Three-step excavation method for shallow-buried extremely-soft rock tunnel and tunnel supporting structure

Abstract

The invention relates to a three-step excavation method for a shallow-buried extremely-soft rock tunnel and a tunnel supporting structure, which ensure that the tunnel is closed to form a ring as soon as possible by strictly controlling the safe step pitch of the tunnel. By means of side wall slotting construction, disturbance of step construction to overall construction of the non-ring-forming tunnel is reduced, structural support of soil in the tunnel is paid attention to in-tunnel soil in the excavation operation process, front-back interference can be effectively reduced, disturbance to stratum soil is relieved, lateral soil pressure and vertical soil pressure in the tunnel excavation process can be effectively resisted through steel pipe pile construction, and construction efficiency is improved. The problems of settlement and large deformation of the tunnel are effectively solved, great potential safety hazards caused by the soft stratum to tunnel construction are eliminated, and the personal safety of constructors and the safety of equipment and property are protected.

Description

Technical Field

[0001] The present application relates to the technical field of tunnel excavation construction, and in particular to a three-step excavation method for a shallow buried extremely soft rock tunnel and a tunnel support structure. Background Art

[0002] Tunnels are engineering structures buried in the ground, and are a form of human use of underground space. According to their uses, tunnels can be divided into traffic tunnels, municipal tunnels, military tunnels, etc. In an environment with complex geological conditions, the entrance slope of the tunnel is Quaternary volcanic deposited clay soil, with a large soil layer thickness, relatively loose soil, high water content, and a large porosity. The original soil layer has a certain structural strength. After the soil is exposed to water and disturbed, its properties deteriorate significantly, and it has special characteristics. After the excavation of the expansive mudstone tunnel, the surrounding rock excavation stress release process, exposure to air and saturation state will cause the surrounding rock cohesion, internal friction angle and strength to decrease sharply, which is manifested in cracking and disintegration after water loss. If it encounters water seepage, it will soften into mud. The above two situations will cause the surrounding rock to lose stability. During the construction process, it is mainly manifested in face collapse, vault settlement, cracking of the initial support, and large deformation.

[0003] For large-span tunnels with great surrounding rock pressure and unstable strata, if conventional tunnel excavation methods are used, it is very easy to cause soil landslides and soil collapses because the stratum soil cannot be effectively supported, which will cause great safety hazards to tunnel construction and threaten the personal safety of construction workers and the safety of equipment and property. Summary of the invention

[0004] Based on this, it is necessary to provide a three-step excavation method and tunnel support structure for a shallow and extremely soft rock tunnel in order to address the problem of soil collapse due to excavation disturbance due to lack of effective support.

[0005] In a first aspect of the present application, a three-step excavation method for a shallow buried extremely soft rock tunnel is provided, wherein the tunnel has a first step, a second step, and a third step, wherein the first step is set as a first portion, the second step has a second portion and a third portion arranged transversely at intervals, and the third step has a fourth portion and a fifth portion arranged transversely at intervals, and the three-step excavation method for the shallow buried extremely soft rock tunnel comprises the following steps:

[0006] Carry out the first excavation:

[0007] Use the advanced small guide tube constructed by the previous cycle steel frame for advanced support;

[0008] Use a small excavator to excavate the first section in sections, push the slag to the top of the middle step, and use a large excavator to excavate the slag on the lower step. At the same time, advance one frame per cycle, and spray 10cm thick concrete to seal the face;

[0009] Construct the initial support and temporary invert around the first pilot pit, that is, spray 4cm thick concrete, set up steel frame and steel mesh, construct locking anchor pipe, set up enlarged arch feet at the two arch feet of the first steel frame, and weld the enlarged arch feet to the steel pipe pile brackets on both sides of the line;

[0010] Carry out the first advance support;

[0011] Initially spray 2cm thick concrete at the bottom of the pilot pit, set up a temporary invert steel frame, spray concrete again to the designed thickness, and close the initial support of the upper pilot pit with the temporary support to form a ring;

[0012] The second excavation:

[0013] After lagging behind the first section by 4.8m, the second section is excavated by an excavator. The excavation process is carried out at the bottom of the temporary invert arch of the upper step. It is forbidden to remove or cut the temporary invert arch of the upper step. At the same time, one frame is advanced in each cycle, and the tunnel face is sealed with 10cm thick concrete.

[0014] The initial support around the second pilot pit was carried out in sections, i.e., 4 cm thick concrete was sprayed, steel frames and steel mesh were erected, and locking anchor pipes were installed. The arch feet on both sides of the second steel frame were connected to the steel pipe piles on both sides of the line through bracket welding;

[0015] The second stage of permanent primary support and advance support is implemented. In the loose mudstone section, it is required to set up an advance small guide tube in each construction cycle.

[0016] The third excavation:

[0017] After lagging behind the second section by 1.2m, the third section is excavated manually, and initial support and temporary support are carried out around the pilot pit. The steps and procedures are the same as those of the second section.

[0018] The third excavation process is to excavate the steps of the middle step, and at the same time remove the temporary invert of the upper step and construct the temporary invert of the middle step;

[0019] When the stability of the tunnel face is poor during the third excavation, concrete must be sprayed to seal the tunnel face in time, and the sealing thickness should not be less than 10cm;

[0020] The fourth excavation:

[0021] After lagging behind the third section by 3m, the fourth section is excavated manually with the help of excavators. When excavating the fourth section, the excavation is carried out at the bottom of the temporary invert arch of the middle step. It is forbidden to remove or cut off the temporary invert arch of the middle step. The excavation soil is excavated to the top surface of the lower step.

[0022] Initially spray 10cm of concrete to seal the lower step face (necessary when the surrounding rock is broken), spray 4cm of concrete for the first time, install the lower step steel frame, and install the foot-locking anchor pipe, and then spray concrete to the designed thickness;

[0023] The fifth excavation is carried out:

[0024] After lagging behind the fourth section by 1.2m, the fifth section was excavated manually with the help of excavators. At the same time, one frame was advanced in each cycle, and one temporary invert of the middle step was removed. A vertical lower step was formed during the excavation process, and the face was sealed with 10cm thick concrete.

[0025] After the initial spraying of 4cm of concrete, install the primary support steel frame, set the locking anchor pipe, and spray concrete again to the designed thickness;

[0026] After the initial support concrete spraying of the fifth section is completed, the sixth section is excavated and the invert is promptly closed to form a ring.

[0027] By adopting the three-step excavation method of this scheme to excavate the shallow buried extremely soft rock tunnel, the safe step distance of the tunnel is strictly controlled to ensure that the tunnel is closed and looped as soon as possible. The side wall groove construction reduces the disturbance of the step construction to the overall construction of the unlooped tunnel. During the excavation operation, attention is paid to the structural support of the soil in the cave, which can effectively reduce the front and rear interference and reduce the disturbance to the stratum soil. The steel pipe pile construction can effectively resist the lateral and vertical soil pressure during the tunnel excavation process, effectively solve the settlement and large deformation of the tunnel, eliminate the great safety hazards caused by the soft stratum to the tunnel construction, and protect the personal safety of construction personnel and the safety of equipment and property.

[0028] The technical solution of this application is further described below:

[0029] In one of the embodiments, before the first excavation is carried out, the process also includes arranging surface settlement observation points.

[0030] In one of the embodiments, the surface settlement observation points are buried by pouring concrete on site with a burial depth of not less than 30 cm. The surface settlement observation points are spaced 5 m horizontally within 1 times the burial depth outside the land acquisition red line. Within 20 m of the exceeding part, if the burial depth is greater than 20 m, an observation point is set at a lateral interval of every 10 m. If the burial depth is less than 20 m, it is still set at a spacing of 5 m.

[0031] In one of the embodiments, the surface settlement observation points are measured using a total station, and the surface settlement measurement starts at the tunnel burial depth + tunnel height in front of the excavation working face until the lining structure is closed and the settlement basically stops.

[0032] In one embodiment, the excavation working surfaces of the first step, the second step and the third step are kept at a distance of 3m to 5m, and the second part and the third part as well as the fourth part and the fifth part are staggered by 1.2m.

[0033] In one of the embodiments, before excavation work is performed, initial support work is required.

[0034] In one of the embodiments, the initial support operation includes shotcrete construction, which includes an initial shotcrete process and a re-shotcrete process. The initial shotcrete process is carried out after the top is found, the hazard removal measurement is verified to meet the design structure dimensions, and the thickness of the shotcrete is 4cm~5cm. The surrounding rock is sealed early and quickly, and the weak surrounding rock is protected by manual spraying on the slag pile. The re-shotcrete process is carried out after the arch frame, net hanging and other operations are completed under the protection of the surrounding rock reinforced by the initial shotcrete layer.

[0035] In a second aspect of the present application, a tunnel support structure is further provided, which is applied to the construction operation of the three-step excavation method of the shallow buried extremely soft rock tunnel as described above, and the tunnel support structure comprises:

[0036] A first steel pipe pile and a second steel pipe pile, wherein the first steel pipe pile and the second steel pipe pile are arranged side by side and spaced apart in the transverse direction of the tunnel, and the first steel pipe pile and the second steel pipe pile are both extended in the vertical direction;

[0037] A primary support arch frame, wherein the primary support arch frame is arranged between the first steel pipe pile and the second steel pipe pile;

[0038] at least one temporary invert, at least one of the temporary inverts being connected to the interior of the primary support arch; and

[0039] A first connecting mechanism and a second connecting mechanism, wherein the first connecting mechanism is arranged on the side of the first steel pipe pile facing the second steel pipe pile and connected to the outer side wall of the primary support arch frame, and the second connecting mechanism is arranged on the side of the second steel pipe pile facing the first steel pipe pile and connected to the outer side wall of the primary support arch frame.

[0040] The tunnel support structure of this scheme is composed of a first steel pipe pile, a second steel pipe pile, a primary support arch, a temporary invert, a first connecting mechanism and a second connecting mechanism. It not only has a simple structural composition, but also has excellent overall structural performance. It can form a stable and reliable support for the stratum soil in the tunnel, prevent the soft and loose surrounding rock from shifting or even collapsing, ensure the safety of construction personnel and equipment, and eliminate potential safety hazards.

[0041] In one embodiment, the first connecting mechanism and the second connecting mechanism both include a first bull foot structure and a second bull foot structure, the first bull foot structure and the second bull foot structure are arranged vertically with an interval between them, and the first bull foot structure and the second bull foot structure are both connected to the primary support arch frame.

[0042] In one of the embodiments, the tunnel support structure further comprises an inverted arch support, wherein the inverted arch support is spaced below the temporary inverted arch, and opposite ends of the inverted arch support in the length direction are connected and fixed to the primary supporting arch support. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application.

[0044] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0045] FIG. 1 is a schematic structural diagram of a longitudinal section of a tunnel according to an embodiment.

[0046] FIG. 2 is a schematic structural diagram of a tunnel support structure according to an embodiment.

[0047] Description of reference numerals:

[0048] 100. tunnel; 10. tunnel support structure; 11. first steel pipe pile; 12. second steel pipe pile; 13. primary arch support; 14. temporary invert; 15. first connecting mechanism; 15a. first bull foot structure; 15b. second bull foot structure; 16. second connecting mechanism; 17. invert support; 20. first step; 30. second step; 40. third step. DETAILED DESCRIPTION

[0049] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present application, so the present application is not limited by the specific embodiments disclosed below.

[0050] In the description of the present application, it should be understood that if the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. appear, the orientation or position relationship indicated by these terms is based on the orientation or position relationship shown in the accompanying drawings, which is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application.

[0051] In addition, if the terms "first" or "second" appear, these terms are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of this application, if the term "plurality" appears, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0052] In this application, unless otherwise clearly specified and limited, if the terms "installed", "connected", "connected", "fixed" and the like appear, these terms should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integrated connection; it can be a mechanical connection or a welding connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to the specific circumstances.

[0053] In the present application, unless otherwise clearly specified and limited, if there is a description that a first feature is "above" or "below" a second feature, etc., or similar descriptions appear, it may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature being "above", "above" and "above" the second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. The first feature being "below", "below" and "below" the second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0054] It should be noted that if an element is referred to as being "fixed to" or "disposed on" another element, it may be directly on the other element or there may be a central element. If an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. If any, the terms "vertical", "horizontal", "upper", "lower", "left", "right" and similar expressions used in this application are for illustrative purposes only and do not represent the only implementation method.

[0055] As shown in FIG1 , an embodiment of the present application provides a three-step excavation method for a shallow buried extremely soft rock tunnel 100. The tunnel 100 has a first step 20, a second step 30, and a third step 40, wherein the first step 20 is set as a first portion, the second step 30 has a second portion and a third portion arranged at intervals in a transverse direction, and the third step 40 has a fourth portion and a fifth portion arranged at intervals in a transverse direction. The three-step excavation method for the shallow buried extremely soft rock tunnel 100 includes the following steps:

[0056] First, the first excavation is carried out. The specific excavation method is: use the advance small guide tube constructed by the previous cycle steel frame for advance support; use a small excavator to excavate the first part in sections, push the slag to the top surface of the middle step, and use a large excavator to excavate the slag on the lower step. At the same time, advance one frame per cycle, and spray 10cm thick concrete on the heading face to seal it; construct the initial support and temporary arch 14 around the first pilot pit, that is, initially spray 4cm thick concrete, erect steel frames and steel mesh, construct locking foot anchor pipes, set enlarged arch feet at the two arch feet of the first steel frame, and weld the enlarged arch feet to the steel pipe pile brackets on both sides of the line; construct the first advance support; initially spray 2cm thick concrete at the bottom of the pilot pit, erect temporary arch 14 steel frames, and re-spray concrete to the designed thickness, and the initial support and temporary support of the upper pilot pit are closed into a ring.

[0057] Then the second excavation is carried out. The specific excavation method is as follows: after lagging behind the first part by 4.8m, the second part is excavated by excavator. The excavation process is carried out at the bottom of the temporary invert arch 14 of the upper step. It is forbidden to dismantle or cut off the temporary invert arch 14 of the upper step. At the same time, one frame is advanced in each cycle, and 10cm thick concrete is sprayed on the face to seal it; the initial support around the second pilot pit is carried out in sections, that is, 4cm thick concrete is sprayed initially, steel frames and steel mesh are erected, and locking foot anchor pipes are constructed. The arch feet on both sides of the second steel frame are connected to the steel pipe piles on both sides of the line through corbel welding; the second permanent initial support advance support is constructed. In the loose mudstone section, it is required to set an advance small guide pipe in each construction cycle.

[0058] Then the third excavation is carried out. The specific excavation method is as follows: after lagging behind the second part by 1.2m, the third part is excavated manually, and initial support and temporary support are constructed around the pilot pit. The steps and procedures are the same as the second part construction. During the third excavation process, the middle step is excavated to form the step, and the temporary invert 14 of the upper step is removed at the same time, and the temporary invert 14 of the middle step is constructed. During the third excavation process, when the stability of the face is poor, concrete must be sprayed in time to seal the face, and the sealing thickness must be not less than 10cm.

[0059] Then the fourth part is excavated. The specific excavation method is as follows: after lagging behind the third part by 3m, the fourth part is excavated manually with the help of excavators. When excavating the fourth part, excavate at the bottom of the temporary invert arch 14 of the middle step. It is forbidden to dismantle or cut off the temporary invert arch 14 of the middle step. The excavation soil is excavated to the top surface of the lower step; 10cm concrete is initially sprayed to seal the lower step face (required when the surrounding rock is broken), 4cm concrete is initially sprayed, the lower step steel frame is installed, and the locking anchor pipe is installed, and the concrete is sprayed again to the designed thickness.

[0060] Finally, the fifth section was excavated. The specific excavation steps were as follows: after lagging behind the fourth section by 1.2m, the fifth section was excavated manually with the help of an excavator. At the same time, one frame was advanced in each cycle, and one temporary invert 14 of the middle step was removed. A vertical lower step was formed during the excavation process, and the face was sealed with 10cm thick concrete. After the initial spraying of 4cm concrete, the primary support steel frame was installed, the locking anchor pipe was installed, and the concrete was sprayed again to the designed thickness. After the primary support concrete spraying of the fifth section was completed, the sixth section was excavated, and the invert was closed to form a ring in time.

[0061] In summary, the implementation of the technical solution of this embodiment will achieve the following beneficial effects: by adopting the three-step excavation method of this solution to excavate the shallow extremely soft rock tunnel 100, the safe step distance of the tunnel is strictly controlled to ensure that the tunnel is closed into a ring as soon as possible. The side wall groove construction reduces the disturbance of the step construction to the overall construction of the un-ringed tunnel. During the excavation operation, attention is paid to the structural support of the soil in the cave, thereby effectively reducing the front and rear interference and reducing the disturbance to the stratum soil. The steel pipe pile construction can effectively resist the lateral soil pressure and vertical soil pressure during the tunnel excavation process, effectively solve the settlement and large deformation of the tunnel, eliminate the great safety hazards caused by the soft stratum to the tunnel construction, and protect the personal safety of construction personnel and the safety of equipment and property.

[0062] On the basis of the above embodiment, before the first excavation, it also includes arranging surface settlement observation points. By setting up surface settlement observation points, continuous settlement monitoring can be performed in the whole process before, during and after the excavation of the tunnel 100, so as to stop construction or adjust the construction plan when bad geology or abnormal conditions occur, ensure the safety of personnel and equipment, and ensure the safety and progress of construction.

[0063] Specifically, the surface settlement observation points are buried by pouring concrete on site, with a burial depth of no less than 30cm. The horizontal spacing of the surface settlement observation points is 5m within the range of 1 times the burial depth outside the land acquisition red line, and within 20m of the exceeding part. If the burial depth is greater than 20m, an observation point is set at a horizontal spacing of every 10m. If the burial depth is less than 20m, it is still set at a spacing of 5m. In this way, the effect of settlement monitoring can be ensured, and potential safety hazards caused by missing monitoring blind spots can be avoided.

[0064] Furthermore, the total station is used to measure the surface settlement observation points. The surface settlement measurement starts at the tunnel 100 burial depth + tunnel 100 height in front of the excavation working face until the lining structure is closed and the settlement basically stops. During the construction, the measurement frequency of surface settlement is the same as the measurement frequency of vault settlement and clearance level convergence. The measurement frequency is determined according to the displacement speed and the distance between the measuring point and the excavation face. When abnormal conditions or poor geology occur, the monitoring measurement frequency is increased.

[0065] In addition, it is necessary to arrange monitoring and measurement points in the tunnel. The monitoring and measurement sections in the tunnel are arranged every 5m. During the excavation stage, monitoring is carried out once a day. If the deformation rate increases, the monitoring frequency is increased (the daily deformation rate safety value is: 5mm / d).

[0066] It should be noted that the distance between the excavation working faces of the first step 20, the second step 30 and the third step 40 is maintained at 3m~5m, and the second part and the third part, as well as the fourth part and the fifth part should be staggered by 1.2m. In this way, a sufficiently large safety interval can be formed between different excavation working faces to avoid mutual interference between different excavation equipment and personnel.

[0067] In addition, based on any of the above embodiments, before excavation, initial support work needs to be performed. Performing initial support work is an effective measure to effectively control the deformation of surrounding rocks and prevent the collapse of loose and weak soil.

[0068] Specifically in this application, the initial support operation includes shotcrete construction, which includes the initial shotcrete process and the re-shotcrete process. The initial shotcrete process is carried out after the top is found, the hazard removal measurement is verified to meet the design structure dimensions, and the thickness of the shotcrete is 4cm~5cm. The surrounding rock is sealed early and quickly, and the weak surrounding rock is protected by manual spraying on the slag pile; the re-shotcrete process is carried out after the arch frame, net hanging and other operations are completed under the protection of the surrounding rock reinforced by the initial shotcrete layer.

[0069] Shotcrete uses C30 plain concrete. In order to reduce dust, the rebound of shotcrete anchor materials and improve the quality of initial support, shotcrete adopts wet spraying technology. Concrete is mixed centrally at a mixing station, concrete mixer trucks deliver materials into the tunnel, and air compressors supply air.

[0070] Shotcrete is sprayed in sections, slices and layers, from bottom to top, from areas without water or little water to areas with water or more water. Pipes are placed in areas with more water to drain the water. When spraying, the nozzle is basically vertical to the sprayed surface, and the distance is kept at 0.6 to 1.8 meters. When setting up a steel frame, the gap between the steel frame and the rock surface is filled with shotcrete. The spraying sequence is symmetrical from bottom to top. The gap between the steel frame and the surrounding rock is sprayed first, and then the gap between the steel frames is sprayed. The steel frame should be covered with shotcrete, and the protective layer should not be less than 4 cm. Before spraying, level the concave part of the sprayed surface, and then move the nozzle slowly and evenly in a spiral shape, pressing the front half of the circle each time, and the circle diameter is about 30 cm, striving to make the sprayed concrete surface smooth and smooth. The thickness of one spraying is controlled below 6 cm, and the length of each section does not exceed 6 m. The sprayed rebound material shall not be reused as a shotcrete material. The newly sprayed concrete shall be sprinkled with water and cured according to regulations.

[0071] Please refer to Figure 2. In the second aspect of the present application, a tunnel support structure 10 is further provided, which is applied to the construction operation of the three-step excavation method of the shallow buried extremely soft rock tunnel 100 as mentioned above. The tunnel support structure 10 includes a first steel pipe pile 11, a second steel pipe pile 12, an initial support arch frame 13, at least one temporary invert arch 14, a first connecting mechanism 15 and a second connecting mechanism 16.

[0072] The first steel pipe pile 11 and the second steel pipe pile 12 are arranged side by side in the transverse direction of the tunnel 100, and the first steel pipe pile 11 and the second steel pipe pile 12 are both extended in the vertical direction; the primary support arch 13 is arranged between the first steel pipe pile 11 and the second steel pipe pile 12; at least one temporary invert 14 is connected to the inside of the primary support arch 13; the first connecting mechanism 15 is arranged on the side of the first steel pipe pile 11 facing the second steel pipe pile 12 and connected to the outer side wall of the primary support arch 13, and the second connecting mechanism 16 is arranged on the side of the second steel pipe pile 12 facing the first steel pipe pile 11 and connected to the outer side wall of the primary support arch 13.

[0073] The tunnel support structure 10 of the present solution is composed of a first steel pipe pile 11, a second steel pipe pile 12, an initial support arch 13, a temporary invert 14, a first connecting mechanism 15 and a second connecting mechanism 16. It not only has a simple structure, but also has excellent overall structural performance. It can form a stable and reliable support for the stratum soil in the tunnel 100, prevent the soft and loose surrounding rock from shifting or even collapsing, ensure the safety of construction personnel and equipment, and eliminate potential safety hazards.

[0074] In one embodiment, the first connection mechanism 15 and the second connection mechanism 16 both include a first bull foot structure 15a and a second bull foot structure 15b, which are arranged vertically with intervals, and the first bull foot structure 15a and the second bull foot structure 15b are both connected to the primary support arch 13. The first bull foot structure 15a and the second bull foot structure 15b arranged vertically with intervals are connected to the primary support arch 13, and multiple connection points can be formed on the left and right sides of the primary support arch 13, thereby further improving the installation strength and stability of the primary support arch 13.

[0075] For example, the first bull foot structure 15a and the second bull foot structure 15b are both connected and fixed to the primary supporting arch frame 13 by welding.

[0076] In addition, in addition to adopting a single metal component structure, the first bull foot structure 15a and the second bull foot structure 15b can also adopt a combined structure of two or more metal components. The two or more metal components are connected to the primary support arch frame 13 at the same time, thereby increasing the connection area between the first bull foot structure 15a and the second bull foot structure 15b and the primary support arch frame 13, thereby improving the connection strength.

[0077] Furthermore, the tunnel support structure 10 further includes an inverted arch support 17, which is disposed below the temporary inverted arch 14 at intervals, and both opposite ends of the inverted arch support 17 in the length direction are connected and fixed to the primary supporting arch frame 13. The inverted arch support 17 can strengthen the primary supporting arch frame 13, thereby improving the overall structural strength of the entire tunnel support structure 10.

[0078] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0079] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent application shall be subject to the attached claims.

Claims

1. A three-step excavation method for a shallow buried extremely soft rock tunnel, wherein the tunnel has a first step, a second step and a third step, wherein the first step is set as a first portion, the second step has a second portion and a third portion arranged transversely at intervals, and the third step has a fourth portion and a fifth portion arranged transversely at intervals, characterized in that: The three-step excavation method for shallow extremely soft rock tunnels includes the following steps: Carry out the first excavation: Use the advanced small guide tube constructed by the previous cycle steel frame for advanced support; Use a small excavator to excavate the first section in sections, push the slag to the top of the middle step, and use a large excavator to excavate the slag on the lower step. At the same time, advance one frame per cycle, and spray 10cm thick concrete to seal the face; Construct the initial support and temporary invert around the first pilot pit, that is, spray 4cm thick concrete, set up steel frame and steel mesh, construct locking anchor pipe, set up enlarged arch feet at the two arch feet of the first steel frame, and weld the enlarged arch feet to the steel pipe pile brackets on both sides of the line; Carry out the first advance support; Initially spray 2cm thick concrete at the bottom of the pilot pit, set up a temporary invert steel frame, spray concrete again to the designed thickness, and close the initial support of the upper pilot pit with the temporary support to form a ring; The second excavation: After lagging behind the first section by 4.8m, the second section is excavated by an excavator. The excavation process is carried out at the bottom of the temporary invert arch of the upper step. It is forbidden to remove or cut the temporary invert arch of the upper step. At the same time, one frame is advanced in each cycle, and the tunnel face is sealed with 10cm thick concrete. The initial support around the second pilot pit was carried out in sections, i.e., 4 cm thick concrete was sprayed, steel frames and steel mesh were erected, and locking anchor pipes were installed. The arch feet on both sides of the second steel frame were connected to the steel pipe piles on both sides of the line through bracket welding; The second stage of permanent primary support and advance support is implemented. In the loose mudstone section, it is required to set up an advance small guide tube in each construction cycle. The third excavation: After lagging behind the second section by 1.2m, the third section is excavated manually, and initial support and temporary support are carried out around the pilot pit. The steps and procedures are the same as those of the second section. The third excavation process is to excavate the steps of the middle step, and at the same time remove the temporary invert of the upper step and construct the temporary invert of the middle step; When the stability of the tunnel face is poor during the third excavation, concrete must be sprayed to seal the tunnel face in time, and the sealing thickness should not be less than 10cm; The fourth excavation: After lagging behind the third section by 3m, the fourth section is excavated manually with the help of excavators. When excavating the fourth section, the excavation is carried out at the bottom of the temporary invert arch of the middle step. It is forbidden to remove or cut off the temporary invert arch of the middle step. The excavation soil is excavated to the top surface of the lower step. Initially spray 10cm of concrete to seal the lower step face (necessary when the surrounding rock is broken), spray 4cm of concrete for the first time, install the lower step steel frame, and install the foot-locking anchor pipe, and then spray concrete to the designed thickness; The fifth excavation is carried out: After lagging behind the fourth section by 1.2m, the fifth section was excavated manually with the help of excavators. At the same time, one frame was advanced in each cycle, and one temporary invert of the middle step was removed. A vertical lower step was formed during the excavation process, and the face was sealed with 10cm thick concrete. After the initial spraying of 4cm of concrete, install the primary support steel frame, set the locking anchor pipe, and spray concrete again to the designed thickness; After the initial support concrete spraying of the fifth section is completed, the sixth section is excavated and the invert is promptly closed to form a ring.

2. The three-step excavation method for a shallow buried extremely soft rock tunnel according to claim 1 is characterized in that: Before the first excavation, it is also necessary to arrange surface settlement observation points.

3. The three-step excavation method for a shallow buried extremely soft rock tunnel according to claim 2 is characterized in that: The surface settlement observation points are buried on-site by pouring concrete with a burial depth of not less than 30cm. The horizontal spacing of the surface settlement observation points is 5m within 1 times the burial depth outside the land acquisition red line. Within 20m of the exceeding part, if the burial depth is greater than 20m, an observation point is set at a horizontal spacing of every 10m. If the burial depth is less than 20m, it is still set at a spacing of 5m.

4. The three-step excavation method for a shallow extremely soft rock tunnel according to claim 3 is characterized in that: The surface settlement observation points are measured using a total station. The surface settlement measurement starts at the tunnel burial depth + tunnel height in front of the excavation working face and continues until the lining structure is closed and the settlement basically stops.

5. The three-step excavation method for a shallow extremely soft rock tunnel according to claim 1, characterized in that: The distance between the excavation working surfaces of the first step, the second step and the third step is maintained at 3m~5m, and the second part and the third part as well as the fourth part and the fifth part should be staggered by 1.2m.

6. The three-step excavation method for a shallow extremely soft rock tunnel according to claim 1, characterized in that: Before excavation work is carried out, initial support work is required.

7. The three-step excavation method for a shallow extremely soft rock tunnel according to claim 6, characterized in that: The initial support operation includes shotcrete construction, which includes the initial shotcrete process and the re-shotcrete process. The initial shotcrete process is carried out after the top is found, the hazard removal measurement is verified to meet the design structure dimensions. The thickness of the shotcrete is 4cm~5cm. The surrounding rock is sealed early and quickly, and the weak surrounding rock is protected by manual spraying on the slag pile. The re-shotcrete process is carried out after the arch frame, net hanging and other operations are completed under the protection of the surrounding rock reinforced by the initial shotcrete layer.

8. A tunnel support structure, applied to the construction of a three-step excavation method for a shallow buried extremely soft rock tunnel as claimed in any one of claims 1 to 7, characterized in that: The tunnel support structure comprises: A first steel pipe pile and a second steel pipe pile, wherein the first steel pipe pile and the second steel pipe pile are arranged side by side and spaced apart in the transverse direction of the tunnel, and the first steel pipe pile and the second steel pipe pile are both extended in the vertical direction; A primary support arch frame, wherein the primary support arch frame is arranged between the first steel pipe pile and the second steel pipe pile; at least one temporary invert, at least one of the temporary inverts being connected to the interior of the primary support arch; and A first connecting mechanism and a second connecting mechanism, wherein the first connecting mechanism is arranged on the side of the first steel pipe pile facing the second steel pipe pile and connected to the outer side wall of the primary support arch frame, and the second connecting mechanism is arranged on the side of the second steel pipe pile facing the first steel pipe pile and connected to the outer side wall of the primary support arch frame.

9. The tunnel support structure according to claim 8, characterized in that: The first connecting mechanism and the second connecting mechanism both include a first bull foot structure and a second bull foot structure, the first bull foot structure and the second bull foot structure are arranged vertically with an interval between them, and the first bull foot structure and the second bull foot structure are both connected to the primary support arch frame.

10. The tunnel support structure according to claim 8, characterized in that: The tunnel support structure further comprises an inverted arch support, which is arranged below the temporary inverted arch at intervals, and opposite ends of the inverted arch support in the length direction are both connected and fixed to the primary supporting arch support.

Images