An asymmetric support structure for layered soft rock tunnels

Abstract

This utility model discloses an asymmetric support structure for layered soft rock tunnels, belonging to the field of tunnel engineering support technology. It includes an initial support layer and a secondary lining layer. The initial support layer is divided into a strong support zone and a weak support zone according to the rock strata dip angle. The strong support zone is equipped with prestressed anchor bolts, reinforced steel arch frames, and a double-layer steel mesh inside the reinforced steel arch frames. The weak support zone is equipped with ordinary mortar anchor bolts, standard steel arch frames, and a single-layer steel mesh. The secondary lining layer includes a reinforced secondary lining zone and an ordinary secondary lining zone. The reinforced secondary lining zone is located inside the strong support zone, and the ordinary secondary lining zone is located inside the weak support zone. This utility model divides the initial support layer into strong and weak support zones according to the rock strata dip of the layered soft rock, achieving targeted support, better adapting to the mechanical properties of layered soft rock, improving the stability and reliability of the support structure, and reducing the risk of tunnel deformation and collapse.

Description

Technical Field

[0001] This utility model relates to the field of tunnel engineering support, and in particular to an asymmetric support structure for layered soft rock tunnels. Background Technology

[0002] In tunnel construction, layered soft rock tunnels present significant challenges to support construction due to the rock strata's obvious anisotropy, low strength, susceptibility to weathering, and tendency to soften upon contact with water. The stress state of layered soft rock varies significantly across different areas due to the thickness and dip angle of the rock strata; the dip side often bears greater surrounding rock pressure, making it prone to deformation, collapse, and other hazards.

[0003] Traditional tunnel support structures often employ a symmetrical design, failing to adequately consider the stress differences in different areas of layered soft rock. This results in insufficient support strength on the dip side of the rock strata, while potentially leading to excessive and wasteful support on the opposite dip side. Such symmetrical support structures are ill-suited to the complex mechanical properties of layered soft rock, frequently causing severe asymmetrical deformation of the support structure, cracking of the shotcrete layer, twisting of the steel frame, and even serious engineering accidents such as tunnel collapse. This not only increases construction costs and time but also poses a significant threat to construction safety.

[0004] Therefore, developing an asymmetric support structure that can provide targeted support based on the stress characteristics of different areas of layered soft rock is of great practical significance. Utility Model Content

[0005] The purpose of this invention is to provide an asymmetric support structure for layered soft rock tunnels to solve the problems in the prior art.

[0006] To achieve the above objectives, this utility model provides an asymmetric support structure for layered soft rock tunnels, comprising an initial support layer and a secondary lining layer disposed within the layered soft rock tunnel. The initial support layer is divided into a strong support zone and a weak support zone according to the rock strata dip angle. The strong support zone is provided with prestressed anchor bolts, reinforced steel arch frames, and a double-layer steel mesh disposed inside the reinforced steel arch frames. The weak support zone is provided with ordinary mortar anchor bolts, standard steel arch frames, and a single-layer steel mesh. The secondary lining layer comprises reinforced reinforced concrete ribs and an ordinary secondary lining zone. The reinforced secondary lining zone is disposed inside the strong support zone, and the ordinary secondary lining zone is disposed inside the weak support zone.

[0007] Preferably, the reinforced steel arch is composed of multiple I20b I-beams connected together, the edges of the double-layer steel mesh are welded to the reinforced steel arch, and the reinforced steel arch and the double-layer steel mesh are wrapped with a steel fiber reinforced concrete spray layer.

[0008] Preferably, the prestressed anchor rod is set on the dip side of the rock stratum, the anchoring end of the prestressed anchor rod is inserted into the rock stratum, the other end of the prestressed anchor rod passes through the double-layer steel mesh and is welded to the mesh of the double-layer steel mesh, and the tail of the prestressed anchor rod is fixed to the flange of the reinforced steel arch frame by a nut.

[0009] Preferably, the contact ends of the reinforced steel arch frame and the standard steel arch frame are connected by a special-shaped connecting plate.

[0010] Preferably, the edge of the single-layer steel mesh is welded to the standard steel arch frame, and the standard steel arch frame and the single-layer steel mesh are wrapped with a fiber-reinforced concrete spray layer.

[0011] Preferably, the ordinary mortar anchor is set on the opposite dip side of the rock stratum, the anchoring end of the ordinary mortar anchor penetrates into the rock stratum, the other end of the ordinary mortar anchor passes through a single layer of steel mesh and is welded to the single layer of steel mesh, and the tail of the ordinary mortar anchor is fixed on a standard steel arch frame.

[0012] Preferably, a reinforced concrete rib is provided in the reinforced secondary lining zone. The cross-section of the reinforced concrete rib is trapezoidal. The reinforced concrete rib contains main bars and stirrups. The reinforced concrete rib is connected to the primary support layer through pre-embedded bars.

[0013] Preferably, the ordinary secondary lining area is formed by thickened ribs and concrete pouring, and a waterstop strip is provided at the joint between the ordinary secondary lining area and the reinforced concrete ribs.

[0014] Therefore, the asymmetric support structure for layered soft rock tunnels of this utility model, which adopts the above-mentioned structure, has the following beneficial effects:

[0015] (1) Based on the rock strata dip of the layered soft rock, this utility model divides the initial support layer into a strong support zone and a weak support zone, realizing targeted support, which can better adapt to the mechanical properties of the layered soft rock, improve the stability and reliability of the support structure, and effectively reduce the risk of tunnel deformation and collapse.

[0016] (2) In the strong support zone, prestressed anchor rods, reinforced steel arch frames and double-layer steel mesh are set up, which can effectively resist the large surrounding rock pressure on the rock stratum dip angle side and prevent excessive deformation of the surrounding rock; in the weak support zone, ordinary mortar anchor rods, standard steel arch frames and single-layer steel mesh are used, which can ensure the support strength while avoiding material waste and improving the stability and reliability of tunnel support as a whole.

[0017] (3) The reinforced steel arch frame is made of I20b I-beams connected together, and with the double-layer steel mesh and steel fiber concrete spray layer, the structural strength of the strong support zone is greatly enhanced; the combination of the ordinary secondary lining zone and the reinforced concrete ribs further improves the bearing capacity of the secondary lining layer and ensures the long-term safety of the tunnel structure.

[0018] (4) The thickened reinforced concrete ribs in the secondary lining correspond to the strong support zone of the primary support layer, which enhances the overall bearing capacity of the structure and improves the safety and durability of the tunnel.

[0019] The technical solution of this utility model will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of an embodiment of the present utility model;

[0021] Figure label:

[0022] 1. Prestressed anchor bolts; 2. Reinforced steel arch frames; 3. Double-layer steel mesh; 4. Steel fiber reinforced concrete sprayed layer; 5. Standard steel arch frames; 6. Ordinary mortar anchor bolts; 7. Single-layer steel mesh; 8. Irregularly shaped connecting plates; 9. Fiber reinforced concrete sprayed layer; 10. Reinforced secondary lining zone; 11. Ordinary secondary lining zone; 12. Embedded reinforcement bars. Detailed Implementation

[0023] The technical solution of this utility model will be further described below with reference to the accompanying drawings and embodiments.

[0024] Unless otherwise defined, the technical or scientific terms used in this utility model shall have the ordinary meaning understood by one of ordinary skill in the art to which this utility model pertains. The terms "first," "second," and similar terms used in this utility model do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0025] Example

[0026] like Figure 1As shown, this utility model provides an asymmetric support structure for layered soft rock tunnels, including an initial support layer and a secondary lining layer installed within the tunnel. The initial support layer is divided into a strong support zone and a weak support zone according to the rock strata dip angle. The strong support zone is equipped with prestressed anchor bolts 1, reinforced steel arch frames 2, and a double-layer steel mesh 3 installed inside the reinforced steel arch frames 2. The reinforced steel arch frames 2 are made of I20b I-beams, processed to design dimensions, with a longitudinal spacing of 0.5m. During installation, adjacent arch frames are connected by 8.8 grade M20 high-strength bolts, with a flange contact area ≥90% and a bolt preload ≥300N·m. The position and elevation of the arch frames are strictly controlled during installation to ensure compliance with design requirements. The double-layer steel mesh 3 is made of... The reinforcing steel mesh is 150×150mm, with the upper and lower layers staggered by 50%. During installation, the mesh edges are securely welded to the reinforcing steel arch frame 2. The reinforcing steel arch frame 2 and the double-layer steel mesh 3 are externally wrapped with a steel fiber reinforced concrete spray layer 4, which uses C25 steel fiber concrete with a steel fiber content of 30kg / m³. 3 The thickness of the sprayed layer should be controlled between 120-150mm. During the spraying process, proceed from the arch foot to the arch crown, spraying in layers, each layer being 5-8cm thick, to ensure that the sprayed layer adheres closely to the surrounding rock surface without defects such as voids or cracks.

[0027] The prestressed anchor rod 1 is a high-strength threaded steel anchor rod with a diameter of 25mm. It is arranged along the arch shoulder and sidewall on the dip side of the rock stratum. The anchor rod is set as perpendicular to the rock stratum as possible or at a small angle to the normal of the rock surface, depending on the actual working conditions. The anchoring end of the prestressed anchor rod 1 penetrates into the rock stratum. In the specific construction, a hole is first drilled with a diameter 10mm larger than the diameter of the anchor rod. Then, the anchor rod is placed into the hole, and the rod body passes through the double-layer steel mesh 3 and is welded to the mesh. The spacing of the weld points is controlled at 80-100mm. The tail of the anchor rod is fixed to the flange of the reinforced steel arch frame 2 with a nut. An 8mm thick steel plate washer is placed between the nut and the web plate. The double nuts are tightened to ensure that the preload meets the requirements.

[0028] The contact ends of the reinforced steel arch frame 2 and the standard steel arch frame 5 are connected by a special-shaped connecting plate 8.

[0029] The weakly supported area is equipped with ordinary mortar anchors 6, standard steel arch frames, and a single-layer steel mesh 7; the single-layer steel mesh 7 uses... Round steel, 200×200mm mesh, is spot-welded to the standard steel arch frame 5 during installation to ensure the mesh is flat and secure. The standard steel arch frame 5 uses I18 I-beams with a longitudinal spacing of 0.5m, and is connected to the reinforced steel arch frame 2 via a special-shaped connecting plate 8. The connecting plate is 16mm thick and is fixed with 4 M20 high-strength bolts, with a bolt tightening torque of 350-400 N·m.

[0030] The standard steel arch frame 5 and the single-layer steel mesh 7 are wrapped with a fiber-reinforced concrete spray layer 9, which is made of C20 concrete and has a thickness of 80-100mm.

[0031] Ordinary mortar anchor bolts 6 are installed on the opposite side of the rock stratum, using 22mm diameter threaded steel anchor bolts, located on the opposite side of the rock stratum and arranged perpendicular to the tunnel axis. During construction, after drilling, the anchor bolts are inserted and anchored with cement mortar. The tail of the anchor bolt is firmly tied to a single layer of steel mesh 7, and the bolt body is embedded in the surrounding rock to a depth of 2.5-3m. The tail is fixed to a standard steel arch frame 5.

[0032] The secondary lining layer includes a reinforced secondary lining zone 10 and a regular secondary lining zone 11. The reinforced secondary lining zone 10 contains reinforced concrete ribs, while the regular secondary lining zone 11 is located inside the weakly supported zone. The thickened reinforced concrete ribs (existing structure) are located inside the strongly supported zone, with a trapezoidal cross-section, 600mm at the bottom and 400mm at the top. They contain Φ22mm main reinforcement bars spaced 150mm apart and Φ10mm stirrups spaced 200mm apart. The main reinforcement bars extend at both ends into the secondary lining layer of the weakly supported zone by more than 500mm. They are connected to the initial support layer via embedded reinforcement bars 12. The embedded reinforcement bars 12 are made of 20mm diameter steel bars with a depth ≥200mm (10d, where d is the steel bar diameter). They are embedded in the initial support, and the embedding location is determined according to the actual working conditions.

[0033] The ordinary secondary lining zone 11 is 300-400mm thick and is cast with C30 concrete, integrally cast with the thickened ribs. Water-swellable sealing strips are installed at the joints, with a width of 30mm and a thickness of 10mm to ensure waterproofing.

[0034] The specific construction method is as follows:

[0035] 1) Delineate support zones: Based on the rock strata survey data, determine the dip direction and angle of the rock strata, and divide the tunnel excavation face into strong support zones (rock strata dip angle side) and weak support zones (rock strata reverse dip angle side).

[0036] 2) Initial support construction in the strong support zone:

[0037] Construction of prestressed anchor rod 1: Drill holes in the rock strata of the strong support zone. The hole depth is determined according to the rock strata conditions, ranging from 3 to 5 meters. Insert the anchoring end of the prestressed anchor rod 1 into the hole in the rock strata and fix it by grouting. The other end of the anchor rod passes through the reserved position for subsequent installation of steel mesh and steel arch frame.

[0038] Install reinforced steel arch frame 2: Connect multiple 120b I-beams with bolts to form reinforced steel arch frame 2, and install it on the tunnel excavation face according to the design position to ensure its accurate and stable position.

[0039] Install double-layer steel mesh 3: Lay the double-layer steel mesh 3 inside the reinforced steel arch 2, and weld the edges to the reinforced steel arch 2. The other end of the prestressed anchor rod 1 passes through the double-layer steel mesh 3 and is welded to the mesh. The tail is fixed to the web of the reinforced steel arch 2 with a nut.

[0040] Shotcrete: Steel fiber reinforced concrete is sprayed onto the exterior of the reinforced steel arch frame 2 and the double-layer steel mesh 3 to ensure that the sprayed layer is uniform and dense.

[0041] 2) Initial support construction in weakly supported areas:

[0042] Construction of ordinary mortar anchor rod 6: Drill holes in the rock strata of the weak support area, insert the anchoring end of the ordinary mortar anchor rod 6 into the rock strata hole, inject mortar for anchoring, and leave sufficient length at the other end of the anchor rod.

[0043] Install standard steel arch frame 5: Install standard steel arch frame 5 at the designed position and connect and fix it to the reinforced steel arch frame 2 in the strong support area with high-strength bolts through the irregular connecting plate 8.

[0044] Install single-layer steel mesh 7: Lay the single-layer steel mesh 7 inside the standard steel arch frame 5, and weld the edges to the standard steel arch frame 5. The other end of the ordinary mortar anchor rod 6 passes through the single-layer steel mesh 7 and is welded to the mesh, and the tail is welded to the standard steel arch frame 5.

[0045] Shotcrete: Fiber-reinforced concrete is sprayed onto the exterior of the standard steel arch frame 5 and the single-layer steel mesh 7 to ensure the quality of the sprayed layer.

[0046] In addition, two anchor pipes should be installed at each arch foot. The anchor pipes are made of Φ42mm seamless steel pipes, arranged in a crisscross pattern at a 25°-35° angle, with a length of 4m. During construction, holes are first drilled, then the anchor pipes are inserted into the holes, and the tail ends are fully welded to the two steel arch frames with a weld length ≥100mm. Finally, cement grout is injected into the pipes using a grouting pump, with a water-cement ratio of 0.5 and the grouting pressure controlled at 0.5-1.0MPa to ensure full grouting.

[0047] 3) Secondary lining construction:

[0048] Construction of reinforced concrete ribs: On the inner side of the strong support zone, tie the main bars and stirrups of the reinforced concrete ribs according to the design dimensions, and connect them firmly to the initial support layer through the pre-embedded bars 12. Then pour concrete and cure it to the design strength.

[0049] Construction of ordinary secondary lining zone 11: On the inner side of the weak support zone, steel bars are tied and thickened ribs are set, and then concrete is poured to form ordinary secondary lining zone 11. Waterstop strips are set at the joint between ordinary secondary lining zone 11 and the reinforced concrete ribs to ensure good joint sealing.

[0050] During construction, we strictly followed the design requirements, construction specifications, and construction sequence, strengthened quality inspection and monitoring, and adjusted construction parameters in a timely manner to ensure the construction quality and safety of the support structure.

[0051] Therefore, this utility model adopts an asymmetric support structure for layered soft rock tunnels with the above-mentioned structure. According to the rock strata dip of the layered soft rock, the initial support layer is divided into a strong support zone and a weak support zone, realizing targeted support. It can better adapt to the mechanical properties of layered soft rock, improve the stability and reliability of the support structure, and effectively reduce the risk of tunnel deformation and collapse.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of this utility model and not to limit it. Although the utility model has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solution of this utility model, and these modifications or equivalent substitutions cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of this utility model.

Claims

1. An asymmetric support structure for layered soft rock tunnels, characterized in that: The system includes an initial support layer and a secondary lining layer installed within a layered soft rock tunnel. The initial support layer is divided into a strong support zone and a weak support zone according to the dip angle of the rock strata. The strong support zone is equipped with prestressed anchor bolts, reinforced steel arch frames, and a double-layer steel mesh installed inside the reinforced steel arch frames. The weak support zone is equipped with ordinary mortar anchor bolts, standard steel arch frames, and a single-layer steel mesh. The secondary lining layer includes a reinforced secondary lining zone and an ordinary secondary lining zone. The reinforced secondary lining zone is located inside the strong support zone, and the ordinary secondary lining zone is located inside the weak support zone.

2. The asymmetric support structure for a layered soft rock tunnel according to claim 1, characterized in that: The reinforced steel arch frame is composed of multiple sections of I-beams connected together. The edges of the double-layer steel mesh are welded to the reinforced steel arch frame. The reinforced steel arch frame and the double-layer steel mesh are wrapped with a steel fiber reinforced concrete spray layer.

3. The asymmetric support structure for a layered soft rock tunnel according to claim 1, characterized in that: The prestressed anchor rod is installed on the dip side of the rock stratum, with the anchoring end of the prestressed anchor rod penetrating deep into the rock stratum. The other end of the prestressed anchor rod passes through a double-layer steel mesh and is welded to the mesh of the double-layer steel mesh. The tail of the prestressed anchor rod is fixed to the flange of the reinforced steel arch frame by a nut.

4. The asymmetric support structure for a layered soft rock tunnel according to claim 1, characterized in that: The contact ends of the reinforced steel arch frame and the standard steel arch frame are connected by a special-shaped connecting plate.

5. The asymmetric support structure for layered soft rock tunnels according to claim 1, characterized in that: The edge of the single-layer steel mesh is welded to the standard steel arch frame, and the standard steel arch frame and the single-layer steel mesh are wrapped with a fiber-reinforced concrete spray layer.

6. The layered soft rock tunnel asymmetric support structure according to claim 1, characterized in that: The ordinary mortar anchor is set on the opposite side of the rock stratum. The anchoring end of the ordinary mortar anchor penetrates into the rock stratum. The other end of the ordinary mortar anchor passes through a single layer of steel mesh and is welded to the single layer of steel mesh. The tail of the ordinary mortar anchor is fixed on a standard steel arch frame.

7. The asymmetric support structure for soft rock tunnel according to claim 1, characterized in that: The reinforced secondary lining zone is provided with reinforced concrete ribs, the cross-section of which is trapezoidal, and the reinforced concrete ribs contain main bars and stirrups.

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