An excavation selection method considering the relationship between initial ground stress direction and tunnel axis

Abstract

The application provides a tunnel excavation selection method considering the relationship between the initial stress direction and the tunnel axis, and relates to the technical field of tunnel construction.The application comprises the following steps: firstly, performing engineering geological survey along the tunnel to be excavated to obtain the stress direction along the tunnel; and then taking the spatial relationship between the maximum principal stress direction and the tunnel axis as a reference standard to determine the partial excavation method.The application verifies that the selection principle of the excavation scheme has a strong control effect on the deformation of surrounding rock in the excavation process through numerical simulation, comprehensive analysis and field monitoring, and the method can provide a reference for the selection of excavation methods in future construction processes.

Description

Technical Field

[0001] This invention relates to the field of tunnel construction technology, and in particular to an excavation selection method that considers the relationship between the initial geostress direction and the tunnel axis. Background Technology

[0002] Since the beginning of the 21st century, with my country's continuous increase in investment in underground space construction, Chinese builders have faced and solved a variety of complex underground engineering problems. In the field of tunnel construction, the sectional excavation method has matured in numerous engineering practices. However, when encountering large differences in initial ground stress and complex spatial relationships between the principal direction of ground stress and the tunnel axis, if a suitable excavation method is not selected, the surrounding rock cannot fully exert its self-stabilizing capacity, making it difficult to achieve both economic and safe objectives.

[0003] In-situ stress refers to the inherent stress state at a point within the Earth's crust and soil under natural conditions. The stress state at any point in the engineering area can be represented by three normal stress components and three shear stress components. When the shear stress component is zero, the three normal stress components are the principal stresses. In-situ stress is the primary driving force causing deformation and failure in various underground engineering projects such as mining, water conservancy, and hydropower. Obtaining the magnitude and direction of the initial in-situ stress in the engineering area is crucial for the layout of the underground engineering axis, excavation method, and selection of reasonable support parameters. How to determine the optimal excavation method based on the spatial relationship between the principal direction of the initial in-situ stress in the engineering area and the tunnel axis, so as to better control the convergence deformation of the surrounding rock during excavation and improve the stability of the surrounding rock, has remained a problem that has not been well solved. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides an excavation selection method that considers the relationship between the initial geostress direction and the tunnel axis.

[0005] A method for selecting excavation locations that considers the relationship between the initial geostress direction and the tunnel axis, specifically including the following steps:

[0006] Step 1: Conduct engineering geological surveys along the tunnel excavation route to obtain the magnitude and direction of ground stress along the tunnel route;

[0007] Step 2: Divide the spatial relationship between the direction of the maximum principal stress along the tunnel and the tunnel axis into three types: the direction of the maximum principal stress is parallel to the tunnel axis, the direction of the maximum principal stress is vertical and perpendicular to the tunnel axis, and the direction of the maximum principal stress is horizontal and perpendicular to the tunnel axis.

[0008] Step 3: Based on the positional relationship between the maximum principal direction of the above three types of ground stress and the tunnel axis, calculate the radial displacement of the tunnel top and the two sidewalls under the action of ground stress.

[0009] The radial displacement is calculated through the following steps:

[0010] Assuming that normal stress is positive for compression and negative for tension, and shear stress is positive for clockwise rotation and negative for counterclockwise rotation, with the pole of the polar coordinate system located at the center of the circular tunnel, and the polar axis being a horizontal ray extending to the right from the pole, with counterclockwise rotation as the positive direction of the angle, and the polar angles of the tunnel crown and sidewalls being 90° and 0° respectively, the radial displacements of the tunnel crown and sidewalls can be calculated using the following formula:

[0011] radial displacement u of the tunnel roof arch roof As shown in the following formula:

[0012]

[0013] Radial displacement u of the sidewalls at both sides wall As shown in the following formula:

[0014]

[0015] Where μ and E are Poisson's ratio and elastic modulus of the surrounding rock of the tunnel, respectively, and σ x σ y These are the horizontal and vertical stresses acting on the tunnel, respectively, where r is the tunnel radius.

[0016] Step 4: Based on the radial displacement of the tunnel arch and sidewalls, two key locations, and the constraint characteristics of the surrounding rock on the sectional excavation method, determine the optimal sectional excavation method.

[0017] The sectional excavation method is the reserved core soil method and the bench method. The reserved core soil method is used when the direction of the maximum principal stress is parallel to the tunnel axis and when the direction of the maximum principal stress is vertical and perpendicular to the tunnel axis. When the direction of the maximum principal stress is horizontal and perpendicular to the tunnel axis, the bench method is used.

[0018] The beneficial effects of adopting the above technical solution are as follows:

[0019] This invention provides an excavation selection method that considers the relationship between the initial geostress direction and the tunnel axis. Based on the spatial relationship between the maximum principal stress direction and the tunnel axis, selecting a targeted excavation method can effectively reduce tunnel convergence deformation caused by different geostress conditions, thereby improving the self-stabilizing ability of the surrounding rock and achieving the goal of economy and safety. Attached Figure Description

[0020] Figure 1 This is a diagram showing the sequence of steps for pre-reserved core earthwork excavation in an embodiment of the present invention.

[0021] Figure 2 This is a step sequence diagram of the bench excavation method in an embodiment of the present invention.

[0022] Figure 3This is a schematic diagram of the spatial location of the maximum principal stress direction in an embodiment of the present invention, which is vertical and perpendicular to the tunnel axis.

[0023] Figure 4 This is a schematic diagram of the spatial location where the direction of the maximum principal stress is horizontal and perpendicular to the tunnel axis in an embodiment of the present invention;

[0024] Figure 5 This is a schematic diagram showing the spatial position of the maximum principal stress direction parallel to the tunnel axis in an embodiment of the present invention. Detailed Implementation

[0025] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0026] To make the content, technical solution and features of the present invention clearer, three embodiments are designed and the present invention is further described in detail with reference to the accompanying drawings. The three embodiments use the same surrounding rock physical and mechanical parameters, as shown in Table 1.

[0027] Table 1 shows the calculations using the surrounding rock physical and mechanical parameters.

[0028] Elastic modulus E / MPa Poisson's ratio μ 1000 0.35

[0029] Example 1:

[0030] Taking a circular tunnel with a radius of r = 10m as an example, the specific implementation steps are as follows:

[0031] Step A1: Conduct engineering geological surveys along the tunnel excavation route to obtain the magnitude and direction of ground stress along the tunnel route, as shown in Table 2;

[0032] Table 2 Magnitude of Geostress

[0033] <![CDATA[σ1 / MPa]]> <![CDATA[σ2 / MPa]]> <![CDATA[σ3 / MPa]]> 10.43 7.28 5.31

[0034] Step A2: The spatial relationship between the direction of the maximum principal stress along the tunnel and the tunnel axis is divided into three types: the direction of the maximum principal stress is parallel to the tunnel axis, the direction of the maximum principal stress is vertical and perpendicular to the tunnel axis, and the direction of the maximum principal stress is horizontal and perpendicular to the tunnel axis.

[0035] In this embodiment, the maximum principal stress σ1 is vertically downward and perpendicular to the tunnel axis, such as Figure 3 As shown.

[0036] Step A3: Based on the positional relationship between the principal directions of ground stress and the tunnel axis, calculate the radial displacements of the tunnel top and sidewalls under the action of ground stress. The radial displacements are calculated using the following steps:

[0037] Assume that normal stress is positive for compression and negative for tension, and shear stress is positive for clockwise rotation and negative for counterclockwise rotation. The polar coordinate system's pole is located at the center of the circular tunnel, and the polar axis is a horizontal ray originating from the pole and pointing to the right, with counterclockwise rotation as the positive direction of the angle. The polar angles of the arch and the sidewalls are 90° and 0°, respectively. The radial displacements at these two points can then be calculated using the following formula:

[0038] Radial displacement of the arch crown:

[0039]

[0040] Radial displacement of sidewall:

[0041]

[0042] Where μ and E are Poisson's ratio and elastic modulus of the surrounding rock of the tunnel, respectively, and σ x σ y Let be the horizontal stress and the vertical stress acting on the tunnel, respectively, and r be the tunnel radius.

[0043] By calculating the radial deformation at the tunnel top and sidewalls, we can obtain: u roof =20.2mm, u wall = 6.4mm. This shows that under these positional conditions, the displacement at the top of the tunnel is greater than the displacement on both sides, causing the tunnel to tend towards a flattened shape. Radial displacement calculations are used to analyze the location of the maximum displacement of the tunnel under different principal stress conditions, and then appropriate construction methods are selected to reduce the occurrence of the maximum displacement.

[0044] Step A4: Based on the actual engineering situation, it is known that the method of reserving core soil is used to suppress the extrusion deformation of the tunnel face, such as... Figure 1 As shown, the excavation includes: 1-1 excavation of the arc-shaped pilot tunnel; 1-2 initial support of the arc-shaped pilot tunnel; 2 core soil excavation; 3-1 lower left-side excavation; 3-2 lower left-side initial support; 4-1 lower right-side excavation; and 4-2 lower right-side initial support. This reduces the pre-deformation of the tunnel face and the subsequent arch settlement during excavation. By excavating the tunnel top area sequentially, a large release of top stress is avoided. Combined with tight support measures, this effectively offsets the tunnel top settlement caused by the upper load. Therefore, this embodiment should employ the pre-reserved core soil method for excavation.

[0045] Example 2:

[0046] Taking a circular tunnel with a radius of r = 10m as an example, the specific implementation steps are as follows:

[0047] Step B1: Conduct engineering geological surveys along the tunnel excavation route to obtain the magnitude and direction of ground stress along the tunnel route, as shown in Table 3.

[0048] Table 3 Magnitude of Geostress

[0049] <![CDATA[σ1 / MPa]]> <![CDATA[σ2 / MPa]]> <![CDATA[σ3 / MPa]]> 12.38 8.34 6.87

[0050] Step B2: Based on the on-site investigation data, determine the spatial relationship between the direction of the maximum principal stress and the tunnel axis as follows: the maximum principal stress σ1 is horizontal and perpendicular to the tunnel axis, such as... Figure 4 As shown.

[0051] Step B3: Based on the positional relationship between the principal directions of ground stress and the tunnel axis, calculate the radial displacement of the tunnel top and sidewalls under the action of ground stress. The radial displacement is calculated through the following steps:

[0052] Assume that normal stress is positive for compression and negative for tension, and shear stress is positive for clockwise rotation and negative for counterclockwise rotation. The polar coordinate system's pole is located at the center of the circular tunnel, and the polar axis is a horizontal ray originating from the pole and pointing to the right, with counterclockwise rotation as the positive direction of the angle. The polar angles of the arch and the sidewalls are 90° and 0°, respectively. The radial displacements at these two points can then be calculated using the following formula:

[0053] Radial displacement of the arch crown:

[0054]

[0055] Radial displacement of sidewall:

[0056]

[0057] Where μ and E are Poisson's ratio and elastic modulus of the surrounding rock of the tunnel, respectively, and σ x σ y Let be the horizontal stress and the vertical stress acting on the tunnel, respectively, and r be the tunnel radius.

[0058] By calculating the radial deformation at the tunnel top and sidewalls, we can obtain: u roof =8.8mm, u wall =23.7mm. Therefore, under these positional conditions, the displacement at the tunnel sidewall is greater than the displacement at the top.

[0059] Step B4: Based on the actual engineering situation, it is known that the bench excavation method should be adopted, such as... Figure 2 As shown, the excavation method is as follows: 1-1 is the upper bench excavation, 1-2 is the upper initial support, 2-1 is the lower bench excavation on the left, 2-2 is the lower bench initial support on the left, 3-1 is the lower bench excavation on the right, and 3-2 is the lower bench initial support on the right. The preserving rock mass on both sides of the tunnel can resist the horizontal principal stress by excavating the rock mass in stages, thereby reducing the convergence deformation on both sides of the tunnel during excavation. Therefore, this embodiment should adopt the bench method for excavation.

[0060] The difference between this embodiment and Embodiment 1 is that the direction of the maximum principal stress is parallel to the tunnel axis, such as... Figure 5 As shown.

[0061] Under these locational conditions, actual engineering verification shows that using the pre-reserved core soil method for excavation can reduce the exposed area of ​​the tunnel face, reduce the squeezing effect of the principal stress parallel to the tunnel axis on the tunnel face, and thus reduce the risk of rock mass collapse in front of the tunnel face, ensuring that the surrounding rock can exert its self-stabilizing capacity. The sectional excavation method follows the basic principles of the New Austrian Tunneling Method (NATM): minimal disturbance, early support, frequent measurement, and tight sealing.

[0062] The above description is merely a preferred embodiment of this disclosure and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in the embodiments of this disclosure is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the above-described inventive concept. For example, technical solutions formed by substituting the above-described features with (but not limited to) technical features with similar functions disclosed in the embodiments of this disclosure.

Claims

1. A method for selecting excavation locations considering the relationship between the initial geostress direction and the tunnel axis, characterized in that, Includes the following steps: Step 1: Conduct engineering geological surveys along the tunnel excavation route to obtain the magnitude and direction of ground stress along the tunnel route; Step 2: Classify the spatial relationship between the direction of the maximum principal stress along the tunnel and the tunnel axis; The spatial relationships described in step 2 are divided into three types: the direction of the maximum principal stress is parallel to the tunnel axis, the direction of the maximum principal stress is vertical and perpendicular to the tunnel axis, and the direction of the maximum principal stress is horizontal and perpendicular to the tunnel axis. Step 3: Based on the positional relationship between the maximum principal direction of the above three types of ground stress and the tunnel axis, calculate the radial displacement of the tunnel top and the two sidewalls under the action of ground stress. In step 3, it is assumed that the normal stress is positive when compressed and negative when tensile, and the shear stress is positive when rotated clockwise and negative when rotated counterclockwise. The pole of the polar coordinate system is located at the center of the circular tunnel, and the polar axis is a ray that runs horizontally to the right from the pole. The positive direction of the angle is rotated counterclockwise. The polar angles of the arch and the sidewalls are 90° and 0°, respectively. Calculate the radial displacement of the tunnel top and the two sidewalls. The radial displacement u of the arch at the top of the tunnel roof As shown in the following formula: ； The radial displacement u of the sidewalls at the positions of the two sidewalls wall As shown in the following formula: ； in E and E represent Poisson's ratio and elastic modulus of the surrounding rock of the tunnel, respectively. , These are the horizontal and vertical stresses acting on the tunnel, respectively, where r is the tunnel radius. Step 4: Based on the radial displacement of the tunnel arch and sidewalls, two key locations, and the constraint characteristics of the surrounding rock on the sectional excavation method, determine the optimal sectional excavation method to be selected. The sectional excavation methods described in step 4 are the core soil reservation method and the bench method; When the direction of the maximum principal stress is parallel to the tunnel axis and when the direction of the maximum principal stress is vertical and perpendicular to the tunnel axis, the pre-reserved core soil method is used for excavation; when the direction of the maximum principal stress is horizontal and perpendicular to the tunnel axis, the bench method is used for excavation.

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