A method for controlling surrounding rock of soft rock roadway in water-rich roof of Jurassic weakly cemented strata

Abstract

The present invention discloses a method for controlling surrounding rock of soft rock tunnels in weakly cemented strata with rich water roof, which belongs to the technical field of surrounding rock control of underground coal mine tunnels. The method analyzes and studies the chemical composition, mineral components and disintegration characteristics of tunnel surrounding rock through XRF, XRD determination and water immersion resistance disintegration experiment; adopts a drying box and a non-destructive atomization immersion system to make standard cylindrical specimens with different water contents; through variable angle compression shear experiment and theoretical calculation, respectively from the perspective of the influence of water on the mechanical properties of weakly cemented soft rock and the range of the plastic zone of the surrounding rock under the coupling effect of water and rock, reveals the degradation law of the hydromechanical properties of weakly cemented soft rock; on this basis, proposes corresponding tunnel surrounding rock control countermeasures, and designs support schemes in a targeted manner. The present invention can effectively control the deformation and damage of soft rock tunnel surrounding rock, realize the overall stability of tunnel surrounding rock, enhance the safety production guarantee capability of the mine, ensure the long-term safe use of the development tunnel, and improve the overall technical and economic benefits of the mine.

Description

Technical Field

[0001] The invention belongs to the technical field of surrounding rock control of underground coal mine tunnels, and in particular relates to a method for controlling surrounding rock of soft rock tunnels in water-rich roof of weakly cemented Jurassic strata. Background Art

[0002] When tunnel excavation is carried out in the weakly cemented strata of the Jurassic system, when there is a discontinuous sandstone aquifer above the tunnel roof, if traditional passive support methods are adopted, such as "shelf support", water from the roof can easily soak the surrounding rock along the steel shed, causing the surrounding rock to soften and disintegrate and the steel shed components to fail; if currently commonly used active support methods are adopted, such as "anchor mesh cable spraying support", once the support scheme is improperly designed, the tunnel surrounding rock will often show continuous nonlinear large deformation, which seriously restricts the safe and efficient production of the mine.

[0003] Therefore, in view of the above problems, it is necessary to propose an effective and reliable method for controlling the surrounding rock of soft rock roadways in water-rich roof of Jurassic weakly cemented strata, so as to effectively control the deformation and damage of the surrounding rock of soft rock roadways and achieve the overall stability of the surrounding rock of the roadways. Summary of the invention

[0004] In view of this, the present invention discloses a method for controlling the surrounding rock of soft rock tunnels in water-rich roof of weakly cemented Jurassic strata, which can effectively control the deformation and damage of the surrounding rock of the soft rock tunnel, achieve overall stability of the tunnel surrounding rock, enhance the mine's production safety guarantee capability, ensure the long-term safe use of the development tunnel, and improve the overall technical and economic benefits of the mine.

[0005] According to the purpose of the present invention, a method for controlling surrounding rock of soft rock roadway in Jurassic weakly cemented stratum with rich water roof is proposed, comprising the following steps:

[0006] Step 1: Collect the surrounding rock samples of the research tunnel on site and transport them to the laboratory, where they are crushed, ground, screened and dried to make standard powder samples. At the same time, the surrounding rock samples of the research tunnel collected on site are made into standard cylindrical specimens in the laboratory through drilling, coring, cutting and grinding.

[0007] Step 2: Use X-ray fluorescence spectrometer and X-ray diffractometer to conduct qualitative and semi-quantitative analysis on the chemical composition and mineral composition of the sample to understand the geological composition of the sample; place the standard cylindrical specimen in a beaker of water, observe the disintegration process of the standard cylindrical specimen in static water, and judge the disintegration resistance of the standard cylindrical specimen.

[0008] Step 3: Take a few more standard cylindrical specimens and place them in an oven to dry them. Take them out and place them in a drying dish for later use.

[0009] Step 4: Based on the disintegration resistance of the standard cylindrical specimen, the standard cylindrical specimen dried in step 3 is prepared into water-containing standard cylindrical specimens with different water contents using a non-destructive atomization immersion test system.

[0010] Step 5: Through the variable angle compression shear test, the normal stress σ and shear force τ data of standard cylindrical specimens with different water content at different shear angles are obtained. Based on the Mohr-Coulomb strength criterion and using the Origin function drawing software, the experimental data are fitted to obtain the cohesion c and internal friction angle of the standard cylindrical specimen with water content. The fitting formulas for the relationship between water content ω are f c (ω) and

[0011] Step 6: f c (ω), Substitute the Fenner equation into the equation to establish the relationship between the plastic zone range and water content of the soft tunnel surrounding rock in the Jurassic weakly cemented strata:

[0012]

[0013] Where: c ω =f c (ω); R p is the plastic zone range of the surrounding rock of the tunnel, m; p0 is the initial stress of the rock mass, MPa; r t is the theoretical radius of the tunnel, m; c ω is the cohesion of rock, MPa; is the internal friction angle of rock, °; ω is the water content of rock, %.

[0014] Step 7: Based on the expression of the relationship between the plastic zone range and the water content, input the relevant data and draw the relationship curve between the plastic zone range and the water content, and theoretically analyze the surrounding rock failure characteristics of the soft rock tunnel with water-rich roof.

[0015] Step 8: Based on the deformation and failure characteristics of the surrounding rock of the soft rock tunnel with water-rich roof, propose corresponding water control measures combining drainage and water blocking, design a reasonable support plan, and control the deformation of the surrounding rock of the tunnel.

[0016] Step nine: Evaluate the support effect of the tunnel surrounding rock through borehole observation and tunnel surface displacement monitoring methods, and verify the rationality and reliability of the control method of the soft rock tunnel surrounding rock in the weakly cemented Jurassic strata with rich water roof.

[0017] Preferably, in step 1, the particle size of the standard powder sample is 400 mesh; the diameter of the standard cylindrical specimen is 50 mm and the height is 50 mm.

[0018] Preferably, in step four, the non-destructive atomization immersion experiment system includes a sealed box, a water-permeable plate, a hygrometer, a water-blocking platform, a PVC pipe and an ultrasonic humidifier; the water-permeable plate is installed in the sealed box; the water-blocking platform is installed on the water-permeable plate, and a standard cylindrical specimen is placed on it; the hygrometer is installed on the sealed box body; one end of the PVC pipe is connected to the air inlet of the sealed box, and the other end is connected to the ultrasonic humidifier.

[0019] Preferably, in step five, the shear angles of the variable angle compression shear test are 55°, 60° and 65° respectively; the moisture contents of the water-containing standard cylindrical specimens are 0, intermediate value and saturation respectively.

[0020] Preferably, in step eight, the surrounding rock support structure includes an arch support structure and a two-side support structure; the arch support structure includes a first steel flat welded mesh, a first ladder beam, a first anchor rod and an anchor cable; the first steel flat welded mesh is laid on the arched top of the tunnel, the first ladder beam is arched, and is a plurality of evenly distributed along the direction of the tunnel, the first anchor rod is evenly distributed on each first ladder beam, the anchor cable is evenly distributed between two adjacent first ladder beams, and two adjacent rows of anchor cables are arranged with two first ladder beams between them; one of the multiple rows of first anchor rods and anchor cables is arranged on the center line of the tunnel; the two-side support structure includes a second steel flat welded mesh, a second ladder beam and a second anchor rod; the second steel flat welded mesh is laid on both sides of the tunnel, the second ladder beam is vertically arranged, and is a plurality of evenly distributed along the direction of the tunnel, and the second anchor rod is evenly distributed on each second ladder beam.

[0021] Compared with the prior art, the method for controlling surrounding rock of soft rock roadway in water-rich roof of Jurassic weakly cemented strata disclosed in the present invention has the following advantages:

[0022] (1) According to the specific geological conditions of the surrounding rock of the soft rock tunnel with water-rich roof in the weakly cemented stratum of the Jurassic system, the present invention designs an experiment on the hydromechanical properties of weakly cemented soft rock under the action of water and rock, introduces the shear strength index into the Finner equation, establishes the relationship expression between the plastic zone range and the water content of the surrounding rock, and further obtains the relationship curve between the plastic zone range and the water content, systematically reveals the deformation and failure mechanism and characteristics of the surrounding rock of the soft rock tunnel with water-rich roof, and designs a reasonable support scheme based on this feature, which can be widely promoted and applied in mines under similar geological conditions.

[0023] (2) The present invention is based on the principle of active support, which can greatly improve the efficiency of tunnel support, ensure the quality of tunnel support, reduce the labor intensity of workers, and improve the on-site working environment. At the same time, while ensuring the safety and stability of the tunnel service period, it can greatly save capital costs such as working hours, workers' wages and material costs, effectively shorten the tunnel layout cycle, and potentially improve the overall economic benefits of the mine.

[0024] (3) The present invention adopts a method combining drilling observation and tunnel surface displacement monitoring to evaluate the support effect, which is more comprehensive, objective and reasonable. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 It is a flowchart of the overall implementation of the embodiment of the present invention.

[0027] Figure 2 This is the structural diagram of the non-destructive atomization immersion experiment system.

[0028] Figure 3 It is a relationship curve diagram between the plastic zone range and water content of the surrounding rock of the tunnel in the embodiment of the present invention.

[0029] Figure 4 It is a schematic diagram of the tunnel support cross section of an embodiment of the present invention.

[0030] Figure 5 It is a schematic diagram of the tunnel support arch support structure in an embodiment of the present invention.

[0031] Figure 6 It is a schematic diagram of the left side support of the tunnel support in the embodiment of the present invention.

[0032] Figure 7 It is a schematic diagram of the right side support of the tunnel support in the embodiment of the present invention.

[0033] In the figure: 1-sealed box; 2-water-permeable plate; 3-humidity meter; 4-water-blocking platform; 5-air inlet; 6-PVC pipe; 7-standard cylindrical specimen; 8-ultrasonic humidifier; 9-anchor cable; 10-first anchor rod; 11-first steel flat welded mesh; 12-first ladder beam; 13-second anchor rod; 14-second steel flat welded mesh; 15-second ladder beam; 16-center line of tunnel. DETAILED DESCRIPTION

[0034] The specific implementation of the present invention is briefly described below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] Figure 1-Figure 7The preferred embodiments of the present invention are shown and analyzed in detail.

[0036] Taking the Xinjiang Hami Dananhu mining area as an example, the soft rock development tunnel of the Jurassic stratum with weak cementation and rich water roof in a coal mine is buried about 300m deep, with a designed net width of 4500mm and a net height of 3650mm, including a wall height of 1400mm, an arch height of 2250mm, and a net section of 14.25m. 2 In the early stage of tunnel excavation, due to the failure to adopt reasonable drainage measures and support methods, the tunnel surrounding rock was severely deformed, the performance of support components was weakened, and the roof water exposed and eroded the tunnel surrounding rock, becoming a major hidden danger threatening the safe and efficient production of the mine.

[0037] like Figure 1 As shown, a method for controlling surrounding rock of soft rock roadway in Jurassic weakly cemented stratum water-rich roof disclosed in the present invention comprises the following steps:

[0038] Step 1: Collect sandy mudstone samples from the +170m level of the mine and transport them to the laboratory for processing into standard powder with a particle size of 400 mesh and standard cylindrical specimens 7 with a diameter of 50mm and a height of 50mm.

[0039] Step 2: X-ray fluorescence spectrometer and X-ray diffractometer were used to conduct qualitative and semi-quantitative analysis on the chemical composition and mineral composition of the sample. The test results showed that the chemical composition of the sandy mudstone at the +170m level of the mine was mainly SiO2 and Al2O3, with contents of 60.29% and 22.17% respectively; the mineral composition was mainly composed of single-particle minerals and clay minerals, and the relative content of clay minerals was as high as 58.5%. The standard cylindrical specimen 7 was placed in a beaker of water, and the disintegration process of the standard cylindrical specimen 7 in static water was observed until the morphology of the standard cylindrical specimen 7 no longer changed, which was considered to be the end of the disintegration, so as to judge the disintegration resistance of the standard cylindrical specimen 7. The results of the immersion disintegration resistance test showed that the standard cylindrical specimen 7 showed the disintegration characteristics from "outside" to "inside", from "small" to "large" and then to "small" after being immersed in water. It had strong disintegration and a fast disintegration rate, and was basically completely disintegrated after 1 hour.

[0040] Step 3: Take three sandy mudstone standard cylindrical specimens 7 and place them in an oven to dry them, then take them out and place them in a drying dish for later use.

[0041] Step 4: Since sandy mudstone has strong disintegration when exposed to water, a non-destructive atomization immersion test system is used to prepare the standard cylindrical specimen 7 dried in step 3 into experimental standard cylindrical specimens 7 with water contents of 0%, 3% and 6%. Figure 2As shown, the non-destructive atomization immersion test system includes a sealed box 1, a permeable plate 2, a hygrometer 3, a water-proof platform 4, a PVC pipe 6 and an ultrasonic humidifier 8; the permeable plate 2 is installed in the sealed box 1; the water-proof platform 4 is installed on the permeable plate 2, and a standard cylindrical specimen 7 is placed thereon; the hygrometer 3 is installed on the body of the sealed box 1; one end of the PVC pipe 6 is connected to the air inlet 5 of the sealed box 1, and the other end is connected to the ultrasonic humidifier 8. The dry standard cylindrical specimen 7 is placed on the water-proof platform 4, the sealed box 1 is closed, and the ultrasonic humidifier 8 is turned on. As the water mist enters the sealed box 1 through the PVC pipe 6, the environmental humidity in the sealed box 1 continues to increase, and the standard cylindrical specimen 7 absorbs water without loss. The standard cylindrical specimen 7 is taken out and weighed at intervals, and the moisture content of the standard cylindrical specimen 7 is calculated. When the moisture content no longer changes, it is considered to be in a saturated state. According to the law of moisture content changing with immersion time, a standard cylindrical specimen 7 with a target moisture content is made.

[0042] Step 5: Through the variable angle compression shear test, the normal stress σ and shear force τ data of three standard cylindrical specimens with different water contents at three shear angles of 55°, 60° and 65° were obtained. Based on the Mohr-Coulomb strength criterion and using the Origin function drawing software, the experimental data were fitted to obtain the cohesion c and internal friction angle of sandy mudstone. The expressions related to the moisture content ω are: c (ω)=1.82028-0.07028e^(ω / 2.00355);

[0043] Step 6: f c (ω), Substituting into Fenner equation, the relationship between the plastic zone range and water content of tunnel surrounding rock is obtained.

[0044]

[0045] Where: c ω =f c (ω)=1.82028-0.07028e^(ω / 2.00355); R p is the plastic zone range of the surrounding rock of the tunnel, m; p0 is the initial stress of the rock mass, MPa; r t is the theoretical radius of the tunnel, m; c ω is the cohesion of rock, MPa; is the internal friction angle of rock, °; ω is the water content of rock, %.

[0046] Step 7: Based on the relationship expression between the plastic zone range and water content of the tunnel surrounding rock, a curve diagram of the relationship between the plastic zone range and water content of the tunnel surrounding rock is drawn. Figure 3As shown in the figure, it can be seen that with the increase of water content, the range of the plastic zone of the surrounding rock can be divided into three stages, namely, slow development stage I, obvious increase stage II and violent expansion stage III, with average growth rates of 0.155m / %, 0.620m / % and 2.510m / %, respectively. Therefore, reducing the erosion and weakening effect of water on weakly cemented surrounding rock is the key to achieving long-term safety and stability of the tunnel.

[0047] Step 8: In view of the obvious influence of water on the surrounding rock of weakly cemented soft rock tunnels, a surrounding rock control strategy of timely and active support, focusing on surface protection components, and blocking water gushing channels was proposed, and a "anchor-net-cable-beam injection" combined support scheme was designed, such as Figures 4 to 7 As shown. The surrounding rock support structure includes an arch support structure and a two-side support structure; the arch support structure includes a first steel flat welded mesh 11, a first ladder beam 12, a first anchor rod 10 and an anchor cable 9; the first steel flat welded mesh 11 is laid on the arched top of the tunnel, the first ladder beam 12 is set in an arch shape, and is a plurality of evenly distributed along the direction of the tunnel, the first anchor rod 10 is evenly distributed on each first ladder beam 12, the anchor cable 9 is evenly distributed between two adjacent first ladder beams 12, and two adjacent rows of anchor cables 9 are set at intervals of two first ladder beams 12; the middle of the multiple rows of first anchor rods 10 and anchor cables 9 are all set on the center line 16 of the tunnel; the two-side support structure includes a second steel flat welded mesh 14, a second ladder beam 15 and a second anchor rod 13; the second steel flat welded mesh 14 is laid on both sides of the tunnel, the second ladder beam 15 is set vertically, and is a plurality of evenly distributed along the direction of the tunnel, and the second anchor rod 13 is evenly distributed on each second ladder beam 15. The first anchor rod 10 in the arch support structure adopts a strong anchor rod made of left-handed non-longitudinal reinforcement threaded steel with a diameter of 20mm and a length of 2200mm, and the spacing between rows is 800mm. The full-length anchor cable 9 adopts a steel strand with a diameter of 18.9mm and a length of 6250mm. The spacing between anchor cables 9 is 1400mm and the spacing between rows is 1600mm. The full-length anchoring of anchor cables 9 is achieved by using rubber anti-seepage sleeves, grouting plugs, grouting pipes, and full-anchor slurry. The length and width of the first steel flat welded mesh 11 are 2000mm and 1000mm respectively, the length and width of the grid are both 100mm, and the mesh overlaps 100mm. The first ladder beam 12 is made of round steel with a diameter of 12mm, a length and width of 5000mm and 70mm respectively, and a hole spacing of 800mm; the anchoring agent adopts a water-resistant type. The parameters of the second anchor rod 13 in the two-side support structure are the same as those of the first anchor rod 10; the parameters of the second steel flat welded mesh 14 are the same as those of the first steel flat welded mesh 11; the second ladder beam 15 is 2600mm long, and the remaining parameters are the same as those of the first ladder beam 12. In the specific construction process, the step-by-step excavation method is adopted. First, the tunnel boring machine cuts the upper step and removes slag; then the first steel flat welded mesh 11 and the first ladder beam 12 are sprayed and laid, and the first anchor rod 10 and the anchor cable 9 are installed; then the tunnel boring machine cuts the lower step and removes slag; then the second steel flat welded mesh 14 and the second ladder beam 15 are laid, the second anchor rod 13 is installed, and finally the grouting is performed.

[0048] Step 9: Apply the design scheme to the project site, and drill surrounding rock peek holes and displacement monitoring points in the tunnel section to evaluate the support effect of the tunnel surrounding rock and verify the rationality and reliability of the surrounding rock control method for the soft rock tunnel in the weakly cemented Jurassic strata with rich water roof.

[0049] The research results were applied to on-site construction. The on-site monitoring results showed that with the redesigned optimized support scheme, the maximum movement of the tunnel roof and bottom plates and the two sides was only 121mm and 91mm; the average range of surrounding rock rupture was about 1.989m, a reduction of 57.71% compared with the original support scheme; the problem of surrounding rock control in weakly cemented soft rock tunnels was effectively solved, and the requirements of long-term safety and stability of the tunnels could be met.

[0050] The above description of the disclosed embodiments enables those skilled in the art to implement and use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit and scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest range consistent with the principles and novel features disclosed herein.

Claims

1. A method for controlling surrounding rock of soft rock roadway in water-rich roof of Jurassic weakly cemented strata, characterized in that: The following steps are involved: Step 1: Collect the surrounding rock samples of the research tunnel on site and transport them to the laboratory, where they are crushed, ground, screened and dried to make standard powder samples; at the same time, the surrounding rock samples of the research tunnel collected on site are made into standard cylindrical specimens in the laboratory by means of drilling, coring, cutting and grinding (7); Step 2: Use an X-ray fluorescence spectrometer and an X-ray diffractometer to conduct qualitative and semi-quantitative analysis on the chemical composition and mineral composition of the sample to understand the geological composition of the sample; place the standard cylindrical specimen (7) in a beaker of water, observe the disintegration process of the standard cylindrical specimen (7) in static water, and determine the disintegration resistance of the standard cylindrical specimen (7); Step 3: Take a plurality of standard cylindrical test pieces (7) and place them in an oven to dry them, then take them out and place them in a drying dish for later use; Step 4: Based on the anti-disintegration characteristics of the standard cylindrical specimen (7), a non-destructive atomization immersion test system is used to prepare the standard cylindrical specimen (7) dried in step 3 into water-containing standard cylindrical specimens (7) with different moisture contents; the non-destructive atomization immersion test system includes a sealed box (1), a water-permeable plate (2), a hygrometer (3), a water-blocking platform (4), a PVC pipe (6) and an ultrasonic humidifier (8); the water-permeable plate (2) is installed in the sealed box (1); the water-blocking platform (4) is installed on the water-permeable plate (2), and the standard cylindrical specimen (7) is placed thereon; the hygrometer (3) is installed on the sealed box (1); one end of the PVC pipe (6) is connected to the air inlet (5) of the sealed box (1), and the other end is connected to the ultrasonic humidifier (8); Step 5: The normal stress σ and shear force τ data of the standard cylindrical specimens (7) with different water contents at different shear angles are obtained through variable angle compression shear tests. Based on the Mohr-Coulomb strength criterion and using the Origin function drawing software, the experimental data are fitted to obtain the cohesion c and internal friction angle of the standard cylindrical specimens (7) with water contents. The fitting formulas for the relationship between water content ω are f c (ω) and Step 6: f c (ω), Substitute the Fenner equation into the equation to establish the relationship between the plastic zone range and water content of the soft tunnel surrounding rock in the Jurassic weakly cemented strata: Where: c ω =f c (ω); R p is the plastic zone range of the surrounding rock of the roadway, m; p0 is the initial stress of the rock mass, MPa; r t is the theoretical radius of the tunnel, m; c ω is the cohesion of rock, MPa; is the internal friction angle of rock, °; ω is the water content of rock, %; Step 7: Based on the relationship expression between the plastic zone range and the water content, relevant data is introduced and the relationship curve between the plastic zone range and the water content is drawn to theoretically analyze the surrounding rock failure characteristics of the soft rock tunnel with water-rich roof; Step 8: Based on the deformation and damage characteristics of the surrounding rock of the soft rock roadway with water-rich roof, propose corresponding water control measures combining drainage and water blocking, design a reasonable support plan, and control the deformation of the surrounding rock of the roadway; Step nine: Evaluate the support effect of the tunnel surrounding rock through borehole observation and tunnel surface displacement monitoring methods, and verify the rationality and reliability of the control method of the soft rock tunnel surrounding rock in the weakly cemented Jurassic strata with rich water roof.

2. A method for controlling surrounding rock of soft rock roadway in water-rich roof of Jurassic weakly cemented strata according to claim 1, characterized in that: In step 1, the particle size of the standard powder sample is 400 mesh; the diameter of the standard cylindrical specimen (7) is 50 mm and the height is 50 mm.

3. The method for controlling surrounding rock of soft rock roadway in water-rich roof of Jurassic weakly cemented strata according to claim 1, characterized in that: In step 5, the shear angles of the variable angle compression shear test are 55°, 60° and 65° respectively; the moisture contents of the water-containing standard cylindrical specimen (7) are 0, intermediate value and saturated respectively.

4. A method for controlling surrounding rock of soft rock roadway in water-rich roof of Jurassic weakly cemented strata according to claim 1, characterized in that: In step eight, the surrounding rock support structure includes an arch support structure and a two-side support structure; the arch support structure includes a first steel flat welded mesh (11), a first ladder beam (12), a first anchor rod (10) and an anchor cable (9); the first steel flat welded mesh (11) is laid on the arched top of the tunnel, the first ladder beam (12) is arranged in an arched shape and is evenly distributed along the direction of the tunnel, the first anchor rod (10) is evenly distributed on each first ladder beam (12), and the anchor cable (9) is evenly distributed between two adjacent first ladder beams (12). Two adjacent rows of anchor cables (9) are arranged with two first ladder beams (12) spaced apart; the multiple rows of first anchor rods (10) and one of the anchor cables (9) are arranged on the center line (16) of the tunnel; the two-side support structure comprises a second steel flat welded mesh (14), a second ladder beam (15) and a second anchor rod (13); the second steel flat welded mesh (14) is laid on both sides of the tunnel, the second ladder beam (15) is arranged vertically and is evenly distributed along the tunnel, and the second anchor rod (13) is evenly distributed on each second ladder beam (15).

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