Method for determining size of core soil reserved in tunnel based on stability of tunnel face

Abstract

The application discloses a tunnel reserved core soil size determination method based on a stable tunnel face, which mainly comprises the following steps: (1) determining the vertical pressure of the top of the tunnel face damage body according to the surrounding rock condition, the tunnel buried depth, the tunnel size and the excavation size; (2) calculating the tunnel face safety factor under a certain reserved core soil height; and (3) calculating the required reserved core soil length for the reserved core soil to meet its own safety. The application can evaluate the tunnel face stability under different sizes of the reserved core soil, and can determine the height of the reserved core soil and the corresponding reserved core soil length according to the allowed safety factor, thereby solving the problem of difficulty in determining the reasonable reserved core soil size in tunnel construction, and being favorable for the design and construction units to optimize the design of the reserved core soil in theory. The method of the application can be applied to the analysis of the tunnel face stability in the construction of mining roadways, hydraulic tunnels, subways and other tunnels and underground engineering constructions with the reserved core soil construction, and can provide a theoretical method reference for the determination of the reasonable core soil size, and is favorable for the safety of the tunnel construction.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of tunnel construction, in particular to a tunnel reserved core soil size determination method based on the stability of the tunnel face. BACKGROUND

[0002] The tunnel annular excavation reserved core soil method is suitable for general soil or soft and weak surrounding rock sections prone to collapse. The upper reserved core soil can support the tunnel face and enhance the stability of the tunnel face. The reserved core soil and the lower excavation are carried out under the initial support of the arch, and the construction safety is good.

[0003] At present, in the construction of soft stratum tunnel, the reserved core soil is a common stability measure. In different situations, the core soil can also be reserved to the middle step and the lower step. However, how to reasonably determine the size of the reserved core soil is rarely analyzed theoretically at present. The existing literature or patents are given for a specific tunnel case, or the monitoring method or numerical simulation method is used for analysis. The stability of the tunnel face is the premise of safe construction of the tunnel. How to reasonably determine the size of the reserved core soil is concerned by the construction unit and the design unit. SUMMARY

[0004] The purpose of the present application is to provide a tunnel reserved core soil size determination method based on the stability of the tunnel face in view of the above technical problems existing in the prior art.

[0005] The above purpose of the present application is realized by the following technical scheme:

[0006] The tunnel reserved core soil size determination method based on the stability of the tunnel face comprises the following steps:

[0007] (1) determining the vertical pressure at the top of the tunnel face failure body, which can be calculated according to the following formula:

[0008] ;

[0009] wherein, p is the vertical pressure at the top of the tunnel face failure body; γ is the specific weight of the tunnel face surrounding rock; b is half of the tunnel excavation span; H is the tunnel buried depth, i.e. the vertical distance from the ground surface to the tunnel vault; λ is the lateral pressure coefficient; is the apparent friction angle of the tunnel face surrounding rock, which is determined according to the following formula:

[0010] ;

[0011] wherein, is the internal friction angle of the tunnel face surrounding rock;

[0012] (2) Calculate the safety factor of the tunnel face under a certain reserved core soil height, which includes the following steps:

[0013] (I) Calculate the reserved core soil force, which is calculated as follows:

[0014] ;

[0015] wherein, F h is the reserved core soil force; h is the reserved core soil height; c is the cohesion of the surrounding rock; β is the fracture angle of the surrounding rock, which is calculated as follows:

[0016] ;

[0017] (II) Calculate the sliding force, which is calculated as follows:

[0018] ;

[0019] wherein, F 下滑力 is the sliding force; D is the height of the tunnel excavation;

[0020] (III) Calculate the anti-sliding force, which is calculated as follows:

[0021] ;

[0022] wherein, F 抗滑力 is the anti-sliding force;

[0023] (IV) Calculate the safety factor of the tunnel face, which is calculated as follows:

[0024] ;

[0025] wherein, K is the safety factor of the tunnel face;

[0026] (3) Calculate the length of the reserved core soil required to meet its own safety, which is calculated as follows:

[0027] ;

[0028] wherein, L is the length of the reserved core soil;

[0029] Thus, the stability safety factor of the tunnel face under different reserved core soil heights is evaluated, and the corresponding reasonable reserved core soil length is determined; and according to the allowed safety factor, the height of the reserved core soil and the corresponding reserved core soil length are determined.

[0030] The present application has the advantages compared with the prior art method: traditional reserved core soil analysis, especially for the determination of the size of the reserved core soil, has little theoretical research, the existing literature mostly analyzes single reserved core soil tunnel case and the influence of the reserved core soil on the deformation stress of the tunnel body, and the method mostly uses numerical simulation software for analysis, and there is little theoretical analysis and research.

[0031] The present application provides a quantitative theoretical method for determining the size of the reserved core soil of the tunnel, and through the method, the stability safety factor of the tunnel face under different reserved core soil heights can be evaluated, and the corresponding reasonable reserved core soil length can be determined; and according to the allowed safety factor, the height of the reserved core soil and the corresponding reserved core soil length can be determined, which solves the problem of determining the reasonable reserved core soil size in tunnel construction, and is beneficial to the design and construction unit to optimize the design of the reserved core soil from the theory. The method of the present application can be applied to the stability analysis of the tunnel face in the construction of mining roadway, hydraulic tunnel, subway and other tunnels and underground engineering, and provides a theoretical method for determining the reasonable core soil size. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 Figure 1 is a calculation schematic diagram of the method for determining the size of the reserved core soil of the tunnel based on the stability of the tunnel face.

[0033] Figure 1 In the figure, 1 is a tunnel; 2 is a tunnel face; 3 is a reserved core soil; 4 is surrounding rock; H is the depth of the tunnel; D is the excavation height of the tunnel; β is the fracture angle of the surrounding rock; AA'B' is a tunnel face collapse body; EBB'E' is a reserved core soil; W is the gravity of the tunnel face collapse body; h is the height of the reserved core soil; L is the length of the reserved core soil; p is the vertical pressure at the top of the tunnel face failure body.

[0034] Figure 2 is the safety factor of the tunnel face under different reserved core soil heights and the corresponding reserved core soil length. DETAILED DESCRIPTION

[0035] The present application will be further described below in combination with the drawings and examples.

[0036] The method of the present application is applied to an engineering example. The specific data of the engineering example is as follows: the specific weight of the surrounding rock of a tunnel face is 20 kN / m 3 , the cohesion of the surrounding rock is 50 kPa, and the internal friction angle of the surrounding rock is c ​is 20°, tunnel buried depth H is 10m, tunnel excavation height D is 6m, tunnel excavation span is 16m, half of tunnel excavation span b is 8m, lateral pressure coefficient λ is 1, the height of the reserved core soil is initially set to 4m.

[0037] Referring to Figure 1 , the size determination method of the tunnel reserved core soil based on the stability of the tunnel face is as follows:

[0038] Step one, determine the vertical pressure at the top of the tunnel face failure body, which can be calculated according to the following formula:

[0039] ;

[0040] wherein, p is the vertical pressure at the top of the tunnel face failure body; γ is the specific weight of the surrounding rock of the tunnel face; b is half of the tunnel excavation span; H is the tunnel buried depth, i.e. the vertical distance from the ground surface to the tunnel vault; λ is the lateral pressure coefficient; is the friction angle of the surrounding rock of the tunnel face, which is determined according to the following formula:

[0041] ;

[0042] wherein, is the internal friction angle of the surrounding rock of the tunnel face;

[0043] Step two, calculate the safety factor of the tunnel face under a certain reserved core soil height, which includes the following steps:

[0044] (I) calculate the reserved core soil force, which is calculated according to the following formula:

[0045] ;

[0046] wherein, F h is the reserved core soil force; h is the height of the reserved core soil; c is the cohesion of the surrounding rock; β is the rupture angle of the surrounding rock, which is calculated according to the following formula:

[0047] ;

[0048] (II) calculate the sliding force, which is calculated according to the following formula:

[0049] ;

[0050] wherein, F is the sliding force;下滑力 For downward force; D This refers to the tunnel excavation height;

[0051] (III) Calculate the anti-skid force using the following formula:

[0052] ;

[0053] in, F 抗滑力 For anti-slip force;

[0054] (IV) Calculate the safety factor at the working face using the following formula:

[0055] ;

[0056] in, K The safety factor is the working face.

[0057] Step 3: Calculate the length of the core soil required to ensure the safety of the core, using the following formula:

[0058] ;

[0059] in, L To allow for the length of the core soil.

[0060] Based on the above method and steps, the height of the reserved core soil can be obtained. h At a depth of 4m, the safety factor K at the tunnel face is 1.32, and the length L of the reserved core soil required to meet its own safety is 5.9m.

[0061] Furthermore, with other parameters remaining unchanged, the height of the reserved core soil is changed. h Then the corresponding safety factor curve of the working face can be obtained as follows: Figure 2 As shown in a, with the height of the reserved core soil h The increase in the value of the working face increases the safety factor.

[0062] Furthermore, with other parameters remaining unchanged, the height of the reserved core soil is changed. h Then the corresponding safety factor curve of the working face can be obtained as follows: Figure 2 As shown in a, with the height of the reserved core soil h As the value increases, the safety factor K at the working face increases.

[0063] Furthermore, a curve diagram showing the length L of the reserved core soil required to ensure its own safety can be obtained, such as... Figure 2 As shown in b.

[0064] Further, see Figure 2, the critical height of the reserved core soil is 2.7 m; if the safety factor K allowed in the field is 2, the height h of the reserved core soil is at least 3.6 m, and the length L of the reserved core soil is at least 5.4 m.

[0065] Referring to Figure 2 The safety of the tunnel face under different heights and lengths of the reserved core soil can be determined; if the safety factor K is less than 1, the height of the reserved core soil should be increased, or other corresponding reinforcement measures should be taken to increase the stability of the tunnel face.

Claims

1. A method for determining the size of a core soil reserved in a tunnel based on a face stability, characterized by It comprises the following steps: (1) determining the vertical pressure at the top of the tunnel face failure body, which can be calculated according to the following formula: ； wherein, p is the vertical pressure on the top of the tunnel face failure body; γ is the specific gravity of the surrounding rock of the tunnel face; b is half of the span of the tunnel excavation; H is the depth of the tunnel, i.e., the vertical distance from the ground surface to the tunnel crown; λ is the lateral pressure coefficient; is the apparent friction angle of the surrounding rock of the tunnel face, determined by the following equation: ； wherein, is the internal friction angle of the wall rock of the working face; (2) calculating the face safety factor under a certain reserved core soil height, which comprises the following steps: (I) calculating the reserved core soil force, which can be calculated according to the following formula: ； wherein, F h is the reserved core soil force; h is the reserved core soil height; c is the surrounding rock cohesion; β is the surrounding rock fracture angle, which is calculated according to the following formula: ； (II) calculating the sliding force, which can be calculated according to the following formula: ； wherein, F 下滑力 is the sliding force; D is the tunnel excavation height; (III) calculating the anti-sliding force, which can be calculated according to the following formula: ； wherein, F 抗滑力 for anti-skid force; (IV) calculating the face safety factor, which can be calculated according to the following formula: ； wherein, K is the face safety factor; (3) calculating the reserved core soil length required for the reserved core soil to meet its own safety, which can be calculated according to the following formula: ； wherein, L Lr is the length of the reserved core soil; Accordingly, the face stability safety factor under different reserved core soil heights is evaluated, and the corresponding reasonable reserved core soil length is determined; and according to the allowable safety factor, the height of the reserved core soil and the corresponding reserved core soil length are determined.

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