An excavation method suitable for shallow buried soft rock tunnel with water-rich sandy soil

Abstract

The present application relates to a kind of excavation methods suitable for shallow water-rich sand-like soft rock tunnel, it is characterized in that: including the following steps: step one, complete the leading water precipitation of working face;Step two, complete the leading support of surrounding rock, and the leading support adopts the mode of medium pipe shed plus leading small catheter;Step three, after the leading support of surrounding rock is completed, upper arc drift excavation and support are carried out, core soil is reserved when excavating, and expansion arch foot is applied at both sides arch foot when supporting;Step four, after 4.2m of upper arc drift is excavated first, middle bench left and right sides are excavated, and temporary inverted arch and large lock foot are applied;Step five, after 14.4m of middle bench is advanced, lower bench is excavated, after 6m of lower bench is advanced, inverted arch excavation and primary support are carried out, after 6m of inverted arch and primary support are completed, inverted arch pouring and filling are carried out;Step six, after 12m of inverted arch pouring and filling are completed, geotextile, waterproof board and secondary lining structure are applied.The present application can effectively reduce the water content of surrounding rock of tunnel body, prevent arch foot and tunnel bottom from being soaked, fine particle loss, etc., improve the bearing capacity of base;Effectively prevent the collapse of working face, late primary support intrusion limit arch replacement, reduce the cost of later treatment, and improve the quality of tunnel body.

Description

Technical Field

[0001] The invention relates to the technical field of tunnel construction, in particular to an excavation method suitable for a shallow tunnel with water-rich sandy soil and soft surrounding rock. Background Art

[0002] In my country's coastal areas, the complex and changeable geological environment, frequent tectonic activities, and heavy typhoon rainfall all pose many challenges to tunnel construction. In particular, tunnels under complex geological conditions such as water-rich, shallow burial, eccentric pressure, and sandy soft rock are prone to surrounding rock instability and structural damage. The traditional three-bench excavation method is no longer applicable in this stratum. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide an excavation method suitable for shallow buried water-rich sandy soft rock tunnels, which can effectively reduce the moisture content of the surrounding rock of the tunnel body, prevent the arch foot and tunnel bottom from being soaked in water, and improve the bearing capacity of the base.

[0004] The present invention is implemented by the following scheme: a method for excavating a shallow tunnel with water-rich sandy soil and weak surrounding rock, comprising the following steps:

[0005] Step 1: Complete advance watering of the tunnel face;

[0006] Step 2: Complete the surrounding rock advance support, which adopts the method of middle pipe shed and advance small pipe;

[0007] Step 3: After the surrounding rock advance support is completed, the arc-shaped pilot pit on the upper part of the tunnel body is excavated and supported. The core soil is reserved during excavation, and the arch feet on both sides are expanded during support.

[0008] Step 4: After the upper arc-shaped pilot pit is excavated to a depth of 4.2m, excavate the left and right sides of the middle step and construct a temporary inverted arch and large locking feet;

[0009] Step 5: After the middle step has advanced 8.4m, the lower step is excavated. After the lower step has advanced 6m, the inverted arch is excavated and the primary support is carried out. After the inverted arch and the primary support are completed for 6m, the inverted arch is cast and filled.

[0010] Step 6: After the invert arch is poured and filled for 12m, geotextile, waterproof board and secondary lining structure are applied.

[0011] Furthermore, in step 1, water is lowered in advance within 30 m in front of the tunnel face, lowering the water level to 0.5 m below the bottom of the inverted arch.

[0012] Furthermore, in step 2, 54 steel flower pipes are arranged in a ring of the middle pipe shed, with a circumferential spacing of 30 cm and evenly distributed within a 150° range of the tunnel arch. The steel flower pipes are 12 meters long, 89 mm in outer diameter, 5 mm in wall thickness, and an external insertion angle of 10°. The grouting material uses cement slurry with a water-cement ratio of 0.8:1 to 1:1, and the grouting pressure is controlled at 0.5~1 MPa.

[0013] Furthermore, in step 2, a small advance guide tube with a diameter of φ42 mm, a length of 3.5 m, a circumferential spacing of 30 cm, and a longitudinal spacing of 2.4 m is installed within the 150° range of the tunnel arch. The front end of the tube is in a pointed cone shape, and grouting holes are provided around the tube wall with a hole diameter of 5~7 mm, a hole spacing of 15 cm, an external insertion angle of 10°~15°, and an overlap length ≥3.0 m.

[0014] Furthermore, in step three, the excavation length of each cycle of the upper arc-shaped guide pit is controlled at 0.6m, that is, the distance of one steel frame. The reserved core soil width and height specifications are 4.5*2m. After excavation, manual trimming is performed. The steel support uses 20b steel and the arch foot is expanded. The expanded arch foot is 50cm long.

[0015] Furthermore, in step four, temporary inverted arches are installed at the rear section of the steps, two at a time. The temporary inverted arches are made of I-16 steel and are installed in two sections. A steel mesh is laid underneath, and the ends are firmly welded to the primary support arch frame with reinforcing bars. The middle steel plates are connected with screws made of φ22 steel bars with a spacing of 1m. After erection, they are sealed with C25 sprayed concrete.

[0016] Furthermore, in step four, a locking foot anchor pipe is driven downward at a 45° angle at a height of 30 cm above the arch foot of the steel frame. The locking foot anchor pipe has a diameter of φ89m, a wall thickness of 5mm, and a length of 5m. The locking foot anchor pipe is firmly welded to the steel frame, and the grouting pressure of the large locking foot is 1MPa.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) It can effectively reduce the water content of the surrounding rock of the tunnel, prevent waterlogging of the arch foot and tunnel bottom, and prevent the loss of fine particles, thereby improving the bearing capacity of the base;

[0019] (2) Compared with the traditional three-step method, it can effectively enhance the bearing capacity of the upper step arch foot and suppress the extrusion deformation of the soft rock tunnel face;

[0020] (3) Compared with the traditional three-step method, it overcomes the disadvantage of late initial support ring formation, enables the initial support to form a ring as early as possible, improves the initial support's mechanical performance, and the large locking foot can resist the initial support's sinking and deformation;

[0021] (4) In complex geological environments, it can effectively prevent the collapse of the tunnel face and the subsequent primary support and arch replacement, reduce the subsequent processing costs, and improve the quality of the tunnel body.

[0022] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below through specific embodiments and related drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a diagram of the tunnel construction process according to an embodiment of the present invention;

[0024] Figure 2 This is a structural diagram of a small catheter according to an embodiment of the present invention;

[0025] Figure 3 This is a structural diagram of the steel flower pipes of the pipe shed in an embodiment of the present invention;

[0026] Figure 4 This is a structural diagram of the locking foot anchor pipe of the large locking foot according to an embodiment of the present invention;

[0027] Explanation of numbers in the figure: 1-dewatering well, 2-middle pipe shed or small guide tube, 3-upper step arc-shaped pilot pit, 4-upper step core soil, 5-upper step initial support, 6-upper step enlarged arch foot, 7. Upper step left side locking foot anchor pipe, 8. Upper step right side locking foot anchor pipe, 9-middle step left side, 10-middle step left side initial support, 11-middle step right side, 12-middle step right side initial support, 13-middle step core soil, 14-middle step temporary invert, 15-middle step left side large locking foot, 16-middle step right side large locking foot, 17-lower step left side, 18-lower step left side primary support, 19-lower step left side locking foot anchor pipe, 20-lower step right side, 21-lower step right side primary support, 22-lower step right side locking foot anchor pipe, 23-invert, 24-invert primary support, 25-invert secondary lining and filling, 26-tunnel secondary lining DETAILED DESCRIPTION

[0028] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present application belongs.

[0029] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0030] like Figures 1 to 4 As shown, a method for excavating a shallow tunnel with water-rich sandy soil and soft surrounding rock includes the following steps:

[0031] Step 1: Complete advance watering of the tunnel face;

[0032] Step 2: Complete the surrounding rock advance support, which adopts the method of middle pipe shed and advance small pipe;

[0033] Step 3: After the surrounding rock advance support is completed, the arc-shaped pilot pit on the upper part of the tunnel body is excavated and supported. The core soil is reserved during excavation, and the arch feet on both sides are expanded during support.

[0034] Step 4: After the upper arc-shaped pilot pit is excavated to a depth of 4.2m, excavate the left and right sides of the middle step and construct a temporary inverted arch and large locking feet;

[0035] Step 5: After the middle step has advanced 8.4m, the lower step is excavated. After the lower step has advanced 6m, the inverted arch is excavated and the primary support is carried out. After the inverted arch and the primary support are completed for 6m, the inverted arch is cast and filled.

[0036] Step 6: After the invert arch is poured and filled for 12m, geotextile, waterproof board and secondary lining structure are applied.

[0037] The present invention realizes the safe, fast and high-quality passage of tunnels under complex geological conditions. Its reasonable excavation sequence and appropriate support and auxiliary measures ensure its technical superiority and economic excellence under complex geological conditions, overcomes the defects of the existing technology, and is a new and practical tunnel excavation method suitable for water-rich, shallow-buried, sandy and soft surrounding rock strata, which solves the limitations of traditional tunnel excavation methods under complex geological conditions. Its reasonable excavation, support and auxiliary construction measures ensure the technical superiority and economic excellence of this method under complex conditions. The present invention has carried out a lot of innovations and optimizations on the basis of traditional excavation technology, and formed an excavation construction method for complex geological conditions. It targets complex geological conditions such as poor surrounding rock integrity, difficulty in self-arching, easy softening when encountering water, shallow-buried water-rich, biased pressure, and sandy and soft rock, and can efficiently solve the problems of slow tunnel excavation, easy collapse, easy large deformation, and primary support peeling and cracking, effectively control the construction progress, and achieve environmental protection and safety goals.

[0038] In this embodiment, in step 1, water is lowered in advance within 30 m in front of the tunnel face, and the water level is lowered to 0.5 m below the bottom of the inverted arch.

[0039] In this embodiment, in step 2, 54 steel flower pipes are arranged in a ring of the middle pipe shed, with a circumferential spacing of 30 cm and evenly distributed within a 150° range of the tunnel arch. The steel flower pipe is 12 m long, with an outer diameter of 89 mm, a wall thickness of 5 mm, an external insertion angle of 10°, and a pointed cone-shaped front end with a cone head length of 20 cm. Grouting holes are provided around the pipe wall with a hole diameter of 12 mm and a hole spacing of 15 cm. The grouting material is cement slurry with a water-cement ratio of 0.8:1 to 1:1, and the grouting pressure is controlled at 0.5 to 1 MPa.

[0040] In this embodiment, in step three, an advance small conduit with a diameter of φ42 mm, a length of 3.5 m, a circumferential spacing of 30 cm, and a longitudinal spacing of 2.4 m is installed within the 150° range of the tunnel arch. The front end of the conical conduit is 10 cm long, and grouting holes are provided around the conical conduit wall with a hole diameter of 5 to 7 mm, a hole spacing of 15 cm, an external insertion angle of 10° to 15°, and an overlap length of ≥3.0 m.

[0041] In this embodiment, in step three, the excavation length of each cycle of the upper arc-shaped guide pit is controlled at 0.6m, that is, the distance of one steel frame, and the reserved core soil width and height specifications are 4.5*2m. After excavation, manual trimming is performed, and the steel support adopts 20b steel, and the arch foot is expanded, and the expanded arch foot is 50cm long.

[0042] In this embodiment, in step four, a temporary inverted arch of the middle step is installed at the rear section of the step, with two arches installed each time. The temporary inverted arch is made of I-16 steel and is installed in two sections. A steel mesh is laid underneath, and the end is firmly welded to the primary support arch frame with reinforcing bars. The middle steel plate is connected with screws, and the screws are made of φ22 steel bars with a spacing of 1m. After erection, C25 sprayed concrete is used to seal it.

[0043] In this embodiment, in step four, a locking foot anchor pipe is driven downward at a height of 30 cm above the arch foot of the steel frame at a 45° angle. The locking foot anchor pipe has a diameter of φ89m, a wall thickness of 5mm, and a length of 5m. Grouting holes are provided around the pipe wall with a hole diameter of 12mm and a hole spacing of 15cm. The front end of the pipe is in a pointed cone shape with a cone head length of 20cm. The locking foot anchor pipe is firmly welded to the steel frame, and the grouting pressure of the large locking foot is 1MPa.

[0044] The following provides a specific construction process embodiment:

[0045] Step 1: Complete advance watering of the tunnel face;

[0046] Specific process:

[0047] Dewatering wells 1 are symmetrically arranged on both sides 5m outside the excavation outline, with a longitudinal spacing of 10m. The well depth is controlled at 15m below the tunnel bottom, and the target dewatering level is 0.5m below the tunnel bottom. Based on the surface position corresponding to the actual pile number of the on-site tunnel face, the dewatering well 30m in front of the surface position is opened to enable normal pumping. After the construction of the invert arch 25 and the secondary lining 26 of the section is completed, the dewatering well corresponding to the section is closed.

[0048] Step 2: Complete the surrounding rock advance support, which adopts the method of middle pipe shed and advance small pipe;

[0049] Specific process:

[0050] 54 steel flower tubes are arranged in a ring in the middle pipe shed 2, with a circumferential spacing of 30 cm, evenly distributed within a 150° range of the tunnel arch, and a longitudinal spacing of 9.6 m. The steel flower tubes are 12 m long, with an outer diameter of 89 mm, a wall thickness of 5 mm, and an outer insertion angle of 10°. The grouting material is cement slurry with a water-cement ratio of 0.8:1 to 1:1, and the grouting pressure is controlled at 0.5-1 MPa.

[0051] A φ42 mm small leading guide tube 2 with a length of 3.5 m is driven within 150° of the tunnel arch. The front end of the tube is in a pointed cone shape with a length of 10 cm. Holes are drilled and grouting is carried out around the tube wall with a hole diameter of 5-7 mm, a hole spacing of 15 cm, an external insertion angle of 10°-15°, and an overlap length of ≥3.0 m.

[0052] Step 3: After the surrounding rock advance support is completed, the arc-shaped pilot pit on the upper part of the tunnel body is excavated and supported. The core soil is reserved during excavation, and the arch feet on both sides are expanded during support.

[0053] Specific process:

[0054] After the arch is advanced supported, the upper arc-shaped pilot pit 3 is excavated in a circular manner, and core soil 4 is reserved. The core soil 4 has a specification of 4.5*2m (width×height). The excavation length of each cycle is controlled at 0.6m, which is the distance of one steel frame. After excavation, the edges are trimmed manually, and 4 cm thick concrete is sprayed in time to seal the working surface.

[0055] Construct initial support 5 for the upper step. Use φ8 mm steel mesh with a mesh spacing of 20 cm × 20 cm. Arrange an arch wall and use I20b steel for steel support. Install the upper step in three sections. Use steel plate screws for circumferential connection and Ø22 steel bars for longitudinal connection. The circumferential spacing of the steel plate screws is 1.0 m. Support the arch foot with precast concrete blocks (40 cm × 30 cm × 15 cm). Build an expanded arch foot 6, extending 50 cm toward the surrounding rock.

[0056] Construct the locking foot anchor pipe 7 on the left side of the upper step and the locking foot anchor pipe 8 on the right side of the upper step. Drive the locking foot anchor pipe 45 degrees downward at a height of 30 cm above the steel frame arch foot. The anchor pipe has a diameter of 42 mm, a wall thickness of 4 mm, and a length of 3.5 m. The locking foot anchor pipe is firmly welded to the steel frame. The locking foot grouting pressure is 1 MPa. After completion, the concrete is sprayed and sealed in time.

[0057] Step 4: After the upper arc-shaped pilot pit is excavated to a depth of 4.2m, excavate the left and right sides of the middle step and construct a temporary inverted arch and large locking feet;

[0058] Specific process:

[0059] After the upper step 3 is advanced 4.2m ahead of the left side 9 of the middle step, the left side 9 of the middle step and the right side 11 of the middle step are excavated, and the core soil 13 is trimmed. The left side 9 of the middle step is advanced 3m ahead of the right side 11 of the middle step. The excavation progress of the middle steps 9 and 11 is the spacing of two arch frames. After excavation, the steel arch frame is erected and the steel mesh is hung. The bottom of the steel arch frame is made of C35 precast concrete pads, and then it is sprayed to the designed thickness.

[0060] Temporary inverted arches 14 for the middle steps are installed at the rear section of the steps, two at a time. Temporary inverted arches 14 use a 16-grade steel frame and are installed in two sections. A steel mesh is laid underneath, and the ends are welded firmly to the primary support arch frame with reinforcement (plates). The middle steel plate is bolted together, and the connecting reinforcement is connected with Ø22 steel bars at a spacing of 1m. After erection, C25 shotcrete is used to seal the arch.

[0061] During the construction of the large lock foot 15 on the left side of the middle step and the large lock foot 16 on the right side of the middle step, a lock foot anchor pipe was driven 30cm above the steel frame arch foot at a 45° angle downward. The anchor pipe had a diameter of 89m, a wall thickness of 5mm, and a length of 5m. The lock foot anchor pipe was firmly welded to the steel frame, and the lock foot grouting pressure was 1MPa.

[0062] Step 5: After the middle step has advanced 8.4m, the lower step is excavated. After the lower step has advanced 6m, the inverted arch is excavated and the primary support is carried out. After the inverted arch and the primary support are completed for 6m, the inverted arch is cast and filled.

[0063] Specific process:

[0064] After the right side 11 of the middle step is 5.4m ahead of the lower step, the lower step is excavated. The left side 17 of the lower step is 3m ahead of the right side. After the excavation of the left side 17 and the right side 20 of the lower step is completed, the initial support 18 of the left side of the lower step and the initial support 21 of the right side of the lower step are immediately completed. After the support is completed, the φ42×3.5mm left side locking anchor pipe 19 and the right side locking anchor pipe 22 of the lower step are installed, and the core soil 23 of the lower step is trimmed.

[0065] When the excavation of upper step 3 reaches 18.6m, the invert arch is excavated. The invert arch is excavated in two steps. After each excavation of 3m, the initial support of the invert arch is immediately carried out 24;

[0066] After the primary support 24 of the inverted arch is completed for 6 m, the secondary lining 25 of the inverted arch is poured;

[0067] Step 6: After the inverted arch is poured and filled for 12m, geotextile, waterproof board and secondary lining structure are applied;

[0068] Specific process: After the excavation and initial support are completed, and after the monitoring measurement determines that the convergence is stable, the secondary lining arch wall 26 will be constructed as soon as possible.

[0069] Unless otherwise stated, for any of the technical solutions disclosed in the present invention, if a numerical range is disclosed, the disclosed numerical range is a preferred numerical range. Any person skilled in the art should understand that the preferred numerical range is merely a numerical range that is representative or has a more obvious technical effect among many feasible numerical values. Due to the large number of numerical values, it is impossible to enumerate them exhaustively. Therefore, the present invention discloses some numerical values ​​to illustrate the technical solutions of the present invention. Moreover, the numerical values ​​listed above should not be construed as limiting the scope of protection of the present invention.

[0070] If the present invention discloses or involves components or structures that are fixedly connected to each other, then, unless otherwise stated, the fixed connection can be understood as: a detachable fixed connection (for example, connection using bolts or screws), and can also be understood as: a non-detachable fixed connection (for example, riveting, welding). Of course, the mutual fixed connection can also be replaced by an integrated structure (for example, manufactured by integral molding using a casting process) (except where it is obviously not possible to use an integrated molding process).

[0071] In addition, unless otherwise stated, the terms used in any technical solution disclosed in the present invention to express positional relationships or shapes include states or shapes that are approximate, similar, or close thereto.

[0072] Any component provided by the present invention may be assembled from multiple separate components, or may be a separate component manufactured by an integral molding process.

[0073] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other manner. Any person skilled in the art may utilize the above-disclosed technical content to modify or modify the present invention into equivalent embodiments. However, any simple modifications, equivalent variations, and modifications to the above embodiments that do not depart from the technical content of the present invention and are based on the technical essence of the present invention shall still fall within the scope of protection of the present invention.

Claims

1. A method for excavating a shallow tunnel in water-rich sandy soil with weak surrounding rock, characterized by: The following steps are involved: Step 1: Complete advance watering of the tunnel face; advance watering is performed within 30m in front of the tunnel face, lowering the water level to 0.5m below the bottom of the invert; Step 2: Complete the advanced support of the surrounding rock. The advanced support adopts the method of central pipe shed plus advanced small pipe. 54 steel flower pipes are arranged in one ring of the central pipe shed, with an annular spacing of 30 cm and evenly distributed within the 150° range of the tunnel arch. The steel flower pipe is 12m long, 89mm in outer diameter, 5mm in wall thickness, and 10° in external insertion angle. The grouting material is cement slurry with a water-cement ratio of 0.8:1 to 1:1, and the grouting pressure is controlled at 0.5-1Mpa. Advanced small pipes with a diameter of φ42mm and a length of 3.5m are set within the 150° range of the tunnel arch. The annular spacing is 30cm and the longitudinal spacing is 2.4m. The front end of the advanced small pipe is conical, and grouting holes are arranged around the pipe wall with a hole diameter of 5-7mm, a hole spacing of 15cm, an external insertion angle of 10°-15°, and an overlap length of ≥3.0m. Step 3: After the surrounding rock advance support is completed, the arc-shaped pilot pit on the upper part of the tunnel is excavated and supported. The core soil is reserved during excavation, and the arch feet are expanded at the arch feet on both sides during support. The excavation length of each cycle of the upper arc-shaped pilot pit is controlled at 0.6m, that is, the distance of one steel frame. The width and height specifications of the reserved core soil are 4.5*2m. After excavation, the edges are manually trimmed. The steel support adopts 20b steel and the arch feet are expanded. The expanded arch feet are 50cm long. Step 4: After the upper arc-shaped pilot pit is excavated 4.2m, the left and right sides of the middle step are excavated, and temporary inverted arches and large locking feet are constructed. The temporary inverted arches of the middle step are installed at the rear section of the step, two at a time. The temporary inverted arches are made of I-16 steel and installed in two sections. The steel mesh is laid underneath, and the ends are firmly welded to the primary arch frame with reinforcing bars. The middle steel plate is connected with screws. The screws are made of φ22 steel bars with a spacing of 1m. After erection, C25 sprayed concrete is used to seal it. The large locking foot is 30cm above the steel frame arch foot and a locking foot anchor pipe is driven downward at a 45° angle. The locking foot anchor pipe has a diameter of φ89m, a wall thickness of 5mm, and a length of 5m. The locking foot anchor pipe is firmly welded to the steel frame. The grouting pressure of the large locking foot is 1MPa. Step 5: After the middle step has advanced 8.4m, the lower step is excavated. After the lower step has advanced 6m, the inverted arch is excavated and the primary support is carried out. After the inverted arch and the primary support are completed for 6m, the inverted arch is cast and filled. Step 6: After the invert arch is poured and filled for 12m, geotextile, waterproof board and secondary lining structure are applied.

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