Support system for tunnel in layered weakly cemented swelling rock

Abstract

The utility model belongs to underground engineering technical field discloses a kind of supporting system for layered weakly cemented swelling rock tunnel, including the surrounding rock pressure-relief joint being set in tunnel floor and side wall, and surrounding rock pressure-relief joint is filled with buffer material;The arch crown and side wall of tunnel are also anchored into reinforced anchor rod;Reinforced anchor rod is adjustable length's anchor rod, including top anchor rod section, several intermediate anchor rod sections and bottom anchor rod section;Top anchor rod section, intermediate anchor rod section, bottom anchor rod section all include hollow pipe, hollow pipe is fixedly connected with hollow circular-truncated-cone pipe outside circumference, and the end of small diameter of circular-truncated-cone pipe is towards the top end of reinforced anchor rod;Side opening is set on the pipe and circular-truncated-cone pipe.In tunnel, surrounding rock pressure-relief joint can release the expansion stress and interlayer slip energy of layered weakly cemented swelling rock, avoid supporting structure to be damaged;Reinforced anchor rod forms sawtooth anchorage body in anchor hole, strengthens the interlayer adhesion of layered weakly cemented swelling rock, effectively controls the interlayer deformation of layered weakly cemented swelling rock.

Description

Technical Field

[0001] This utility model belongs to the field of underground engineering technology, specifically relating to a support system for layered weakly cemented expansive rock tunnels. Background Technology

[0002] The statements in this section are merely background information related to this utility model and do not necessarily constitute prior art.

[0003] The structural characteristics of layered, weakly cemented expansive rock are as follows: 1) The rock mass consists of layered rocks and weak interlayers with weak interlayer bonding; 2) The cementation between rock particles is weak, making it prone to breakage and weathering; 3) The rock mass contains clay minerals such as montmorillonite, which expand in volume upon contact with water, generating enormous expansion force; 4) The strength of the rock mass decreases significantly under the influence of water; 5) Under high ground stress, it is prone to unloading relaxation and compression deformation. When constructing tunnels in layered, weakly cemented expansive rock, traditional support systems often adopt a circumferentially uniform arrangement, failing to fully consider the changes in bedding direction and the influence of expansion pressure, resulting in the lining structure bearing asymmetrical loads and being prone to failure.

[0004] Existing technology discloses an asymmetric support structure for layered soft rock tunnels, including pipe roof support perpendicular to the bedding plane of the layered soft rock, pipe roof support not perpendicular to the bedding plane of the layered soft rock, steel arch frame, mortar anchors perpendicular to the bedding plane of the layered soft rock, mortar anchors not perpendicular to the bedding plane of the layered soft rock, and pressure-type anchor cables. By employing an asymmetric support structure, and targeting layered soft rock strata with different bedding plane dip angles, the support structure is strengthened in the direction perpendicular to the bedding plane where compression failure is more likely to occur, effectively improving the stress state of the tunnel support structure.

[0005] While the above solution can address the problem that traditional support systems with uniform circumferential arrangement are susceptible to failure under asymmetric loads, the following issues still exist: Although the above scheme uses asymmetrically arranged anchor bolts for support, its support method is still mainly based on rigid resistance, which cannot release the expansion stress and interlayer slip energy of the layered weakly cemented expansive rock. This may lead to the failure of the support structure, such as initial support cracking and steel frame twisting. In addition, the mortar anchor bolts in the above scheme are traditional structures that only adapt to the bedding direction through length differences. They cannot strengthen the interlayer bonding of the layered weakly cemented expansive rock. When the layered weakly cemented expansive rock is deformed, it cannot effectively control the interlayer deformation. Utility Model Content

[0006] In view of this, the purpose of this utility model is to provide a support system for layered weakly cemented expansive rock tunnels, which can solve the technical problems in the prior art where the support structure is mainly based on rigid resistance, which may lead to the destruction of the support structure, and traditional anchor bolts cannot strengthen the interlayer bonding of layered weakly cemented expansive rock.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A support system for layered, weakly cemented, expansive rock tunnels is provided, including rock pressure relief joints opened in the tunnel floor and sidewalls, the rock pressure relief joints being filled with buffer material; reinforced anchor bolts are also anchored into the tunnel arch and sidewalls. The reinforced anchor bolt is an adjustable length anchor bolt, including a top anchor bolt section, several intermediate anchor bolt sections, and a bottom anchor bolt section; the top anchor bolt section, intermediate anchor bolt section, and bottom anchor bolt section all include a hollow round tube, and a hollow frustum tube is fixedly connected to the outer circumference of the round tube, with the smaller diameter end of the frustum tube facing the top of the reinforced anchor bolt; both the round tube and the frustum tube have side openings.

[0008] Preferably, a flexible steel wire rope bundle is also connected to the side opening. The fixed end of the steel wire rope bundle is welded to the inner wall of the round tube of the intermediate anchor section, and the free end of the steel wire rope bundle passes through the side opening of the round tube and the frustum tube and extends out of the intermediate anchor section.

[0009] Preferably, the top outer walls of the bottom anchor bolt section and the middle anchor bolt section are provided with external threads, and the bottom inner walls of the top anchor bolt section, the middle anchor bolt section and the bottom anchor bolt section are provided with internal threads.

[0010] Preferably, the top anchor section, the middle anchor section, and the bottom anchor section are all open at both ends.

[0011] Preferably, when the layered weakly cemented expansive rock has inclined or vertical bedding, the pressure relief joints of the surrounding rock are parallel to the direction of the bedding; when the layered weakly cemented expansive rock has horizontal bedding, the pressure relief joints of the surrounding rock of the bottom plate are perpendicular to the direction of the bedding, and the pressure relief joints of the surrounding rock of the side walls on both sides cut into the layered weakly cemented expansive rock in the direction away from the tunnel.

[0012] Preferably, the depth of the rock pressure relief joint is greater than half the width of the tunnel floor slab, and the width should be 200-300mm.

[0013] Preferably, the strength of the buffer material is no more than 70% of the strength of the underlying rock stratum.

[0014] Preferably, when the bedding of the layered weakly cemented expansive rock is horizontal, the reinforced anchor bolts are denser in the tunnel arch; when the bedding of the layered weakly cemented expansive rock is inclined, the reinforced anchor bolts are denser in the arch and diagonal areas parallel to the bedding; when the bedding of the layered weakly cemented expansive rock is inclined, the reinforced anchor bolts are denser on both sidewalls of the tunnel.

[0015] Preferably, the length of the reinforced anchor bolt is greater than or equal to one tunnel span.

[0016] Preferably, the support system also includes initial support and drainage ditches opened on the tunnel floor.

[0017] Compared with the prior art, the advantages and positive effects of this utility model are: This invention involves creating rock pressure relief joints in the tunnel floor and sidewalls, filling these joints with buffer material to alter the stress state of the surrounding rock. This places the tunnel strata in a stress-reduced zone, shifting the maximum stress within the layered, weakly cemented expansive rock tunnel inward by 1 to 3 times the tunnel radius. This releases the expansion stress and interlayer slip energy of the layered, weakly cemented expansive rock, preventing damage to the support structure. The reinforced anchor rod features a smaller diameter end facing the top of the reinforced anchor rod, and a larger diameter end facing the tail end. The reinforced anchor rod forms a sawtooth-like, undulating anchor body within the anchor hole, providing a one-way locking function. This strengthens the anchor rod's pull-out resistance, preventing it from detaching from the rock mass, and enhances the interlayer bonding of the layered, weakly cemented expansive rock, effectively controlling its interlayer deformation. Attached Figure Description

[0018] The accompanying drawings, which form part of this specification, are used to provide a further understanding of this utility model. The illustrative embodiments of this utility model and their descriptions are used to explain this utility model and do not constitute an improper limitation of this utility model.

[0019] Figure 1 This is a schematic diagram of a support system for a layered, weakly cemented, expansive rock tunnel according to an embodiment of this utility model; Figure 2 This is a schematic diagram of a reinforced anchor bolt according to an embodiment of the present utility model; Figure 3 This is a schematic diagram of the intermediate anchor section of an embodiment of the present utility model; Figure 4 This is a schematic diagram of the bottom end of the bottom anchor section in an embodiment of this utility model; Figure 5 This is a schematic diagram of the arrangement of pressure relief joints in the surrounding rock under inclined bedding according to an embodiment of this utility model; Figure 6 This is a schematic diagram of the arrangement of pressure relief joints in the surrounding rock under vertical bedding according to an embodiment of this utility model; Figure 7 This is a schematic diagram of the arrangement of pressure relief joints in the surrounding rock under horizontal bedding according to an embodiment of this utility model; Figure 8 This is a schematic diagram of the arrangement of reinforced anchor bolts under horizontal stratification according to an embodiment of the present utility model; Figure 9 This is a schematic diagram of the arrangement of reinforced anchor bolts under inclined strata according to an embodiment of the present invention; Figure 10 This is a schematic diagram of the arrangement of vertically layered reinforced anchor bolts according to an embodiment of the present invention; In the picture: 1. Tunnel; 2. Surrounding rock pressure relief joint; 3. Buffer material; 4. Reinforced anchor bolt; 41. Top anchor bolt section; 42. Middle anchor bolt section; 43. Bottom anchor bolt section; 44. Circular pipe; 45. Frustum-shaped pipe; 46. Side opening; 47. Wire rope bundle. Detailed Implementation

[0020] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0021] The present invention will now be described in detail with reference to the accompanying drawings. This embodiment discloses a support system for layered, weakly cemented, expansive rock tunnels, such as... Figure 1 , Figure 8 As shown, the application in tunnel 1 includes rock pressure relief joints 2 formed in the floor slab and sidewalls of tunnel 1, with buffer material 3 filling the rock pressure relief joints 2. Filling the rock pressure relief joints 2 with buffer material 3 has two functions: first, it reduces the deformation of the tunnel surrounding rock and relieves pressure; second, it prevents water on the floor slab from seeping downwards into the deep layered, weakly cemented, expansive rock strata.

[0022] In this embodiment, the surrounding rock pressure relief joint 2 can change the stress state of the tunnel surrounding rock, so that the tunnel strata are in a stress reduction zone to ensure the stability of the surrounding rock. The surrounding rock pressure relief joint 2 can move the maximum stress in the surrounding rock of the layered weak cemented expansive rock tunnel inward by 1 to 3 times the tunnel radius.

[0023] It should be noted that during the tunnel excavation process, rock drills were used to simultaneously cut surrounding rock pressure relief joints 2 on the bottom slab and sidewalls. These joints, as part of tunnel 1, fully utilize their pressure relief function. Furthermore, by creating these joints, the expansion stress and interlayer slip energy of the layered, weakly cemented expansive rock can be released, preventing damage to the support structure.

[0024] like Figure 1 As shown, reinforced anchor bolts 4 are also anchored into the arch and sidewalls of tunnel 1. Figure 1 , Figure 2 As shown, the reinforced anchor bolt 4 is an adjustable-length anchor bolt, comprising a top anchor bolt section 41, several intermediate anchor bolt sections 42, and a bottom anchor bolt section 43. It is understood that the length of the reinforced anchor bolt 4 varies depending on its installation location, and can be changed by increasing or decreasing the number of intermediate anchor bolt sections 42.

[0025] In this embodiment, as Figures 1 to 3As shown, the top anchor section 41, the middle anchor section 42, and the bottom anchor section 43 all include a hollow circular tube 44. A hollow frustum tube 45 is fixedly connected to the outer periphery of the circular tube 44. The smaller diameter end of the frustum tube 45 faces the top of the reinforced anchor 4. Both the circular tube 44 and the frustum tube 45 have side openings 46. When the circular tube 44 and the frustum tube 45 are placed horizontally, the vertical projections of the side openings 46 coincide.

[0026] It should be noted that when the reinforced anchor rod 4 is placed in the pre-drilled anchor hole, during grouting, the grout enters from the bottom anchor rod section 43 of the reinforced anchor rod 4 and fills the reinforced anchor rod 4. Under pressure, the grout flows out from the side openings 46 of each round tube 44, first filling the frustum tube 45 and then filling the gap between the reinforced anchor rod 4 and the anchor hole. After the grout solidifies, it forms an integral anchor body with the reinforced anchor rod 4.

[0027] It should also be noted that, since the smaller diameter end of the frustum tube 45 faces the top of the reinforced anchor rod 4 and the larger diameter end faces the tail end of the reinforced anchor rod 4, the reinforced anchor rod 4 forms a sawtooth-like undulating surface in the anchor hole, providing a one-way locking function. This strengthens the pull-out resistance of the anchor rod 4 and prevents it from falling out of the rock mass. The side opening 46 is located on the side of the middle anchor rod section 42, and when the round tube 44 and the frustum tube 45 are placed horizontally, the vertical projection of the side opening 46 coincides, which facilitates grout diffusion and improves the anchoring effect. Because the reinforced anchor rod 4 penetrates the layered weakly cemented expansive rock, forming a sawtooth-like undulating surface, it can also strengthen the interlayer bonding of the layered weakly cemented expansive rock and effectively control the interlayer deformation of the layered weakly cemented expansive rock.

[0028] like Figure 2 , Figure 3 As shown, a flexible wire rope bundle 47 is also connected to the side opening 46 of the intermediate anchor section 42. The fixed end of the wire rope bundle 47 is welded to the inner wall of the circular tube 44 of the intermediate anchor section 42 (in this embodiment, it is welded to the inner wall of the port at the front end of the intermediate anchor section 42). The diameter of the wire rope bundle 47 is smaller than the diameter of the side opening 46. The free end of the wire rope bundle 47 passes through the side opening 46 of the circular tube 44 and the frustum tube 45 of the intermediate anchor section 42, and extends out of the intermediate anchor section 42 and spreads out.

[0029] In this embodiment, the wire rope bundle 47 is made of multiple high-strength steel wires twisted together, with a nominal tensile strength of not less than 1770 MPa; the anchor rod section is made of high-strength alloy steel, with a yield strength of not less than 785 MPa.

[0030] In this embodiment, the wire rope bundle 47 has the following functions: multiple wires guide the grout to diffuse in a directional manner, and the free ends spread out to form a "root-like" three-dimensional mechanical interlocking structure with the grout. After solidification, it forms a high-strength and complete reinforcement zone containing the wire rope bundle, grout, and rock mass, which strengthens the pull-out resistance and overall stability of the anchor bolt 4. At the same time, the wire rope bundle 47 spreads out in the solidified grout to play a reinforcing effect similar to reinforced concrete, forming a tough composite structure, improving tensile strength and deformation adaptability, realizing uniform diffusion of anchoring force, and comprehensively improving the reliability and long-term effectiveness of support in layered rock mass.

[0031] In this embodiment, the length of the free end extending radially out of the intermediate anchor section 42 must be less than half the difference between the diameter of the anchor hole and the outer diameter of the reinforced anchor 4. This ensures that when the reinforced anchor 4 with the wire rope bundle 47 is inserted into the anchor hole, the flexible wire rope bundle 47 can bend to conform to the shape of the anchor hole wall without causing rigid interference or jamming, ensuring smooth installation while ensuring close contact between the wire rope bundle 47 and the bedding plane of the layered weakly cemented expansive rock strata.

[0032] In this embodiment, the top anchor section 41, several intermediate anchor sections 42, and the bottom anchor section 43 are threaded together. Specifically, as shown... Figure 3 , Figure 4 As shown, the top outer walls of the bottom anchor section 43 and each intermediate anchor section 42 are provided with external threads, while the bottom inner walls of the top anchor section 41, the bottom ends of each intermediate anchor section 42, and the bottom end of the bottom anchor section 43 are provided with internal threads. The top anchor section 41, several intermediate anchor sections 42, and the bottom anchor section 43 are interconnected by external and internal threads. The total length of the reinforced anchor 4 can be adjusted by increasing or decreasing the number of intermediate anchor sections 42. The bottom internal thread of the bottom anchor section 43 is used to connect with the corresponding sealing bolt to seal the grouting port at the bottom of the bottom anchor section 43 after grouting.

[0033] It should be noted that the top anchor section 41, several intermediate anchor sections 42 and the bottom anchor section 43 are all open at both ends, so that the grout can be injected from the bottom end of the bottom anchor section 43 and flow out from the top end of the top anchor section 41, realizing the axial grouting of the entire length of the reinforced anchor 4, and wrapping the gap between the rod body of the reinforced anchor 4 and the anchor hole wall.

[0034] In this embodiment, the top anchor section 41, the middle anchor section 42, and the bottom anchor section 43 are all prefabricated in the factory. During on-site construction, the top anchor section, several middle anchor sections, and the bottom anchor section are sequentially connected according to the design length to form the reinforced anchor 4. Anchor holes are drilled at the designed locations, with the diameter of the anchor holes being a set distance larger than the maximum outer diameter of the reinforced anchor 4 (in this embodiment, the set distance is 25-30 mm). After drilling, high-pressure air is used to clean the holes. The reinforced anchor 4 is then installed into the anchor holes (generally using a special anchor trolley equipped with a hydraulic clamp or a handheld hydraulic anchor drilling machine to install the reinforced anchor 4 into the anchor holes); after the reinforced anchor 4 is in place, grouting is performed by connecting it to the bottom grouting port through a grouting pipe.

[0035] In this embodiment, grouting should be carried out under controllable pressure. In the initial stage, a lower pressure is used. After the grout flows out steadily from the grout outlet at the top of the top anchor section 41, the pressure is gradually increased so that the grout can effectively diffuse through the side opening 46 and fully wrap the wire rope bundle, while avoiding excessive pressure that could cause the surrounding rock to split. After grouting is completed, the grouting port at the bottom of the bottom anchor section 43 is quickly sealed with bolts.

[0036] In this embodiment, the length of the reinforcing anchor 4 needs to penetrate all potentially deformable rock strata, wherein the depth of rock strata destruction is generally 0.5 to 0.75 times the tunnel span, and can be up to one time the tunnel span. Therefore, the length of the reinforcing anchor 4 is greater than or equal to one time the tunnel span.

[0037] In this embodiment, the cutting direction of the surrounding rock pressure relief joint 2 and the arrangement of the reinforced anchor bolts 4 are both related to the bedding of the layered, weakly cemented, expansive rock. Specifically, as shown in the figure... Figure 5 As shown, for the layered, weakly cemented, expansive rock with inclined bedding, the pressure relief joints 2 of the surrounding rock at the bottom of the tunnel 1 sidewall and the bottom slab are both cut downwards, and the direction of the pressure relief joints 2 is parallel to the dip direction of the bedding. Figure 6 As shown, for layered, weakly cemented, expansive rock with vertical bedding, the pressure relief joints 2 in the surrounding rock at the bottom of the tunnel 1 sidewall and the floor slab are both cut downwards, and the direction of the pressure relief joints 2 is parallel to the vertical direction of the bedding. However, for layered, weakly cemented, expansive rock with horizontal bedding, such as... Figure 7 As shown, a rock pressure relief joint 2 perpendicular to the stratum direction is opened in the center of the bottom slab of tunnel 1. The rock pressure relief joints 2 at the bottom of the side walls on both sides cut into the layered weak cemented expansive rock in the direction away from the tunnel. The rock pressure relief joints 2 on the side walls on both sides are symmetrical to the rock pressure relief joint 2 in the center of the bottom slab.

[0038] In this embodiment, the cutting direction of the surrounding rock pressure relief joint 2 is generally parallel to the principle of layered weak cemented expansive rock bedding, so that the surrounding rock pressure relief joint 2 can exert the pressure relief effect to the maximum extent; however, when encountering special horizontal bedding, the surrounding rock pressure relief joint 2 retains the pressure relief function, but no longer pursues a greater pressure relief effect.

[0039] It should be noted that when using a rock drill for cutting, the rock debris inside the joint should be cleaned up in time after the cutting is completed, and then the pre-prepared buffer material should be filled in. The filling operation should ensure the compactness and avoid voids or joints. After filling, the surface should be treated (smoothed) to make it flush with the surrounding rock surface of the tunnel floor or sidewall.

[0040] In this embodiment, the geometric parameters of the surrounding rock pressure relief joint 2 are determined according to specific engineering conditions, mainly including two indicators: depth and width. The depth of the surrounding rock pressure relief joint 2 needs to consider the stress distribution characteristics and deformation patterns of the surrounding rock, while the width must ensure effective pressure relief space during the deformation process of the surrounding rock. In this embodiment, the cutting depth of the surrounding rock pressure relief joint 2 is greater than half the width of the tunnel 1 floor slab. To prevent the surrounding rock pressure relief joint 2 from completely closing, the maximum width of the surrounding rock pressure relief joint 2 should be within the range of 200–300 mm.

[0041] In this embodiment, the buffer material in the surrounding rock pressure relief joint 2 must have strength and deformation performance. The strength of the buffer material is no more than 70% of the strength of the bottom rock layer. Its strength value is lower than the strength of the surrounding rock. It can effectively transfer stress and avoid generating new stress concentration. For example, low-grade concrete can be selected.

[0042] In this embodiment, the key to the density of the reinforced anchor bolt 4 lies in the integrity of the layered weak cemented expansive rock strata of the tunnel 1 floor and the required support resistance. An excessively high anchor bolt density can only be used in soft, broken, and high-stress floor rock strata; otherwise, it will increase the support cost.

[0043] like Figures 8 to 10 As shown, the arrangement density of reinforced anchor bolts 4 is non-uniformly densified based on the bedding of the layered, weakly cemented, expansive rock. For example... Figure 8 As shown, when the bedding of the layered weakly cemented expansive rock is horizontal, the reinforced anchor bolts 4 are denser in the arch of tunnel 1, and the reinforced anchor bolts 4 installed at the top and bottom of the tunnel are perpendicular to the bedding of the layered weakly cemented expansive rock.

[0044] like Figure 9 As shown, when the bedding of the layered weakly cemented expansive rock is inclined, the reinforced anchor bolts 4 are denser in the arch and diagonal regions parallel to the bedding, and the reinforced anchor bolts 4 installed in the arch and diagonal regions parallel to the bedding are perpendicular to the bedding of the layered weakly cemented expansive rock.

[0045] like Figure 10 As shown, when the bedding of the layered weakly cemented expansive rock is perpendicular, the reinforced anchor bolt 4 is densified on both sides of the tunnel sidewall; the reinforced anchor bolt 4 on both sides of the tunnel sidewall is perpendicular to the bedding of the layered weakly cemented expansive rock.

[0046] In this embodiment, a support system for a layered, weakly cemented, expansive rock tunnel also includes initial support. After the surrounding rock pressure relief joint 2 is cut, initial support is provided by shotcrete. The thickness of the shotcrete should be uniformly or non-uniformly distributed depending on the lateral pressure coefficient. The lateral pressure coefficient is obtained from a detailed geological survey report. When the lateral pressure coefficient equals 1, it indicates that the surrounding rock is in a relatively uniform stress state, and a uniform shotcrete thickness is used. When the lateral pressure coefficient is less than 1, the vertical stress is more significant, and the plastic zone at the crown expands. In this case, the arch support should be strengthened, and the sidewall thickness reduced. When the lateral pressure coefficient is greater than 1, it indicates that the horizontal stress is dominant, and the plastic zone at the sidewall is larger. The concrete thickness at the sidewall needs to be increased, and the crown thickness reduced accordingly.

[0047] In this embodiment, a support system for a layered weakly cemented expansive rock tunnel also includes a drainage ditch (not shown in the figure) opened on the bottom slab of tunnel 1 to remove water accumulation on the bottom slab.

[0048] Although the specific embodiments of the present utility model have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present utility model. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solution of the present utility model are still within the scope of protection of the present utility model.

Claims

1. A support system for a tunnel in a layered, weakly cemented swelling rock, characterized in that This includes rock pressure relief joints formed in the tunnel floor and sidewalls, which are filled with cushioning material; and reinforced anchor bolts are also anchored into the tunnel arch and sidewalls. The reinforced anchor bolt is an adjustable length anchor bolt, including a top anchor bolt section, several intermediate anchor bolt sections, and a bottom anchor bolt section; the top anchor bolt section, intermediate anchor bolt section, and bottom anchor bolt section all include a hollow circular tube, and a hollow frustum tube is fixedly connected to the outer circumference of the circular tube, with the smaller diameter end of the frustum tube facing the top of the reinforced anchor bolt; both the circular tube and the frustum tube have side openings.

2. The support system for layered, weakly cemented, expansive rock tunnels as described in claim 1, characterized in that, A flexible steel wire rope bundle is also connected to the side opening. The fixed end of the steel wire rope bundle is welded to the inner wall of the circular tube of the intermediate anchor section, and the free end of the steel wire rope bundle passes through the side opening of the circular tube and the frustum tube and extends out of the intermediate anchor section.

3. The support system for layered, weakly cemented, expansive rock tunnels as described in claim 1, characterized in that, The top outer walls of the bottom anchor section and the middle anchor section are provided with external threads, and the bottom inner walls of the top anchor section, the middle anchor section and the bottom anchor section are provided with internal threads.

4. A support system for tunnels in weakly cemented swelling rocks according to claim 1, characterized in that, The top anchor section, the middle anchor section, and the bottom anchor section all have openings at both ends.

5. A support system for tunnels in weakly cemented swelling rocks according to claim 1, characterized in that, When the layered weakly cemented expansive rock has inclined or vertical bedding, the pressure relief joints of the surrounding rock are parallel to the direction of the bedding; when the layered weakly cemented expansive rock has horizontal bedding, the pressure relief joints of the surrounding rock of the bottom plate are perpendicular to the direction of the bedding, and the pressure relief joints of the surrounding rock of the two side walls cut into the layered weakly cemented expansive rock in the direction away from the tunnel.

6. A support system for tunnels in weakly cemented swelling rocks according to claim 1, characterized in that, The depth of the surrounding rock pressure relief joint should be greater than half the width of the tunnel floor slab, and the width should be 200-300mm.

7. A support system for tunnels in weakly cemented swelling rocks according to claim 1, characterized in that, The strength of the buffer material is no more than 70% of the strength of the underlying rock stratum.

8. A support system for tunnels in weakly cemented swelling rocks according to claim 1, characterized in that, When the bedding of the layered weakly cemented expansive rock is horizontal, the reinforced anchor bolts are denser in the tunnel arch; when the bedding of the layered weakly cemented expansive rock is inclined, the reinforced anchor bolts are denser in the arch and diagonal areas parallel to the bedding; when the bedding of the layered weakly cemented expansive rock is inclined, the reinforced anchor bolts are denser on both sides of the tunnel sidewalls.

9. A support system for tunnels in weakly cemented swelling rocks according to claim 1, characterized in that, The length of the reinforced anchor bolt is greater than or equal to one tunnel span.

10. The support system for layered, weakly cemented, expansive rock tunnels as described in claim 1, characterized in that, The support system also includes initial support and drainage ditches opened on the tunnel floor.

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