Core soil size optimization method based on control of pre-deformation of tunnel face

Abstract

A core soil size optimization method based on control of a pre-deformation of a tunnel face, relating to the technical field of tunnel construction. The method comprises: first determining a tunnel construction scheme, and dividing a section according to a tunnel excavation sequence; and then establishing different reserved core soil size numerical models for simulated excavation calculation, wherein core soil sizes corresponding to the minimum pre-deformation amount are optimal sizes. The method compensates fills the gap in optimization of core soil sizes by considering the influence of the core soil sizes on a pre-deformation of a tunnel face at present, thereby providing a reference for determining core soil sizes in future construction processes using the new Italian tunneling method.

Description

A core soil size optimization method based on controlling tunnel face pre-deformation Technical Field

[0001] The present invention relates to the technical field of tunnel construction, and in particular to a core soil size optimization method based on controlling tunnel face pre-deformation. Background Art

[0002] In recent years, the scale and speed of tunnel construction worldwide have been increasing day by day. Tunnels are gradually moving into mountainous areas, and more and more tunnels are traversing various complex soft rock and adverse geological environments, as shown in Figure 1. Therefore, certain measures and construction technologies need to be taken to further improve the level of tunnel construction.

[0003] Currently, glass fiber anchors are mainly used for pre-reinforcement of tunnels in soft rock and soil, followed by pre-grouting of the surrounding rock through the anchor's central pipe. However, pre-reinforcement methods such as glass fiber anchors require a certain amount of time to be applied, and effective control of tunnel stability cannot be achieved before the application is completed. In addition, the cost is relatively high.

[0004] In the mid-1970s, Italian Professor Pietro Lunardi began conducting theoretical and field experimental research on hundreds of tunnels, eventually developing the Geotechnical Controlled Deformation Analysis Method (ADECO-RS), also known as the New Italian Tunnel Construction Method (or simply "New Italian Method"). This method involves surveying and measuring the advanced core soil ahead of the tunnel face to predict the stress-strain pattern of the surrounding rock. After tunnel excavation, the surrounding rock is classified into three types: A, B, and C, based on stability, temporary stability, and instability. Based on this, information-based design and construction is conducted to ensure safe passage through various strata (especially complex and unfavorable strata) and full-face excavation. The strength and deformation characteristics of the advance core soil are the real reasons for tunnel deformation (extrusion deformation, pre-convergence deformation and convergence deformation). By protecting and reinforcing the advance core soil and improving its strength, the deformation of the advance core soil (extrusion deformation and pre-convergence deformation) can be controlled, and ultimately the deformation of the tunnel (convergence deformation) can be controlled. The strength and deformation characteristics of the advance core soil play a decisive role in the long-term and short-term stability of the tunnel.

[0005] Core soil size is one of the important indicators affecting the strength of advanced core soil. If the core soil size is too large, it will compress the construction space and affect the installation of anchors or the arrangement of monitoring equipment. If the size is too small, the stability of the tunnel cannot be guaranteed. Therefore, it is crucial to select an appropriate core soil size.

[0006] At present, the Kirch solution is mainly used to calculate the stress state of circular tunnels, as follows:

[0007] Where, σ r is the radial stress at a point in the rock mass around the cave, σ θ is the tangential stress at a point in the rock and soil around the cave, τ rθ is the shear stress at a point in the surrounding rock mass, r and θ are the distance from the point to the tunnel center and the angle between the line connecting the point and the tunnel center and the horizontal, respectively; p0 is the vertical stress; λ is the in-situ stress coefficient, which is equal to the ratio of the lateral stress to the vertical stress; and R0 is the tunnel radius. However, the Kirch solution is primarily designed to account for the two-dimensional stress state of circular tunnels and cannot account for three-dimensional deformation.

[0008] Summary of the Invention

[0009] In view of the problems existing in the prior art, the present invention provides a core soil size optimization method based on controlling the pre-deformation of the tunnel core soil.

[0010] A core soil size optimization method based on controlling tunnel core soil pre-deformation specifically comprises the following steps:

[0011] Step 1: Determine the tunnel construction plan and adopt the reserved core soil method. Divide the circular cross section into ① upper arc-shaped pilot pit, ② reserved core soil, ③ left half of the middle step 1, ③ right half of the middle step 2, and ④ bottom layer according to the planned excavation sequence. The reserved core soil cross section is trapezoidal, with the upper length a, the lower length b, and the height h (unit: meters).

[0012] Step 2: Using the existing numerical simulation technology method: the stratum-structure method, different values ​​of a, b, and h are selected to simulate the excavation calculation of the tunnel model in the tunnel site area to fully restore the actual excavation process of the tunnel;

[0013] The numerical simulation calculation steps are as follows:

[0014] Step 2-1: According to the mechanical constitutive equation of the tunnel, assign the tunnel model to the corresponding constitutive model and apply the actual ground stress level to form the initial stress field;

[0015] Step 2-2: simulate excavation of the tunnel model according to the construction plan determined in step 1;

[0016] Step 2-3: To ensure the accuracy of the calculation, in addition to applying actual ground stress conditions, the actual excavation method and support structure are combined to simulate the calculation using elastic equivalent method. The initial support is shotcrete and arch support.

[0017] Step 3: To avoid the influence of boundary effects, when the tunnel model is excavated to half the depth, the surrounding rock displacement u' at the tunnel face is extracted; after the tunnel is broken through, the surrounding rock displacement u is extracted at the same position; during tunnel excavation, due to stress release, before the initial support is applied, the tunnel produces a certain degree of convergence deformation, which is manifested as tunnel face extrusion. This deformation is the pre-deformation u'. The displacement u measured after the tunnel is broken through is the total deformation of the tunnel. The actual measurable displacement of the tunnel is calculated by the following formula: Δu = uu'

[0018] From the above formula, we know that when the value of the measurable displacement Δu of the tunnel remains basically unchanged, reducing the value of the pre-deformation u′ can reduce the total displacement u, and the value of the pre-deformation u′ is related to the cross-sectional dimensions a, b, and h of the core soil;

[0019] Step 4: Summarize the extrusion conditions of the tunnel face with different reserved core soil cross-sectional sizes. The size with the smallest u′ value is selected as the optimal core soil size, which has the best effect on controlling the extrusion deformation of the tunnel face.

[0020] Beneficial technical effects of the present invention:

[0021] Traditional reserved core soil analysis, especially the determination of reserved core soil size, does not consider the impact of tunnel pre-deformation caused by tunnel extrusion before the tunnel face on tunnel stability. Therefore, the present invention will provide a core soil size optimization method based on controlling tunnel face pre-deformation, filling the current gap in core soil size optimization under the premise of considering the impact of core soil size on pre-deformation before the tunnel face. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG1 is a schematic diagram of a tunnel passing through a complex and adverse geological environment according to a specific embodiment of the present invention;

[0023] FIG2 is a flow chart of a method for optimizing core soil size based on controlling pre-deformation of tunnel core soil according to a specific embodiment of the present invention;

[0024] FIG3 is a schematic diagram of the cross-section division of a tunnel constructed by the reserved core earth method in a specific embodiment of the present invention;

[0025] FIG4 is a schematic cross-sectional view of a tunnel face extrusion pre-deformation according to a specific embodiment of the present invention;

[0026] FIG5 is a schematic diagram of a numerical excavation calculation model in a specific embodiment of the present invention;

[0027] FIG6 is a schematic diagram of the cross-sectional dimensions of core soil in a specific embodiment of the present invention;

[0028] FIG7 is a line graph of u′ values ​​under different core soil cross-sectional dimensions in a specific embodiment of the present invention; DETAILED DESCRIPTION

[0029] The specific implementation of the present invention is further described in detail below with reference to the accompanying drawings and examples.

[0030] A circular tunnel with a radius of r = 15.64m is used as an example for detailed description. A schematic diagram of a tunnel passing through a complex and adverse geological environment is shown in FIG1 . A core soil size optimization method based on controlling the pre-deformation of the tunnel core soil is shown in FIG2 . The specific implementation steps are as follows:

[0031] Step 1: Determine the tunnel construction plan and adopt the reserved core soil method. Divide the circular section into ① upper arc pilot tunnel, ② reserved core soil, ③-1 middle step left half, ③-2 middle step right half, and ④ bottom layer according to the expected excavation order. Divide the circular tunnel section into four layers: upper arc pilot tunnel, reserved core soil, middle step, and bottom layer. The reserved core soil cross-section is trapezoidal, with an upper length of a, a lower length of b, and a height of h, as shown in Figure 6. The unit is meter. The schematic diagram of the tunnel section division using the reserved core soil method is shown in Figure 3. The unit is meter.

[0032] Step 2: Using the existing numerical simulation technology method: the stratum-structure method, different values ​​of a, b, and h are selected to simulate the excavation calculation of the tunnel model in the tunnel site area to fully restore the actual excavation process of the tunnel;

[0033] The numerical simulation calculation steps are as follows:

[0034] Step 2-1: According to the mechanical constitutive equation of the tunnel, assign the tunnel model to the corresponding constitutive model and apply the actual ground stress level to form the initial stress field;

[0035] Step 2-2: simulate excavation of the tunnel model according to the construction plan determined in step 1;

[0036] Step 2-3: To ensure the accuracy of the calculation, in addition to applying actual ground stress conditions, the actual excavation method and initial support structure are combined to simulate the calculation using elastic equivalent method. The initial support structure is shotcrete and arch support. The support structure also includes secondary lining, but it is not considered in the excavation stage.

[0037] This embodiment uses FLAC 3DFinite-difference software was used to establish a stratigraphic-structural model consistent with the geological characteristics of the project area. While keeping other dimensions constant, numerical models with five core soil dimensions were established based on different values ​​of a, b, and h. Specific values ​​are shown in Table 1. To fully reproduce the actual tunnel excavation process, the model was assigned a Mohr-Coulomb constitutive model and self-weight stress was applied to form an initial geostress field. The model was excavated in the order of upper arc-shaped pilot pit, reserved core soil, middle bench, and bottom layer. Initial support was immediately applied after excavation, with initial support simulated using an elastic equivalent method. The numerical model is shown in Figure 5.

[0038] Table 1 Calculation conditions for reserved core soil size;

[0039] Step 3: To avoid the influence of boundary effects, when the tunnel model is excavated to half the depth, the surrounding rock displacement u' at the tunnel face is extracted; after the tunnel is broken through, the surrounding rock displacement u is extracted at the same position; during tunnel excavation, due to stress release, before the initial support is applied, the tunnel produces a certain degree of convergence deformation, which is manifested as tunnel face extrusion. This deformation is the pre-deformation u', as shown in Figure 4, in meters. The displacement u measured after the tunnel is broken through is the total deformation of the tunnel. The actual measurable displacement of the tunnel is calculated by the following formula: Δu = uu'

[0040] From the above formula, we know that when the value of the measurable displacement Δu of the tunnel remains basically unchanged, reducing the value of the pre-deformation u′ can reduce the total displacement u, and the value of the pre-deformation u′ is related to the cross-sectional dimensions a, b, and h of the core soil;

[0041] Step 4: Summarize the extrusion conditions of the tunnel face with different reserved core soil cross-sectional sizes. The size with the smallest u′ value is selected as the optimal core soil size, which has the best effect on controlling the extrusion deformation of the tunnel face.

[0042] This embodiment summarizes the values ​​of pre-deformation u′ under five different core soil size calculation conditions; the optimal solution is a=6m, b=9m, h=3m, and the pre-deformation is 22mm, as shown in Figure 7.

Claims

1. A core soil size optimization method based on controlling tunnel face pre-deformation, characterized in that: The specific steps include: Step 1: Determine the tunnel construction plan and adopt the reserved core soil method. Divide the circular section according to the expected excavation sequence. The reserved core soil section is a trapezoid with an upper length of a, a lower length of b, and a height of h (unit: meters). Step 2: Using existing numerical simulation technology, select different values ​​of a, b, and h to simulate the excavation calculation of the tunnel model in the tunnel site area to fully restore the actual excavation process of the tunnel; Step 3: To avoid the influence of boundary effects, the surrounding rock displacement u′ at the tunnel face is extracted when the tunnel model is excavated to half the depth. After the tunnel is broken through, the surrounding rock displacement u is extracted at the same location. During tunnel excavation, due to stress release, before the initial support is applied, the tunnel undergoes convergent deformation, which manifests as extrusion of the tunnel face. This deformation is the pre-deformation u′. The displacement u measured after the tunnel is broken through is the total deformation of the tunnel, and the actual measurable displacement of the tunnel is calculated. Step 4: Summarize the extrusion conditions of the tunnel face with different reserved core soil cross-sectional sizes. The size with the smallest u′ value is selected as the optimal core soil size, which has the best effect on controlling the extrusion deformation of the tunnel face.

2. The core soil size optimization method based on controlling tunnel face pre-deformation according to claim 1 is characterized in that: Step 1: Divide the circular section into ① upper arc-shaped pilot pit, ② reserved core soil, ③-1 middle step left half, ③-2 middle step right half, and ④ bottom layer according to the expected excavation order.

3. The core soil size optimization method based on controlling tunnel face pre-deformation according to claim 2 is characterized in that: Step 2: The existing numerical simulation technology method is the stratum-structure method.

4. The core soil size optimization method based on controlling tunnel face pre-deformation according to claim 1 is characterized in that: Step 2 The numerical simulation calculation steps are as follows: Step 2-1: According to the mechanical constitutive equation of the tunnel, assign the tunnel model to the corresponding constitutive model and apply the actual ground stress level to form the initial stress field; Step 2-2: simulate excavation of the tunnel model according to the construction plan determined in step 1; Step 2-3: To ensure the accuracy of the calculation, in addition to applying actual ground stress conditions, simulation calculations are also carried out in combination with actual excavation methods and support structures.

5. The core soil size optimization method based on controlling tunnel face pre-deformation according to claim 3 is characterized in that: Step 2-3 Support structure includes initial support by sprayed concrete and arch support.

6. The core soil size optimization method based on controlling tunnel face pre-deformation according to claim 3 is characterized in that: Steps 2-3 use elastic equivalent method to perform simulation calculations.

7. The core soil size optimization method based on controlling tunnel face pre-deformation according to claim 1 is characterized in that: The actual measurable displacement of the tunnel is calculated by the following formula: Δu=uu′ From the above formula, we know that when the value of the measurable displacement Δu of the tunnel remains basically unchanged, reducing the value of the pre-deformation u′ can reduce the total displacement u, and the value of the pre-deformation u′ is related to the cross-sectional dimensions a, b, and h of the core soil.

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