A soft rock large deformation tunnel supporting system

Abstract

The utility model provides a kind of soft rock large deformation tunnel supporting system, including active protective net and multiple self-advancing hollow grouting anchor rods;The anchoring end of self-advancing hollow grouting anchor rod is inserted into stable rock layer, active protective net is fixedly installed in anchor rod tail end, to form space grid structure, active protective net forms preliminary closed layer by spraying concrete, to fill the surface depression of soft rock and enhance the integrity of soft rock;Foam buffer layer, off-wall primary support layer, reserved deformation space layer and secondary lining layer are sequentially arranged in the inside of preliminary closed layer, to form multilayer support to soft rock large deformation tunnel.The utility model can dynamically respond the rheological property of soft rock through multilayer support, realize soft rock-support dynamic balance, effectively control long-term deformation of soft rock, and inhibit soft rock convergence, so that the structure of primary support arch is long-term stable.

Description

Technical Field

[0001] This utility model relates to the field of underground engineering construction technology, and in particular to a support system for large deformation tunnels in soft rock. Background Technology

[0002] During tunnel construction, when encountering soft rock with large deformation, existing technology can reinforce the soft rock mass by grouting to form a stable skeleton. However, after grouting, the rock mass still suffers from continuous creep and large deformation, making it difficult to effectively suppress soft rock convergence.

[0003] Applying active support force through the synergistic use of prestressed anchor cables and W-shaped steel strips can significantly improve the overall stiffness of the support structure. However, the grouting and tensioning processes both require time, resulting in a significant lag in the support. Furthermore, a single support method cannot meet the dynamic equilibrium requirements and is insufficient to effectively control long-term deformation of soft rock. Long-term deformation of soft rock significantly increases the deformation of the initial support arch, leading to localized stress concentration in the support structure. This can cause steel frame twisting, cracking and spalling of shotcrete, and even induce collapse, seriously threatening construction safety. After the steel frame twists and deforms, it poses a serious threat to the clearance of the lining structure, requiring multiple replacements of the steel frame to release the deformation pressure. However, multiple replacements lead to a significant increase in construction costs and severe delays in the construction period. Utility Model Content

[0004] This utility model aims to provide a support system for soft rock tunnels with large deformation, so as to provide immediate support for soft rock tunnels with large deformation through self-advancing hollow grouting anchors and active protective nets. By dynamically responding to the rheological characteristics of soft rock through multi-layer support, a dynamic balance between soft rock and support is achieved, effectively controlling the long-term deformation of soft rock and inhibiting soft rock convergence. This ensures the long-term stability of the initial support arch structure, guarantees construction safety, reduces construction costs, and ensures the timely completion of construction.

[0005] Therefore, the technical solution adopted by this utility model is: a soft rock large deformation tunnel support system, including an anchor support structure, wherein the anchor support structure includes an active protection net and multiple self-advancing hollow grouting anchor rods;

[0006] Multiple self-drilling hollow grouting anchors cover the entire tunnel cross-section except for the invert arch. The self-drilling hollow grouting anchors are driven vertically into the tunnel inner wall and the anchoring end extends into the stable rock layer. The active protection net is fixedly installed at the tail end of all the self-drilling hollow grouting anchors, thereby forming a spatial grid structure to suppress block fall and local instability. The active protection net forms a preliminary sealing layer by spraying concrete to fill the depressions on the soft rock surface and enhance the integrity of the soft rock.

[0007] The inner side of the initial sealing layer is sequentially provided with a foam buffer layer, a wall-separated initial support layer, a reserved deformation space layer, and a secondary lining layer, thereby forming a multi-layer support for the soft rock tunnel with large deformation.

[0008] As a preferred embodiment of the above scheme, the foam buffer layer is made of polyurethane foam, and the foam buffer layer is fixedly installed between the initial sealing layer and the initial support layer separated from the wall, with a thickness of 40-50cm.

[0009] More preferably, the primary support layer separated from the wall includes a primary support concrete structure and multiple primary support arches, all of which are fixedly installed in the primary support concrete structure.

[0010] More preferably, the initial support arch is an I20 I-beam or an H-beam, and the distance between two adjacent initial support arches is 0.8 to 1 m.

[0011] A further preferred embodiment is that a monitoring section is set up every two meters along the length of the tunnel, and a monitoring point is set at the top of the initial support arch and the two sides of the arch waist in the monitoring section, which serves as a joint observation point for the total station and convergence meter to determine the stability of the initial support layer away from the wall.

[0012] More preferably, the thickness of the reserved deformation space layer is 15-20 cm.

[0013] More preferably, the secondary lining layer is made of reinforced concrete with a strength of C30 and a thickness of 45-55cm.

[0014] The beneficial effects of this utility model are:

[0015] 1. When the soft rock deforms and squeezes the foam buffer layer downward to its limit, it will squeeze the primary support layer away from the wall downward, thus causing the primary support layer away from the wall to deform toward the secondary lining layer. The reserved deformation space layer can give the primary support layer away from the wall enough deformation space, avoid the deformation of the primary support layer away from the wall squeezing the secondary lining layer, and improve the safety of the secondary lining layer.

[0016] 2. The use of self-drilling hollow grouting anchors allows for rapid drilling and immediate grouting and anchoring, forming early support stiffness and effectively suppressing initial deformation of soft rock. The use of active protection nets can form a spatial grid structure together with the self-drilling hollow grouting anchors, enhancing the overall integrity of the soft rock surface and effectively suppressing block fall and local instability, thereby achieving immediate support for tunnels with large deformation in soft rock.

[0017] 3. The foam in the foam buffer layer can quickly foam and fill the soft rock surface, sealing shallow cracks and forming a flexible buffer layer, effectively slowing down the stress redistribution rate. As the soft rock gradually deforms, the foam buffer layer becomes a controllable compression zone between the initial support layer and the soft rock, releasing some compressive stress and preventing instantaneous overload of the initial support layer. Using a preliminary sealing layer, foam buffer layer, initial support layer, and secondary lining layer can form a multi-layered support for tunnels with large deformations in soft rock. This releases some compressive stress and provides timely controllable resistance, combining rigidity and flexibility to dynamically respond to the rheological characteristics of soft rock, achieving a dynamic balance between soft rock and support. This effectively controls the long-term deformation of the soft rock and inhibits soft rock convergence, ensuring the long-term stability of the initial support arch structure. It eliminates the need for repeated replacement of the initial support arch to release deformation pressure, ensuring construction safety, reducing construction costs, and guaranteeing timely completion of the project.

[0018] 4. Through the synergistic effect of the detached initial support layer and the foam buffer layer, the sudden deformation of soft rock can be effectively suppressed, and the deformation rate of the detached initial support layer is significantly reduced. The measured data shows that the maximum settlement rate of the detached initial support layer is 15.5 mm / d, the cumulative settlement is below 105.5 mm, the maximum convergence rate is 10 mm / d, and the cumulative convergence deformation does not exceed 90.6 mm. This is a significant improvement compared with the situation under traditional support conditions, and effectively ensures the structural stability and operational safety of the detached initial support layer during construction.

[0019] 5. During implementation, the combined rigid and flexible construction strategy significantly reduced the damage rate of the support structure and decreased the frequency of subsequent maintenance and reinforcement. Field application showed that the integrity of the initial support structure remained good, and the crack incidence rate decreased by approximately 30%, essentially avoiding the frequent rework problems caused by stress concentration in traditional construction methods. Simultaneously, construction safety and operational efficiency were improved, providing an efficient and reliable technical approach for the construction of large deformation tunnels in soft rock.

[0020] 6. The foam buffer layer effectively blocks groundwater erosion and chemical corrosion of soft rock, delaying the deterioration of the initial support concrete. Combined with its compressible properties and stress-regulating function, this invention maintains stable mechanical properties during long-term service. Under soft rock conditions, the effective service life of this invention is increased by more than 30% compared to traditional support structures, significantly reducing the total life-cycle maintenance cost. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of this utility model. Detailed Implementation

[0022] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0023] like Figure 1As shown, a soft rock large deformation tunnel support system includes an anchoring support structure, which includes an active protection net and multiple self-advancing hollow grouting anchor rods 1.

[0024] Multiple self-drilling hollow grouting anchor bolts 1 cover the entire tunnel cross section except for the invert arch. The self-drilling hollow grouting anchor bolts 1 are driven vertically into the inner wall of the tunnel and the anchoring end extends into the stable rock layer. An active protection net is fixedly installed at the tail end of all the self-drilling hollow grouting anchor bolts 1, thereby forming a spatial grid structure to suppress block fall and local instability. The active protection net forms a preliminary sealing layer 2 by spraying concrete to fill the depressions on the soft rock surface and enhance the integrity of the soft rock.

[0025] Inside the initial sealing layer 2, a foam buffer layer 3, a wall-separated initial support layer 4, a reserved deformation space layer 5, and a secondary lining layer 6 are sequentially arranged to form a multi-layer support for the soft rock tunnel with large deformation.

[0026] Before construction, a representative test section was selected to conduct a detailed investigation of the soft rock geological conditions, clarifying the distribution range of soft rock, joint development characteristics, and groundwater activity. An initial deformation prediction model was established based on monitoring and measurement data. The working condition of the self-propelled hollow grouting anchor bolt 1, grouting equipment, active protection net (not shown in the attached diagram), and polyurethane foaming equipment was checked to ensure that the material performance met the technical requirements. After all procedures were prepared, the formal construction phase began.

[0027] Based on the characteristics of soft rock, blasting or mechanical excavation methods are selected. The disturbance to soft rock is reduced by controlling the excavation length. Generally, the excavation length is controlled within the range of 1 to 1.2 meters. The tunnel construction method can adopt the three-stage method or the CD method. A foam buffer layer 3 is reserved. After the excavation is completed, the removal of dangerous rocks and surface leveling operations are carried out immediately.

[0028] Drill Φ32 self-drilling hollow grouting anchor bolts 1 into the soft rock surface. The drilling depth is controlled between 5 and 10 m. The anchor bolt length can be adjusted reasonably according to the height of the bench on site. The drilling angle forms a certain angle with the joint surface of the soft rock to enhance the anchoring effect and ensure that the anchoring end of the anchor bolt enters the stable rock layer. The spacing between two adjacent self-drilling hollow grouting anchor bolts 1 is controlled between 0.6 and 0.8 m, and the spacing can be appropriately increased to ensure the overall stability of the support system. Immediately after the self-drilling hollow grouting anchor bolts 1 are installed, early-strength cement grout is injected through the hollow channel to achieve rapid anchoring and filling of soft rock fissures. The grouting pressure is controlled between 0.5 and 1.0 MPa to ensure sufficient diffusion without splitting the soft rock. After grouting is completed, the active protection net is quickly laid and fastened to the end of the anchor bolt with anchor plates and nuts to ensure that the force of the active protection net is evenly transmitted. The active protection net is reserved with an appropriate deformation margin to avoid being in a high tension state in the early stage. After the soft rock has undergone a certain displacement, the bearing capacity of the net body is gradually activated, thereby improving the adaptability and ductility of the support system.

[0029] After the active protection netting is completed, spray C25 concrete 5-8cm thick as a preliminary sealing layer 2 to fill the depressions on the soft rock surface and enhance the integrity of the soft rock.

[0030] The foam buffer layer 3 is made of polyurethane foam. The foam buffer layer 3 is fixedly installed between the initial sealing layer 2 and the wall-mounted initial support layer 4, and its thickness is 40-50cm.

[0031] The polyurethane foam uses a two-component high-elasticity polyurethane material. To improve its strength, cement grout can be added. 42.5 grade ordinary Portland cement is selected, with a cement-to-water weight ratio of 0.6:1 to 0.8:1. Simultaneously, 0.5% to 1.0% of silane coupling agent by weight of the cement is added to enhance interfacial bonding performance. After mixing the two-component high-elasticity polyurethane material, cement grout, and silane coupling agent, grouting should be completed within 3 to 5 minutes to prevent premature curing. During polyurethane foam filling, a high-pressure grouting machine is used for simultaneous injection through two pipes. The grouting pressure is controlled at 0.8 to 1.5 MPa. The foaming status is monitored in real time during grouting, and a moderate expansion ratio (volume expansion rate of 20 to 30 times) is maintained to avoid excessive expansion that could cause splitting and damage to soft rock.

[0032] During grouting, start from the bottom up and from the arch foot to the arch crown to avoid the grout concentrating in the lower part and causing voids in the upper part. When the polyurethane is injected to the point where it overflows from the adjacent grouting pipe and the pressure rises steadily, it can be determined that the filling is dense and the grouting port should be sealed in time.

[0033] The initial support layer 4, which is separated from the wall, includes an initial support concrete structure and multiple initial support arch frames, all of which are fixedly installed in the initial support concrete structure.

[0034] The initial support arch is made of I20 I-beams or H-beams, and the distance between two adjacent initial support arches is 0.8 to 1m.

[0035] First, construct the initial support layer 4 separated from the wall, then construct the foam buffer layer 3 between the initial support layer 4 and the preliminary sealing layer 2. This allows for reasonable deformation space (i.e., the space where the foam buffer layer 3 is located), preventing the initial support layer 4 from prematurely bearing high-stress impact. When installing the initial support arch frame (not shown in the attached diagram), ensure that the joint plate bolts are tightened and the segment connections are secure. Use two Φ42 steel pipes for the anchor pipes, each with a length of not less than 4 meters. Use Φ22 connecting steel bars spaced 1m apart and staggered between adjacent initial support arch frames to enhance overall stability. Maintain a 40-50cm gap between the outer edge of the initial support arch frame and the preliminary sealing layer 2 to form the space separated from the wall (the space where the foam buffer layer 3 is located), ensuring uniformity of the space and avoiding stress concentration caused by local contact. Lay Φ8 steel mesh with geotextile on the outer edge between the initial support arch frames. The mesh size is 20×20cm. Each steel mesh sheet is overlapped and securely tied to ensure no gaps are formed, preventing shotcrete from being sprayed into the space separated from the wall and causing blockage. The reinforcing mesh should be exposed 40-50cm so that when polyurethane is injected later, the reinforcing mesh can be bent in the opposite direction and fit tightly against the outer edge of the space away from the wall to form a closed barrier layer and prevent leakage during polyurethane foaming.

[0036] Install polyurethane grouting pipes with a diameter of 25-32cm. The exposed length of the pipe inside the initial support arch should be controlled to 10-15cm, maintaining a distance of 20-30cm from the soft rock surface. During installation, ensure the end of the polyurethane grouting pipe is located in the middle of the gap between the soft rock and the initial support arch to avoid clogging during polyurethane injection. The grouting pipes should be evenly distributed circumferentially along the center of both initial support arches, with a spacing controlled within 1m.

[0037] Before spraying concrete, check whether the grouting pipe is installed firmly and in the correct position, and then block it. Then spray C25 concrete in layers to the designed thickness to form the initial support concrete structure (not shown in the attached diagram).

[0038] After the initial support layer 4 was constructed, settlement and convergence monitoring points were set up. To improve monitoring accuracy, a monitoring section was set up every two meters along the tunnel length. A monitoring point was set up at the crown of the initial support arch and on both sides of the arch within the monitoring section, serving as joint observation points for the total station and convergence meter to determine the stability of the initial support layer 4. During step-by-step construction, monitoring points were simultaneously set up on both sides of each step to ensure data correspondence between upper and lower steps. A combined observation using a total station and convergence meter was employed, initially monitoring twice daily, gradually adjusted to once weekly based on the deformation rate. When monitoring data showed a daily settlement rate below 0.15 mm / d and a convergence displacement rate below 0.2 mm / d for 2-3 consecutive weeks, the initial support layer 4 was considered to be stabilizing.

[0039] Settlement and convergence monitoring data should be analyzed promptly. Data analysis can determine the creep and deformation of soft rock. Simultaneously, based on data trends, support parameters and the reserved thickness of the foam buffer layer 3 should be dynamically optimized and adjusted to ensure the safety and reliability of the support system. If the monitoring data shows abrupt changes or the convergence rate exceeds the standard, the monitoring frequency should be increased immediately, and enhanced support measures should be taken, such as adding temporary supports and radial grouting at the arch, to ensure effective control of soft rock deformation.

[0040] The thickness of the reserved deformation space layer 5 is 15-20cm. There is nothing in the reserved deformation space layer 5, which provides sufficient deformation space for the primary support layer 4 away from the wall, avoids the primary support layer 4 away from the wall from directly contacting the secondary lining layer 6, and prevents the primary support layer 4 away from the wall from deforming and squeezing the secondary lining layer 6.

[0041] After the soft rock deformation stabilizes, a waterproof membrane is laid inside the initial support layer 4, which is separated from the wall. Then, secondary lining concrete is poured to form the secondary lining layer 6. The secondary lining concrete is C30 reinforced concrete with a thickness of 45-55 cm, thus completing the construction of the entire composite support system of this invention. This invention can significantly shorten the support response time and improve the control capability for large deformations in soft rock, making it suitable for safe tunnel construction in environments with high ground stress and strong rheological properties.

[0042] Although embodiments of the present invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A support system for large deformation tunnels in soft rock, characterized in that: It includes an anchoring support structure, which includes an active protective net and multiple self-advancing hollow grouting anchors (1). Multiple self-propelled hollow grouting anchors (1) cover the entire tunnel section except for the invert arch. The self-propelled hollow grouting anchors (1) are driven vertically into the tunnel wall and the anchoring end extends into the stable rock layer. The active protection net is fixedly installed at the tail end of all the self-propelled hollow grouting anchors (1), thereby forming a spatial grid structure to suppress block fall and local instability. The active protection net forms a preliminary sealing layer (2) by spraying concrete to fill the depression on the soft rock surface and enhance the integrity of the soft rock. The inner side of the initial sealing layer (2) is provided with a foam buffer layer (3), a wall-separated initial support layer (4), a reserved deformation space layer (5), and a secondary lining layer (6), thereby forming a multi-layer support for the soft rock large deformation tunnel.

2. The soft rock large deformation tunnel support system according to claim 1, characterized in that: The foam buffer layer (3) is made of polyurethane foam. The foam buffer layer (3) is fixedly installed between the initial sealing layer (2) and the wall-mounted initial support layer (4), and its thickness is 40-50cm.

3. The soft rock large deformation tunnel support system according to claim 1, characterized in that: The wall-detached initial support layer (4) includes an initial support concrete structure and multiple initial support arch frames, all of which are fixedly installed in the initial support concrete structure.

4. The soft rock large deformation tunnel support system according to claim 3, characterized in that: The initial support arch is made of I20 I-beams or H-beams, and the distance between two adjacent initial support arches is 0.8 to 1 m.

5. The soft rock large deformation tunnel support system according to claim 1, characterized in that: A monitoring section is set up every two meters along the length of the tunnel. A monitoring point is set at the top of the initial support arch and the waist of both sides of the arch in the monitoring section, which serves as a joint observation point for the total station and convergence meter to determine the stability of the initial support layer (4) away from the wall.

6. The soft rock large deformation tunnel support system according to claim 1, characterized in that: The thickness of the reserved deformation space layer (5) is 15-20cm.

7. The soft rock large deformation tunnel support system according to claim 1, characterized in that: The secondary lining layer (6) is made of reinforced concrete with a strength of C30 and a thickness of 45-55cm.

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