Construction method for complex surrounding rock section of shallow-buried bias-pressure double-hole large-span tunnel

Abstract

The invention discloses a construction method for a complex surrounding rock section of a shallow-buried unsymmetrical-pressure double-hole large-span tunnel. The technical purpose of reducing the surrounding rock deformation risk in the tunnel excavation process is achieved. Comprising the following steps: performing surrounding rock pressure distribution analysis on the surrounding rock section, and drawing a pressure distribution field; performing integral grouting reinforcement on the surrounding rock section, wherein the reinforcement degree of the integral grouting reinforcement on the surrounding rock section is in gradient distribution from weak to strong according to the distribution condition of the pressure in the pressure distribution field from large to small; and after the integral grouting reinforcement is completed, tunnel excavation construction is carried out. The low-pressure area which is easier to deform is strengthened in a more targeted manner, so that the deformation of the surrounding rock is more effectively controlled, and the deformation risk of the surrounding rock in the tunnel excavation process is effectively reduced; according to the differentiated grouting reinforcement mode, resource distribution is optimized, excessive reinforcement of the high-pressure area is avoided, materials and construction cost can be saved, and unnecessary disturbance to the surrounding environment is reduced.

Description

Technical Field

[0001] The invention relates to a tunnel construction technology under special geological conditions, and in particular to a construction method for a shallowly buried biased double-hole large-span tunnel with a complex surrounding rock section. Background Art

[0002] The complex surrounding rock section of a shallow-buried biased double-hole large-span tunnel refers to: 1) shallow burial: the tunnel is shallow, usually ≤40m; 2) biased pressure: the stratum pressure distribution is uneven, resulting in uneven stress on the tunnel structure; 3) double-hole: with a shallow side tunnel and a deep side tunnel; 4) large span: refers to the excavation width or diameter of the tunnel reaching a certain value, usually ≥12m; 5) complex surrounding rock: the surrounding rock geological conditions are complex, which may include weak rock formations, broken zones, aquifers, etc. The existing construction scheme for the complex surrounding rock section of a shallow-buried biased double-hole large-span tunnel mainly focuses on the tunnel step-by-step excavation method, support structure design, tunnel deformation and surrounding rock change monitoring, etc. For weak surrounding rock, stratum grouting reinforcement can also be carried out when necessary. At present, one of the difficulties in the construction process of the complex surrounding rock section of a shallow-buried biased double-hole large-span tunnel is that the surrounding rock stress redistribution will occur during the tunnel excavation process, and the superposition of biased pressure, complex geological conditions and other factors can easily lead to the risk of surrounding rock deformation. Summary of the invention

[0003] The purpose of the present invention is to provide a construction method for a shallow-buried, biased, double-hole, large-span tunnel with complex surrounding rock sections, so as to solve the technical problem of reducing the risk of surrounding rock deformation during tunnel excavation.

[0004] To this end, a construction method for a shallow-buried, biased, double-hole, large-span tunnel with a complex surrounding rock section is provided, comprising: analyzing the surrounding rock pressure distribution of the surrounding rock section and drawing a pressure distribution field; performing overall grouting reinforcement on the surrounding rock section, wherein the degree of reinforcement of the surrounding rock section by the overall grouting reinforcement is distributed in a gradient from weak to strong according to the distribution of pressure from large to small in the pressure distribution field; after the overall grouting reinforcement is completed, tunnel excavation construction is performed.

[0005] As an improvement and / or instantiation of the above-mentioned shallow-buried biased double-hole large-span tunnel complex surrounding rock section construction method, further: the pressure distribution field includes: a low-pressure zone, the low-pressure zone is mainly distributed in the upper area of ​​the shallow-buried side tunnel and the outer area of ​​the shallow-buried side tunnel; a medium-pressure zone, the medium-pressure zone is mainly distributed in the area between the shallow-buried side tunnel and the deep-buried side tunnel and the upper area of ​​the deep-buried side tunnel; a high-pressure zone, the high-pressure zone is mainly distributed in the inner area of ​​the deep-buried side tunnel, the lower area of ​​the deep-buried side tunnel and the lower area of ​​the shallow-buried side tunnel; during the overall grouting reinforcement, the degree of strengthening of the low-pressure zone is greater than the degree of strengthening of the medium-pressure zone and the degree of strengthening of the low-pressure zone.

[0006] As an improvement and / or instantiation of the above-mentioned shallow-buried biased double-hole large-span tunnel complex surrounding rock section construction method, further: the degree of strengthening is determined according to the uniaxial compression strength gain multiple of the corresponding rock mass before and after the overall grouting reinforcement.

[0007] As an improvement and / or instantiation of the above-mentioned shallow buried biased double-hole large-span tunnel complex surrounding rock section construction method, further: the uniaxial compression strength gain multiple of the low-pressure zone before and after the overall grouting reinforcement is 3.5-5 times; the uniaxial compression strength gain multiple of the medium-pressure zone before and after the overall grouting reinforcement is 2.2-3.2 times; the uniaxial compression strength gain multiple of the high-pressure zone before and after the overall grouting reinforcement is 1.2-2 times.

[0008] As an improvement and / or instantiation of the above-mentioned shallow-buried biased double-hole large-span tunnel complex surrounding rock section construction method, further: the overall grouting reinforcement is achieved by opening inclined grouting holes at the edge of the tunnel excavation face at an angle of 5°-15° with the tunnel centerline along the excavation direction and grouting through these grouting holes; during the overall grouting reinforcement, the overall grouting reinforcement schemes for the low-pressure zone, the medium-pressure zone and the high-pressure zone are specifically as follows: A. Overall grouting reinforcement scheme for low-pressure zone: A1. Grouting hole arrangement: Annular spacing: 0.8-1.3m; Longitudinal spacing: 0.8-1.3m; Spacing: 1.2-1.8m; radial arrangement: 3-5 rows; hole diameter: 50-60mm; A2. Grouting material: The material composition of the grouting material is: ultrafine cement with a median particle size of less than 5μm; expansion agent: 2-5%; water reducer: 0.8-2%; water-cement ratio: 0.5-0.8; A3. Grouting pressure: initial pressure: 0.3-1.2MPa; end pressure: 1.5-3.5MPa; A4. Single hole grouting volume: 250-400L / m; B. Overall grouting reinforcement plan for medium pressure area: B1. Grouting hole arrangement: circumferential spacing: 1.5 -2.2m; longitudinal spacing: 1.8-2.5m; radial arrangement: 2-4 rows; hole diameter: 45-55mm; B2. Grouting material: The material composition of the grouting material is: Material composition: fine cement with a median particle size of less than 10μm; expansion agent: 1.5-3.5%; water reducer: 0.6-1.5%; water-cement ratio: 0.6-0.8; B3. Grouting pressure: initial pressure: 0.8-2.0MPa; end pressure: 2.5-4.5MPa; B4. Single hole grouting volume: 170-280L / m; C. High pressure area overall grouting Solidification plan: C1. Grouting hole arrangement: circumferential spacing: 2.0-3.0m; longitudinal spacing: 2.5-3.5m; radial arrangement: 1-3 rows; hole diameter: 40-50mm; C2. Grouting material: The material composition of the grouting material is: material composition: ordinary Portland cement; expansion agent: 0.5-2.5%; water reducing agent: 0.3-1.2%; water-cement ratio: 0.65-0.85; C3. Grouting pressure: initial pressure: 1.2-2.5MPa; termination pressure: 3.5-5.5MPa; C4. Single hole grouting volume: 100-200L / m.

[0009] As an improvement and / or instantiation of the above-mentioned shallow-buried biased double-hole large-span tunnel complex surrounding rock section construction method, further: the tunnel excavation construction is carried out in a manner of first excavating a shallow-buried side tunnel of a set depth, and then excavating a deep-buried side tunnel of a set depth.

[0010] As an improvement and / or instantiation of the above-mentioned shallow-buried biased double-hole large-span tunnel complex surrounding rock section construction method, further: after excavating the shallow-buried side tunnel of a set depth, a shallow-buried side tunnel support structure is set; after excavating the deep-buried side tunnel of a set depth, a deep-buried side tunnel support structure is set.

[0011] As an improvement and / or instantiation of the above-mentioned shallow-buried biased double-hole large-span tunnel complex surrounding rock section construction method, further: the shallow-buried side tunnel support structure includes: the initial support includes 25-28cm thick shotcrete, matched with system anchor rods with a diameter of 20-25mm and a spacing of 95-105cm, and I18a steel arch frame with a spacing of 75-85cm; the invert arch adopts 26-30cm thick reinforced concrete; the deep-buried side tunnel support structure includes: the initial support includes 28-32cm thick shotcrete, matched with system anchor rods with a diameter of 20-25mm and a spacing of 75-85cm, and I20a steel arch frame with a spacing of 55-65cm; the reinforced support uses prestressed anchor cables with a diameter of 30-35mm and a length of 8-10m, and the arrangement spacing is (1.4-1.6m)×(1.4-1.6m); the invert arch adopts 30-35cm thick reinforced concrete.

[0012] As an improvement and / or instantiation of the above-mentioned shallow-buried biased double-hole large-span tunnel complex surrounding rock section construction method, further: the overall grouting reinforcement is carried out in steps according to the order of pressure from small to large in the pressure distribution field.

[0013] As an improvement and / or instantiation of the above-mentioned shallow buried biased double-hole large-span tunnel complex surrounding rock section construction method, further: first the low-pressure zone is subjected to overall grouting reinforcement, and after the overall grouting reinforcement of the low-pressure zone is completed, the medium-pressure zone is subjected to overall grouting reinforcement, and after the overall grouting reinforcement of the medium-pressure zone is completed, the high-pressure zone is subjected to overall grouting reinforcement.

[0014] The internal pressure distribution of the complex surrounding rock section of the shallow-buried biased double-hole large-span tunnel is highly uneven. Before tunnel excavation, the original low-pressure area often has low rock strength or loose structure, which is closer to the limit of its bearing capacity. After tunnel excavation, the stress of the surrounding rock will be redistributed, and the original low-pressure area will often be more prone to deformation due to the sudden pressure exceeding its original bearing capacity. In the construction method of the complex surrounding rock section of the shallow-buried biased double-hole large-span tunnel of the present invention, by integrally grouting the surrounding rock section, the weak surrounding rock with insufficient strength can be reinforced to prevent the deformation of the weak surrounding rock. More importantly, since the degree of reinforcement of the surrounding rock section by overall grouting reinforcement presents a gradient distribution from weak to strong according to the distribution of pressure from large to small in the pressure distribution field, the low-pressure area that is more easily deformed can be strengthened in a more targeted manner, thereby more effectively controlling the deformation of the surrounding rock and effectively reducing the risk of surrounding rock deformation during tunnel excavation; secondly, this differentiated grouting reinforcement method optimizes resource allocation, avoids excessive reinforcement of high-pressure areas, saves material and construction costs, and reduces unnecessary disturbance to the surrounding environment; in addition, this differentiated grouting reinforcement method can create a more homogeneous surrounding rock environment, improve the stress condition of the overall tunnel structure, and improve long-term stability.

[0015] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments. Additional aspects and advantages of the present invention will be partially given in the following description, partially become apparent from the following description, or be learned through practice. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings constituting a part of this specification are used to assist the understanding of the present invention. The contents provided in the drawings and the related descriptions in this specification can be used to explain the present invention, but do not constitute improper limitations on the present invention.

[0017] Figure 1 The present invention discloses a shallow-buried biased double-hole large-span tunnel model targeted at a construction method for a complex surrounding rock section of a shallow-buried biased double-hole large-span tunnel according to an embodiment of the present invention.

[0018] Figure 2 for Figure 1 The simulation diagram of the pressure distribution field in the complex surrounding rock section of a shallow-buried, biased, double-hole, large-span tunnel is shown. Figure 2 The X-axis represents the horizontal coordinate value (in meters), the Y-axis represents the vertical coordinate value (in meters), and the colors correspond to different pressure values ​​(in KPa).

[0019] Figure 3 The present invention is a schematic diagram of the distribution of grouting holes in a method for constructing a shallow-buried, biased, double-hole, large-span tunnel with a complex surrounding rock section according to an embodiment of the present invention.

[0020] Figure 4 for Figure 3A partial enlarged view of . DETAILED DESCRIPTION

[0021] The present invention is described clearly and completely below in conjunction with the accompanying drawings. A person skilled in the art will be able to implement the present invention based on these descriptions. Before describing the present invention in conjunction with the accompanying drawings, it should be particularly noted that:

[0022] The technical solutions and technical features provided in each section, including the following description, can be combined with each other without conflict. In addition, where possible, these technical solutions, technical features and related combinations can be assigned specific technical themes and protected by relevant patents.

[0023] The embodiments of the present invention involved in the following description are generally only a part of the embodiments rather than all the embodiments. Based on these embodiments, all other embodiments obtained by ordinary technicians in this field without making creative work should fall within the scope of patent protection.

[0024] Regarding the terms and units in this specification: The terms "include", "comprises", "have" and any variations thereof in this specification and the corresponding claims and related parts are intended to cover non-exclusive inclusions. In addition, other relevant terms and units can be reasonably interpreted based on the relevant content provided in this specification.

[0025] The complex surrounding rock section of the shallow-buried biased double-hole large-span tunnel refers to: 1) shallow burial: the tunnel is shallow, usually ≤40m; 2) biased pressure: the stratum pressure distribution is uneven, resulting in uneven stress on the tunnel structure; 3) double-hole: with a shallow side tunnel and a deep side tunnel; 4) large span: refers to the excavation width or diameter of the tunnel reaching a certain value, usually ≥12m; 5) complex surrounding rock: the surrounding rock geological conditions are complex, which may include weak rock formations, broken zones, aquifers, etc. The existing construction scheme for the complex surrounding rock section of the shallow-buried biased double-hole large-span tunnel mainly focuses on the tunnel step-by-step excavation method, support structure design, tunnel deformation and surrounding rock change monitoring, etc. For weak surrounding rock, stratum grouting reinforcement can also be carried out when necessary. At present, one of the difficulties in the construction process of the complex surrounding rock section of the shallow-buried biased double-hole large-span tunnel is that the surrounding rock stress redistribution will occur during the tunnel excavation process, and the superposition of biased pressure overlap, complex geological conditions and other factors can easily lead to the risk of surrounding rock deformation. The main reason is that the internal pressure distribution in the complex surrounding rock section of the shallow-buried biased double-hole large-span tunnel is highly uneven. Before tunnel excavation, the original low-pressure area often has lower rock strength or looser structure, which is closer to the limit of its bearing capacity. After tunnel excavation, the stress of the surrounding rock will be redistributed, and the original low-pressure area will often be more prone to deformation due to the sudden pressure exceeding its original bearing capacity.

[0026] The method for constructing a complex surrounding rock section of a shallow-buried biased double-hole large-span tunnel of the present invention comprises: analyzing the surrounding rock pressure distribution of the surrounding rock section and drawing the pressure distribution field; performing overall grouting reinforcement on the surrounding rock section, wherein the degree of strengthening of the surrounding rock section by the overall grouting reinforcement is distributed in a gradient from weak to strong according to the distribution of pressure from large to small in the pressure distribution field; after the overall grouting reinforcement is completed, tunnel excavation construction is performed. In the above-mentioned method for constructing a complex surrounding rock section of a shallow-buried biased double-hole large-span tunnel, by performing overall grouting reinforcement on the surrounding rock section, weak surrounding rocks with insufficient strength can be reinforced to prevent deformation of the weak surrounding rocks. More importantly, since the degree of reinforcement of the surrounding rock section by overall grouting reinforcement presents a gradient distribution from weak to strong according to the distribution of pressure from large to small in the pressure distribution field, the low-pressure area that is more easily deformed can be strengthened in a more targeted manner, thereby more effectively controlling the deformation of the surrounding rock and effectively reducing the risk of surrounding rock deformation during tunnel excavation; secondly, this differentiated grouting reinforcement method optimizes resource allocation, avoids excessive reinforcement of high-pressure areas, saves material and construction costs, and reduces unnecessary disturbance to the surrounding environment; in addition, this differentiated grouting reinforcement method can create a more homogeneous surrounding rock environment, improve the stress condition of the overall tunnel structure, and improve long-term stability.

[0027] Figure 1 The present invention discloses a shallow-buried biased double-hole large-span tunnel model targeted at a construction method for a complex surrounding rock section of a shallow-buried biased double-hole large-span tunnel according to an embodiment of the present invention. Figure 2 for Figure 1 The simulation diagram of the pressure distribution field in the complex surrounding rock section of a shallow-buried biased double-hole large-span tunnel is shown in Figure 1. Figure 1-Figure 2 As shown, the tunnel in the surrounding rock section is buried 30-40m deep, the single tunnel span is about 18m, the geological conditions are strongly weathered sandstone intercalated with mudstone, the rock mass is broken, and the RQD (rock quality index) is less than 25%. The left tunnel is the deep buried side tunnel 1, and the right tunnel is the shallow buried side tunnel 2. Figure 2 It can also be seen that the pressure distribution field includes: a low-pressure zone, a medium-pressure zone and a high-pressure zone. The low-pressure zone (blue area) is mainly distributed in the upper area of ​​the shallow buried side tunnel 2 and the outer area of ​​the shallow buried side tunnel 2; the medium-pressure zone (yellow area) is mainly distributed in the area between the shallow buried side tunnel 2 and the deep buried side tunnel 1 and the upper area of ​​the deep buried side tunnel 1; the high-pressure (red area) zone is mainly distributed in the inner area of ​​the deep buried side tunnel 1, the lower area of ​​the deep buried side tunnel and the lower area of ​​the shallow buried side tunnel.

[0028] The determination of the above-mentioned pressure distribution field is usually carried out through the following steps: first, collect geological data of the tunnel project, including rock and soil properties, geological structure, groundwater conditions, etc.; then, use finite element analysis software (such as FLAC3D, ANSYS, etc.) to establish a three-dimensional numerical model of the tunnel and surrounding rock mass, and input relevant physical and mechanical parameters; then, set appropriate boundary conditions and initial stress fields, considering factors such as gravity, water pressure, and tectonic stress; then, run numerical simulation calculations to obtain the stress distribution state of the rock mass around the tunnel; finally, visualize the calculation results and draw a pressure distribution cloud map to clearly show the distribution of high-pressure areas, medium-pressure areas, and low-pressure areas.

[0029] In the construction method of the shallow-buried biased double-hole large-span tunnel with complex surrounding rock section of the present embodiment, the degree of reinforcement of the low-pressure zone by the overall grouting reinforcement is greater than the degree of reinforcement of the medium-pressure zone, which is greater than the degree of reinforcement of the low-pressure zone. Among them, the degree of reinforcement is specifically determined according to the gain multiple of the uniaxial compression strength of the corresponding rock mass before and after the overall grouting reinforcement. According to research, the gain multiple of the uniaxial compression strength of the low-pressure zone before and after the overall grouting reinforcement can be 3.5-5 times; the gain multiple of the uniaxial compression strength of the medium-pressure zone before and after the overall grouting reinforcement can be 2.2-3.2 times; the gain multiple of the uniaxial compression strength of the pressure zone before and after the overall grouting reinforcement can be 1.2-2 times.

[0030] In the above scheme, by setting a progressive reinforcement strength range for different pressure zones, the continuity and balance of the reinforcement effect are ensured, while the flexibility of adjustment during the construction process is retained. The larger reinforcement range (3.5-5 times) in the low-pressure zone reflects the focus on high-risk areas, while the smaller reinforcement range (1.2-2 times) in the high-pressure zone reflects the consideration of resource optimization.

[0031] Figure 3 The present invention is a schematic diagram of the distribution of grouting holes in a method for constructing a shallow-buried, biased, double-hole, large-span tunnel with a complex surrounding rock section according to an embodiment of the present invention. Figure 4 for Figure 3 A partial enlarged view of Figure 3-Figure 4 As shown, specifically, the overall grouting reinforcement is achieved by opening an inclined grouting hole 3 at the edge of the tunnel excavation face at an angle of 5°-15° with the tunnel centerline along the excavation direction and grouting through these grouting holes; during the overall grouting reinforcement, the overall grouting reinforcement schemes for the low pressure zone, the medium pressure zone and the high pressure zone are specifically as follows:

[0032] A. Overall grouting reinforcement scheme for low-pressure areas: A1. Grouting hole arrangement: circumferential spacing: 0.8-1.3m; longitudinal spacing: 1.2-1.8m; radial arrangement: 3-5 rows; hole diameter: 50-60mm; A2. Grouting material: The material composition of the grouting material is: ultrafine cement with a median particle size of less than 5μm; expansion agent: 2-5%; water reducer: 0.8-2%; water-cement ratio: 0.5-0.8; A3. Grouting pressure: initial pressure: 0.3-1.2MPa; termination pressure: 1.5-3.5MPa; A4. Single hole grouting volume: 250-400L / m;

[0033] B. Overall grouting reinforcement scheme for medium pressure zone: B1. Grouting hole arrangement: circumferential spacing: 1.5-2.2m; longitudinal spacing: 1.8-2.5m; radial arrangement: 2-4 rows; hole diameter: 45-55mm; B2. Grouting material: The material composition of the grouting material is: Material composition: fine cement with a median particle size of less than 10μm; expansion agent: 1.5-3.5%; water reducer: 0.6-1.5%; water-cement ratio: 0.6-0.8; B3. Grouting pressure: initial pressure: 0.8-2.0MPa; termination pressure: 2.5-4.5MPa; B4. Single hole grouting volume: 170-280L / m;

[0034] C. Overall grouting reinforcement plan for high-pressure areas: C1. Grouting hole arrangement: circumferential spacing: 2.0-3.0m; longitudinal spacing: 2.5-3.5m; radial arrangement: 1-3 rows; hole diameter: 40-50mm; C2. Grouting material: The material composition of the grouting material is: Material composition: ordinary Portland cement; expansion agent: 0.5-2.5%; water reducing agent: 0.3-1.2%; water-cement ratio: 0.65-0.85; C3. Grouting pressure: initial pressure: 1.2-2.5MPa; termination pressure: 3.5-5.5MPa; C4. Single hole grouting volume: 100-200L / m.

[0035] The above-mentioned overall grouting reinforcement scheme for the low-pressure zone, the medium-pressure zone and the high-pressure zone has the following characteristics: 1) Accuracy and adaptability: The scheme formulates detailed grouting parameters, including hole arrangement, material ratio, grouting pressure and grouting volume, according to the characteristics of the low-pressure zone, the medium-pressure zone and the high-pressure zone. This precise design can solve the specific problems of each area in a targeted manner and improve the reinforcement effect. 2) Resource optimization: From the low-pressure zone to the high-pressure zone, the spacing of the grouting holes gradually increases, the number of radial rows decreases, the hole diameter becomes smaller, and the grouting volume of a single hole decreases. 3) Rationality of material selection: Ultrafine cement with the smallest particle size is used in the low-pressure zone, microfine cement is used in the medium-pressure zone, and ordinary silicate cement is used in the high-pressure zone. This selection takes into account the permeability differences of rock masses in different regions to ensure that the grouting materials can effectively penetrate and play a role. 4) Gradient design of grouting pressure: From the low-pressure zone to the high-pressure zone, the grouting pressure gradually increases. This design is coordinated with the original stress state of each region, which can not only ensure the grouting effect, but also avoid rock mass damage caused by improper pressure. 5) Reasonable application of auxiliary materials: The dosage of expansion agent and water reducing agent also shows a gradient change, with the largest dosage in the low-pressure area and the smallest dosage in the high-pressure area, which helps to improve the grouting effect and the performance of the grouting material.

[0036] Generally speaking, the tunnel excavation construction is carried out in the manner of first excavating a shallow side tunnel of a set depth, and then excavating a deep side tunnel of a set depth. Specifically, after excavating the shallow side tunnel of a set depth, a shallow side tunnel support structure is set; after excavating the deep side tunnel of a set depth, a deep side tunnel support structure is set. Shallow side tunnels usually face greater risks of surface subsidence and rock deformation. Constructing the shallow side first can control these risks early and prevent surface subsidence from affecting the surrounding environment. After excavating the shallow side tunnel, the stress of the surrounding rock mass will be redistributed. At this time, stress redistribution is usually beneficial to the excavation of the deep side tunnel because part of the stress may be transferred or released.

[0037] Optionally, the shallow buried side tunnel support structure includes: initial support includes 25-28cm thick shotcrete, combined with system anchor rods with a diameter of 20-25mm and a spacing of 95-105cm, and I18a steel arch frame with a spacing of 75-85cm; the invert arch adopts 26-30cm thick reinforced concrete; the deep buried side tunnel support structure includes: initial support includes 28-32cm thick shotcrete, combined with system anchor rods with a diameter of 20-25mm and a spacing of 75-85cm, and I20a steel arch frame with a spacing of 55-65cm; reinforced support uses prestressed anchor cables with a diameter of 30-35mm and a length of 8-10m, and the arrangement spacing is (1.4-1.6m)×(1.4-1.6m); the invert arch adopts 30-35cm thick reinforced concrete.

[0038] In addition, the overall grouting reinforcement is carried out in steps according to the order of pressure from small to large in the pressure distribution field. Specifically, the low-pressure area is firstly subjected to overall grouting reinforcement, and when the overall grouting reinforcement of the low-pressure area is completed, the medium-pressure area is then subjected to overall grouting reinforcement, and when the overall grouting reinforcement of the medium-pressure area is completed, the high-pressure area is then subjected to overall grouting reinforcement. The low-pressure area is more unstable, and reinforcing the low-pressure area first can quickly control the greatest risk.

[0039] The above is a description of the relevant contents of the present invention. A person skilled in the art will be able to implement the present invention based on these descriptions. Based on the above contents of this specification, all other embodiments obtained by a person skilled in the art without making any creative work shall fall within the scope of patent protection.

Claims

1. A construction method for a shallowly buried biased double-hole large-span tunnel with a complex surrounding rock section, characterized by: include: Performing surrounding rock pressure distribution analysis on the surrounding rock section and drawing a pressure distribution field; The surrounding rock section is integrally grout-reinforced, wherein the degree of strengthening of the surrounding rock section by the integral grout-reinforcement is distributed in a gradient from weak to strong according to the distribution of pressure from large to small in the pressure distribution field; After the overall grouting reinforcement is completed, tunnel excavation construction is carried out.

2. The construction method of shallow buried biased double-hole large-span tunnel with complex surrounding rock section as claimed in claim 1, characterized in that: The pressure distribution field comprises: A low-pressure area, wherein the low-pressure area is mainly distributed in an upper area of ​​the shallow buried side tunnel and an outer area of ​​the shallow buried side tunnel; A medium pressure zone, wherein the medium pressure zone is mainly distributed in the area between the shallow buried side tunnel and the deep buried side tunnel and in the area above the deep buried side tunnel; A high-pressure area, wherein the high-pressure area is mainly distributed in the inner area of ​​the deep-buried side tunnel, the lower area of ​​the deep-buried side tunnel, and the lower area of ​​the shallow-buried side tunnel; During the overall grouting reinforcement, the degree of reinforcement of the low-pressure zone is greater than the degree of reinforcement of the medium-pressure zone, which is greater than the degree of reinforcement of the low-pressure zone.

3. The construction method of shallow buried biased double-hole large-span tunnel with complex surrounding rock section as claimed in claim 2, characterized in that: The degree of strengthening is determined according to the gain multiple of the uniaxial compression strength of the corresponding rock mass before and after the overall grouting reinforcement.

4. The construction method of shallow buried biased double-hole large-span tunnel with complex surrounding rock section as claimed in claim 3, characterized in that: The uniaxial compression strength gain multiple of the low-pressure zone before and after the overall grouting reinforcement is 3.5-5 times; the uniaxial compression strength gain multiple of the medium-pressure zone before and after the overall grouting reinforcement is 2.2-3.2 times; the uniaxial compression strength gain multiple of the pressure zone before and after the overall grouting reinforcement is 1.2-2 times.

5. The construction method of shallow buried biased double-hole large-span tunnel with complex surrounding rock section as claimed in claim 4, characterized in that: The overall grouting reinforcement is achieved by opening inclined grouting holes at the edge of the tunnel excavation face at an angle of 5°-15° with the tunnel centerline along the excavation direction and grouting through these grouting holes; during the overall grouting reinforcement, the overall grouting reinforcement schemes for the low pressure zone, the medium pressure zone and the high pressure zone are specifically as follows: A. Overall grouting reinforcement scheme for low-pressure areas: A1. Grouting hole arrangement: circumferential spacing: 0.8-1.3m; longitudinal spacing: 1.2-1.8m; radial arrangement: 3-5 rows; hole diameter: 50-60mm; A2. Grouting material: The material composition of the grouting material is: ultrafine cement with a median particle size of less than 5μm; Bulking agent: 2-5%; Water reducing agent: 0.8-2%; Water-cement ratio: 0.5-0.8; A3. Grouting pressure: initial pressure: 0.3-1.2MPa; final pressure: 1.5-3.5MPa; A4. Grouting volume per hole: 250-400L / m; B. Overall grouting reinforcement scheme for medium pressure zone: B1. Grouting hole arrangement: circumferential spacing: 1.5-2.2m; longitudinal spacing: 1.8-2.5m; radial arrangement: 2-4 rows; hole diameter: 45-55mm; B2. Grouting material: The material composition of the grouting material is: Material composition: fine cement with a median particle size of less than 10μm; expansion agent: 1.5-3.5%; water reducer: 0.6-1.5%; water-cement ratio: 0.6-0.8; B3. Grouting pressure: initial pressure: 0.8-2.0MPa; termination pressure: 2.5-4.5MPa; B4. Single hole grouting volume: 170-280L / m; C. Overall grouting reinforcement plan for high-pressure areas: C1. Grouting hole arrangement: circumferential spacing: 2.0-3.0m; longitudinal spacing: 2.5-3.5m; radial arrangement: 1-3 rows; hole diameter: 40-50mm; C2. Grouting material: The material composition of the grouting material is: Material composition: ordinary Portland cement; expansion agent: 0.5-2.5%; water reducing agent: 0.3-1.2%; water-cement ratio: 0.65-0.85; C3. Grouting pressure: initial pressure: 1.2-2.5MPa; termination pressure: 3.5-5.5MPa; C4. Single hole grouting volume: 100-200L / m.

6. The construction method of a shallow-buried biased double-hole large-span tunnel with complex surrounding rock section as claimed in any one of claims 1 to 5, characterized in that: The tunnel excavation construction is carried out in a manner of first excavating a shallow buried side tunnel of a set depth, and then excavating a deep buried side tunnel of a set depth.

7. The construction method of shallow buried biased double-hole large-span tunnel with complex surrounding rock section as claimed in claim 6, characterized in that: After the shallow side tunnel of the set depth is excavated, the shallow side tunnel support structure is set up; after the deep side tunnel of the set depth is excavated, the deep side tunnel support structure is set up.

8. The construction method of shallow-buried biased double-hole large-span tunnel with complex surrounding rock section as claimed in claim 7, characterized in that: The shallow buried side tunnel support structure includes: the initial support includes 25-28cm thick shotcrete, matched with system anchor rods with a diameter of 20-25mm and a spacing of 95-105cm, and I18a steel arch frame with a spacing of 75-85cm; the invert arch adopts 26-30cm thick reinforced concrete; the deep buried side tunnel support structure includes: the initial support includes 28-32cm thick shotcrete, matched with system anchor rods with a diameter of 20-25mm and a spacing of 75-85cm, and I20a steel arch frame with a spacing of 55-65cm; the reinforced support uses prestressed anchor cables with a diameter of 30-35mm and a length of 8-10m, and the arrangement spacing is (1.4-1.6m)×(1.4-1.6m); the invert arch adopts 30-35cm thick reinforced concrete.

9. The construction method of a shallow-buried biased double-hole large-span tunnel with complex surrounding rock section as claimed in any one of claims 1 to 5, characterized in that: The overall grouting reinforcement is carried out in steps according to the order of pressure from small to large in the pressure distribution field.

10. The construction method of shallow buried biased double-hole large-span tunnel with complex surrounding rock section as claimed in claim 9, characterized in that: First, the low-pressure zone is subjected to overall grouting reinforcement. After the overall grouting reinforcement of the low-pressure zone is completed, the medium-pressure zone is subjected to overall grouting reinforcement. After the overall grouting reinforcement of the medium-pressure zone is completed, the high-pressure zone is subjected to overall grouting reinforcement.

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