A tunnel construction method and support structure under deep clay layer surrounding rock conditions

Abstract

This invention relates to the field of tunnel construction technology, and particularly to a tunnel construction method and support structure under deep clay layer surrounding rock conditions. The tunnel construction method includes the following steps: S1. After completing the support of the excavated section, inserting a pipe into the structure to be excavated in the tunnel, with the pipe extending longitudinally along the tunnel; S2. Pushing the pipe longitudinally along the tunnel so that the tail end of the pipe is in front of the tunnel face; excavating the soil between the tail end of the pipe and the tunnel face; constructing a support structure for the newly excavated tunnel section; S3. Repeating step S2. The tunnel construction method under deep clay layer surrounding rock conditions described in this invention, by pre-inserting the pipe into the structure to be excavated in front of the tunnel face, can improve the stability of the soil in front of the tunnel face, reduce the risk of tunnel collapse caused by tunnel face creep during construction, and facilitate increasing the area of ​​the single excavation section during construction, thereby improving construction efficiency.

Description

Technical Field

[0001] This invention relates to the field of tunnel construction technology, and in particular to a tunnel construction method and support structure under the condition of deep clay layer surrounding rock. Background Technology

[0002] Deep clay layers refer to clayey soil layers with a relatively large thickness (usually considered to be more than 10-15 meters) and relatively uniform properties. These soil layers have low permeability, high water content, high compressibility, and significant creep. When excavating tunnels, soft soil strata are often encountered, especially in karst areas where large areas of karst-filled geology are encountered, requiring tunnels to traverse deep clay layers that can be several kilometers long. When excavating tunnels in these strata, tunnel collapse is easily caused by face creep. To ensure construction safety, the design generally requires sectional excavation, which breaks down the tunnel excavation section into smaller sections, reducing the size of each excavation section, and using segmented support to control face deformation and settlement of the initial tunnel support structure. This method can meet the requirements of tunnel construction, but due to the numerous procedures and small excavation sections, mechanized operations are difficult to achieve, resulting in extremely low construction efficiency. The monthly planned progress is generally less than 15 meters, putting enormous pressure on construction organization. Summary of the Invention

[0003] This invention provides a tunnel construction method and support structure under the condition of deep clay layer surrounding rock, which aims to solve the problem of low tunnel excavation efficiency in deep clay layer surrounding rock to at least a certain extent.

[0004] In a first aspect, the present invention provides a tunnel construction method under conditions of deep clay layer surrounding rock, comprising the following steps:

[0005] S1. After the support of the excavated section is completed, a pipe is installed in the structure to be excavated in the tunnel, and the pipe extends longitudinally along the tunnel.

[0006] S2. Push the insertion tube longitudinally along the tunnel so that the tail end of the insertion tube is in front of the tunnel face;

[0007] Excavate the soil between the tail end of the inserted tube and the working face;

[0008] Construction of support structures for newly excavated tunnel sections;

[0009] S3. Repeat step S2.

[0010] In some embodiments, the tunnel is constructed using the full-face method; as the full-face tunnel face advances forward, an invert arch is excavated at a position lagging behind the full-face tunnel face by a first distance, and the support structure is closed into a ring.

[0011] In some embodiments, the tunnel is constructed using a two-stage method, with the insertion pipe placed in the soil corresponding to the upper stage; as the upper stage face advances forward, the lower stage is excavated at a position lagging behind the upper stage face by a second distance, and the invert arch is excavated at a position lagging behind the upper stage face by a third distance, and the support structure is closed into a ring, wherein the third distance is greater than or equal to the second distance.

[0012] In some embodiments, in step S1, a tube is driven into the tunnel face along the longitudinal direction of the tunnel, so that the tube is at least partially embedded in the structure to be excavated, and a plurality of tubes are arranged in layers on the tunnel face.

[0013] In some embodiments, in step S2, the insertion tube is pushed along the longitudinal direction of the tunnel so that the tail end of the insertion tube is located within 0.6-1.0m in front of the tunnel face.

[0014] In some embodiments, the structure to be excavated is divided into unreinforced sections and reinforced sections distributed longitudinally along the tunnel according to the location of the tail end of the insertion tube, wherein the reinforced sections are located on the side of the unreinforced sections away from the tunnel face; in step S2, the unreinforced sections are excavated.

[0015] In some embodiments, when pushing the insertion pipe along the longitudinal direction of the tunnel: an excavator hydraulic cannon is used to push the insertion pipe, the end of which is provided with a sleeve, which is fitted onto the tail end of the insertion pipe.

[0016] In some embodiments, when constructing a support structure and spraying concrete on a newly excavated tunnel section, the following steps are included:

[0017] Initial shotcrete application to the sidewalls of the newly excavated tunnel;

[0018] Erect a steel frame on the solidified concrete;

[0019] Anchor bolts are installed along the steel frame and embedded in the surrounding rock.

[0020] The newly excavated tunnel sidewalls were sprayed with concrete again.

[0021] In a second aspect, the present invention provides a tunnel support structure under conditions of deep clay layer surrounding rock, and a tunnel construction method under conditions of deep clay layer surrounding rock as described above, comprising:

[0022] Structure to be excavated;

[0023] An insert is embedded in the structure to be excavated. The insert extends longitudinally along the tunnel. The insert includes a pipe body and concrete filler. The pipe body is a steel component. The head end of the pipe body is pointed, and the tail end of the pipe body is spaced apart from the tunnel face.

[0024] In some embodiments, a plurality of the insertion tubes are arranged at vertical and horizontal intervals on the tunnel cross section; the outer diameter of the insertion tubes is 76mm-108mm.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] The tunnel construction method for deep clay-surrounded rock conditions described in this invention improves the stability of the soil in front of the tunnel face by pre-inserting pipes into the structure to be excavated ahead of the tunnel face. This reduces the risk of tunnel collapse caused by face creep during construction, and allows for an increase in the area of ​​the single excavation section, thus improving construction efficiency. Increasing the area of ​​the single excavation section reduces the number of tunnel excavation sections, thereby reducing the amount of temporary support measures required, saving construction costs, shortening the initial support closure time, facilitating control of initial support deformation, ensuring structural safety, and avoiding the safety risk of initial support arch replacement due to secondary excavation caused by deformation. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the tunnel support structure under the condition of thick clay layer surrounding rock as described in the embodiment of the present invention (full-section construction method).

[0028] Figure 2 This is a longitudinal sectional view of the tunnel support structure under the surrounding rock condition of a thick clay layer as described in the embodiment of the present invention (construction using the full-section method).

[0029] Figure 3 This is a longitudinal sectional view of the tunnel support structure under the surrounding rock condition of a thick clay layer as described in the embodiment of the present invention (two-step construction method).

[0030] Figure 4 This is a schematic cross-sectional view of the cannula described in an embodiment of the present invention;

[0031] Figure 5 This is a side view of the cannulation method described in an embodiment of the present invention.

[0032] Marked in the image:

[0033] 1-Structure to be excavated;

[0034] 11 - Unreinforced segment; 12 - Reinforced segment;

[0035] 2-Intubation;

[0036] 21-Head end; 22-Tail end; 23-Pipe body; 24-Concrete filler; 25-Pointed tip;

[0037] 3-Working face;

[0038] 3a - Full-section face; 3b - Upper-step face; 3c - Lower-step face;

[0039] 4-Inverted arch work area;

[0040] 5-Pier;

[0041] 6-Surrounding rock;

[0042] 7-Steel frame. Detailed Implementation

[0043] The present invention will now be described in further detail with reference to specific embodiments. However, this should not be construed as limiting the scope of the present invention to the following embodiments; all technologies implemented based on the content of the present invention fall within the scope of the present invention.

[0044] Unless otherwise specified, the use of terms such as "upper," "lower," "left," "right," "center," "inner," and "outer" to indicate orientation or positional relationships in the description of specific embodiments of the present invention is based on the orientation or positional relationships shown in the accompanying drawings, or the orientation or positional relationship in which the product / equipment / device is typically placed during use. These terms are merely for the purpose of facilitating the description of the present invention or simplifying the description in specific embodiments, enabling those skilled in the art to quickly understand the solution, and do not indicate or imply that a particular device / component / element must have a specific orientation, or be constructed and operated in a specific positional relationship. Therefore, they should not be construed as limitations on the present invention.

[0045] Furthermore, the use of terms such as "horizontal," "vertical," "suspended," and "parallel" does not imply that the corresponding device / component / element must be absolutely horizontal, vertical, suspended, or parallel, but rather that it can be slightly tilted or have a deviation. For example, "horizontal" merely means that its direction is more horizontal relative to "vertical," not that the structure must be completely horizontal, but that it can be slightly tilted. Alternatively, it can be simplified to mean that the corresponding device / component / element, when set in a "horizontal," "vertical," "suspended," or "parallel" direction, can have an error / deviation of ±10% relative to the corresponding direction, more preferably within ±8%, more preferably within ±6%, more preferably within ±5%, and more preferably within ±4%. As long as the corresponding device / component / element is within the error / deviation range, it can still achieve its function in the present invention.

[0046] Furthermore, the use of terms such as "first," "second," and "third" in terminology is merely for distinguishing descriptions of identical or similar components and should not be interpreted as emphasizing or implying the relative importance of a particular component.

[0047] Furthermore, in the description of the embodiments of the present invention, "several", "more than", and "a number of" represent at least two. The number can be any number, such as 2, 3, 4, 5, 6, 7, 8, or 9, and can even exceed nine.

[0048] Furthermore, in the description of the technical solution of this invention, unless otherwise explicitly specified / limited / restricted, the terms "set up," "install," "connect," "link," "provided with," "laid out," and "arranged" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to common connection methods in the art, such as welding, riveting, bolting, and threaded connections. Such connections can be mechanical, electrical, or communication connections; they can be direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components.

[0049] This application is described below with reference to the accompanying drawings and specific embodiments:

[0050] Combination Figures 1 to 5 In a first aspect, embodiments of the present invention provide a tunnel construction method under conditions of deep clay layer surrounding rock, comprising the following steps:

[0051] S1. After the support of the excavated section is completed, a pipe 2 is installed in the tunnel structure 1 to be excavated, and the pipe 2 extends longitudinally along the tunnel.

[0052] S2. Push the insertion tube 2 longitudinally along the tunnel so that the tail end 22 of the insertion tube 2 is in front of the tunnel face 3;

[0053] Excavate the soil between the tail end 22 of the inserted pipe 2 and the working face 3;

[0054] Construction of support structures for newly excavated tunnel sections;

[0055] S3. Repeat step S2.

[0056] In step S1: completing the support of the excavated section refers to supporting the existing excavated part of the tunnel so that the tunnel structure has sufficient strength to maintain the stability of the surrounding rock during subsequent excavation.

[0057] The tunnel's unexcavated structure 1 refers to the soil, rock, etc., located in front of the tunnel face 3 that are planned to be excavated but have not yet been excavated; the area behind the tunnel face 3 refers to all the excavated and supported tunnel sections starting from the tunnel face 3 and heading towards the tunnel entrance; the area in front of the tunnel face 3, in contrast to the area behind, refers to the tunnel sections that have not yet been excavated starting from the tunnel face 3.

[0058] The insertion tube 2 is a rod-shaped structural component, and its length direction is approximately parallel to the longitudinal direction of the tunnel. The insertion tube 2 can be embedded in the tunnel structure 1 to be excavated. By arranging the insertion tube 2 in the tunnel structure 1 to be excavated, the friction between the insertion tube 2 and the surrounding soil can be used to connect the relatively loose soil to form a relatively compact consolidated body, thereby improving the integrity and stability of the soil and reducing the risk of tunnel collapse caused by creep of the face 3 during construction. On this basis, since the soil in front of the face 3 is reinforced, the area of ​​the single excavation section can be increased while maintaining the stability of the face 3, thereby reducing the number of sections in the tunnel sectional excavation process. Tunnel sectional excavation refers to the method of dividing the cross-section into several small parts during tunnel construction, excavating and supporting them step by step in a certain order, and finally forming a complete tunnel structure. The number of sections refers to the number of small parts into which the cross-section is divided. Since each part in the tunnel sectional excavation needs to be supported after excavation, reducing the number of sections means reducing the number of support measures, which means fewer construction steps and higher construction efficiency. Especially for deep clay layers, by setting several insertion pipes 2 in the structure to be excavated 1 in front of the tunnel face 3, the probability of the tunnel face 3 collapsing, sliding or gushing forward can be greatly reduced. This allows the full-face method or two-stage method to be used when tunneling in deep clay layers, greatly reducing the number of sections in tunnel excavation and the number of temporary support measures, thereby improving construction efficiency.

[0059] Optionally, the length dimension of the intubation tube 2 is 20 times or more greater than the dimensions in the other two directions; the intubation tube 2 is arranged parallel to the longitudinal direction of the tunnel. Exemplarily, the diameter of the intubation tube 2 is 76 mm and the length is 9000 mm.

[0060] Optionally, insert pipes 2 are driven into the tunnel face 3 along the longitudinal direction of the tunnel, so that the insert pipes 2 are at least partially embedded in the structure 1 to be excavated, and several insert pipes 2 are arranged in layers on the tunnel face 3 to facilitate mechanical excavation.

[0061] To facilitate control of the direction of the insertion tube 2, a borehole parallel to the longitudinal direction of the tunnel can be pre-drilled on the tunnel face 3. The depth of the borehole is less than the length of the insertion tube 2. The reason for not drilling an excessively long borehole is that, compared to pushing the insertion tube 2 into the excavated structure 1 of the tunnel, drilling a borehole in advance and then inserting the insertion tube 2 would weaken the friction between the insertion tube 2 and the surrounding soil, reducing the effect of the insertion tube 2 in reinforcing the soil. Therefore, it is only necessary to set a borehole of a length that can serve as a guide, for example, the length of the borehole can be 0.2 meters to 1 meter.

[0062] Layered arrangement refers to the method of arranging the insertion tubes 2 in orderly rows and columns on the working face 3, for example... Figure 1The tubes are arranged in a 3-layer, 6-column configuration, with 3 vertical layers and 6 horizontal columns. Optionally, all tubes 2 in each layer are located at the same height, and the vertical projections of all tubes 2 in each row overlap or partially overlap. Depending on the shape of the face, the tubes 2 in different layers and different columns can be the same or different. Optionally, the layer spacing and row spacing of the tubes 2 are no more than 3 meters, and can be controlled at 2-3 meters.

[0063] In step S2: Construction equipment can be used to apply a thrust approximately parallel to the longitudinal direction of the tunnel to the insertion pipe 2, so as to push the insertion pipe 2 to move along the longitudinal direction of the tunnel until the tail end 22 of the insertion pipe 2 is located in front of the working face 3 and at a certain distance from the working face 3; that is, by pushing the insertion pipe 2, the tail end 22, which was originally protruding from or close to the working face 3, is extended into the excavated structure 1 in front of the working face 3, and the tail end 22 is at a certain distance from the working face 3, which can be the length of a single tunnel excavation.

[0064] Combination Figure 2 and Figure 3 Based on the distance between the intubation tube 2 and the working face 3, the two ends of the intubation tube 2 can be divided into the head end 21 and the tail end 22, respectively. The head end 21 is farther from the working face 3 than the tail end 22 is farther from the working face 3.

[0065] In some embodiments, an excavator hydraulic cannon is used to push the insertion tube 2. The excavator hydraulic cannon has a sleeve at its end, which is fitted onto the tail end 22 of the insertion tube 2. The excavator hydraulic cannon, also known as an excavator breaker, refers to a drilling device installed at the end of the excavator's robotic arm for impacting and breaking rock formations. It mainly uses the excavator's main pump to provide high-pressure hydraulic oil to drive the internal piston to reciprocate at high speed, thereby applying a huge impact force to the target object. To reduce the serious damage to the insertion tube 2 caused by the excavator hydraulic cannon during impact and to facilitate alignment of the insertion tube 2, the cannon's drill bit can be replaced with a sleeve that can fit over the insertion tube 2. The sleeve includes an outer shell and an inner cavity formed by the outer shell. One end of the inner cavity is open to allow the tail end 22 of the insertion tube 2 to enter, and the other end of the inner cavity is provided with an impact part for striking the insertion tube 2. During impact, the sleeve moves back and forth along the length of the insertion tube 2, causing the impact part to reciprocate to strike the tail end 22 of the insertion tube 2, pushing the insertion tube 2 forward. Excavator-mounted hydraulic cannons are common equipment in tunnel construction. Using the installation head of the excavator-mounted hydraulic cannon to push and insert the pipe 2 has the advantages of simple modification and convenient construction.

[0066] Optionally, the inner cavity has a certain depth so that the tail end 22 of the insertion tube 2 can always be located in the inner cavity of the sleeve during the impact of the excavator oil cannon, reducing the probability of the insertion tube 2 being deflected during the impact.

[0067] In some embodiments, during step S2, when pushing the insertion tube 2 longitudinally along the tunnel, the tail end 22 of the insertion tube 2 is positioned within a range of 0.6m-1.0m in front of the tunnel face 3, that is... Figure 2 and Figure 3 The length of L is a value between 0.6m and 1.0m, which is the length of a single tunnel excavation.

[0068] After pushing the tail end 22 to a certain position in front of the tunnel face 3, the soil between the tail end 22 and the tunnel face 3 is excavated, allowing the tunnel face 3 to advance forward. Then, a support structure is constructed for the newly excavated tunnel section. At this time, the newly formed tunnel face 3 is close to the tail end 22 of the insertion pipe 2. The insertion pipe 2 is embedded in the soil in front of the newly formed tunnel face 3. The insertion pipe 2 can reduce the probability of the newly formed tunnel face 3 collapsing, giving the construction workers time to construct a support structure for the newly excavated tunnel section. Moreover, since the insertion pipe 2 has been pushed forward, it is not necessary to cut or break the insertion pipe 2 when excavating the soil. On the one hand, this reduces the difficulty of excavation, and on the other hand, it allows the insertion pipe 2 to be reused multiple times without the need to repeatedly install the insertion pipe 2.

[0069] Optionally, the structure to be excavated 1 is divided into an unreinforced section 11 and a reinforced section 12 distributed along the longitudinal direction of the tunnel according to the location of the tail end 22 of the insertion tube 2. The reinforced section 12 is located on the side of the unreinforced section 11 away from the tunnel face 3. In step S2, the unreinforced section 11 is excavated, and there is no insertion tube 2 in the unreinforced section 11.

[0070] For the support structure constructed on newly excavated tunnel sections, existing tunnel construction techniques can be referenced. Demonstration support techniques may include: initial shotcrete → erection of steel frame 7 → installation of anchor bolts → installation of pre-support anchor bolts → installation of radial anchor bolts → re-shotcrete, etc.

[0071] Optionally, when constructing a support structure and spraying concrete on a newly excavated tunnel section, the following steps may be included:

[0072] S2031. Apply initial shotcrete to the newly excavated tunnel sidewalls, covering the tunnel arch and sidewalls;

[0073] S2032. A steel frame 7 is erected on the solidified concrete. The steel frame 7 is an arc-shaped structure, with its two ends supported by the surrounding rock 6 on both sides of the tunnel, and its top supporting the tunnel arch.

[0074] S2033. Anchor bolts are installed along the steel frame 7. The anchor bolts are embedded in the surrounding rock 6. The anchor bolts may include locking anchor bolts at both ends of the steel frame 7 and radial anchor bolts arranged at intervals along the circumference of the tunnel. Both the locking anchor bolts and the radial anchor bolts are embedded in the surrounding rock 6 and partially protrude from the tunnel sidewall. The protruding part is connected to the steel frame 7.

[0075] S2034. Apply sprayed concrete to the newly excavated tunnel sidewalls, and cover the steel frame 7 with the sprayed concrete.

[0076] After the newly excavated tunnel section is supported, step S2 is repeated for cyclical construction. The insertion pipe 2 is pushed forward so that the tail end 22 of the insertion pipe 2 is in front of the newly excavated tunnel face 3. The soil between the tail end 22 of the insertion pipe 2 and the newly excavated tunnel face 3 is excavated and a support structure is constructed.

[0077] The tunnel construction method described in this embodiment under deep clay layer surrounding rock conditions improves the stability of the soil in front of the tunnel face 3 by pre-inserting the insertion pipe 2 into the excavation structure 1 in front of the tunnel face 3. This reduces the risk of tunnel collapse caused by creep of the tunnel face 3 during construction, and allows for an increase in the area of ​​the single excavation section, thus improving construction efficiency. Increasing the area of ​​the single excavation section reduces the number of tunnel excavation sections, thereby reducing the number of temporary support measures, saving construction costs, shortening the initial support closure time, facilitating control of initial support deformation, ensuring structural safety, and avoiding the safety risk of initial support arch replacement caused by secondary excavation due to deformation.

[0078] Combination Figure 1 and Figure 2 In some embodiments, the tunnel is constructed using the full-face method, which refers to excavating and shaping the entire tunnel excavation section as a whole in one go. Unlike excavation and support in multiple steps, the full-face method has only one complete working face, which is very suitable for the use of large and efficient mechanized equipment. It has high construction efficiency, and the one-time shaping avoids repeated disturbance to the surrounding rock 6 by multiple blasting, making the excavation outline smoother and more accurate, with less over-excavation. The initial support is implemented on a complete section, which can quickly form a closed and high-bearing-capacity support ring, which is very beneficial to the stability of the surrounding rock 6. It also eliminates the need for support system conversion, which helps to avoid the safety risks brought about by arch replacement.

[0079] Optionally, as the full-section tunnel face 3a advances, the invert arch is excavated using a simple trestle bridge at a certain distance behind the full-section tunnel face 3a, and the full-section support structure is closed into a ring. This distance can be defined as the first distance, which can be selected as 15-20 meters.

[0080] The term "full-section face 3a" refers to the complete face formed by full-section excavation.

[0081] The invert arch is a reverse arch structure at the bottom of the tunnel. Its function is to resist the pressure of the strata and, together with the tunnel lining, form a complete and stable load-bearing ring, i.e., a closed ring. When constructing the invert arch, a groove needs to be excavated on the ground to form an invert arch working area 4. The simple trestle bridge refers to a temporary bridge structure erected above the invert arch working area 4 to facilitate the passage of transport vehicles. Using the simple trestle bridge for excavation can realize a three-dimensional operation mode of "vehicles on the bridge and construction under the bridge", avoiding the risk of cross-operation of vehicles and personnel. The two key processes of "excavation and muck removal" and "invert arch construction", which originally needed to be carried out in sections and sequentially, are now carried out simultaneously, significantly shortening the single-cycle operation time and accelerating the overall construction progress.

[0082] The construction of the invert arch can refer to existing tunnel construction techniques, and may include the following steps:

[0083] Step 1: Move trestle 5 above the planned excavation section of the invert arch;

[0084] Step 2: Enter the area under the trestle 5 from one end or a specific side entrance, and excavate according to the measured outline and depth. After excavating to the design elevation, check the geological conditions of the foundation and, if necessary, compact, replace, or grout for reinforcement.

[0085] Step 3: Transport the prefabricated inverted arch steel frame or grid steel frame to the area below trestle bridge 5 for installation, ensuring that the steel frame is firmly connected to the steel frame of the side wall to form a closed support ring;

[0086] Step 4: After the steel frame is installed, spray concrete immediately to cover the steel frame and seal the rock surface, forming the initial support system for the invert arch;

[0087] Step 5: Lay a geotextile buffer layer on the initial support surface, then lay a tunnel-specific waterproof membrane (such as HDPE), with the overlap width meeting the requirements, and use hot-melt welding;

[0088] Step Six: Tie the secondary lining reinforcement of the invert arch onto the waterproof layer;

[0089] Step 7: Erect the formwork and pour the inverted arch concrete, and use a vibrator to fully compact it;

[0090] Step 8: Once the invert concrete reaches the required strength, move trestle 5 forward and construct the invert filling layer or central drainage ditch on the exposed, poured invert concrete. At this point, trestle 5 is moved to the next position, with one end of trestle 5 placed on the freshly poured invert concrete and the other end placed on the soil at the bottom of the tunnel. Steps 1 to 7 can be repeated to carry out the invert construction at the next position.

[0091] During the construction of the aforementioned inverted arch, transport vehicles can pass normally via trestle bridge 5.

[0092] Combination Figure 3 In some embodiments, the tunnel is constructed using a two-stage method, with the insertion pipe 2 placed in the soil corresponding to the upper stage. The two-stage method refers to dividing the entire tunnel cross-section vertically into two parts, like two steps, and excavating and supporting them sequentially. The advantages of the two-stage method are its flexibility, safety, and adaptability to geology. Compared to construction methods with more sections, such as the three-stage method, the two-stage method has only two steps, resulting in relatively higher construction efficiency. Compared to the full-section method, the two-stage method can significantly reduce the disturbance to the surrounding rock 6 during a single excavation, which is beneficial for controlling the deformation of the surrounding rock 6.

[0093] Optionally, as the upper bench face 3b advances forward, the lower bench is excavated at a position two distances behind the upper bench face 3b, and the invert arch is excavated at a position three distances behind the upper bench face 3b. The support structure is then closed into a ring, with the third distance being greater than or equal to the second distance. The second distance can be selected as 15-20 meters, and the third distance can be selected as 15-20 meters.

[0094] The upper bench face 3b refers to the face corresponding to the upper bench in the two-bench method of construction. In the two-bench method, in addition to the upper bench face 3b, there is also the lower bench face 3c, which lags behind the upper bench face 3b by a second distance. After the excavation of the lower bench face 3c is completed, the invert can be constructed within the newly excavated tunnel section. The excavation and construction of the lower bench can refer to existing tunnel construction techniques, and may include the following steps:

[0095] Step 1: Follow-up excavation: After advancing a certain safe distance on the upper bench, start excavating the lower bench. This distance is a key parameter. If it is too short, there will be mutual interference. If it is too long, it will not be conducive to support and early closure.

[0096] Step 2: Extend the steel frame: After the lower step is excavated, extend the steel frame of the upper step to the bottom of the side wall;

[0097] Step 3: Sidewall support: The same anchor bolt, wire mesh, and shotcrete operations are carried out to complete the initial support of the sidewall.

[0098] In summary, by adopting the tunnel construction method provided by this invention, the stability of the soil in front of the tunnel face 3 can be improved, thereby increasing the area of ​​the excavation section in one go. This allows for the use of the full-section method or the two-stage method in tunnel construction in areas such as deep clay layers, significantly improving the efficiency of tunnel construction under special geological conditions, reducing the number of temporary support measures, saving construction costs, reducing the initial support closure time, controlling the deformation of the initial support, and ensuring structural safety. At the same time, it can effectively avoid the problem that in multi-part excavation, the support structure of the previously excavated part is easily deformed by the later excavated part, which requires arch replacement, which poses a very high safety risk. It also reduces the amount of over-excavation and over-filling caused by differential deformation and facilitates mechanized construction.

[0099] In a second aspect, embodiments of the present invention provide a tunnel support structure under conditions of deep clay layer surrounding rock, based on the tunnel construction method under conditions of deep clay layer surrounding rock as described above, including a plurality of insert pipes 2 embedded in the structure to be excavated 1, the insert pipes 2 being arranged to extend longitudinally along the tunnel.

[0100] Combination Figure 4 and Figure 5 In some embodiments, the insertion tube 2 includes a tube body 23 and concrete filler 24. The tube body 23 is a steel component. The head end 21 of the tube body 23 is provided with a pointed tip 25, and the tail end 22 of the tube body 23 is spaced apart from the working face 3.

[0101] Optionally, the concrete filler 24 in the pipe body 23 is poured before the insertion pipe 2 is driven into the structure 1 to be excavated. The pipe body 23 can be a steel pipe. Steel pipe has high strength and rigidity, which can reduce the probability of hole expansion during the pushing and pressing of the insertion pipe 2 and maintain the integrity of the insertion pipe 2.

[0102] In some embodiments, a plurality of insertion tubes 2 are arranged at intervals along the vertical and horizontal sides in the tunnel cross-section; the outer diameter of the insertion tubes 2 is 76mm-108mm, which is much larger than that of existing tunnel anchors, reaching more than 4 times; in some embodiments, the insertion tubes 2 are also referred to as pipe sheds. Exemplarily, the pipe body 23 is a steel round pipe with a diameter of 76mm, a wall thickness of 5mm, and a length of 9000mm, and the head end 21 of the pipe body 23 is tapered to form a pointed tip 25.

[0103] In a third aspect, embodiments of the present invention provide a tunnel construction method under conditions of deep clay layer surrounding rock, comprising the following steps:

[0104] In the high-step area, oil cannons (vibrating mechanical equipment) can be used to push and press 76-108 pipe roofs (concrete is poured into the steel pipes to increase the pushing stiffness) in layers along the longitudinal direction of the tunnel face 3. The pipe roofs are spaced at certain intervals to form a reinforced structure of the surrounding soil 6, which restricts the plastic deformation or collapse of the soil at the face 3. Each advance is 0.6 meters to 1.0 meters. After timely support is completed, the excavation continues. As the tunnel is excavated, the pipe roofs are continuously pushed and pressed behind the face 3 to ensure the stability of the face 3.

[0105] Specifically, it includes the following steps:

[0106] ① Complete the support of the excavated section to form a normal high-step construction condition;

[0107] ② Lay out the points and lines on the working face 3 to determine the position of the pipe 2. In principle, the layer spacing and row spacing should not be greater than 3 meters (controlled by 2-3 meters). To facilitate mechanical excavation, the support points are arranged in rows.

[0108] ③ Fabricate a tube 2 with a diameter of 76mm, a wall thickness of 5mm, and a length of 9000mm. To ensure the rigidity of the tube 2, fill the tube with concrete and sharpen the front end.

[0109] ④ Make a connector for the excavator hydraulic cannon, that is, replace the cannon's drill bit with a connector that can fit the 76 plug tube 2 ends;

[0110] ⑤ Transport pipe 2 into the tunnel, and use the excavator's ram and jack to push pipe 2 forward along the planned point in the longitudinal direction of the tunnel (in the same direction as the tunnel) until it is fully pushed in, and push the end into the tunnel face 360-100cm.

[0111] ⑥ Use an excavator to excavate the unpipe-free soil behind the working face 3, and use a construction support trolley to carry out support operations such as steel frame installation and anchor pipe installation;

[0112] ⑦ After the shotcrete of the support structure is completed and meets a certain strength, the next cycle of construction will be carried out, and the jack head will continue to push the insertion pipe 2.

[0113] ⑧ The inverted arch and the lower step are excavated about 15-20m behind using a simple trestle bridge, and the full-section support structure is closed into a ring.

[0114] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A tunnel construction method under conditions of deep clay layer surrounding rock, characterized in that, The tunnel support structure includes a tunnel support structure under the condition of deep clay layer surrounding rock. The tunnel support structure under the condition of deep clay layer surrounding rock includes a structure to be excavated (1) and a pipe (2). The pipe (2) is embedded in the structure to be excavated (1). The pipe (2) extends along the longitudinal direction of the tunnel. The pipe (2) includes a pipe body (23) and concrete filler (24). The pipe body (23) is a steel component. The head end (21) of the pipe body (23) is provided with a pointed tip (25). The tail end (22) of the pipe body (23) is spaced apart from the tunnel face (3). On the tunnel cross section, several of the pipes (2) are arranged at intervals in the vertical and horizontal directions. The outer diameter of the pipe (2) is 76mm-108mm. The tunnel construction method includes the following steps: S1. After the support of the excavated section is completed, a pipe (2) is installed in the structure (1) to be excavated in the tunnel, and the pipe (2) extends longitudinally along the tunnel. S2. Push the insertion tube (2) along the longitudinal direction of the tunnel so that the tail end (22) of the insertion tube (2) is in front of the tunnel face (3); Excavate the soil between the tail end (22) of the inserted tube (2) and the working face (3); Construction of support structures for newly excavated tunnel sections; S3. Repeat step S2; The tunnel is constructed using the two-stage method, and the insertion pipe (2) is placed in the soil corresponding to the upper stage; As the upper step face (3b) advances forward, the lower step is excavated at a position that lags behind the upper step face (3b) by a second distance, and the invert arch is excavated at a position that lags behind the upper step face (3b) by a third distance, and the support structure is closed into a ring, wherein the third distance is greater than or equal to the second distance.

2. The tunnel construction method under deep clay layer surrounding rock conditions according to claim 1, characterized in that, In step S1, a pipe (2) is driven into the tunnel face (3) along the longitudinal direction of the tunnel, so that the pipe (2) is at least partially embedded in the structure to be excavated (1), and several pipes (2) are arranged in layers on the tunnel face (3).

3. The tunnel construction method under deep clay layer surrounding rock conditions according to claim 1, characterized in that, In step S2, the insertion tube (2) is pushed along the longitudinal direction of the tunnel so that the tail end (22) of the insertion tube (2) is located within 0.6-1.0m in front of the tunnel face (3).

4. The tunnel construction method under deep clay layer surrounding rock conditions according to claim 1, characterized in that, According to the location of the tail end (22) of the insertion tube (2), the structure (1) to be excavated is divided into an unreinforced section (11) and a reinforced section (12) distributed along the longitudinal direction of the tunnel. The reinforced section (12) is located on the side of the unreinforced section (11) away from the tunnel face (3). In step S2, the unreinforced section (11) is excavated.

5. The tunnel construction method under deep clay layer surrounding rock conditions according to claim 1, characterized in that, When pushing the insertion pipe (2) along the longitudinal direction of the tunnel: the excavator oil cannon is used to push the insertion pipe (2), and the end of the excavator oil cannon is provided with a sleeve, which is inserted into the tail end (22) of the insertion pipe (2).

6. The tunnel construction method under deep clay layer surrounding rock conditions according to any one of claims 1-5, characterized in that, When constructing support structures and spraying concrete on newly excavated tunnel sections, the following steps are included: Initial shotcrete application to the sidewalls of the newly excavated tunnel; Erect a steel frame on the solidified concrete (7). Anchor bolts are installed along the steel frame (7) and embedded in the surrounding rock (6). The newly excavated tunnel sidewalls were sprayed with concrete again.

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