A construction technology applicable to tunnels in soft rock and soil strata

Abstract

The present invention relates to a construction process applicable to tunnels in soft rock and soil layers, belonging to the technical field of tunnel construction. First, the upper bench is excavated with a step length of L. Then, several rows of small crushed stones are arranged on the inner wall of the excavated rock and soil tunnel from bottom to top. After staggering by a length of S from the upper bench, the middle bench is excavated. Then, according to the design of the lowermost row of small crushed stones, a medium-sized crushed stone is arranged directly below the center of the connection line between two adjacent small crushed stones. Several rows of medium-sized crushed stones are arranged on the inner wall of the excavated middle bench rock and soil tunnel from top to bottom. After staggering by a length of S from the middle bench, the lower bench is excavated. According to the design of the lowermost row of medium-sized crushed stones, a large-sized crushed stone is arranged directly below the center of the connection line between two adjacent medium-sized crushed stones. Several rows of large-sized crushed stones are arranged on the inner wall of the excavated middle bench rock and soil tunnel from top to bottom, thereby improving the stability of the overall rock and soil layer of the excavated tunnel, reducing the rebound rate of shotcrete, and saving materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of tunnel construction, and particularly relates to a construction technology suitable for tunnels in soft rock and soil layers. Background Technique

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

[0003] Currently, when excavating carbonaceous and argillaceous soft rock and soil tunnels, after each part of the excavation, it is necessary to immediately carry out the support of the rock and soil tunnel and spray concrete. However, due to the instability of the rock and soil layers of the carbonaceous and argillaceous soft rock and soil tunnels, the rebound rate of the sprayed concrete may increase, resulting in material waste. At the same time, during the subsequent excavation process after the support, the stress of the soft rock tunnel gradually releases, and the continuous rheology of the rock mass and the swelling characteristics shown after encountering water cause the surrounding rock deformation load to continuously increase, and the stress on the support system gradually increases. The currently adopted support measures often have difficulty in restraining the continuously increasing deformation pressure, and it is easy to cause distortion or shear at the support structure due to excessive load, and the sprayed concrete appears cracking and other phenomena. In view of this, a construction technology suitable for tunnels in soft rock and soil layers is proposed. Summary of the Invention

[0004] In order to solve the above problems existing in the prior art, the present invention provides a construction technology suitable for tunnels in soft rock and soil layers, which solves the problem that in the prior art, due to the instability of the rock and soil layers of the carbonaceous and argillaceous soft rock and soil tunnels, the rebound rate of the sprayed concrete may increase, resulting in material waste.

[0005] The object of the present invention can be achieved by the following technical solutions: A construction technology suitable for tunnels in soft rock and soil layers, comprising the following steps:

[0006] S1: While excavating the upper bench, increase the stability of the rock and soil layer. First, excavate the upper bench with a step length of L, and then arrange several rows of small gravels from bottom to top on the inner wall of the excavated rock and soil tunnel. The small gravels in adjacent rows are staggered, and a knocking mechanism is used to knock the gravels to make the inner wall of the rock and soil tunnel flat;

[0007] S2: Support the upper bench. First, use a wet concrete spraying device to initially spray concrete into the gaps between adjacent small gravels from bottom to top, then lay a steel mesh, erect a steel arch, and then re-spray to the designed thickness;

[0008] S3: While excavating the middle bench, enhance the stability of the rock and soil layer. After staggering the excavation of the middle bench by a length S from the upper bench, according to the design of the smallest gravel in the lowest row in S1, set a medium-sized gravel directly below the center of the connection line between two adjacent small gravels. Arrange several rows of medium-sized gravels from top to bottom on the inner wall of the rock and soil layer tunnel of the excavated middle bench, and make the adjacent two rows of medium-sized gravels stagger. Then, use the knocking mechanism to knock the gravels to make the inner wall of the rock and soil layer tunnel flat;

[0009] S4: Support the middle bench. First, use a wet concrete spraying device to initially spray concrete into the gaps between adjacent medium-sized gravels from bottom to top. Then, lay a steel mesh and erect a steel arch, and then re-spray to the designed thickness;

[0010] S5: While excavating the lower bench, enhance the stability of the rock and soil layer. After staggering the excavation of the lower bench by a length S from the middle bench, according to the design of the medium-sized gravel in the lowest row in S3, set a large-sized gravel directly below the center of the connection line between two adjacent medium-sized gravels. Arrange several rows of large-sized gravels from top to bottom on the inner wall of the rock and soil layer tunnel of the excavated middle bench, and make the adjacent two rows of large-sized gravels stagger. Then, use the knocking mechanism to knock the gravels to make the inner wall of the rock and soil layer tunnel flat;

[0011] S6: Support the lower bench. First, use a wet concrete spraying device to initially spray concrete into the gaps between adjacent large-sized gravels from bottom to top. Then, lay a steel mesh and erect a steel arch, and then re-spray to the designed thickness.

[0012] As a further solution of the present invention, the methods of excavating the upper bench, middle bench and lower bench in S1, S3 and S5 respectively are micro-bench method excavation, and the total bench length is less than or equal to 12 m, the distance between the inverted arch and the heading face is less than or equal to 15 m, and the distance between the secondary lining and the heading face is less than or equal to 50 m.

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

[0014] As a further solution of the present invention, when supporting the upper, middle and lower benches in S2, S4 and S6, it is necessary to construct and close into a ring in time, and the position where the initial support closes into a ring should be less than 15 m from the heading face.

[0015] As a further solution of the present invention, when initially spraying 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 close the exposed rock surface to prevent the surrounding rock from spalling. The re-sprayed concrete is carried out after the installation of bolts, wire meshes and arch frames to form the overall force of the initial support.

[0016] As a further solution of the present invention, radial supplementary grouting reinforcement is carried out when the measured displacement value of the middle bench exceeds 1 / 2 of the designed reserved deformation amount, and radial supplementary grouting reinforcement is carried out when the measured displacement value of the upper bench exceeds 1 / 3 of the designed reserved deformation amount, so as to give full play to the self-bearing capacity of the surrounding rock while reinforcing the surrounding rock.

[0017] As a further solution of the present invention, channel steel is padded at the arch foot part of the upper bench in S2, and the channel steel is used to increase the stress 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 crushed stones, medium-sized crushed stones and large-sized crushed stones are all round or oval crushed stones, and each row of small-sized crushed stones or each row of medium-sized crushed stones or each row of large-sized crushed stones is evenly spaced.

[0019] As a further solution of the present invention, the knocking mechanism includes a crank-rocker part, a knocking part for knocking the crushed stones, and a spring part sleeved on the knocking part. The crank-rocker part drives the knocking part to move back and forth, and the knocking part drives the spring part to stretch and contract back and forth.

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

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

[0022] First, the upper bench is excavated with a step length of L, and then several rows of small-sized crushed stones are arranged on the inner wall of the excavated rock and soil tunnel from bottom to top. The small-sized crushed stones in adjacent two rows are staggered. The knocking mechanism is used to knock the crushed stones to make the inner wall of the rock and soil tunnel flat. After staggering S length from the upper bench, the middle bench is excavated. Then, according to the design of the lowermost row of small-sized crushed stones, a medium-sized crushed stone is arranged directly below the center of the connection line between two adjacent small-sized crushed stones. Several rows of medium-sized crushed stones are arranged on the inner wall of the excavated rock and soil tunnel of the middle bench from top to bottom, and the medium-sized crushed stones in adjacent two rows are staggered. The knocking mechanism is used again to knock the crushed stones to make the inner wall of the rock and soil tunnel flat. After staggering S length from the middle bench, the lower bench is excavated. According to the design of the lowermost row of medium-sized crushed stones, a large-sized crushed stone is arranged directly below the center of the connection line between two adjacent medium-sized crushed stones. Several rows of large-sized crushed stones are arranged on the inner wall of the excavated rock and soil tunnel of the middle bench from top to bottom, and the large-sized crushed stones in adjacent two rows are staggered. The knocking mechanism is used again to knock the crushed stones to make the inner wall of the rock and soil tunnel flat. At the same time, a wet concrete spraying device is used to initially spray concrete into the gaps between adjacent crushed stones, then a steel mesh is laid, a steel arch is erected, and then it is sprayed again 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 sprayed concrete, and saving materials. Description of the Drawings

[0023] For the convenience of those skilled in the art to understand, the present invention will be further described below in conjunction with the accompanying drawings.

[0024] Figure 1 Schematic diagram of the distribution of small crushed stones, medium crushed stones and large crushed stones of the present invention;

[0025] Figure 2 Side view of the excavation of the upper bench, middle bench and lower bench of the present invention;

[0026] Figure 3 Front view of the excavation of the upper bench, middle bench and lower bench of the present invention;

[0027] Figure 4 Schematic diagram of the structure of the knocking mechanism of the present invention.

[0028] Description of the main component symbols:

[0029] In the figure: 1, small crushed stone; 2, medium crushed stone; 3, large crushed stone; 4, inner wall of the tunnel; 5, upper bench; 6, middle bench; 7, lower bench; 8, frame; 9, crank rocker part; 10, knocking part; 11, spring part; 12, fixed sleeve. Specific embodiments

[0030] To further elaborate on the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following will describe in detail the specific embodiments, structures, features and their effects of the present invention in conjunction with the accompanying drawings and preferred embodiments.

[0031] Please refer to Figures 1-4 , this embodiment provides a construction technology applicable to tunnels in soft rock and soil layers, including the following steps:

[0032] S1: When excavating the upper bench 5, increase the stability of the rock and soil layer at the same time. First, excavate the upper bench 5 with a step length of L, and then arrange several rows of small crushed stones 1 on the inner wall 4 of the excavated rock and soil tunnel from bottom to top. The adjacent two rows of small crushed stones 1 are staggered. Use a knocking mechanism to knock the crushed stones to make the inner wall 4 of the rock and soil tunnel flat; the step length L here is determined according to the actual specified excavation depth each time, and here it is determined according to the national standard. Since it is a tunnel in carbonaceous and muddy soft rock and soil, the step length L cannot be too long;

[0033] S2: Support the upper bench 5. First, use a wet concrete spraying device to initially spray concrete into the gaps between adjacent small crushed stones 1 from bottom to top, then lay a steel mesh, erect a steel arch, and then re-spray to the design thickness;

[0034] S3: While excavating the middle bench 6, enhance the stability of the rock and soil layer. After staggering the excavation of the middle bench 6 by a length S from the upper bench 5, according to the design of the lowermost row of small crushed stones 1 in S1, set a medium-sized crushed stone 2 directly below the center of the connection line between two adjacent small crushed stones 1. Arrange several rows of medium-sized crushed stones 2 from top to bottom on the inner wall 4 of the rock and soil layer tunnel of the excavated middle bench 6, and make the adjacent two rows of medium-sized crushed stones 2 stagger. Then, use the knocking mechanism to knock the crushed stones to make the inner wall 4 of the rock and soil layer tunnel flat;

[0035] S4: Support the middle bench 6. First, use a wet concrete spraying device to initially spray concrete into the gaps between adjacent medium-sized crushed stones 2 from bottom to top, then lay a steel mesh, erect a steel arch, and then re-spray to the designed thickness;

[0036] S5: While excavating the lower bench 7, enhance the stability of the rock and soil layer. After staggering the excavation of the lower bench 7 by a length S from the middle bench 6, according to the design of the lowermost row of medium-sized crushed stones 2 in S3, set a large-sized crushed stone 3 directly below the center of the connection line between two adjacent medium-sized crushed stones 2. Arrange several rows of large-sized crushed stones 3 from top to bottom on the inner wall 4 of the rock and soil layer tunnel of the excavated middle bench 6, and make the adjacent two rows of large-sized crushed stones 3 stagger. Then, use the knocking mechanism to knock the crushed stones to make the inner wall 4 of the rock and soil layer tunnel flat;

[0037] S6: Support the lower bench 7. First, use a wet concrete spraying device to initially spray concrete into the gaps between adjacent large-sized crushed stones 3 from bottom to top, then lay a steel mesh, erect a steel arch, and then re-spray to the designed thickness. The above design of different sizes of crushed stones on the tunnel surfaces of the upper, middle, and lower benches 7 aims to, because the lower bench 7 itself needs to bear a greater force and is more prone to collapse in the carbonaceous and argillaceous soft rock and soil tunnels. Therefore, large-sized crushed stones 3 are used in the lower bench 7, and the large-sized crushed stones 3 are knocked into the tunnel interior to form a stable support structure with the lower bench 7. The middle bench 6 is subject to less force compared to the lower bench 7, so medium-sized crushed stones 2 are used. The upper bench 5 is subject to even less force compared to the middle bench 6, so small-sized crushed stones 1 are used. Here, the upper bench 5 is excavated first, then the middle bench 6, and finally the lower bench 7. This method is the three-bench excavation method used during tunnel excavation. The above steps S1 - S6 are only partial steps in the construction of soft rock and soil layer tunnels, mainly to ensure the stability of the rock and soil layer during excavation, reduce the rebound rate of sprayed concrete, and save materials. Additionally, after arranging the small-sized crushed stones 1, medium-sized crushed stones 2, and large-sized crushed stones 3, when viewed longitudinally, the number of small-sized crushed stones 1, medium-sized crushed stones 2, and large-sized crushed stones 3 in each longitudinal direction is the same, such as Figure 1As shown in the figure, since the stress borne by the middle bench 6 is relatively concentrated, and since the upper and lower benches 7 have been excavated, the soil or rock on both sides of the middle bench 6 is supported, while the middle bench 6 itself needs to bear the weight of the unexcavated part above, which leads to stress concentration. In this regard, small crushed stones 1 are added between every two adjacent medium-sized crushed stones 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 plague the industry. For example, carbonaceous mudstone, muddy siltstone, carbonaceous shale, etc. Due to the weak self-bearing capacity of the surrounding rock, the surrounding rock has the characteristics of fast deformation speed, large deformation volume, and long duration during the stress adjustment stage after excavation, resulting in a relatively large total deformation in the end. Therefore, how to select a suitable excavation method and supporting system has become the key to the success or failure of the construction. Currently, when using traditional construction to excavate carbonaceous and muddy soft rock tunnels, after each part is excavated, it is necessary to immediately carry out the support of the rock tunnel and spray concrete. However, due to the instability of the rock and soil layers of the carbonaceous and muddy soft rock tunnels, the rebound rate of the sprayed concrete may increase, resulting in material waste.

[0039] To solve the problem that the rebound rate of shotcrete may increase due to the instability of the rock and soil layers in carbonaceous and muddy soft rock tunnels, resulting in material waste, in this embodiment, the upper bench 5 is first excavated with a step length of L, and then several rows of small crushed stones 1 are arranged on the inner wall 4 of the excavated rock and soil tunnel from bottom to top. The adjacent two rows of small crushed stones 1 are staggered. A knocking mechanism is used to knock the crushed stones to make the inner wall 4 of the rock and soil tunnel flat. After staggering a length of S from the upper bench 5, the middle bench 6 is excavated. Then, according to the design of the lowermost row of small crushed stones 1, a medium-sized crushed stone 2 is arranged directly below the center of the connection line between two adjacent small crushed stones 1. Several rows of medium-sized crushed stones 2 are arranged on the inner wall 4 of the excavated middle bench 6 from top to bottom, and the adjacent two rows of medium-sized crushed stones 2 are staggered. The knocking mechanism is used again to knock the crushed stones to make the inner wall 4 of the rock and soil tunnel flat. After staggering a length of S from the middle bench 6, the lower bench 7 is excavated. According to the design of the lowermost row of medium-sized crushed stones 2, a large-sized crushed stone 3 is arranged directly below the center of the connection line between two adjacent medium-sized crushed stones 2. Several rows of large-sized crushed stones 3 are arranged on the inner wall 4 of the excavated middle bench 6 from top to bottom, and the adjacent two rows of large-sized crushed stones 3 are staggered. The knocking mechanism is used again to knock the crushed stones to make the inner wall 4 of the rock and soil tunnel flat. At the same time, a wet concrete spraying device is used to initially spray concrete into the gaps between adjacent crushed stones, then a steel mesh is laid, a steel arch is erected, and then sprayed again 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. In addition, the small crushed stones 1, medium-sized crushed stones 2, and large-sized crushed stones 3 are all round or oval crushed stones, and each row of small crushed stones 1 or each row of medium-sized crushed stones 2 or each row of large-sized crushed stones 3 is evenly spaced. The evenly spaced arrangement helps to improve the drainage efficiency. When the round or oval crushed stones fill the inner wall 4 of the tunnel, they can be arranged more closely, reducing voids, thereby improving the overall stability.

[0040] It should be added that during the construction of tunnels in soft rock and soil layers, during the subsequent excavation after adopting conventional support, the stress of the soft rock tunnel gradually releases. The continuous rheology of the rock mass and the swelling characteristics after encountering water cause the surrounding rock deformation load to continuously increase, and the stress on the support system gradually increases. The currently adopted support measures often have difficulty in restraining the continuously increasing deformation pressure, and it is easy to cause distortion or shearing at the support structure due to excessive load, and the sprayed concrete cracks and other phenomena. To solve this problem, in one embodiment, when using the bench method for construction, the bench length needs to be controlled within the range of 3 - 5m. The bench should not be too long, and the area of the core soil should be not less than 50% of the cross-sectional area. The purpose is to retain enough core soil to reduce the ground settlement caused by excavation, and the impact on surface buildings and facilities is relatively small. The length of S in S3 and S5 is 2 - 3m. Both sides of the same set of arch frames should not be suspended simultaneously. The lower bench 7 should be excavated after the sprayed concrete strength of the upper bench 5 reaches 70% of the design strength. This can effectively prevent the soil mass from losing stability caused by both sides of the same set of arch frames being suspended simultaneously, and reduce the ground settlement and displacement caused by excavation operations. The excavation methods for the upper bench 5, the middle bench 6, and the lower bench 7 in S1, S3, and S5 are micro-bench method excavation, and the total bench length is less than or equal to 12m. The distance between the inverted arch and the heading face is less than or equal to 15m, and the distance between the secondary lining and the heading face is less than or equal to 50m. Tunnel construction has certain risks, especially in areas with soft surrounding rock or complex geological conditions. A smaller distance can ensure that once accidents such as collapses occur at the front heading face, the impact on the inverted arch and the secondary lining is minimized, and the safety of construction workers is guaranteed. After the advanced support of the arch part is completed, the upper bench 5 circular pilot tunnel can be excavated. In the upper bench 5 of S2, channel steel is padded at the arch foot. The channel steel is used to increase the stress area of the arch foot to slow down the settlement rate of the primary support. When the measured displacement value of the middle bench 6 exceeds 1 / 2 of the designed reserved deformation amount, radial supplementary grouting reinforcement is carried out. When the measured displacement value of the upper bench 5 exceeds 1 / 3 of the designed reserved deformation amount, radial supplementary grouting reinforcement is carried out. While giving full play to the self-bearing capacity of the surrounding rock, the surrounding rock is also reinforced. The excavation footage of each cycle with core soil retained for each bench should be consistent with that of other step-by-step cycles. When initially spraying concrete in S2, S4, and S6, 4cm thick C25 concrete is sprayed. After spraying 4cm thick C25 concrete, the first layer of steel mesh is laid to close the exposed rock surface and prevent the surrounding rock from peeling off. The re-sprayed concrete is carried out after the installation of bolts, wire mesh, and arch frames to form the integral stress of the initial support.In addition, most of the tunnel body is located in strongly weathered limestone, shale, and fault fracture zones. The surrounding rock is extremely soft. To reduce the arch replacement rate due to the initial support encroaching on the limit, it is particularly crucial to control the overall settlement at the bottom of the initial support of the upper and middle benches. In addition to promptly implementing locking feet and grouting measures during construction, it is required that the initial support be promptly constructed and closed into a ring after the tunnel excavation. The position where the initial support is closed into a ring should be less than 15 m away from the tunnel face, and the time for the initial support to form a ring after excavation should not be more than 15 days. Through the construction of the above steps, the continuously increasing deformation pressure can be inhibited, avoiding phenomena such as distortion or shearing of the support structure due to excessive loading and cracking of the sprayed concrete. The above requirements for data are formulated according to relevant construction specifications and standards, which 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 tunnels with large deformation of soft rock, the sprayed concrete needs to quickly reach a certain strength in the early stage to form a combined support with the steel mesh, locking feet, and steel supports to jointly limit the deformation of the surrounding rock in the initial stage of the surrounding rock deformation. Therefore, the above requires the use of C25 early-strength concrete. When necessary, steel fibers can be added to increase the flexibility and flexural strength of the sprayed concrete. Generally, the wet spraying process is used for the sprayed concrete. When the surrounding rock at the tunnel face is relatively moist, the semi-dry spraying process can be used. The initial spraying of concrete is to immediately spray 4 cm thick C25 concrete after the tunnel face is excavated, and immediately spray 4 cm thick C25 concrete on the surrounding rock and then lay the first layer of steel mesh to close the exposed rock surface as soon as possible to prevent the surrounding rock from peeling off. The re-spraying of concrete is carried out after the installation of bolts, mesh, and arches to form the overall force of the initial support and inhibit the deformation of the surrounding rock. The space between the arches is sprayed flat with concrete and has sufficient protective layers.

[0042] It is worth mentioning that since it is the construction of a tunnel in carbonaceous and argillaceous soft rock and soil, when setting the crushed stones, it is necessary to quickly knock the crushed stones into the tunnel. If manually knocking the crushed stones, the efficiency is low and it is easy to cause subsequent tunnel collapses. For this reason, for the crushed stone construction of this carbonaceous and argillaceous soft rock and soil tunnel, a knocking mechanism is specially designed to knock the crushed stones. In one embodiment, the knocking mechanism includes a crank-rocker part 9, a knocking part 10 for knocking the crushed stones, 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 expand and contract back and forth. The crank-rocker part 9 is connected to a frame 8, and the crank-rocker part 9 is connected to the frame 8 through a universal joint. Rollers are installed under the frame 8, and the frame 8 is moved by pushing the rollers. Here, the crank of the crank-rocker part 9 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, during actual use, the rotation of the crank of the crank-rocker part 9 drives the rocker to move, and the rocker drives the percussion part 10 to move back and forth, thereby driving the spring to stretch and contract back and forth. When the vibration force generated when the percussion part 10 strikes the crushed stones is transmitted to the percussion part 10, the spring can prevent the percussion part 10 from being damaged.

[0043] The above are only the preferred embodiments of the present invention, and do not impose any formal restrictions on the present invention. Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to equivalent embodiments by using the above-disclosed technical content within the scope of the technical solution of the present invention. However, as long as it does not depart from the content of the technical solution of the present invention, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A construction technology applicable to tunnels in soft rock and soil layers, characterized in that, It includes the following steps: S1: When excavating the upper bench, the stability of the rock and soil layer is increased simultaneously. First, the upper bench is excavated with a step length of L. Then, several rows of small crushed stones are set on the inner wall of the excavated rock and soil layer tunnel from bottom to top, and the adjacent two rows of small crushed stones are staggered. A knocking mechanism is used to knock the crushed stones to make the inner wall of the rock and soil layer tunnel flat; S2: Support the upper bench. First, use a wet concrete spraying device to initially spray concrete into the gaps between adjacent small crushed stones from bottom to top. Then, lay a steel mesh and erect a steel arch. Then, spray again to the designed thickness; S3: When excavating the middle bench, the stability of the rock and soil layer is increased simultaneously. After staggering a length of S from the upper bench, the middle bench is excavated. Then, according to the design of the lowermost row of small crushed stones in S1, a medium-sized crushed stone is set directly below the center of the connection line between two adjacent small crushed stones. Several rows of medium-sized crushed stones are set on the inner wall of the excavated middle bench rock and soil layer tunnel from top to bottom, and the adjacent two rows of medium-sized crushed stones are staggered. The knocking mechanism is used again to knock the crushed stones to make the inner wall of the rock and soil layer tunnel flat; S4: Support the middle bench. First, use a wet concrete spraying device to initially spray concrete into the gaps between adjacent medium-sized crushed stones from bottom to top. Then, lay a steel mesh and erect a steel arch. Then, spray again to the designed thickness; S5: When excavating the lower bench, the stability of the rock and soil layer is increased simultaneously. After staggering a length of S from the middle bench, the lower bench is excavated. According to the design of the lowermost row of medium-sized crushed stones in S3, a large-sized crushed stone is set directly below the center of the connection line between two adjacent medium-sized crushed stones. Several rows of large-sized crushed stones are set on the inner wall of the excavated middle bench rock and soil layer tunnel from top to bottom, and the adjacent two rows of large-sized crushed stones are staggered. The knocking mechanism is used again to knock the crushed stones to make the inner wall of the rock and soil layer tunnel flat; S6: Support the lower bench. First, use a wet concrete spraying device to initially spray concrete into the gaps between adjacent large-sized crushed stones from bottom to top. Then, lay a steel mesh and erect a steel arch. Then, spray again to the designed thickness; The lower bench itself needs to bear a relatively large force. In a tunnel with carbonaceous and argillaceous soft rock and soil, collapse is more likely to occur. Therefore, large-sized crushed stones are used in the lower bench, and the large-sized crushed stones are knocked into the tunnel interior, so that the lower bench and the large-sized crushed stones form a stable support structure. Relatively speaking, the middle bench bears less force than the lower bench, so medium-sized crushed stones are used. Relatively speaking, the upper bench bears less force than the middle bench, so small-sized crushed stones are used; The small-sized crushed stones, medium-sized crushed stones and large-sized crushed stones are all round or oval crushed stones, and each row of small-sized crushed stones or each row of medium-sized crushed stones or each row of large-sized crushed stones is evenly spaced.

2. The construction process for a tunnel applicable to soft rock and soil layers according to claim 1, wherein The methods of excavating the upper bench, middle bench and lower bench in S1, S3 and S5 respectively are micro-bench method excavation, and the total bench length is less than or equal to 12 m, the distance between the inverted arch and the heading face is less than or equal to 15 m, and the distance between the secondary lining and the heading face is less than or equal to 50 m.

3. A construction process for a tunnel applicable to soft rock and soil strata according to claim 1, characterized in that The length of S in S3 and S5 is 2 - 3 m, and the lower bench should be excavated after the concrete strength of the upper bench reaches 70% of the designed strength.

4. A construction process for a tunnel applicable to soft rock and soil layers according to claim 1, characterized in that, When supporting the upper, middle and lower benches in S2, S4 and S6, it is necessary to construct and close the loop in time, and the position where the initial support closes the loop should be less than 15 m away from the tunnel face.

5. The construction process for a tunnel applicable to soft rock and soil layers according to claim 1, characterized in that, When initially spraying 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 close the exposed rock surface and prevent the surrounding rock from spalling. The concrete is re-sprayed after the installation of bolts, wire meshes and arches to form the integral stress of the initial support.

6. The construction process for a tunnel applicable to soft rock and soil layers according to claim 1, characterized in that, When the measured displacement value of the middle bench exceeds 1 / 2 of the designed reserved deformation amount, radial supplementary grouting reinforcement is carried out. When the measured displacement value of the upper bench exceeds 1 / 3 of the designed reserved deformation amount, radial supplementary grouting reinforcement is carried out, which not only gives full play to the self-bearing capacity of the surrounding rock but also reinforces the surrounding rock.

7. A construction process for a tunnel applicable to soft rock and soil layers according to claim 1, characterized in that, Channel steel is padded at the arch feet of the upper bench in S2, and the channel steel is used to increase the stress area of the arch feet to slow down the settlement rate of the initial support.

8. The construction process for a tunnel applicable to soft rock and soil layers according to claim 1, characterized in that, The knocking mechanism includes a crank-rocker part, a knocking part for knocking crushed stones, and a spring part sleeved on the knocking part. The crank-rocker part drives the knocking part to move back and forth, and the knocking part drives the spring part to expand and contract back and forth.

9. A construction process for a tunnel applicable to soft rock and soil layers according to claim 8, characterized in that, The crank-rocker part is connected with a frame, and the crank-rocker part and the frame are connected through a universal joint.

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