Construction technology suitable for soft rock-soil layer tunnel

Abstract

The invention relates to a construction technology suitable for a soft rock-soil layer tunnel, and belongs to the technical field of tunnel construction.The construction technology comprises the steps that an upper step is excavated with the step L as the length, then a plurality of rows of small gravel are arranged on the inner wall of the excavated rock-soil layer tunnel from bottom to top, and a middle step is excavated after the small gravel and the upper step are staggered by the S length; then according to the design of the small gravel in the lowermost row, medium-sized gravel is arranged under the center of the connecting line of every two adjacent small gravel, a plurality of rows of medium-sized gravel are arranged on the inner wall of the excavated middle-step rock-soil layer tunnel from top to bottom, the middle-sized gravel and the middle step are staggered by the length S, then a lower step is excavated, and according to the design of the medium-sized gravel in the lowermost row, the middle-sized gravel is excavated; one large gravel is arranged under the center of the connecting line of every two adjacent middle gravels, and a plurality of rows of large gravels are arranged on the inner wall of the excavated middle-step rock-soil layer tunnel from top to bottom, so that the stability of the whole rock-soil layer of the excavated tunnel is improved, the rebound rate of sprayed concrete is reduced, and materials are saved.

Description

Technical Field

[0001] The invention belongs to the technical field of tunnel construction, and in particular relates to a construction process suitable for tunnels in soft rock and soil layers. Background Art

[0002] The problem of large deformation of soft rock in tunnels has always been one of the engineering problems that has plagued the industry. For example, carbonaceous mudstone, mud siltstone, carbonaceous shale, etc. have weak self-bearing capacity of the surrounding rock, resulting in fast deformation speed, large deformation, and long duration of surrounding rock during the stress adjustment stage after excavation, resulting in a large total deformation. Therefore, how to choose a suitable excavation method and supporting support system has become the key to the success of the construction.

[0003] At present, when excavating a tunnel in soft rock and soil of carbon or mud, it is necessary to immediately support the rock and soil tunnel and spray concrete after each excavation. However, due to the instability of the rock and soil layer of the soft rock and soil tunnel, the rebound rate of the sprayed concrete may increase, resulting in material waste. At the same time, in the subsequent excavation process after support, the stress of the soft rock tunnel is gradually released, and the continuous rheology of the rock mass and the expansion after encountering water make the deformation load of the surrounding rock continue to increase, and the force of the support system gradually increases. The support measures currently used are often difficult to suppress the continuously increasing deformation pressure, which can easily cause the support structure to be twisted or sheared due to excessive load, and the sprayed concrete to crack. In this regard, a construction process suitable for tunnels in soft rock and soil layers is proposed. Summary of the invention

[0004] In order to solve the above-mentioned problems existing in the prior art, the present invention provides a construction process suitable for tunnels in soft rock and soil layers, which solves the problem in the prior art that due to the instability of the rock and soil layers of carbon and mud soft rock and soil tunnels, the rebound rate of shotcrete may increase, resulting in material waste.

[0005] The purpose of the present invention can be achieved by the following technical solution: A construction process suitable for a tunnel in a soft rock layer, comprising the following steps:

[0006] S1: While excavating the upper step, the stability of the rock and soil layer is increased. The upper step is excavated first with a step length of L, and then several rows of small crushed stones are set from bottom to top on the inner wall of the excavated rock and soil tunnel. The small crushed stones of two adjacent rows are staggered, and the crushed stones are hammered with a hammering mechanism to make the inner wall of the rock and soil tunnel flat;

[0007] S2: For the upper step support, use the wet concrete spraying equipment to spray concrete from bottom to top in the gaps between adjacent small gravels, then lay the steel mesh, erect the steel arch frame, and then spray again to the designed thickness;

[0008] S3: While excavating the middle step, increase the stability of the rock and soil layer. Excavate the middle step after staggering it with the upper step by a length of S. Then, according to the design of the lowest row of small crushed stones in S1, set a medium-sized crushed stone just below the center of the line connecting two adjacent small crushed stones. Set several rows of medium-sized crushed stones from top to bottom on the inner wall of the rock and soil layer tunnel of the excavated middle step, and make the adjacent rows of medium-sized crushed stones staggered. Use the hammering mechanism to hammer the crushed stones again to make the inner wall of the rock and soil layer tunnel smooth.

[0009] S4: For the middle step support, use the wet concrete spraying equipment to spray concrete in the gaps between adjacent medium-sized crushed stones from bottom to top, then lay the steel mesh, erect the steel arch frame, and then spray again to the designed thickness;

[0010] S5: While excavating the lower step, increase the stability of the rock and soil layer, and then excavate the lower step after staggering it with the middle step by a length of S. According to the design of the lowest row of medium-sized gravel in S3, a large-sized gravel is set just below the center of the line connecting two adjacent medium-sized gravel. Several rows of large-sized gravel are set from top to bottom on the inner wall of the rock and soil layer tunnel of the excavated middle step, and the adjacent rows of large-sized gravel are staggered. Then, a hammering mechanism is used to hammer the gravel to make the inner wall of the rock and soil layer tunnel smooth;

[0011] S6: For the support of the lower step, use the wet concrete spraying equipment to spray concrete in the gaps between adjacent large crushed stones from bottom to top, then lay the steel mesh, erect the steel arch frame, and then spray again to the designed thickness.

[0012] As a further solution of the present invention, the method for excavating the upper step, the middle step and the lower step in S1, S3 and S5 respectively is micro-step excavation, and the total step length is less than or equal to 12m, the distance between the invert and the tunnel face is less than or equal to 15m, and the distance between the second lining and the tunnel face is less than or equal to 50m.

[0013] As a further solution of the present invention, the length of S in S3 and S5 is 2 to 3 m, and the lower step should be excavated after the strength of the sprayed concrete of the upper step reaches 70% of the design strength.

[0014] As a further solution of the present invention, the support for the upper, middle and lower steps in S2, S4 and S6 needs to be implemented in a timely manner and closed into a ring, and the initial support closed ring position should be less than 15m away from the tunnel face.

[0015] As a further solution of the present invention, during the initial spraying of concrete in S2, S4 and S6, 4 cm thick C25 concrete is sprayed. After spraying 4 cm thick C25 concrete, the first layer of steel mesh is laid to seal the exposed rock surface and prevent surrounding rock from peeling off. The re-spraying of concrete is carried out after the installation of anchor rods, hanging mesh and arch frames to form an initial support for overall force.

[0016] As a further solution of the present invention, radial grouting reinforcement is applied when the measured displacement value of the middle step exceeds 1 / 2 of the designed reserved deformation, and radial grouting reinforcement is applied when the measured displacement value of the upper step exceeds 1 / 3 of the designed reserved deformation, thereby fully exerting the self-bearing capacity of the surrounding rock while reinforcing the surrounding rock.

[0017] As a further solution of the present invention, a channel steel is provided at the arch foot of the upper step in S2, and the channel steel is used to increase the stress-bearing area of ​​the arch foot to slow down the initial support settlement rate.

[0018] As a further solution of the present invention, the small-sized gravel, medium-sized gravel and large-sized gravel are all circular or elliptical gravel, and each row of small-sized gravel, each row of medium-sized gravel or each row of large-sized gravel are distributed at equal intervals.

[0019] As a further solution of the present invention, the striking mechanism includes a crank rocker portion, a striking portion for striking gravel, and a spring portion sleeved on the striking portion, the crank rocker portion drives the striking portion to reciprocate, and the striking portion drives the spring portion to reciprocate and extend.

[0020] As a further solution of the present invention, the crank rocker part is connected to a frame, and the crank rocker part and the frame are connected via a universal joint.

[0021] The beneficial effects of the present invention are:

[0022] The upper step is first excavated with a step length of L, and then several rows of small crushed stones are arranged from bottom to top on the inner wall of the excavated rock and soil layer tunnel, and the small crushed stones of two adjacent rows are staggered. The crushed stones are hammered by a hammering mechanism to make the inner wall of the rock and soil layer tunnel flat, and the middle step is excavated after being staggered with the upper step by a length of S. Then, according to the design of the small crushed stones in the lowest row, a medium-sized crushed stone is arranged directly below the center of the line connecting two adjacent small crushed stones, and several rows of medium-sized crushed stones are arranged from top to bottom on the inner wall of the rock and soil layer tunnel of the excavated middle step, and the medium-sized crushed stones of two adjacent rows are staggered. The crushed stones are hammered again by a hammering mechanism to make the inner wall of the rock and soil layer tunnel flat, and then the middle step is staggered with the middle step. After staggering the length S, the lower step is excavated. According to the design of the lowest row of medium-sized crushed stones, a large crushed stone is set just below the center of the line connecting two adjacent medium-sized crushed stones. Several rows of large crushed stones are set from top to bottom on the inner wall of the rock and soil layer tunnel of the excavated middle step, and the large crushed stones of two adjacent rows are staggered. The crushed stones are then beaten by a beating mechanism to make the inner wall of the rock and soil layer tunnel smooth. At the same time, tidal concrete spraying equipment is used to initially spray concrete on the gaps between adjacent crushed stones, and then steel mesh is laid, steel arch frames are erected, and then re-spraying is performed to the designed thickness, thereby improving the stability of the overall rock and soil layer of the excavated tunnel, reducing the rebound rate of shotcrete, and saving materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to facilitate understanding by those skilled in the art, the present invention is further described below with reference to the accompanying drawings.

[0024] Figure 1 It is a schematic diagram of the distribution of small-sized gravel, medium-sized gravel and large-sized gravel of the present invention;

[0025] Figure 2 It is a side view of the excavation of the upper step, the middle step and the lower step of the present invention;

[0026] Figure 3 It is the front view of the excavation of the upper step, the middle step and the lower step of the present invention;

[0027] Figure 4 It is a schematic diagram of the structure of the striking mechanism of the present invention.

[0028] Description of main component symbols:

[0029] In the figure: 1. small crushed stone; 2. medium crushed stone; 3. large crushed stone; 4. inner wall of tunnel; 5. upper step; 6. middle step; 7. lower step; 8. frame; 9. crank rocker part; 10. striking part; 11. spring part; 12. fixing sleeve. DETAILED DESCRIPTION

[0030] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation methods, structures, features and effects of the present invention are described in detail below in conjunction with the accompanying drawings and preferred embodiments.

[0031] See also Figure 1-4 This embodiment provides a construction process suitable for tunnels in soft rock and soil layers, comprising the following steps:

[0032] S1: While excavating the upper step 5, the stability of the rock and soil layer is increased. The upper step 5 is excavated first with a step length of L, and then several rows of small crushed stones 1 are arranged from bottom to top on the inner wall 4 of the excavated rock and soil layer tunnel. The small crushed stones 1 of two adjacent rows are staggered, and the crushed stones are beaten by a beating mechanism to make the inner wall 4 of the rock and soil layer tunnel flat. The step L here is determined according to the actual excavation depth each time, and here it is determined according to the national standard. Since it is a soft rock and soil tunnel of carbon and mud, the step L cannot be too long;

[0033] S2: For the support of the upper step 5, use the wet concrete spraying equipment to spray concrete from bottom to top in the gaps between the adjacent small crushed stones 1, then lay the steel mesh, erect the steel arch frame, and then spray again to the designed thickness;

[0034] S3: while excavating the middle step 6, the stability of the rock and soil layer is increased. The middle step 6 is excavated after being staggered with the upper step 5 by a length of S. Then, according to the design of the small gravel 1 in the lowest row in S1, a medium-sized gravel 2 is arranged just below the center of the line connecting two adjacent small gravel 1. Several rows of medium-sized gravel 2 are arranged from top to bottom on the inner wall 4 of the rock and soil layer tunnel of the excavated middle step 6, and the medium-sized gravel 2 in two adjacent rows is staggered. The gravel is knocked again by a knocking mechanism to make the inner wall 4 of the rock and soil layer tunnel flat.

[0035] S4: For the support of the middle step 6, use the wet concrete spraying equipment to spray concrete from bottom to top in the gap between the adjacent medium-sized crushed stones 2, then lay the steel mesh, erect the steel arch frame, and then spray again to the designed thickness;

[0036] S5: Excavate the lower step 7 while increasing the stability of the rock and soil layer, then excavate the lower step 7 after staggering the length S from the middle step 6. According to the design of the lowest row of medium-sized gravel 2 in S3, a large-sized gravel 3 is set just below the center of the line connecting two adjacent medium-sized gravel 2. Several rows of large-sized gravel 3 are set from top to bottom on the inner wall 4 of the rock and soil layer tunnel of the excavated middle step 6, and the large-sized gravel 3 of two adjacent rows are staggered. Then, a beating mechanism is used to beat the gravel to make the inner wall 4 of the rock and soil layer tunnel smooth.

[0037] S6: For the support of the lower step 7, a tidal concrete spraying device is used to spray concrete from bottom to top on the gaps between adjacent large crushed stones 3, and then a steel mesh is laid, a steel arch frame is erected, and then the concrete is sprayed again to the designed thickness. Different sizes of crushed stones are designed on the tunnel surfaces of the upper, middle and lower steps 7. The purpose is that because the lower step 7 itself needs to withstand a large force, it is more likely to collapse in a coal and muddy soft rock tunnel. Therefore, large crushed stones 3 are used on the lower step 7 and knocked into the tunnel, so that the lower step 7 and the large crushed stones 3 form a stable supporting structure. Compared with the lower step 7, the middle step 6 will be subjected to less force, so it is used With the medium-sized gravel 2, the upper step 5 will be subjected to less force than the middle step 6, so the small-sized gravel 1 is used. Here, the upper step 5 is excavated first, then the middle step 6 is excavated, and finally the lower step 7 is excavated. This method is a three-step excavation method used in tunnel excavation. The above steps S1-S6 are only part of the steps in the construction of tunnels in soft rock and soil layers. The main purpose is to ensure the stability of the rock and soil layer during excavation, reduce the rebound rate of shotcrete, and save materials. In addition, after the small-sized gravel 1, the medium-sized gravel 2 and the large-sized gravel 3 are arranged, from the longitudinal direction, the number of small-sized gravel 1, medium-sized gravel 2 and large-sized gravel 3 in each longitudinal direction is the same. Figure 1As shown, since the stress on the middle step 6 is relatively concentrated, and since the upper and lower steps 7 have been excavated, the soil or rocks on both sides of the middle step 6 are supported, and the middle step 6 itself needs to bear the weight of the unexcavated part above, which leads to stress concentration. In this regard, small-sized gravel 1 is added between two adjacent medium-sized gravel 2 in each row to increase stability and avoid stress concentration.

[0038] At present, the problem of large deformation of soft rock in tunnels has always been one of the engineering problems that has troubled the industry. For example, carbonaceous mudstone, mud siltstone, carbonaceous shale, etc. have weak self-bearing capacity of the surrounding rock, resulting in fast deformation speed, large deformation, and long duration of surrounding rock in the stress adjustment stage after excavation, resulting in a large total deformation in the end. Therefore, how to choose a suitable excavation method and supporting support system has become the key to the success of the construction. At present, when traditional construction is used to excavate carbonaceous and muddy soft rock and soil tunnels, after each excavation, rock and soil tunnel support and shotcrete must be carried out immediately. However, due to the instability of the rock and soil layer of carbonaceous and muddy soft rock and soil tunnels, the rebound rate of shotcrete may increase, resulting in material waste.

[0039] In order to solve the problem that the rebound rate of shotcrete may increase and cause material waste due to the instability of the rock layer of the soft rock and soil tunnel of carbon and mud, in this embodiment, the upper step 5 is first excavated with a step length of L, and then a plurality of rows of small crushed stones 1 are arranged from bottom to top on the inner wall 4 of the excavated rock and soil layer tunnel, and the small crushed stones 1 of two adjacent rows are staggered, and the crushed stones are knocked by a knocking mechanism to make the inner wall 4 of the rock and soil layer tunnel flat, and the middle step is excavated after being staggered with the upper step 5 by a length of S. 6, then according to the design of the bottom row of small crushed stones 1, a medium crushed stone 2 is set just below the center of the line connecting two adjacent small crushed stones 1, and several rows of medium crushed stones 2 are set from top to bottom on the inner wall 4 of the rock and soil layer tunnel of the excavated middle step 6, and the medium crushed stones 2 of the adjacent two rows are staggered, and the crushed stones are hammered again by the hammering mechanism to make the inner wall 4 of the rock and soil layer tunnel flat, and then the lower step 7 is excavated after being staggered with the middle step 6 by a length of S. According to the design of the bottom row of medium crushed stones 2, a medium crushed stone 2 is set on the inner wall 4 of the rock and soil layer tunnel of the excavated middle step 6. A large crushed stone 3 is arranged directly below the center of the line connecting the two medium-sized crushed stones 2. Several rows of large crushed stones 3 are arranged from top to bottom on the inner wall 4 of the rock and soil layer tunnel of the excavated middle step 6, and the large crushed stones 3 of two adjacent rows are staggered. The crushed stones are then beaten by a beating mechanism to make the inner wall 4 of the rock and soil layer tunnel smooth. At the same time, tidal concrete spraying equipment is used to initially spray concrete on the gaps between adjacent crushed stones, and then steel mesh is laid, steel arch frames are erected, and then re-spraying is performed to the designed thickness, thereby improving the stability of the overall rock and soil layer of the excavated tunnel, reducing the rebound rate of the shotcrete, and saving materials. In addition, the small crushed stones 1, the medium crushed stones 2 and the large crushed stones 3 are all circular or elliptical crushed stones, and each row of small crushed stones 1 or each row of medium crushed stones 2 or each row of large crushed stones 3 are evenly spaced. The evenly spaced arrangement helps to improve the drainage efficiency. When filling the inner wall 4 of the tunnel, the circular or elliptical crushed stones can be arranged more closely to reduce gaps, thereby improving the overall stability.

[0040] It should be added that, in the construction of soft rock and soil tunnels, after the conventional support is adopted and the subsequent excavation process is carried out, the stress of the soft rock tunnel is gradually released, the continuous rheology of the rock mass and the expansion characteristics after encountering water make the deformation load of the surrounding rock continue to increase, and the force of the support system gradually increases. The support measures currently used are often difficult to suppress the continuously growing deformation pressure, which can easily cause the support structure to be twisted or sheared due to excessive load, and the sprayed concrete to crack. In order to solve this problem, in one embodiment, the step length needs to be controlled within the range of 3 to 5 meters during the step method construction, the step should not be too long, and the core soil area should not be less than 50% of the cross-sectional area. The purpose is to retain enough core soil to reduce the ground settlement caused by excavation. The impact on surface buildings and facilities is small. The length of S in S3 and S5 is 2 to 3m. Both sides of the same arch frame shall not be suspended at the same time. The lower step 7 should be excavated after the strength of the shotcrete of the upper step 5 reaches 70% of the design strength. This can effectively prevent the instability of the soil caused by the simultaneous suspension of both sides of the same arch frame and reduce the ground settlement and displacement caused by excavation operations. The excavation method for the upper step 5, the middle step 6 and the lower step 7 in S1, S3 and S5 is micro-step excavation, and the total step length is less than or equal to 12m, the distance between the invert and the tunnel face is less than or equal to 15m, and the distance between the second lining and the tunnel face is less than or equal to 50m. There are certain risks in tunnel construction, especially in areas with weak surrounding rock or complex geological conditions. The smaller distance can ensure that once the front face collapses, the impact on the invert and secondary lining is minimized, ensuring the safety of construction workers. After the arch advance support is completed, the upper step 5 annular guide pit can be excavated. The arch foot of the upper step 5 in S2 is padded with channel steel, which is used to increase the force-bearing area of ​​the arch foot to slow down the initial support settlement rate. When the measured displacement value of the middle step 6 exceeds 1 / 2 of the design reserved deformation, radial grouting reinforcement is applied. When the measured displacement value of the upper step 5 exceeds 1 / 3 of the design reserved deformation, radial grouting reinforcement is applied. The surrounding rock is reinforced while giving full play to the self-bearing capacity of the surrounding rock. The excavation advance of each cycle of core soil left on each step should be consistent with the advance of other step-by-step cycles. When the initial concrete is sprayed in S2, S4 and S6, 4 cm thick C25 concrete is sprayed. After spraying 4 cm thick C25 concrete, the first layer of steel mesh is laid to close the exposed rock surface and prevent surrounding rock from peeling off. The re-spraying of concrete is carried out after the installation of anchor rods, hanging nets and arch frames to form the overall force of the initial support.In addition, most of the tunnel body is located in strongly weathered limestone, rock, shale and fault fracture zone, and the surrounding rock is extremely soft. In order to reduce the initial support intrusion and arch replacement rate, the control of the overall settlement of the bottom of the upper and middle steps 6 is particularly critical. In addition to timely construction of locking feet and grouting measures during the construction process, it is required that the initial support should be implemented and closed into a ring in time after tunnel excavation. The distance between the initial support closed ring position and the heading face should be less than 15m, and the initial support should be formed into a ring for no more than 15 days after excavation. Through the construction of the above steps, the continuously increasing deformation pressure can be suppressed, avoiding the distortion or shearing of the support structure due to excessive load, and the cracking of the sprayed concrete. The above data requirements are formulated in accordance with relevant construction specifications and standards. These specifications are based on a large number of engineering practices and scientific research to ensure the construction quality and safety of the tunnel.

[0041] In addition, for soft rock large deformation tunnels, shotcrete needs to quickly reach a certain strength in the early stage to form a joint support with steel mesh, lock feet, and steel support to jointly limit the deformation of the surrounding rock in the early stage of surrounding rock deformation. Therefore, C25 early strength concrete is required. If necessary, steel fiber can be added to increase the flexibility and flexural strength of shotcrete. In general, shotcrete adopts wet spraying technology. When the surrounding rock of the face is relatively wet, the wet spraying technology can be used. The initial shotcrete is sprayed with 4cm thick C25 concrete immediately after the face is excavated. The surrounding surrounding rock is immediately sprayed with 4cm thick C25 concrete and the first layer of steel mesh is laid to close the exposed rock surface as soon as possible to prevent the surrounding rock from peeling off. The re-spraying is carried out after the anchor rods, hanging nets and arch frames are installed to form the initial support overall force and inhibit the deformation of the surrounding rock. The arch frames are sprayed flat with concrete and have a sufficient protective layer.

[0042] It is worth mentioning that, due to the construction of a tunnel with soft rock and soil such as coal and mud, the gravel needs to be quickly knocked into the tunnel when it is set. If the gravel is knocked manually, the efficiency is low and it is easy to cause subsequent tunnel collapse. In this regard, a knocking mechanism is specially designed to knock the gravel for the gravel construction of the tunnel with soft rock and soil such as coal and mud. In one embodiment, the knocking mechanism includes a crank rocker part 9, a knocking part 10 for knocking the gravel, and a spring part 11 sleeved on the knocking part 10, the knocking part 10 is a knocking hammer, and the spring part 11 is a spring. The crank rocker part 9 drives the knocking part 10 to move back and forth, and the knocking part 10 drives the spring part 11 to reciprocate. The crank rocker part 9 is connected to the frame 8, and the crank rocker part 9 and the frame 8 are connected by a universal joint. A roller is installed under the frame 8, and the frame 8 is driven to move by pushing the roller. The crank of the crank rocker part 9 here is driven by a motor, and the crank rocker part 9, the knocking part 10 and the spring part 11 are all arranged in a fixed sleeve 12, such as Figure 4As shown, in actual use, the crank rotation of the crank rocker part 9 drives the rocker to move, and the rocker drives the striking part 10 to move back and forth, thereby driving the spring to reciprocate and extend. When the vibration force when the striking part 10 strikes the gravel is transmitted to the striking part 10, the spring can prevent the striking part 10 from being damaged.

[0043] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A construction process suitable for tunnels in soft rock and soil layers, characterized in that: The following steps are involved: S1: While excavating the upper step, the stability of the rock and soil layer is increased. The upper step is excavated first with a step length of L, and then several rows of small crushed stones are set from bottom to top on the inner wall of the excavated rock and soil tunnel. The small crushed stones of two adjacent rows are staggered, and the crushed stones are hammered with a hammering mechanism to make the inner wall of the rock and soil tunnel flat; S2: For the upper step support, use the wet concrete spraying equipment to spray concrete from bottom to top in the gaps between adjacent small gravels, then lay the steel mesh, erect the steel arch frame, and then spray again to the designed thickness; S3: While excavating the middle step, increase the stability of the rock and soil layer. Excavate the middle step after staggering it with the upper step by a length of S. Then, according to the design of the lowest row of small crushed stones in S1, set a medium-sized crushed stone just below the center of the line connecting two adjacent small crushed stones. Set several rows of medium-sized crushed stones from top to bottom on the inner wall of the rock and soil layer tunnel of the excavated middle step, and make the adjacent rows of medium-sized crushed stones staggered. Use the hammering mechanism to hammer the crushed stones again to make the inner wall of the rock and soil layer tunnel smooth. S4: For the middle step support, use the wet concrete spraying equipment to spray concrete in the gaps between adjacent medium-sized crushed stones from bottom to top, then lay the steel mesh, erect the steel arch frame, and then spray again to the designed thickness; S5: While excavating the lower step, increase the stability of the rock and soil layer, and then excavate the lower step after staggering it with the middle step by a length of S. According to the design of the lowest row of medium-sized gravel in S3, a large-sized gravel is set just below the center of the line connecting two adjacent medium-sized gravel. Several rows of large-sized gravel are set from top to bottom on the inner wall of the rock and soil layer tunnel of the excavated middle step, and the adjacent rows of large-sized gravel are staggered. Then, a hammering mechanism is used to hammer the gravel to make the inner wall of the rock and soil layer tunnel smooth; S6: For the support of the lower step, use the wet concrete spraying equipment to spray concrete in the gaps between adjacent large crushed stones from bottom to top, then lay the steel mesh, erect the steel arch frame, and then spray again to the designed thickness.

2. The construction process for tunnels in soft rock and soil layers according to claim 1 is characterized in that: The method for excavating the upper step, middle step and lower step in S1, S3 and S5 is micro-step excavation, and the total step length is less than or equal to 12m, the distance between the invert and the tunnel face is less than or equal to 15m, and the distance between the second lining and the tunnel face is less than or equal to 50m.

3. The construction process for tunnels in soft rock and soil layers according to claim 1 is characterized in that: The length of S in S3 and S5 is 2 to 3 m, and the lower step should be excavated after the strength of the sprayed concrete of the upper step reaches 70% of the design strength.

4. The construction process for tunnels in soft rock and soil layers according to claim 1 is characterized in that: The support for the upper, middle and lower steps in S2, S4 and S6 needs to be implemented in a timely manner and closed into a ring, and the initial support closed ring position should be less than 15m away from the heading face.

5. The construction process for tunnels in soft rock and soil layers according to claim 1 is characterized in that: During the initial spraying of concrete in S2, S4 and S6, 4 cm thick C25 concrete is sprayed. After spraying 4 cm thick C25 concrete, the first layer of steel mesh is laid to seal the exposed rock surface and prevent surrounding rock from peeling off. The re-spraying of concrete is carried out after the installation of anchor rods, hanging mesh and arch frame to form the initial support overall force.

6. The construction process for tunnels in soft rock and soil layers according to claim 1 is characterized in that: When the measured displacement value of the middle step exceeds 1 / 2 of the designed reserved deformation, radial grouting reinforcement is applied. When the measured displacement value of the upper step exceeds 1 / 3 of the designed reserved deformation, radial grouting reinforcement is applied, which fully utilizes the self-bearing capacity of the surrounding rock while strengthening the surrounding rock.

7. The construction process for tunnels in soft rock and soil layers according to claim 1 is characterized in that: The upper step arch foot portion in S2 is padded with channel steel, and the channel steel is used to increase the stress-bearing area of ​​the arch foot to slow down the initial support settlement rate.

8. The construction process for tunnels in soft rock and soil layers according to claim 1 is characterized in that: The small-sized crushed stones, medium-sized crushed stones and large-sized crushed stones are all circular or elliptical crushed stones, and each row of small-sized crushed stones, each row of medium-sized crushed stones or each row of large-sized crushed stones are distributed at equal intervals.

9. The construction process for tunnels in soft rock and soil layers according to claim 1, characterized in that: The striking mechanism comprises a crank rocker part, a striking part for striking gravel, and a spring part sleeved on the striking part. The crank rocker part drives the striking part to move back and forth, and the striking part drives the spring part to reciprocate and extend.

10. The construction process for tunnels in soft rock and soil layers according to claim 9, characterized in that: The crank rocker part is connected to the frame, and the crank rocker part and the frame are connected through a universal joint.

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