14 is constructed from back to front in step 2, the steel cage in the arch wall secondary lining 14 is tied from back to front on the inverted arch secondary lining 15 that has been constructed, and the tied steel cage is tightly connected with the inverted arch steel cage directly below it, and the tied steel cage is the arch wall steel cage; in the process of tying the arch wall steel cage from back to front, the arch wall secondary lining 14 is poured with concrete from back to front, the arch wall steel cage that has been tied is cast in the arch wall secondary lining 14, and the constructed arch wall secondary lining 14 is tightly connected with the initial support inverted arch 13 below it, and the constructed arch wall secondary lining 14 is tightly connected with the arch wall initial support structure 12 located outside it as one;

[0183] The binding progress of the inverted arch steel cage is faster than that of the arch wall steel cage, and the concrete pouring progress of the inverted arch secondary lining 15 is faster than that of the arch wall secondary lining 14. In this embodiment, the upper surface of the inverted arch steel cage is a horizontal plane.

[0184] like Figure 2 As shown, in this embodiment, when the secondary lining construction and the invert backfill are carried out in step 2, the construction progress of the invert backfill layer 16 is the same as the construction progress of the invert secondary lining 15, which can effectively speed up the tunnel construction progress. At the same time, since the interface between the invert backfill layer 16 and the invert secondary lining 15 is a horizontal plane, the concrete pouring of the invert backfill layer 16 and the invert secondary lining 15 does not affect each other, and there will be no problem that the concrete mixing of the invert backfill layer 16 and the invert secondary lining 15 affects the construction quality of the invert backfill layer 16 and the invert secondary lining 15.

[0185] During actual construction, the inverted arch backfill layer 16 and the inverted arch secondary lining 15 form a tunnel inverted arch and backfill structure. The construction progress of the inverted arch backfill layer 16 and the inverted arch secondary lining 15 are the same. When constructing the tunnel inverted arch and backfill structure, the forming template used is composed of two symmetrically arranged side templates 24 on the left and right and a front template 25 for forming the front side wall of the tunnel inverted arch and backfill structure. The upper surface of the inverted arch secondary lining 15 does not need to use a template. The forming template structure is simple. The side formwork 24 is a rectangular formwork and is a vertical formwork for forming the left side wall or the right side wall of the inverted arch backfill layer 16. The two side formworks 24 are arranged along the longitudinal extension direction of the tunnel, and the net distance between the two side formworks 24 is the same as the lateral width of the inverted arch backfill layer 16; the height of the two side formworks 24 is not less than the layer thickness of the inverted arch backfill layer 16, and the bottom surfaces of the two side formworks 24 are arranged on the same horizontal plane and the bottom surfaces of the two are flush with the upper surface height of the inverted arch secondary lining 15; Figure 6 As shown, the front template 25 and the side template 24 are arranged vertically, and the front template 25 is a vertical template for forming the front side wall of the inverted arch backfill layer 16 and the inverted arch secondary lining 15; Figure 6 As shown, the front template 25 is composed of an upper template and a lower template located directly below the upper template, the lower template is a template for molding the front side wall of the inverted arch secondary lining 15, the shape and size of the lower template are the same as the cross-sectional shape and size of the inverted arch secondary lining 15, and the bottom of the lower template is supported on the initial support inverted arch 13; the upper template is a template for molding the front side wall of the inverted arch backfill layer 16, the upper template is a rectangular template and its height is not less than the layer thickness of the inverted arch backfill layer 16, and the bottom surface of the upper template is flush with the upper surface of the inverted arch secondary lining 15. In this embodiment, the upper template and the lower template are processed and manufactured as one body.

[0186] In this embodiment, the movable inverted arch trestle 17 includes a trestle body and the forming template installed at the bottom of the trestle body.

[0187] In this embodiment, the constructed loess tunnel is divided into multiple tunnel segments from back to front along the longitudinal extension direction of the tunnel;

[0188] The invert backfill layer 16 and the invert secondary lining 15 form a tunnel invert and backfill structure. When the secondary lining construction and invert backfill are carried out in step 2, a movable invert trestle 17 is used to construct the tunnel invert and backfill structure from back to front.

[0189] When the movable inverted arch trestle 17 is used to construct the tunnel inverted arch and backfill structure from back to front, the tunnel inverted arch and backfilling construction are respectively carried out from back to front on the multiple tunnel segments of the constructed loess tunnel, and the length of each tunnel segment is not greater than the working length of the movable inverted arch trestle 17; the tunnel inverted arch and backfilling construction methods of the multiple tunnel segments are the same;

[0190] When performing tunnel invert and backfill construction on any of the tunnel sections of the constructed loess tunnel, the process is as follows:

[0191] Step A1: Horizontally moving the trestle forward: along the longitudinal extension direction of the tunnel, the movable inverted arch trestle 17 is horizontally moved forward to the construction position of the tunnel segment currently under construction;

[0192] Step A2, pouring of secondary lining of the invert: using the movable invert trestle 17 moved into place in step A1, concrete is poured from bottom to top on the secondary lining 15 of the invert of the tunnel segment currently under construction;

[0193] Step A3, backfilling the invert: after the secondary lining pouring of the invert is completed in step A2, the movable invert trestle 17 moved into place in step A1 is used to pour concrete on the invert backfill layer 16 of the tunnel segment currently under construction from bottom to top;

[0194] After the concrete poured in step A2 and step A3 has finally set, the tunnel invert and backfill construction process of the tunnel section currently under construction is completed;

[0195] Step A4, returning to step A1, performing tunnel invert and backfill construction on one of the tunnel segments.

[0196] The movable inverted arch bridge 17 is an inverted arch construction bridge. Since the upper surface of the tunnel bottom backfill soil layer 7 is flush with the upper surface of the inverted arch backfill layer 16, the tunnel bottom backfill soil layer 7 and the inverted arch backfill layer 16 form a horizontal movable platform for the movable inverted arch bridge 17 to move. Figure 2 As shown, the front side of the movable inverted arch trestle 17 is supported on the backfill soil layer 7 at the bottom of the tunnel, and the rear side of the movable inverted arch trestle 17 is supported on the inverted arch backfill layer 16 that has been constructed and formed, and the actual construction is very simple.

[0197] In this embodiment, before tunnel inverting and backfilling construction is performed on any tunnel segment of the constructed loess tunnel, the tunnel bottom backfill soil layer 7 in the currently constructed tunnel segment is first cleaned from back to front along the longitudinal extension direction of the tunnel.

[0198] In this embodiment, the bottom of the inverted arch steel bar cage includes a plurality of arched steel bars arranged from the back to the front, each of the arched steel bars is located on a tunnel cross section of the tunnel hole 1, and the plurality of arched steel bars are arranged in parallel and their shapes are the same as the shape of the inverted arch secondary lining 15; the left and right ends of each arched steel bar extend above the inverted arch secondary lining 15, and the sections at both ends of each arched steel bar extending above the inverted arch secondary lining 15 are all exposed steel bar sections for connecting the arch wall steel bar cage;

[0199] During the process of tying the arch wall steel cage from back to front, the tied arch wall steel cage is fastened and connected with the exposed steel bar section located therebelow.

[0200] like Figure 1 , Figure 2 As shown, in this embodiment, the tunnel advance support structure includes a plurality of advance small duct grouting support structures for advance support of the arch of the tunnel hole 1 from back to front along the longitudinal extension direction of the tunnel; the structures of the plurality of advance small duct grouting support structures are the same, and the overlap length between the two adjacent advance small duct grouting support structures is not less than 0.5m;

[0201] Each of the advanced small-duct grouting support structures comprises a plurality of grouting small ducts 22 drilled from back to front into the soil in front of the tunnel face 1 and a small duct guide frame for guiding the plurality of grouting small ducts 22, and the plurality of grouting small ducts 22 are arranged from left to right on the same tunnel section along the arch contour line of the upper tunnel body 1-1; the structures and sizes of all the grouting small ducts 22 in each of the advanced small-duct grouting support structures are the same; the small duct guide frame is an upper arch frame 2-1, and the small duct guide frame is provided with a plurality of guide holes for guiding the grouting small ducts 22, and the plurality of guide holes are arranged from left to right along the arch contour line of the upper tunnel body 1-1.

[0202] In this embodiment, the grouting small conduit 22 is a hot-rolled seamless steel pipe with a diameter of Φ42mm and a wall thickness of 3.5mm. The length of the grouting small conduit 22 is 3.5m to 4.0m, and the grouting small conduit 22 is set within the 120° range of the arch of the tunnel hole 1, and the circumferential spacing of the grouting small conduit 22 is 40cm. Before tunnel excavation and initial support in step 1, the advanced small conduit grouting support structure is first used to advance support the arch of the constructed tunnel.

[0203] The installation of the grouting small pipe 22 adopts the drilling method, that is, first drill a hole according to the design requirements, then pass the grouting small pipe 22 through the small pipe guide frame, and push it in with a hammer or a drill. The pushing length is not less than 90% of the total length of the grouting small pipe 22, and the exposed length is convenient for the access of the grouting pipeline, and the sand and gravel in the steel pipe are blown out with high-pressure wind. In addition, when grouting with the grouting small pipe 22, the grouting liquid is cement mortar to enhance the strength of the grouting small pipe 22.

[0204] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent structural change made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A large-section loess tunnel support system, characterized by: The invention comprises a tunnel advance support structure for providing advance support to the arch of a tunnel hole (1) of a loess tunnel to be constructed, a tunnel initial support structure for providing initial support to the tunnel hole (1), and a tunnel secondary lining arranged inside the tunnel initial support structure, wherein the tunnel advance support structure is located above the tunnel initial support structure, the tunnel initial support structure and the tunnel secondary lining are both full-section support structures for providing full-section support to the tunnel hole of the loess tunnel (1) to be constructed, and the tunnel secondary lining is a reinforced concrete lining; the cross-sectional area of ​​the tunnel hole (1) is greater than 100m 2 The tunnel (1) is divided into an upper tunnel body (1-1), a middle tunnel body (1-2) and a lower tunnel body (1-3) from top to bottom; the upper tunnel body (1-1) is a tunnel body formed by excavating the upper step of the loess tunnel from back to front, the middle tunnel body (1-2) is a tunnel body formed by excavating the middle step of the loess tunnel from back to front, and the lower tunnel body (1-3) is a tunnel body formed by excavating the lower step of the loess tunnel from back to front; The tunnel initial support structure is divided into an arch wall initial support structure (12) for initially supporting the arch wall of the tunnel hole (1) and an initial support invert (13) for initially supporting the bottom of the tunnel hole (1); the tunnel secondary lining is divided into an arch wall secondary lining (14) for supporting the arch wall of the tunnel hole (1) and an invert secondary lining (15) for supporting the bottom of the tunnel hole (1); the invert secondary lining (15) is located above the initial support invert (13); an invert backfill layer (16) is arranged on the invert secondary lining (15); the upper surface of the invert secondary lining (15) is a horizontal plane; the left and right bottoms of the arch wall secondary lining (14) are both horizontal planes; the arch wall secondary lining (14) is supported on the invert secondary lining (15) and the two are cast as one; the invert backfill layer (16) is a concrete filling layer; The tunnel initial support structure comprises a full-section support structure for providing full-section support for the tunnel hole (1), an arch wall mesh spraying support structure for providing initial support for the arch wall of the tunnel hole (1), and an inverted arch initial support structure for providing initial support for the bottom of the tunnel hole (1); The full-section support structure comprises a plurality of full-section support frames arranged from back to front along the longitudinal extension direction of the tunnel, wherein two adjacent full-section support frames are fastened together by a plurality of longitudinal connecting steel bars, the longitudinal connecting steel bars are arranged horizontally and along the longitudinal extension direction of the tunnel, and the plurality of longitudinal connecting steel bars are arranged along the contour of the full-section support frame; the shape of the full-section support frame is the same as the cross-sectional shape of the tunnel hole (1), and each of the full-section support frames is formed by splicing an arch wall support arch frame for supporting the arch wall of the tunnel hole (1) and a tunnel inverted arch support (2) for supporting the bottom of the tunnel hole (1); the tunnel inverted arch support (2) is located directly below the arch wall support arch frame and the two are located on the same tunnel cross section; the tunnel inverted arch support (2) and the arch wall support arch frame form a closed full-section support; The arch wall mesh spraying support structure and the arch wall steel arch frame in the full-section support structure form an arch wall initial support structure (12), and the inverted arch initial support structure and the tunnel inverted arch support (2) in the full-section support structure form an initial support inverted arch (13); the inverted arch initial support structure is a layer of inverted arch concrete spraying layer (20) sprayed on the bottom of the tunnel hole (1), and the tunnel inverted arch support (2) is fixed in the inverted arch concrete spraying layer (20); The arch wall support arch frame is composed of an upper arch frame (2-1) located in the upper cave body (1-1), two middle side brackets (5) symmetrically arranged below the left and right sides of the upper arch frame (2-1) and both located in the middle cave body (1-2), and two lower side brackets (6) symmetrically arranged below the left and right sides of the upper arch frame (2-1) and both located in the lower cave body (1-3); the tunnel inverted arch bracket (2) is located in the lower cave body (1-3); each of the middle side brackets (5) is connected between the upper end of one of the lower side brackets (6) and the upper arch frame (2-1); the left end of the tunnel inverted arch bracket (2) is fastened to the bottom of one of the lower side brackets (6), and the right end of the tunnel inverted arch bracket (2) is fastened to the bottom of another of the lower side brackets (6); An anchoring system is arranged outside the full-section support structure, the anchoring system comprises a plurality of anchoring groups arranged from back to front along the longitudinal extension direction of the tunnel, one anchoring group is arranged outside each full-section support frame, and each full-section support frame and the anchoring group arranged thereon are arranged on the same cross section of the tunnel (1); Each of the anchoring groups comprises two groups of upper locking foot anchor pipes (8) symmetrically arranged on the outer sides of the bottom of the left and right sides of the upper arch frame (2-1), two groups of middle locking foot anchor pipes (9) symmetrically arranged on the left and right sides, and two groups of lower locking foot anchor pipes (10) symmetrically arranged on the left and right sides. The two groups of upper locking foot anchor pipes (8), the two groups of middle locking foot anchor pipes (9) and the two groups of lower locking foot anchor pipes (10) are all arranged on the same cross section of the tunnel hole (1); a group of middle locking foot anchor pipes (9) is arranged on the outer side of the bottom of each of the middle side brackets (5); and the bottom of each of the lower side brackets (6) is provided with a plurality of middle locking foot anchor pipes (9). A group of lower locking foot anchor pipes (10) are arranged on the outer side of each part; each group of upper locking foot anchor pipes (8) includes two upper and lower upper locking foot anchor pipes (8) arranged in parallel, each group of middle locking foot anchor pipes (9) includes two upper and lower middle locking foot anchor pipes (9) arranged in parallel, and each group of lower locking foot anchor pipes (10) includes two upper and lower lower locking foot anchor pipes (10) arranged in parallel; the upper locking foot anchor pipes (8), the middle locking foot anchor pipes (9) and the lower locking foot anchor pipes (10) are all locking foot anchor pipes that enter the soil layer on the side of the tunnel hole (1) from the inside to the outside, and the three gradually tilt downward from the inside to the outside; The excavation heights of the upper cave body (1-1) and the middle cave body (1-2) are both 3.5 m to 4.5 m. A tunnel bottom backfill soil layer (7) is arranged behind the excavation surface of the lower cave body (1-3). The tunnel bottom backfill soil layer (7) is located in the lower cave body (1-3). The tunnel bottom backfill soil layer (7) is located on the initial support invert (13). The tunnel bottom backfill soil layer (7) is a temporary mobile platform for the wet spraying manipulator (21) to move forward and backward. The tunnel advance support structure comprises a plurality of advance small duct grouting support structures for providing advance support to the arch of the tunnel hole (1) from the rear to the front along the longitudinal extension direction of the tunnel; the structures of the plurality of advance small duct grouting support structures are the same, and the overlap length between two adjacent advance small duct grouting support structures is not less than 0.5 m; Each of the advanced small-duct grouting support structures comprises a plurality of grouting small ducts (22) drilled from the rear to the front into the soil in front of the tunnel face (1) and a small-duct guide frame for guiding the plurality of grouting small ducts (22); the plurality of grouting small ducts (18) are arranged from left to right on the same tunnel section along the arch contour line of the upper tunnel body (1-1); the structures and dimensions of all the grouting small ducts (22) in each of the advanced small-duct grouting support structures are the same; the small-duct guide frame is an upper arch frame (2-1); the small-duct guide frame is provided with a plurality of guide holes for guiding the grouting small ducts (22); the plurality of guide holes are arranged from left to right along the arch contour line of the upper tunnel body (1-1).

2. A construction method for supporting a loess tunnel using the support system as claimed in claim 1, characterized in that: The method comprises the following steps: Step 1, tunnel excavation and initial support: excavating the constructed loess tunnel from back to front along the longitudinal extension direction of the tunnel, and simultaneously performing initial support on the excavated tunnel hole (1) from back to front during the excavation process to obtain the constructed initial support structure of the tunnel; Step 2, secondary lining construction and backfilling of the invert: in the process of performing initial support on the excavated tunnel hole (1) from the back to the front in step 1, the secondary lining of the tunnel is constructed from the back to the front along the longitudinal extension direction of the tunnel on the inner side of the completed initial support structure of the tunnel; When constructing the secondary lining of the tunnel from back to front, the secondary lining of the inverted arch (15) is constructed from back to front on the completed initial support inverted arch (13) to obtain the constructed secondary lining of the inverted arch (15); when constructing the secondary lining of the inverted arch (15) from back to front, the secondary lining of the arch wall (14) is constructed from back to front on the completed secondary lining of the inverted arch (15), and the constructed secondary lining of the arch wall (14) is connected to the secondary lining of the inverted arch (15) located below it as a whole to obtain the constructed secondary lining of the tunnel; In this step, during the construction of the inverted arch secondary lining (15) from the back to the front, the inverted arch backfill layer (16) is constructed from the back to the front along the longitudinal extension direction of the tunnel on the completed inverted arch secondary lining (15).

3. The construction method according to claim 2, characterized in that: When tunnel excavation and initial support are carried out in step 1, the following steps are included: Step B1, excavation of the upper tunnel and initial support: excavating the upper tunnel (1-1) of the constructed loess tunnel from back to front along the longitudinal extension direction of the tunnel; During the excavation of the upper cave body (1-1), mesh spraying is performed on the arch of the excavated upper cave body (1-1) from the back to the front, and at the same time, the upper arch frame (2-1) is installed in the excavated upper cave body (1-1) from the back to the front, thereby completing the excavation and initial support construction process of the upper cave body (1-1); Step B2, excavation of the middle cavern and initial support: During the process of excavating the upper cavern and initial support in step B1, the middle cavern (1-2) is excavated from the back to the front below the excavated upper cavern (1-1) along the longitudinal extension direction of the tunnel; During the excavation of the middle cave body (1-2), mesh spraying support is respectively performed on the left and right sides of the excavated middle cave body (1-2) from back to front, and at the same time, middle side supports (5) are respectively installed on the left and right sides of the excavated middle cave body (1-2) from back to front, and each of the middle side supports (5) is fastened and connected to the upper arch frame (2-1) in step B1 as a whole, thereby completing the excavation and initial support construction process of the middle cave body (1-2); In this step, the excavation surface of the middle cave body (1-2) is located behind the excavation surface of the upper cave body (1-1) and the horizontal distance between the two is 4m to 6m; Step B3, excavation of the lower cavern and initial support: During the excavation of the middle cavern and initial support in step B2, the lower cavern (1-3) is excavated from the back to the front below the excavated middle cavern (1-2) along the longitudinal extension direction of the tunnel; During the excavation of the lower cave body (1-3), mesh spraying support is respectively performed on the left and right sides of the excavated lower cave body (1-3) from back to front. During the mesh spraying support, lower side supports (6) are respectively installed from back to front on the left and right sides of the excavated lower cave body (1-3), and each of the lower side supports (6) is fastened and connected to the middle side support (5) in step B2 as a whole; at the same time, a tunnel invert support (2) is installed from back to front at the bottom of the lower cave body (1-3), and the installed tunnel invert support (2) is fastened and connected to the lower side supports (6) installed on the left and right sides of the lower cave body (1-3) as a whole; during the installation of the tunnel invert support (2), a layer of concrete is sprayed from back to front at the bottom of the tunnel hole (1) to form an invert concrete spraying layer (20), and the tunnel invert support (2) is fixed in the invert concrete spraying layer (20), thereby completing the excavation and initial support construction process of the lower cave body (1-3); In this step, the excavation surface of the lower cave body (1-3) is located behind the excavation surface of the middle cave body (1-2) and the horizontal distance between the two is 4m to 6m; In this step, during the process of excavating the lower cave body (1-3) from the back to the front, an excavated tunnel hole (1) is obtained; after mesh spraying is performed on the left and right sides of the excavated lower cave body (1-3) from the back to the front, the constructed arch wall mesh spraying support structure is obtained; and the arch wall mesh spraying support structure is connected to the invert arch concrete spraying layer (20).

4. The construction method according to claim 3, characterized in that: The plurality of full-section support frames in the full-section support structure are evenly arranged, and the spacing between two adjacent full-section support frames is L, wherein the value range of L is 0.5m to 1m; When excavating the upper cave and providing initial support in step B1, the excavation footage of the upper cave (1-1) is 2L to 3L; When the middle cave body is excavated and initially supported in step B2, the excavation footage of the middle cave body (1-2) is 2L to 3L; When the lower cave body is excavated and initially supported in step B3, the excavation footage of the lower cave body (1-3) is 2L to 3L.

5. The construction method according to claim 2, 3 or 4, characterized in that: The arch wall mesh spraying support structure comprises an arch wall steel mesh mounted on the arch wall of the tunnel hole (1) and an arch wall concrete spraying layer (19) sprayed on the arch wall of the tunnel hole (1), the arch wall steel mesh being fixed on the arch wall steel arch frame, and the arch wall steel mesh and the arch wall steel arch frame being both fixed in the arch wall concrete spraying layer (19); When the mesh spraying support is performed on the arch of the upper cave body (1-1) from back to front in step B1, the arch steel mesh is first mounted on the arch of the upper cave body (1-1) from back to front, and the upper arch frame (2-1) is installed in the upper cave body (1-1) from back to front, and the mounted arch steel mesh is fastened to the installed upper arch frame (2-1); then, a layer of concrete is sprayed from back to front on the inner wall of the excavated upper cave body (1-1) to form an arch concrete spraying layer, and the mounted arch steel mesh and the installed upper arch frame (2-1) are both fixed in the arch concrete spraying layer, thereby completing the excavation and initial support construction process of the upper cave body (1-1); When mesh spraying support is performed on the left and right sides of the middle cave body (1-2) from back to front in step B2, firstly, the middle steel mesh is respectively mounted on the left and right sides of the middle cave body (1-2) from back to front, and the middle side brackets (5) are respectively installed on the left and right sides of the middle cave body (1-2) from back to front, and the mounted middle steel mesh is tightly connected to the installed middle side brackets (5), and the mounted middle steel mesh is tightly connected to the arch steel mesh in step B1; then, a layer of concrete is sprayed on the inner walls of the left and right sides of the middle cave body (1-2) from back to front to form a middle concrete spraying layer, and the middle concrete spraying layer is connected to the arch concrete spraying layer in step B1, and the mounted middle steel mesh and the installed middle side brackets (5) are both fixed in the middle concrete spraying layer, thereby completing the excavation and initial support construction process of the middle cave body (1-2); When mesh spraying support is performed on the left and right sides of the lower cave body (1-3) from back to front in step B3, firstly, lower steel mesh sheets are respectively mounted on the left and right sides of the lower cave body (1-3) from back to front, and lower side brackets (6) are respectively installed on the left and right sides of the lower cave body (1-3) from back to front, and the mounted lower steel mesh sheets are fastened and connected to the installed lower side brackets (6), and the mounted lower steel mesh sheets are fastened and connected to the middle steel mesh sheets described in step B2; then, a layer of concrete is sprayed on the inner walls of the left and right sides of the lower cave body (1-3) from back to front to form a lower concrete spraying layer, and the lower concrete spraying layer is connected to the middle concrete spraying layer described in step B2, and the mounted lower steel mesh sheets and the installed lower side brackets (6) are both fixed in the lower concrete spraying layer, completing the mesh spraying support process on the left and right sides of the lower cave body (1-3), and obtaining the constructed arch wall mesh spraying support structure; The arch steel mesh described in step B1, the middle steel mesh described in step B2 and the lower steel mesh described in step B3 are connected from top to bottom to form the arch wall steel mesh, and the arch concrete spraying layer described in step B1, the middle concrete spraying layer described in step B2 and the lower concrete spraying layer described in step B3 are connected from top to bottom to form the arch wall concrete spraying layer (19); The arch wall concrete spraying layer (19) and the invert arch concrete spraying layer (20) are both concrete layers sprayed by a wet spraying manipulator (21).

6. The construction method according to claim 5, characterized in that: The excavation footage of the upper cavern (1-1) in step B1, the excavation footage of the middle cavern (1-2) in step B2 and the excavation footage of the lower cavern (1-3) in step B3 are all the same; When tunnel excavation and initial support are performed in step 1, the wet spraying manipulator (21) moves forward in multiple steps along the longitudinal extension direction of the tunnel through the backfill soil layer (7) at the bottom of the tunnel, and the distance of each forward movement is the same as the excavation footage of the lower cave body (1-3); Each time the wet spraying manipulator (21) moves forward to a position, the length of the excavated lower cave body (1-3) located in front of the tunnel bottom backfill soil layer (7) is the same as the excavation footage of the lower cave body (1-3). At this time, the excavated lower cave body (1-3) located in front of the tunnel bottom backfill soil layer (7) is the currently excavated lower cave body; After the wet spraying manipulator (21) moves forward to a position each time, the wet spraying manipulator (21) is first used to spray the lower concrete spraying layer and the invert concrete spraying layer (20) in the currently excavated lower cave body from back to front, and the excavation and initial support construction process of the currently excavated lower cave body is completed at the same time; after the excavation and initial support construction process of the currently excavated lower cave body is completed, a tunnel bottom backfill soil layer (7) is constructed on the initial support invert (13) that has been constructed and formed in the currently excavated lower cave body, and the tunnel bottom backfill soil layer (7) constructed at this time serves as a mobile platform for the wet spraying manipulator (21) to move forward next time; After the lower concrete spraying layer and the invert concrete spraying layer (20) in the currently excavated lower cavern are sprayed, a wet spraying manipulator (21) is used to spray concrete from the back to the front on the upper cavern (1-1) and the middle cavern (1-2) which are located in front of the currently excavated lower cavern and have been excavated and formed at this time, respectively, thereby completing the excavation and initial support construction process of the upper cavern (1-1) and the middle cavern (1-2) located in front of the currently excavated lower cavern; After the concrete spraying in the upper cavern (1-1) and the middle cavern (1-2) which are located in front of the currently excavated lower cavern and have been excavated and formed at this time is completed, the wet spraying manipulator (21) is moved forward for the next time.

7. The construction method according to claim 2, 3 or 4, characterized in that: The two left and right short side walls (18) of the secondary lining of the tunnel are lining segments at the bottom of the left and right sides of the secondary lining of the arch wall (14); When the secondary lining (14) of the arch wall is constructed in step 2, a secondary lining trolley is used to construct the secondary lining (14) of the arch wall from the back to the front along the longitudinal extension direction of the tunnel; When the secondary lining construction and invert backfilling are carried out in step 2, the construction progress of the invert secondary lining (15) is faster than the construction progress of the arch wall secondary lining (14).

8. The construction method according to claim 2, 3 or 4, characterized in that: When the secondary lining construction and the invert backfill are carried out in step 2, the construction progress of the invert backfill layer (16) is the same as the construction progress of the invert secondary lining (15); The constructed loess tunnel is divided into multiple tunnel segments from back to front along the longitudinal extension direction of the tunnel; The invert backfill layer (16) and the invert secondary lining (15) form a tunnel invert and backfill structure. When the secondary lining construction and invert backfill are carried out in step 2, a movable invert trestle (17) is used to construct the tunnel invert and backfill structure from back to front. When the movable inverted arch trestle (17) is used to construct the tunnel inverted arch and backfill structure from the back to the front, the tunnel inverted arch and backfill construction are respectively carried out from the back to the front on the multiple tunnel sections of the constructed loess tunnel; the tunnel inverted arch and backfill construction methods of the multiple tunnel sections are the same; When performing tunnel invert and backfill construction on any of the tunnel sections of the constructed loess tunnel, the process is as follows: Step A1: Horizontally moving the trestle forward: along the longitudinal extension direction of the tunnel, the movable inverted arch trestle (17) is horizontally moved forward to the construction position of the tunnel segment currently under construction; Step A2, pouring of secondary lining of the invert: using the movable invert trestle (17) moved into position in step A1, concrete is poured from bottom to top on the secondary lining (15) of the invert of the tunnel segment currently under construction; Step A3, backfilling the invert: after the secondary lining pouring of the invert is completed in step A2, the movable invert trestle (17) moved into place in step A1 is used to pour concrete from bottom to top on the invert backfill layer (16) of the tunnel segment currently under construction; After the concrete poured in step A2 and step A3 has finally set, the tunnel invert and backfill construction process of the tunnel section currently under construction is completed; Step A4, returning to step A1, performing tunnel invert and backfill construction on one of the tunnel segments.

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