Support method and structure for a large-section shallow-buried tunnel with an inner cavity in soft strata

Abstract

The present invention discloses a support method and structure for a tunnel with a large cross-section and shallow burial in soft strata. The technical solution is as follows: pre-reinforce the soil mass of the upper bench inside the tunnel. After the reinforcement is stable, install advanced pipe-roof pre-support; excavate the lower bench, and install small pipes for grouting to reinforce the foundation of the soil mass below the inverted arch of the lower bench; after the initial support of the lower bench is closed and there is no settlement in the lower bench, excavate and support the upper bench until the tunnel excavation is closed. The present invention adopts the method of first reinforcing the lower bench and then excavating and supporting the upper bench inside the tunnel, which greatly reduces the overall ground settlement of the tunnel.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel construction, and particularly relates to a support method and structure for a shallow-buried large-section tunnel with an inner cavity in soft strata. Background Art

[0002] With the development of cities, the ground roads can no longer meet the increasing vehicle traffic, and only the construction of underground roads can be used to relieve the situation. How to construct underground roads on the main traffic arteries is an urgent problem to be solved, especially in areas with poor geological conditions. For example, when the underground road passes through strata mainly composed of miscellaneous fill and collapsible loess, all the strata within the tunnel body range, the overburden soil above the tunnel roof, and the soil layer below the tunnel invert are poor geological conditions.

[0003] The inventor found that the following problems exist during the initial support construction of the tunnel:

[0004] 1. The overburden soil layer of the tunnel roof is poor, especially the soil mass within the excavation arch crown range of the tunnel is broken and has poor self-stability. When the upper bench of the tunnel is excavated, if the soil mass above the tunnel roof is not pre-reinforced in advance, the soil mass is extremely likely to collapse during the excavation process, and the excavation contour cannot be formed, and the excavation conditions are not available.

[0005] 2. The ground within the tunnel range is the main urban road, and the conditions for pre-reinforcement on the ground are not allowed.

[0006] 3. The tunnel invert is on a soft foundation, and the bearing capacity of the foundation is insufficient. After the construction of the initial support invert of the tunnel is completed, obvious settlement will occur. The influence of the final settlement will be transmitted to the ground surface, causing obvious settlement on the ground surface. Summary of the Invention

[0007] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a support method and structure for a shallow-buried large-section tunnel with an inner cavity in soft strata, adopting the excavation support method of first reinforcing the lower bench and then the upper bench in the tunnel, which greatly reduces the overall ground settlement of the tunnel.

[0008] In order to achieve the above purpose, the present invention is realized through the following technical solutions:

[0009] In the first aspect, an embodiment of the present invention provides a support method for a shallow-buried large-section tunnel with an inner cavity in soft strata. The upper bench soil mass in the tunnel is pre-reinforced. After being stabilized by reinforcement, an advanced pipe shed is driven for pre-support; the lower bench is excavated, and small pipes are driven for grouting to reinforce the soil mass below the invert of the lower bench; after the initial support of the lower bench is closed and there is no settlement in the lower bench, the upper bench is excavated and supported until the tunnel excavation is closed.

[0010] As a further implementation method, the pre-reinforcement process of the upper bench is as follows: sleeve valves are uniformly driven in the soft strata area between the face contour line and the grouting reinforcement outer contour line, and grouting reinforcement is carried out.

[0011] As a further implementation method, a grout stop wall is constructed before the installation of the sleeve valve pipe.

[0012] As a further implementation method, an advanced pipe shed is installed at the boundary between the upper bench and the lower bench of the tunnel body.

[0013] As a further implementation method, the advanced pipe shed is installed in a self-advancing and segmented manner.

[0014] As a further implementation method, the excavation process of the lower bench is as follows: an inverted arch is installed on the bottom surface of the lower bench, and small ducts are vertically and uniformly installed on the bottom surface of the lower bench and grouted for reinforcement;

[0015] The CD method is used for excavation, and after excavation, an intermediate arch frame and a transverse arch frame fixedly connected to both ends of the inverted arch are installed in a timely manner.

[0016] In a second aspect, an embodiment of the present invention further provides a support structure for a shallow-buried large-section tunnel with an inner cavity in a soft stratum, including:

[0017] Sleeve valve pipes uniformly arranged in the area between the face contour line and the outer contour line of grouting reinforcement;

[0018] An advanced pipe shed arranged at the boundary between the upper bench and the lower bench of the tunnel body;

[0019] An inverted arch arranged on the bottom surface of the lower bench, with an intermediate arch frame fixed between the arch bottom of the inverted arch and the advanced pipe shed; transverse arch frames located below the advanced pipe shed are fixedly connected to the upper ends of the intermediate arch frame at both ends of the inverted arch respectively;

[0020] Small ducts for grouting the foundation are uniformly arranged on the bottom surface of the lower bench.

[0021] As a further implementation method, the advanced pipe shed is horizontally arranged and has multiple sections, and adjacent sections of the advanced pipe shed are connected by screw threads.

[0022] As a further implementation method, a grout stop wall is arranged at one end of the advanced pipe shed, and the sleeve valve pipes are arranged in a plum blossom shape along the surface of the grout stop wall.

[0023] As a further implementation method, the small ducts are uniformly arranged in the vertical direction.

[0024] The beneficial effects of the above embodiments of the present invention are as follows:

[0025] (1) One or more embodiments of the present invention utilize the effective space of the excavation face to pre-reinforce the soil mass of the upper bench inside the tunnel. After the reinforcement is stabilized, an advanced pipe shed is installed for pre-support. First, the lower bench is excavated, and vertical small pipes are driven into the soil mass below the inverted arch of the lower bench for foundation reinforcement. After the initial support of the lower bench is closed and the settlement rate is stable, the upper bench is excavated, and finally, the entire tunnel is closed into a ring, greatly reducing the overall ground settlement of the tunnel.

[0026] (2) One or more embodiments of the present invention construct a grout stop wall before driving the sleeve valve pipes. The grid arch is arranged along the excavation face and connected to the arch of the tunnel excavation support to form a whole. Under the action of the grout stop wall, the grouting pressure can be increased, enabling the grouting liquid to effectively contact the soil mass of the excavation face and form a grout solidified body. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings forming a part of this specification are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0028] Figure 1 is the construction flow chart according to one or more embodiments of the present invention;

[0029] Figure 2 is the schematic diagram of the support structure according to one or more embodiments of the present invention;

[0030] Figure 3 is the side view of the support structure according to one or more embodiments of the present invention;

[0031] Wherein, 1. Excavation face contour line, 2. Outer contour line of grouting reinforcement, 3. Sleeve valve pipe, 4. Small pipe, 5. Grout stop wall, 6. Advanced pipe shed, 7. Inverted arch, 8. Middle arch, 9. Cross arch. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] Example 1:

[0033] This embodiment provides a support method for a shallow-buried large-section tunnel with a cavity inside in a soft stratum. The method of first reinforcing the lower bench and then excavating and supporting the upper bench inside the shallow-buried large-section tunnel in a soft stratum is adopted, which is applicable to the field of underground engineering such as underground roads, utility tunnels, and cable tunnels in the built-up core area of the city.

[0034] During the tunnel excavation construction process, if the entire cross-section of the tunnel is located in a soft stratum, according to the conventional construction sequence, the upper bench is constructed first, and then the lower bench is constructed. The soil mass of the upper bench cannot be effectively reinforced, resulting in surface settlement during the excavation process. When constructing the lower bench, it will also cause secondary disturbance to the upper bench, triggering the overall settlement of the tunnel and the surface.

[0035] To solve the settlement problem, within the tunnel body range, advanced pipe roofs are first driven in the middle of the tunnel body, dividing the original tunnel body section into upper and lower half-sections, forming two independent tunnel body sections. First, advanced grouting reinforcement is carried out on the upper tunnel, and the lower tunnel is excavated, while the foundation of the tunnel invert is reinforced. After the effect of the grouting reinforcement of the upper tunnel reaches the required level, the upper tunnel is then excavated and connected to the lower tunnel to form an integral tunnel body section; this is the excavation method with a tunnel within a tunnel.

[0036] In this embodiment, the excavation mode of "a tunnel within a tunnel" is adopted. Utilizing the effective space of the excavation face, the soil mass of the upper bench is pre-reinforced inside the tunnel. After the reinforcement is stable, an advanced pipe roof 6 is driven for pre-support. First, the lower bench is excavated, and vertical small pipes 4 are driven into the soil mass below the invert 7 of the lower bench for grouting to reinforce the foundation. After the initial support of the lower bench is closed and stabilized for a period of time, and when the settlement rate is stable, the upper bench is then excavated. Finally, the entire tunnel is closed into a ring, which greatly reduces the overall ground settlement of the tunnel.

[0037] Specifically, as Figure 1 shown, the construction steps of this embodiment include:

[0038] a. Pre-reinforcement of the upper bench:

[0039] First, a grout stop wall 5 is constructed, using a lattice girder with wire mesh to spray C25 concrete with a thickness of 25 cm. Sleeve valves 3 are evenly driven in the weak stratum area between the face contour line 1 and the outer contour line 2 of the grouting reinforcement, and grouting reinforcement is carried out.

[0040] As Figure 3 shown, the sleeve valves 3 are evenly arranged in a plum blossom pattern along one side surface of the grout stop wall 5; under the action of the grout stop wall 5, the grouting pressure can be increased, enabling the grouting liquid to effectively contact the face soil mass and form a grout solidified body.

[0041] In this embodiment, within the tunnel, the effective space of the upper bench is utilized to pre-reinforce the soil mass of the upper bench and within a set range outside the contour line of the upper bench, and pre-grouting is carried out using sleeve valves 3. Sleeve valve 3 grouting can be repeated multiple times, and according to the settlement monitoring situation, the grouting frequency and grouting volume are dynamically controlled. Due to the relatively large construction space of the upper bench, the longitudinal and transverse spacing of the sleeve valves 3 is set to 0.5 - 1 m, which can effectively reinforce the soil mass of the upper bench and the tunnel arch.

[0042] b. Driving the advanced pipe roof 6:

[0043] The advanced pipe roof 6 is driven at the boundary between the upper and lower benches of the tunnel body in the weak stratum; the advanced pipe roof 6 is self-advancing and is driven in segmented sections, and adjacent sections of the advanced pipe roof 6 are connected by screw threads; grouting is carried out in a timely manner after the pipe roof is driven.

[0044] Further, the advanced pipe shed 6 is horizontally arranged, and the length of each section is set according to the actual support requirements. In this embodiment, the length of each section is 2.5 m.

[0045] c. Excavation of the lower bench:

[0046] An inverted arch 7 is constructed on the bottom surface of the lower bench, and small pipes 4 are vertically and uniformly driven downward on the bottom surface of the lower bench for grouting reinforcement; the CD method is used to excavate in two left and right sections, and the middle arch frame 8 and the transverse arch frame 9 fixedly connected to both ends of the inverted arch 7 are erected in time after excavation.

[0047] d. Excavation of the upper bench:

[0048] After there is no settlement in the lower bench, the upper bench is excavated and supported until the tunnel excavation is closed.

[0049] Embodiment 2:

[0050] This embodiment provides a support structure for a shallow-buried large-section tunnel with an inner cavity in soft strata, as Figure 2 and Figure 3 shown, including the sleeve valve pipe 3, the small pipe 4, the grout stop wall 5, the advanced pipe shed 6, the inverted arch 7, the middle arch frame 8, and the transverse arch frame 9; the sleeve valve pipes 3 are uniformly arranged in the area between the face contour line 1 of the tunnel body and the grouting reinforcement outer contour line 2.

[0051] Further, the sleeve valve pipes 3 are arranged in a plum blossom pattern in the plane, and the vertical and horizontal spacings are set to 0.5 - 1 m. The sleeve valve pipes 3 can be grouted repeatedly, and the grouting frequency and grouting volume are dynamically controlled according to the settlement monitoring situation. Since there is a large construction space in the upper bench, setting the vertical and horizontal spacings of the sleeve valve pipes 3 to 0.5 - 1 m can effectively reinforce the soil body in the upper bench and the tunnel arch.

[0052] Further, the grouting reinforcement outer contour line 2 is arranged outside the face contour line 1, and the face contour line 1 and the grouting reinforcement outer contour line 2 are concentrically arranged. In this embodiment, the vertical distance between the face contour line 1 and the grouting reinforcement outer contour line 2 is 3.5 - 5.5 m. Preferably, the vertical distance is set to 5 m. Inside the tunnel, using the effective space of the upper bench, the soil body in the upper bench and within the above range outside the upper bench contour line is pre-reinforced, and pre-grouting is carried out using the sleeve valve pipes 3.

[0053] Further, the advanced pipe shed 6 is arranged at the boundary between the upper bench and the lower bench and is horizontally arranged. An inverted arch 7 is constructed on the bottom surface of the lower bench. A middle arch frame 8 is fixedly installed between the arch bottom of the inverted arch 7 and the advanced pipe shed 6, and transverse arch frames 9 are fixedly connected to the upper ends of the middle arch frame 8 at both ends of the inverted arch 7 and are located below the advanced pipe shed 6. A number of small pipes 4 for grouting the foundation are vertically and uniformly driven on the bottom surface of the lower bench.

[0054] The grout stop wall 5 is constructed before driving the sleeve valve pipes 3, asFigure 2 As shown, the grouting stop wall 5 is located on one side of the advanced pipe shed 6; the grid arch is arranged along the heading face and connected to the arch of the tunnel excavation support to form an integral whole. Under the action of the grouting stop wall 5, the grouting pressure can be increased, enabling the grouting liquid to effectively contact the heading face soil and form a grout solidified body.

[0055] The above are only the preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A support method for a shallow-buried large-section tunnel with an inner cavity in soft strata, characterized in that, pre-reinforce the soil mass of the upper bench in the tunnel. After the reinforcement is stable, install an advanced pipe shed for pre-support; excavate the lower bench, and install small pipes for grouting to reinforce the foundation for the soil mass below the inverted arch of the lower bench; after the initial support of the lower bench is closed and there is no settlement in the lower bench, excavate and support the upper bench until the tunnel excavation is closed. The process of pre-reinforcing the upper bench is as follows: uniformly install sleeve valves in the soft strata area between the face contour line and the outer contour line of grouting reinforcement, and grout for reinforcement. A grout stop wall is constructed before installing the sleeve valves. Install an advanced pipe shed at the boundary between the upper bench and the lower bench of the tunnel body. The advanced pipe shed is installed in a self-advancing and segmented manner. The process of excavating the lower bench is as follows: construct an inverted arch on the bottom surface of the lower bench, and uniformly install small pipes vertically downward on the bottom surface of the lower bench for grouting reinforcement. Use the CD method for excavation, and promptly install a middle arch frame and a transverse arch frame that are fixedly connected to both ends of the inverted arch after excavation.

2. A support structure for a shallow-buried large-section tunnel with an inner cavity in soft strata, adopting the support method for a shallow-buried large-section tunnel with an inner cavity in soft strata as described in claim 1, characterized in that, it includes: Sleeve valves uniformly arranged in the area between the face contour line and the outer contour line of grouting reinforcement; An advanced pipe shed arranged at the boundary between the upper bench and the lower bench of the tunnel body; An inverted arch arranged on the bottom surface of the lower bench, with a middle arch frame fixed between the arch bottom of the inverted arch and the advanced pipe shed; transverse arch frames located below the advanced pipe shed are fixedly connected to the upper ends of the middle arch frame at both ends of the inverted arch respectively; Small pipes for grouting the base are uniformly arranged on the bottom surface of the lower bench.

3. The support structure for a shallow-buried large-section tunnel with an inner cavity in soft strata according to claim 2, characterized in that, the advanced pipe shed is horizontally arranged and has multiple sections, and adjacent sections of the advanced pipe shed are connected by screw threads.

4. The support structure for a shallow-buried large-section tunnel with an inner cavity in soft strata according to claim 2, characterized in that, a grout stop wall is arranged at one end of the advanced pipe shed, and the sleeve valves are arranged in a plum blossom pattern along the surface of the grout stop wall.

5. The support structure for a shallow-buried large-section tunnel with an inner cavity in soft strata according to claim 2, characterized in that, the small pipes are uniformly arranged in the vertical direction.

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