Soft soil stratum forepoling structure and forepoling design calculation method

Abstract

The invention relates to a soft soil stratum forepoling structure and a forepoling design calculation method.The soft soil stratum forepoling structure comprises a plurality of tunnel supporting steel supports and a plurality of forepoling, the excavation section of a tunnel is in the shape of a city gate opening or a horseshoe or a circle, the tunnel supporting steel supports are arranged on the inner wall of the tunnel, and the forepoling steel supports are arranged on the outer wall of the tunnel. The multiple tunnel supporting steel supports are arranged at intervals in the extending direction of a tunnel. The advance supports are arranged in a soft soil bottom layer at the top of the tunnel and are arranged in the circumferential direction of the tunnel at intervals. The forepoling is at least one of a pipe shed, a forepoling small pipe or a forepoling anchor rod, the supporting range formed by the forepoling on the top of the tunnel is 120-180 degrees, and the distance between every two adjacent forepoling is 0.3-0.5 m. The tunnel supporting steel supports are steel arches, and the distance between every two adjacent tunnel supporting steel supports ranges from 0.5 m to 1 m. The forepoling structure for the soft soil stratum can optimize project investment on the premise of ensuring project progress.

Description

Technical Field

[0001] The present application relates to the technical field of underground tunnel construction, and in particular to an advance support structure for soft soil strata and an advance support design and calculation method. Background Art

[0002] When the geological conditions of soft soil or surrounding rock are poor, the underground cavern excavation method often adopts advance support, and full-section steel support is carried out at the same time, supplemented by short excavation footage, to meet the needs of underground cavern stability and deformation control during the excavation and support stage. Advance support generally adopts pipe sheds, small guide tubes or advance anchors, supported by steel arch frames. The strength of different advance support materials varies greatly. If the support strength is too low, the underground cavern stability risk is high. If the support strength is too high, the project investment will be greatly increased. At the same time, the determination of advance support parameters is not only related to the material itself, but also closely related to the single excavation footage of the tunnel. Therefore, in the face of complex geological conditions, it is a key and difficult point in design to reasonably select different advance support types according to the spacing of steel arch frames and the single excavation footage of the tunnel. Summary of the invention

[0003] A first aspect of the present application provides a soft soil layer advance support structure, which can optimize the project investment under the premise of ensuring the progress of the project.

[0004] The soft soil stratum advance support structure provided in the first aspect of the present application is used for advance support of tunnels, and includes multiple tunnel support steel supports and multiple advance supports. The excavation section of the tunnel is a city gate tunnel type, a horseshoe shape or a circle. The tunnel support steel supports are arranged on the inner wall of the tunnel, and the multiple tunnel support steel supports are arranged at intervals along the extension direction of the tunnel; the advance support is arranged in the soft soil bottom layer at the top of the tunnel, and the multiple advance supports are arranged at intervals along the circumference of the tunnel.

[0005] In addition, the soft soil stratum advance support structure provided in this application may also have the following additional technical features:

[0006] In an optional scheme, the advance support is at least one of a pipe roof, an advance small pipe or an advance anchor rod. The support range formed by the advance support at the top of the tunnel is 120° to 180°, and the distance between two adjacent advance supports is 0.3 to 0.5m.

[0007] In an optional solution, the tunnel support steel supports are steel arch frames, and the distance between two adjacent tunnel support steel supports is 0.5 to 1 m.

[0008] The second aspect of the present application provides a soft soil layer advance support design calculation method, which can ensure that the cavern, under the premise of ensuring stability and deformation, reasonably selects the advance support type and parameters according to the support spacing of the steel arch frame, and verifies the excavation footage of the tunnel, thereby optimizing the project investment under the premise of ensuring the project progress. The soft soil layer advance support design calculation method specifically includes the following steps:

[0009] a. Preset single excavation footage of the tunnel and support spacing of tunnel support steel supports;

[0010] b. Calculate and determine the resistance of the advance support according to the advance support parameters designed for the tunnel section;

[0011] c. Calculate the vertical uniformly distributed load on the tunnel arch according to the Terzaghi formula;

[0012] d. Simulate the surrounding rock and support between the advance support and the steel arch frame of the tunnel support steel support as a spring, and calculate the spring stiffness coefficient according to the Wei Xike calculation formula;

[0013] e. Use finite element software to establish a calculation model;

[0014] f. Calculate the bending moment and shear force of the advance support during the excavation and support periods, and compare and analyze them with the bending and shear strength of the material itself;

[0015] g. Review the rationality of the advanced support design parameters based on the analysis results;

[0016] h. If the advance support parameters are too strong or too weak, adjust the support design parameters and repeat steps b to g; if necessary, re-plan the excavation advance and support spacing of the tunnel support steel supports.

[0017] In an optional solution, the Terzaghi formula used in step c is:

[0018]

[0019] Where Pv is the vertical pressure of the top arch, B is the calculated width of the tunnel, and for a circular tunnel, R is the tunnel excavation radius, H is the tunnel top cover thickness, γ is the soil or surrounding rock bulk density, C is the stratum cohesion, is the formation friction angle.

[0020] In an optional solution, the Wei Xi Ke calculation formula used in step d is:

[0021]

[0022] In the formula, K nis the spring stiffness coefficient, L is the length of the advance support, v is the Poisson's ratio of the stratum between the advance support and the steel arch, E k It is the elastic modulus of the stratum between the advance support and the steel arch.

[0023] In an optional scheme, in step b, the advance support parameters of the tunnel section design include the material of the advance support, the circumferential spacing of the advance support and the range of the top arch advance support, and the resistance of the advance support includes the bending strength and shear strength of the material.

[0024] In an optional scheme, in step e, the advance support is simulated as a horizontal continuous support beam, the steel arch frame is simulated as a continuous beam foundation, the starting position of the advance support and the position 0.5m deep into the excavation face are used as simply supported constraints, the stratum between the steel arch frame and the advance support is simulated as a vertical spring constraint, a vertical uniformly distributed load is applied, and a calculation model is established.

[0025] In an optional solution, in step g, reviewing the rationality of the advance support design parameters includes: comparing the result of step f with the structural resistance of step b to confirm the rationality of the support strength.

[0026] The beneficial effects of this application are:

[0027] The advance support structure for soft soil strata in this application can optimize the project investment under the premise of ensuring the progress of the project by arranging the tunnel support steel support and advance support. In addition, the advance support design and calculation method for soft soil strata successfully solves the problem that it is difficult to quantitatively determine the advance support parameters when the surrounding rock is poor by performing a refined calculation of the advance support for the tunnel. According to the excavation footage of the tunnel, reasonable advance support parameters are calculated and determined, and the project investment is further optimized while guiding the on-site construction.

[0028] It should be understood that the foregoing general description and the following detailed description are exemplary only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The longitudinal section of the advance support provided for this application;

[0030] Figure 2 Cross-sectional view of the tunnel advance support provided for this application;

[0031] Figure 3 A simplified diagram of the Terzaghi formula calculation provided for this application;

[0032] Figure 4 A simplified diagram of the advance support calculation provided for this application.

[0033] Figure numerals: advance support 1, advance support circumferential spacing 2, tunnel support steel support 3, tunnel 4, top arch advance support range 5, coverage thickness 6, steel support spacing 7, single excavation advance 8, excavation face 9, tunnel calculation width 10, soft soil layer 11, calculation angle 12, simply supported constraint 13, spring constraint 14, vertical uniformly distributed load 15, horizontal continuous support beam 16.

[0034] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application. DETAILED DESCRIPTION

[0035] In order to better understand the technical solution of the present application, the embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0036] It should be clear that the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other technical solutions obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0037] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0038] It should be understood that the term "and / or" used in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0039] It should be noted that the directional words such as "upper", "lower", "left", and "right" described in the embodiments of the present application are described at the angles shown in the accompanying drawings and should not be understood as limiting the embodiments of the present application. In addition, in the context, it is also necessary to understand that when it is mentioned that an element is connected to another element "upper" or "lower", it can not only be directly connected to another element "upper" or "lower", but also indirectly connected to another element "upper" or "lower" through an intermediate element.

[0040] like Figure 1-2As shown, the first aspect of the embodiment of the present application provides a soft soil layer advance support structure, which is mainly suitable for soft soil layers 11 or underground caverns with poor geological conditions, and can optimize the project investment under the premise of ensuring the progress of the project. Specifically, the soft soil layer advance support structure is used for advance support of the tunnel 4, which includes a plurality of tunnel support steel supports 3 and a plurality of advance supports 1, the excavation section of the tunnel 4 is a gate tunnel type, a horseshoe shape or a circle, the tunnel support steel supports 3 are arranged on the inner wall of the tunnel 4, and the plurality of tunnel support steel supports 3 are arranged at intervals along the extension direction of the tunnel 4; the advance support 1 is arranged in the soft soil bottom layer 11 at the top of the tunnel 4, and the plurality of advance supports 1 are arranged at intervals along the circumference of the tunnel 4.

[0041] like Figure 1-2 As shown, in a specific embodiment, the advance support 1 is at least one of a pipe shed, an advance small pipe or an advance anchor. Generally speaking, the support range formed by the advance support 1 at the top of the tunnel 4 (i.e., the top arch advance support range 5) is 120° to 180°, and the spacing between two adjacent advance supports (i.e., the advance support annular spacing 2) is 0.3 to 0.5m. In addition, the tunnel support steel support 3 is a steel arch frame, and the spacing between two adjacent tunnel support steel supports 3 (steel support spacing 7) is 0.5 to 1m.

[0042] like Figure 1-4 As shown, the second aspect of the embodiment of the present application provides a soft soil layer advance support design calculation method, and the soft soil layer advance support design calculation method specifically includes the following steps:

[0043] a. The single excavation footage 8 of the preset tunnel and the steel support spacing 7 between the tunnel support steel supports 3.

[0044] b. According to the advance support parameters designed for the tunnel section, calculate and determine the resistance of the advance support, where the advance support parameters designed for the tunnel section include the material of the advance support 1, the advance support annular spacing 2 and the top arch advance support range 5, and the resistance of the advance support includes the bending strength and shear strength of the material.

[0045] c. According to Terzaghi's formula, calculate the vertical uniformly distributed load of the tunnel crown arch 15:

[0046]

[0047] Where Pv is the vertical pressure of the arch, B is the calculated width of the tunnel 10, for a circular tunnel, R is the radius of tunnel excavation, H is the cover thickness of the tunnel top6, γ is the bulk density of soil or surrounding rock, C is the cohesion of the stratum, is the formation friction angle. Figure 3 As shown, reference numeral 12 is the calculation angle of the tunnel calculation width 10.

[0048] d. The surrounding rock and support between the advance support and the steel arch frame of the tunnel support steel support are simulated as spring constraints 14. According to the Wei Xike calculation formula, the spring stiffness coefficient (stiffness) is calculated:

[0049]

[0050] In the formula, K n is the spring stiffness coefficient, L is the length of the advance support, v is the Poisson's ratio of the stratum between the advance support and the steel arch, E k It is the elastic modulus of the stratum between the advance support and the steel arch.

[0051] e. The advance support 1 is simulated as a horizontal continuous support beam 16, the steel arch frame is simulated as a continuous beam foundation, the starting position of the advance support 1 and the position about 0.5m deep into the excavation face 9 are used as simply supported constraints 13, the stratum between the steel arch frame and the advance support 1 is simulated as a vertical spring constraint 14, a vertical uniformly distributed load is applied 15, and a calculation model is established.

[0052] f. Calculate the bending moment and shear force of the advance support during the excavation and support periods, and compare and analyze them with the material's own bending and shear strength.

[0053] g. Based on the analysis results, review the rationality of the advance support design parameters; reviewing the rationality of the advance support design parameters includes: comparing the results of step f with the structural resistance of step b to confirm the rationality of the support strength.

[0054] h. If the advance support parameters are too strong or too weak, adjust the support design parameters and repeat steps b to g; if necessary, re-draft the excavation footage and the support spacing of the tunnel support steel support. Specifically, if the advance support design parameters are too strong or too weak, it is necessary to adjust the support design parameters, such as the type of advance support, circumferential spacing and other parameters, and repeat steps b to g; if the advance support has been encrypted to the minimum distance and the strongest support type has been selected, when the support parameters cannot be adjusted, it is necessary to shorten the single excavation footage of the tunnel and the support spacing of the steel support, and repeat steps b to h.

[0055] The soft soil stratum advance support design calculation method in this embodiment successfully solves the problem that the advance support parameters are difficult to quantitatively determine when the surrounding rock is poor by performing detailed calculations on the tunnel advance support. According to the tunnel excavation progress, reasonable advance support parameters are calculated and determined, thereby further optimizing the project investment while guiding on-site construction.

[0056] The above are only preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A soft soil stratum advance support structure, used for advance support of tunnels, characterized in that: It comprises a plurality of tunnel support steel supports and a plurality of advance supports, the excavation section of the tunnel is a city gate tunnel type, a horseshoe shape or a circle, the tunnel support steel supports are arranged on the inner wall of the tunnel, and a plurality of the tunnel support steel supports are arranged at intervals along the extension direction of the tunnel; the advance supports are arranged in the soft soil bottom layer at the top of the tunnel, and a plurality of the advance supports are arranged at intervals along the circumference of the tunnel.

2. The soft soil advance support structure according to claim 1 is characterized in that: The advance support is at least one of a pipe rack, an advance small pipe or an advance anchor rod. The support range formed by the advance support at the top of the tunnel is 120° to 180°, and the distance between two adjacent advance supports is 0.3 to 0.5m.

3. The soft soil advance support structure according to claim 1 or 2, characterized in that: The tunnel support steel supports are steel arch frames, and the spacing between two adjacent tunnel support steel supports is 0.5 to 1 m.

4. A calculation method for advanced support design of soft soil strata, characterized in that: The following steps are involved: a. Preset the single excavation footage of the tunnel and the support spacing of the tunnel support steel support; b. Calculate and determine the resistance of the advance support according to the advance support parameters designed for the tunnel section; c. Calculate the vertical uniformly distributed load on the tunnel arch according to the Terzaghi formula; d. Simulate the surrounding rock and support between the advance support and the steel arch frame of the tunnel support steel support as a spring, and calculate the spring stiffness coefficient according to the Wei Xike calculation formula; e. Use finite element software to establish a calculation model; f. Calculate the bending moment and shear force of the advance support during the excavation and support periods, and compare and analyze them with the bending and shear strength of the material itself; g. Review the rationality of the advanced support design parameters based on the analysis results; h. If the advance support parameters are too strong or too weak, adjust the support design parameters and repeat steps b to g; If necessary, re-plan the excavation depth and support spacing of tunnel support steel supports.

5. The calculation method for designing advanced support for soft soil according to claim 4 is characterized in that: The Terzaghi formula used in step c is: Where Pv is the vertical pressure of the top arch, B is the calculated width of the tunnel, and for a circular tunnel, R is the tunnel excavation radius, H is the tunnel top cover thickness, γ is the soil or surrounding rock bulk density, C is the stratum cohesion, is the formation friction angle.

6. The method for designing and calculating the advance support of soft soil according to claim 4 or 5, characterized in that: The Wei Xike calculation formula used in step d is: In the formula, K n is the spring stiffness coefficient, L is the length of the advance support, v is the Poisson's ratio of the stratum between the advance support and the steel arch, E k It is the elastic modulus of the stratum between the advance support and the steel arch.

7. The method for designing and calculating the advanced support of soft soil according to claim 6 is characterized in that: In the step b, the advance support parameters of the tunnel section design include the material of the advance support, the circumferential spacing of the advance support and the range of the top arch advance support, and the resistance of the advance support includes the bending strength and shear strength of the material.

8. The method for designing and calculating the advanced support for soft soil according to claim 4, 5 or 7, characterized in that: In the step e, the advance support is simulated as a horizontal continuous support beam, the steel arch is simulated as a continuous beam foundation, the starting position of the advance support and the position 0.5m deep into the excavation face are used as simply supported constraints, the stratum between the steel arch and the advance support is simulated as a vertical spring constraint, a vertical uniformly distributed load is applied, and a calculation model is established.

9. The method for designing and calculating the advance support for soft soil according to claim 4, 5 or 7, characterized in that: In the step g, reviewing the rationality of the advance support design parameters includes: comparing the result of step f with the structural resistance of step b to confirm the rationality of the support strength.

Images