Calculation Method for Loess Collapse Amount at Tunnel Foundation

Abstract

The present invention relates to a method for calculating the collapsibility of loess at the tunnel base, which comprises the following steps: establishing a numerical model for the tunnel under construction, and simulating the tunnel excavation by using the numerical model to obtain the vertical stress at each position along the tunnel base; calculating the ratio of the vertical stress at each position to the initial vertical stress at the corresponding position, and obtaining a relationship curve between each position and the corresponding vertical stress ratio, and performing normalization processing on the relationship curve to obtain the stress ratio curve of the vertical section of the tunnel; establishing a pressure calculation model according to the stress ratio curve, calculating the actual stress value at each position according to the pressure calculation model and the Flamant solution, and obtaining the collapsibility of the loess according to the actual stress value. It solves the problem that the design and construction according to the current loess specification are unreasonable. By providing a calculation method for loess collapsibility that can adapt to different working conditions, a more valuable reference system is provided for the construction, so that the construction plan is more reasonable and the construction quality and efficiency are guaranteed.

Description

Technical Field

[0001] The present invention relates to the field of construction, and particularly to a method for calculating the collapsibility of loess at the tunnel base Background Art

[0002] Underground projects such as tunnels have different load patterns from surface buildings. Generally, due to the excavation of the invert in tunnel projects, it is a unloading or loading effect on a certain area of the surrounding soil layer. Moreover, most tunnels are buried deeply, and the collapsibility of deep loess needs to be considered. However, currently, the existing loess specifications are applied to test, evaluate, and treat tunnels. However, tunnels at different depths have a great impact on the collapsibility of the bottom loess, and it is unreasonable to implement according to a unified specification, resulting in the irrationality of the design scheme Summary of the Invention

[0003] The purpose of the present invention is to overcome the defects of the prior art, provide a method for calculating the collapsibility of loess at the tunnel base, solve the problem of unreasonable design and construction according to the existing loess specifications, and provide a calculation method for the collapsibility of yellow soil that can adapt to different working conditions, so as to provide a more valuable reference system for construction, making the construction plan more reasonable and ensuring construction quality and efficiency

[0004] The technical solution to achieve the above purpose is as follows

[0005] The present invention provides a method for calculating the collapsibility of loess at the tunnel base, including the following steps

[0006] Establish a numerical model for the tunnel to be constructed, and use the numerical model to simulate the tunnel excavation to obtain the vertical stress at each position along the tunnel base

[0007] Calculate the ratio of the vertical stress at each position to the initial vertical stress at the corresponding position, and obtain the relationship curve between each position and the corresponding vertical stress ratio. Normalize the relationship curve to obtain the stress ratio curve of the vertical section of the tunnel

[0008] Establish a pressure calculation model according to the stress ratio curve, including

[0009] Define the part of the stress ratio curve where the vertical stress ratio is less than 1 and the vertical stress ratio gradually increases as zone I, the part where the vertical stress ratio is greater than or equal to 1 and the vertical stress ratio gradually increases as zone II, the part where the vertical stress ratio is greater than or equal to 1 and the vertical stress ratio gradually decreases as zone III, and the part where the vertical stress ratio is equal to 1 and the vertical stress ratio no longer changes as zone IV

[0010] According to Flamant's solution, obtain the corresponding expressions for the I region, the II region, the III region, and the IV region, and establish the pressure calculation model based on the expressions. Calculate the actual stress values at each position according to the pressure calculation model and Flamant's solution, and obtain the loess collapsibility amount based on the actual stress values.

[0011] The present invention proposes a calculation method for the loess collapsibility amount of a tunnel foundation. By using a numerical model to simulate tunnel excavation, the stress ratio curve is obtained and the pressure calculation model is established. Calculate the actual stress values at each position according to the pressure calculation model and Flamant's solution, and obtain the loess collapsibility amount based on the actual stress values. Guide the construction according to the loess collapsibility amount, solve the problem that the design and construction according to the current loess specification are unreasonable, and provide a more valuable reference system for the construction by providing a loess collapsibility calculation method that can adapt to different working conditions, so as to make the construction plan more reasonable and ensure the construction quality and construction efficiency.

[0012] A further improvement of the calculation method for the loess collapsibility amount of the tunnel foundation of the present invention is that when normalizing the relationship curve, it further includes:

[0013] Divide the horizontal axis coordinate value of the relationship curve by half of the width of the tunnel cross-section to obtain the stress ratio curve, so as to display the stress ratios of each position point at the foundation of the tunnel vertical section.

[0014] A further improvement of the calculation method for the loess collapsibility amount of the tunnel foundation of the present invention is that it further includes:

[0015] Take the position point representing the center line of the tunnel foundation in the stress ratio curve as the characteristic point m, take the position point with the largest vertical stress ratio value in the stress ratio curve as the characteristic point o, and obtain the vertical stress ratios of the characteristic point m and the characteristic point o.

[0016] Obtain the actual pressure values of each position point of the tunnel foundation according to the vertical stress ratios of the characteristic point m and the characteristic point o and the pressure calculation model.

[0017] A further improvement of the calculation method for the loess collapsibility amount of the tunnel foundation of the present invention is that the value range of the vertical stress ratio of the characteristic point m is (0.36, 0.54), and the value range of the vertical stress ratio of the characteristic point o is (1.10, 1.18).

[0018] A further improvement of the calculation method for the loess collapsibility amount of the tunnel foundation of the present invention is that it further includes:

[0019] Take the position point where the vertical stress ratio is 1 in the part where the vertical stress ratio in the stress ratio curve gradually increases as the characteristic point n, and use the pressure calculation model to obtain the actual stress values of the characteristic point m and the characteristic point n.

[0020] A further improvement of the calculation method for the collapsibility of loess at the tunnel foundation of the present invention lies in that when calculating the actual pressure value using the pressure calculation model, it further includes:

[0021] Using Flamant's solution, the uniform load calculation formula on a strip foundation, and the superposition of the additional stress load calculation formula at any point of a triangle to calculate the actual pressure values at different depths below the characteristic point m and the characteristic point n.

[0022] A further improvement of the calculation method for the collapsibility of loess at the tunnel foundation of the present invention lies in that the formula for the actual stress value is as follows:

[0023] σ = σ0 + η t p0

[0024] Where σ is the actual stress value, σ0 is the initial vertical stress, p0 is the initial vertical stress from the ground to the center of the tunnel foundation, and η t is the vertical additional stress coefficient.

[0025] A further improvement of the calculation method for the collapsibility of loess at the tunnel foundation of the present invention lies in that the vertical additional stress coefficient η t is calculated according to the tunnel span and the vertical distance between the position point to be calculated and the base surface.

[0026] A further improvement of the calculation method for the collapsibility of loess at the tunnel foundation of the present invention lies in that the formula for the initial vertical stress from the ground to the center of the tunnel foundation is as follows:

[0027] p0 = γh

[0028] Where p0 is the initial vertical stress from the ground to the center of the tunnel foundation, γ is the soil density, and h is the vertical distance from the ground to the center of the tunnel foundation. Description of the Drawings

[0029] Figure 1 It is a schematic diagram of the pressure calculation model in the calculation method for the collapsibility of loess at the tunnel foundation of the present invention. Detailed Embodiments

[0030] The present invention will be further described below in conjunction with the drawings and specific embodiments.

[0031] The present invention provides a method for calculating the collapsibility of loess at the tunnel base. By using a numerical model to simulate tunnel excavation, a stress ratio curve is obtained and a pressure calculation model is established. According to the pressure calculation model and Flamant's solution, the actual stress values at each position are calculated, and the collapsibility of loess is obtained based on the actual stress values. The construction is guided according to the collapsibility of loess, solving the problem that the design and construction according to the current loess specification are unreasonable. By providing a calculation method for loess collapsibility that can adapt to different working conditions, a more valuable reference system is provided for construction, making the construction plan more reasonable and ensuring construction quality and efficiency. The method for calculating the collapsibility of loess at the tunnel base of the present invention will be described below with reference to the accompanying drawings.

[0032] Refer to Figure 1 which is a schematic diagram of the pressure calculation model in the method for calculating the collapsibility of loess at the tunnel base of the present invention. The method for calculating the collapsibility of loess at the tunnel base of the present invention will be described below in conjunction with Figure 1 to illustrate the method for calculating the collapsibility of loess at the tunnel base of the present invention.

[0033] As Figure 1 shown, the present invention provides a method for calculating the collapsibility of loess at the tunnel base, including the following steps:

[0034] Establish a numerical model for the tunnel to be constructed, and use the numerical model to simulate tunnel excavation to obtain the vertical stresses at each position along the tunnel base;

[0035] Calculate the ratio of the vertical stress at each position to the initial vertical stress at the corresponding position, and obtain the relationship curve between each position and the corresponding vertical stress ratio. Normalize the relationship curve to obtain the stress ratio curve of the vertical section of the tunnel;

[0036] Establish a pressure calculation model according to the stress ratio curve, calculate the actual stress values at each position according to the pressure calculation model and Flamant's solution, and obtain the collapsibility of loess based on the actual stress values.

[0037] As a preferred embodiment of the present invention, when normalizing the relationship curve, it further includes:

[0038] Divide the abscissa value of the relationship curve by half of the width of the tunnel cross-section to obtain the stress ratio curve, so as to show the stress ratios at each position point at the base of the vertical section of the tunnel.

[0039] Furthermore, it further includes:

[0040] Define the part where the vertical stress ratio in the stress ratio curve is less than 1 and the vertical stress ratio gradually increases as Zone I, the part where the vertical stress ratio in the stress ratio curve is greater than or equal to 1 and the vertical stress ratio gradually increases as Zone II, the part where the vertical stress ratio in the stress ratio curve is greater than or equal to 1 and the vertical stress ratio gradually decreases as Zone III, and the part where the vertical stress ratio in the stress ratio curve is equal to 1 and the vertical stress ratio no longer changes as Zone IV;

[0041] According to Flamant's solution, obtain the expressions corresponding to Zone I, Zone II, Zone III, and Zone IV, and establish a pressure calculation model based on the expressions.

[0042] Specifically, it also includes:

[0043] Take the position point at the center line representing the tunnel base in the stress ratio curve as the characteristic point m, take the position point with the maximum vertical stress ratio value in the stress ratio curve as the characteristic point o, and obtain the vertical stress ratios of the characteristic point m and the characteristic point o;

[0044] According to the vertical stress ratios of the characteristic point m and the characteristic point o and the pressure calculation model, obtain the actual pressure values of each position point of the tunnel base.

[0045] Preferably, the value range of the vertical stress ratio of the characteristic point m is (0.36, 0.54), and the value range of the vertical stress ratio of the characteristic point o is (1.10, 1.18). If the tunnel construction has less disturbance to the base, smaller values can be used; if the tunnel construction has greater disturbance to the base, larger values can be used.

[0046] Furthermore, it also includes:

[0047] Take the position point where the vertical stress ratio is 1 in the part where the vertical stress ratio in the stress ratio curve gradually increases as the characteristic point n, and use the pressure calculation model to obtain the actual stress values of the characteristic point m and the characteristic point n.

[0048] Furthermore, when using the pressure calculation model to calculate the actual pressure value, it also includes:

[0049] Use Flamant's solution, the uniform load calculation formula on a strip foundation, and the additional stress load calculation formula at any point of a triangle to superimpose and calculate the actual pressure values at different depths below the characteristic point m and the characteristic point n.

[0050] Specifically, the formula for the actual stress value is as follows:

[0051] σ = σ0 + η t p0

[0052] Where σ is the actual stress value, σ0 is the initial vertical stress, p0 is the initial vertical stress from the ground to the center of the tunnel base, and η t is the vertical additional stress coefficient.

[0053] Preferably, the vertical additional stress coefficient η t is calculated according to the tunnel span and the vertical distance between the position point to be calculated and the base surface.

[0054] Specifically, the calculation formula for the initial vertical stress from the ground to the center of the tunnel base is as follows:

[0055] p0 = γh

[0056] where p0 is the initial vertical stress from the ground to the center of the tunnel base, γ is the soil density, and h is the vertical distance from the ground to the center of the tunnel base.

[0057] The specific implementation manner of the present invention is as follows:

[0058] Establish a numerical model for the tunnel to be constructed, and use the numerical model to simulate the tunnel excavation to obtain the vertical stress at each position along the length direction of the tunnel base;

[0059] Calculate the ratio of the vertical stress at each position to the initial vertical stress at the corresponding position, and obtain the relationship curve between each position along the length direction of the tunnel base and the corresponding vertical stress ratio. Normalize the relationship curve, that is, divide the abscissa value (the position coordinate value along the length direction of the base) of the relationship curve by half of the width of the tunnel vertical section to obtain the stress ratio curve, that is, the abscissa is each position point along the width direction at the tunnel vertical section and the ordinate is the vertical stress ratio corresponding to each position point (as shown in Figure 1 ), Figure 1 The curve in shows the stress ratio curve along the width direction on the right half side of the tunnel center line. That is, the positive direction of the X-axis represents each position point of the tunnel base from the center line to the right side, and the P-axis represents the vertical stress ratio;

[0060] In the stress ratio curve, the part where the vertical stress ratio is less than 1 is the unloading area and the part greater than 1 is the loading area. That is, Figure 1 in , the line segment mn is area I, the line segment no is area II, the line segment op is area III, and the right side of point p is area IV. Obtain the expression for each area according to Flamant's solution, and establish a pressure calculation model according to the expression;

[0061] The value range of the vertical stress ratio of the characteristic point m is (0.36, 0.54), and the value range of the vertical stress ratio of the characteristic point o is (1.10, 1.18). If the tunnel construction has less disturbance to the base, smaller values can be adopted. If the tunnel construction has greater disturbance to the base, larger values can be adopted;

[0062] Taking the calculation of the actual stress value at point m as an example, since the vertical additional stress coefficient η tIt is calculated based on the tunnel span and the vertical distance between the position point to be calculated and the base surface, and the calculation formula for the actual stress value at point m can be obtained as follows:

[0063]

[0064] Among them, σ m is the actual stress value at a certain position point below point m, B t is the tunnel span, is the vertical stress ratio of the characteristic point m (which can refer to the above value range), is the vertical stress ratio of the characteristic point o (which can refer to the above value range), p0 is the initial vertical stress from the ground to the center of the tunnel base, and z is the vertical distance between the position point to be calculated and the base surface;

[0065] Figure 1 In , the characteristic points m, n, o, and P are all relatively key research nodes, and the actual stress values at different positions and different depths below each characteristic point can be calculated respectively in the above manner;

[0066] The actual stress values at different position points below the base can be calculated using the pressure calculation model, and the collapsibility of loess under the actual stress state can be obtained through experiments according to the operation process of the collapsibility coefficient in the current loess specification, so as to know the subsequent construction design.

[0067] The present invention has been described in detail above in combination with the embodiments in the accompanying drawings. Those of ordinary skill in the art can make various variations of the present invention according to the above description. Therefore, some details in the embodiments should not constitute a limitation to the present invention, and the protection scope of the present invention will be defined by the scope defined in the appended claims.

Claims

1. A calculation method for the collapsibility of loess in the tunnel foundation, characterized in that, The steps are as follows: Establish a numerical model for the tunnel to be constructed, and use the numerical model to simulate the tunnel excavation to obtain the vertical stress at each position along the tunnel base; Calculate the ratio of the vertical stress at each position to the initial vertical stress at the corresponding position, and obtain the relationship curve between each position and the corresponding vertical stress ratio. Normalize the relationship curve to obtain the stress ratio curve of the vertical section of the tunnel; Establish a pressure calculation model according to the stress ratio curve, including: Define the part of the stress ratio curve where the vertical stress ratio is less than 1 and gradually increases as zone I, the part where the vertical stress ratio is greater than or equal to 1 and gradually increases as zone II, the part where the vertical stress ratio is greater than or equal to 1 and gradually decreases as zone III, and the part where the vertical stress ratio is equal to 1 and no longer changes as zone IV; Obtain the corresponding expressions for zone I, zone II, zone III, and zone IV according to Flamant's solution, establish the pressure calculation model according to the expressions, calculate the actual stress values at each position according to the pressure calculation model and Flamant's solution, and obtain the loess collapsibility according to the actual stress values.

2. The calculation method of the collapsibility of loess in the tunnel foundation as described in claim 1, wherein, When normalizing the relationship curve, it also includes: Divide the abscissa value of the relationship curve by half of the width of the vertical section of the tunnel to obtain the stress ratio curve, so as to show the stress ratio of each position point at the base of the vertical section of the tunnel.

3. The calculation method of the collapsibility of loess in the tunnel foundation as described in claim 1, characterized in that, It also includes: Take the position point representing the center line of the tunnel base in the stress ratio curve as feature point m, take the position point with the maximum vertical stress ratio value in the stress ratio curve as feature point o, and obtain the vertical stress ratios of feature point m and feature point o; Obtain the actual stress values of each position point of the tunnel base according to the vertical stress ratios of feature point m and feature point o and the pressure calculation model.

4. The calculation method of the collapsibility of loess in the tunnel foundation as described in claim 3, characterized in that, The value range of the vertical stress ratio of feature point m is (0.36, 0.54), and the value range of the vertical stress ratio of feature point o is (1.10, 1.18).

5. The calculation method of the collapsibility of loess in the tunnel foundation as described in claim 3, characterized in that, It also includes: Take the position point with a vertical stress ratio of 1 in the part where the vertical stress ratio gradually increases in the stress ratio curve as feature point n, and use the pressure calculation model to obtain the actual stress values of feature point m and feature point n.

6. The calculation method of the collapsibility of loess at the tunnel foundation as described in claim 5, characterized in that, When using the pressure calculation model to calculate the actual stress value, it also includes: Superimpose and calculate the actual stress values at different depths below feature point m and feature point n by using Flamant's solution, the uniform load calculation formula on a strip foundation, and the additional stress load calculation formula at any point of a triangle.

7. The calculation method of the collapsibility of loess in the tunnel foundation as described in claim 6, characterized in that, The formula for the actual stress value is as follows: σ = σ0 + η t p0 Among them, σ is the actual stress value, σ0 is the initial vertical stress, p0 is the initial vertical stress from the ground to the center of the tunnel base, and η t is the vertical additional stress coefficient.

8. The calculation method of the collapsibility of loess in the tunnel foundation as described in claim 7, characterized in that, The vertical additional stress coefficient η t is calculated based on the tunnel span and the vertical distance between the point to be calculated and the base surface.

9. The calculation method of the collapsibility of loess in the tunnel foundation as described in claim 7, characterized in that, The formula for the initial vertical stress from the ground to the center of the tunnel base is as follows: p0 = γh where p0 is the initial vertical stress from the ground to the center of the tunnel base, γ is the soil density, and h is the vertical distance from the ground to the center of the tunnel base.

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