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

Abstract

The application provides a core soil size optimization method based on control of a tunnel face pre-deformation, and relates to the technical field of tunnel construction; first, a tunnel construction scheme is determined, and a section is grouped according to a tunnel excavation subsequence; then, a numerical model of different pre-reserved core soil sizes is established to simulate excavation calculation, and the core soil size with the minimum pre-deformation is the optimal size; the application fills the vacancy of core soil size optimization under the premise of considering the influence of the core soil size on the pre-deformation of the face, and can provide a reference for determination of the core soil size in the construction process of the new method in the future.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of tunnel construction, in particular to a core soil size optimization method based on control of tunnel face pre-deformation. BACKGROUND

[0002] In recent years, the scale and speed of tunnel construction worldwide have been increasing day by day, and tunnels have gradually advanced to mountainous areas, with more and more tunnels passing through various complex soft rock and poor geological environments, such as Figure 1 Therefore, certain measures and construction techniques need to be taken to further improve the level of tunnel construction.

[0003] At present, in the control of short-term and long-term stability of soft rock mass tunnels, glass fiber anchor rods are mainly used for pre-reinforcement, and then the surrounding rock is grouted through the central pipeline of the anchor rod, but the pre-reinforcement method such as glass fiber anchor rod needs a certain construction time, and the tunnel stability cannot be effectively controlled before the construction is completed, and the cost is relatively high.

[0004] In the mid-1970s, Professor Pietro Lunardi of Italy began to conduct theoretical and field test research on hundreds of tunnels, and gradually established the rock and soil control deformation analysis method (ADECO-RS method), namely the new Italian tunnel construction method, referred to as "new Italian method". The new Italian method is a tunnel design and construction method that ensures the safety of tunnel passing through various strata (especially complex and poor strata) and realizes full-face excavation by surveying and measuring the advanced core soil in front of the tunnel face, predicting the stress-strain form of the surrounding rock, and dividing the surrounding rock into A, B and C three types according to the stability, temporary stability and instability of the surrounding rock after tunnel excavation, and then conducting information design and construction. The strength and deformation characteristics of the advanced core soil are the real reasons for the tunnel deformation (extrusion deformation, pre-convergence deformation and convergence deformation), which can improve the strength of the advanced core soil by protection and reinforcement to control the deformation of the advanced core soil (extrusion deformation and pre-convergence deformation), and ultimately achieve the purpose of controlling the tunnel deformation (convergence deformation); the strength and deformation characteristics of the advanced core soil play a decisive role in the long-term and short-term stability of the tunnel.

[0005] The size of the core soil is one of the important indicators affecting the strength of the advanced core soil, and the size of the core soil is too large to compress the construction space and affect the arrangement of anchor rod construction or monitoring equipment, and the size of the core soil is too small to ensure the stability of the tunnel, so it is very important to select the appropriate size of the core soil.

[0006] At present, the calculation of the stress state of the circular tunnel mainly uses the Kirsch solution, which is as follows:

[0007]

[0008]

[0009]

[0010] where σ r is the radial stress of a point in the rock-soil mass around the tunnel, σ θ is the tangential stress of a point in the rock-soil mass around the tunnel, τ rθ is the shear stress of a point in the rock-soil mass around the tunnel, r and θ are the distance of the point from the center of the tunnel and the angle between the line connecting the point and the center of the tunnel and the horizontal line, respectively; p0 is the vertical stress; λ is the stress coefficient, equal to the ratio of the horizontal stress to the vertical stress; and R0 is the radius of the tunnel. However, the Kirsch solution is mainly used to solve the two-dimensional stress state of a circular tunnel and cannot consider three-dimensional deformation. SUMMARY

[0011] In view of the problems in the prior art, the present application provides a core soil size optimization method based on control of pre-deformation of core soil of a tunnel.

[0012] A core soil size optimization method based on control of pre-deformation of core soil of a tunnel, specifically comprising the following steps:

[0013] Step 1, determining a tunnel construction scheme, adopting a reserved core soil method to construct, dividing a circular section into ① an upper arc-shaped pilot tunnel, ② a reserved core soil, ③-1 a middle step left half width, ③-2 a middle step right half width, and ④ a bottom layer according to a predicted excavation sequence, wherein the reserved core soil section is trapezoidal, the upper side length is a, the lower side length is b, and the height is h, with units of meters;

[0014] Step 2, selecting different a, b, and h values to simulate excavation calculation of a tunnel model in a tunnel site area through an existing numerical simulation technology method: stratum-structure method, and fully restoring the actual excavation process of the tunnel;

[0015] The numerical simulation calculation steps are as follows:

[0016] Step 2-1, according to a mechanical constitutive equation of the tunnel, assigning a corresponding constitutive model to the tunnel model and applying an actual ground stress level to form an initial stress field;

[0017] Step 2-2, simulating excavation of the tunnel model according to the construction scheme determined in step 1;

[0018] Step 2-3, to ensure the accuracy of the calculation, in addition to applying the actual ground stress condition, the actual excavation method and support structure are combined to perform simulation calculation in an elastic equivalent manner; wherein the initial support is sprayed concrete and an arch frame;

[0019] Step 3, in order to avoid the influence of boundary effect, the displacement u' of surrounding rock at the working face is extracted when the tunnel model is excavated to half footage; after the tunnel is penetrated, the displacement u of surrounding rock at the same position is extracted; during the tunnel excavation, due to stress release, a certain degree of convergence deformation of the tunnel occurs before the primary support is made, which is manifested as extrusion of the working face, and this deformation is the pre-deformation u'; the displacement u measured after the tunnel is penetrated is the total deformation of the tunnel, and the real measurable displacement of the tunnel is calculated by the following formula:

[0020] Delta u = u-u'

[0021] From the above formula, when the value of the measurable displacement Delta u 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 core soil section sizes a, b and h;

[0022] Step 4, the extrusion of the working face of different pre-reserved core soil section sizes is arranged, and the size with the smallest u' value is selected as the best core soil size, and the control effect on the extrusion deformation of the working face is best.

[0023] The present application has the beneficial technical effects:

[0024] The traditional pre-reserved core soil analysis, especially the determination of the pre-reserved core soil size, does not consider the influence of the pre-deformation of the tunnel in front of the working face caused by the extrusion of the tunnel on the stability of the tunnel, therefore, the present application provides a core soil size optimization method based on control of the pre-deformation of the tunnel working face, which fills the gap of the optimization of the core soil size under the premise of considering the influence of the core soil size on the pre-deformation in front of the working face. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The present application has the beneficial technical effects:

[0026] Figure 2 The present application has the beneficial technical effects:

[0027] Figure 3 The present application has the beneficial technical effects:

[0028] Figure 4 The present application has the beneficial technical effects:

[0029] Figure 5 The present application has the beneficial technical effects:

[0030] Figure 6 The present application has the beneficial technical effects:

[0031] Figure 7 Figure 1 is a u' value broken line graph for different core soil section sizes in the specific embodiment of the present application; DETAILED DESCRIPTION

[0032] The specific embodiment of the present application is described in further detail below in combination with the drawings and examples.

[0033] A circular tunnel with a radius r = 15.64 m is taken as an example for detailed description. A schematic diagram of the tunnel passing through a complex adverse geological environment is shown in Figure 1. Figure 1 A core soil size optimization method based on control of tunnel core soil predeformation is shown in Figure 2. The specific implementation steps are as follows: Figure 2

[0034] Step 1, determine the tunnel construction scheme, adopt the reserved core soil method for construction, divide the circular section into ① upper arc-shaped pilot tunnel, ② reserved core soil, ③-1 middle step left half, ③-2 middle step right half, ④ bottom layer according to the predicted excavation sequence, divide the circular tunnel section into four layers, namely the upper arc-shaped pilot tunnel, the reserved core soil, the middle step and the bottom layer, wherein the reserved core soil section is trapezoidal, the upper side length is a, the lower side length is b, the height is h, and the unit is meter, as shown in Figure 3; the reserved core soil method for construction of tunnel section division schematic diagram is shown in Figure 4, and the unit is meter; Figure 6 Figure 3

[0035] Step 2, through the existing numerical simulation technology method: stratum-structure method, select different a, b, h values to simulate the excavation calculation of the tunnel model in the tunnel site area, and fully restore the actual excavation process of the tunnel;

[0036] The numerical simulation calculation steps are as follows:

[0037] Step 2-1, according to the mechanical constitutive equation of the tunnel, give the corresponding constitutive model to the tunnel model and apply the actual ground stress level to form the initial stress field;

[0038] Step 2-2, according to the construction scheme determined in step 1, simulate the excavation of the tunnel model;

[0039] Step 2-3, in order to ensure the accuracy of the calculation, in addition to applying the actual ground stress condition, the actual excavation method and the primary support structure are combined, and the elastic equivalent method is used for simulation calculation; wherein the primary support of the support structure is shotcrete and arch frame; the support structure also includes secondary lining, but is temporarily not considered in the excavation stage;

[0040] In this embodiment, FLAC 3D ​​​The finite difference software is used to build a stratum-structure model in accordance with the geological characteristics of the engineering area; the numerical models of five different core soil sizes are respectively established according to different values of a, b and h, and the specific values are shown in Table 1; in order to fully restore the actual excavation process of the tunnel, the model is endowed with a Mohr-Coulomb constitutive model and a self-weight stress to form an initial geostress field; the model is excavated in the order of the upper arc-shaped pilot tunnel, the reserved core soil, the middle layer step and the bottom layer; the primary support is immediately applied after the excavation, wherein the primary support is simulated in an elastic equivalent manner, and the numerical model is as shown in Figure 5

[0041] Table 1 Calculation conditions of the reserved core soil size

[0042]

[0043] Step 3, in order to avoid the influence of the boundary effect, the displacement u' of the surrounding rock at the tunnel face is extracted when the tunnel model is excavated to half the footage; after the tunnel is penetrated, the displacement u of the surrounding rock at the same position is extracted; during the tunnel excavation, due to stress release, the tunnel produces a certain degree of convergence deformation before the primary support is applied, which is manifested as extrusion of the tunnel face, and this deformation is the pre-deformation u', as shown in Figure 4 The displacement u measured after the tunnel is penetrated is the total deformation of the tunnel, and the real measurable displacement of the tunnel is calculated by the following formula:

[0044] Δu = u - u'

[0045] From the above formula, 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 core soil cross-sectional dimensions a, b and h;

[0046] Step 4, the extrusion of the tunnel face under different reserved core soil cross-sectional dimensions is arranged, and the size with the smallest value of u' is selected as the optimal core soil size, which has the best control effect on the extrusion deformation of the tunnel face.

[0047] In this embodiment, the values of the pre-deformation u' under five different core soil size calculation conditions are arranged; the optimal scheme is a = 6 m, b = 9 m and h = 3 m, and the pre-deformation is 22 mm at this time. As shown in the accompanying Figure 7 .​

Claims

1. A core soil size optimization method based on controlling pre-deformation of a tunnel face, characterized by, Specifically comprising the following steps: Step 1, determining a tunnel construction scheme, adopting a reserved core soil method, and dividing a circular section according to an expected excavation sequence, wherein a reserved core soil section is a trapezoid, an upper side length is a, a lower side length is b, and a height is h, units are meters; Step 2, selecting different a, b, and h values to simulate excavation calculation of a tunnel model in a tunnel site area through an existing numerical simulation technical method, and fully restoring an actual excavation process of the tunnel; Step 3: To avoid the influence of boundary effects, when the tunnel model has been excavated to half its depth, the displacement of the surrounding rock at the tunnel face is extracted. After the tunnel is completed, the displacement of the surrounding rock is extracted at the same location. During tunnel excavation, due to stress release, the tunnel undergoes convergent deformation before the initial support is installed. This deformation manifests as extrusion at the tunnel face and is known as pre-deformation. Displacement measured after tunnel completion To calculate the total deformation of the tunnel, calculate the actual measurable displacement of the tunnel. The real measurable displacement of the tunnel is calculated by the following formula: ； From the above equation, it is known that when the value of the measurable displacement of the tunnel remains substantially unchanged, reducing the value of the pre-deformation can reduce the total displacement , and the value of the pre-deformation is related to the cross-sectional dimensions a, b, h of the core soil. Step 4, arrange different reserved core soil section size of the face extrusion, select The minimum size is the best core soil size, and the control effect of face extrusion deformation is the best.

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

3. The method of claim 2, wherein the core soil size is optimized based on the pre-deformation of the tunnel face. Step 2 the existing numerical simulation technical method is a stratum-structure method.

4. The method for core soil size optimization based on controlling pre-deformation of tunnel face according to claim 1, characterized in that, Step 2 the numerical simulation calculation steps are as follows: Step 2-1, according to a mechanical constitutive equation of the tunnel, the tunnel model is endowed with a corresponding constitutive model and an actual ground stress level is applied to form an initial stress field; Step 2-2, the tunnel model is simulated to excavate according to the construction scheme determined in step 1; Step 2-3, to ensure the accuracy of calculation, in addition to applying the actual ground stress condition, the actual excavation method and the supporting structure are combined to perform simulation calculation.

5. The method of claim 3, wherein the core soil size is optimized based on the pre-deformation of the tunnel face. Step 2-3 the initial support in the supporting structure is shotcrete and an arch.

6. The method of claim 3, wherein the core soil size is optimized based on the pre-deformation of the tunnel face. Step 2-3 the simulation calculation is performed in an elastic equivalent manner.

Images