Shallow-buried tunnel full-section excavation safety footage calculation method

Abstract

The invention belongs to the field of geotechnical engineering, and particularly relates to a shallow-buried tunnel full-section excavation safety footage calculation method which comprises the steps of model parameter setting, model assumption condition setting, fractured area score calculation, soil pressure calculation at any height on a straight wall AB, coordinate calculation of a point D, static balance calculation and safety footage analysis. According to the method, the problem of safe footage length calculation in the shallow-buried tunnel construction process can be solved; the problems of complex parameters and tedious modeling in the traditional calculation process are solved; the method has the advantages of being high in calculation accuracy, accurate in result and high in reliability.

Description

Technical Field

[0001] The invention belongs to the field of geotechnical engineering, and particularly relates to a method for calculating safe advance of full-section excavation of a shallow tunnel. Background Art

[0002] At present, my country is vigorously promoting the construction of urban subways, highways and other projects, and the tunnel projects involved, especially shallow buried tunnels, are an important part of them. In the process of full-section excavation of shallow buried tunnels, safe advance is an important indicator to ensure excavation efficiency and safe operation of the face.

[0003] At present, numerical calculation and theoretical methods are mainly used for its safe advance. Due to the complex parameters of numerical calculation, it has high requirements for modeling, and the results are greatly affected by the accuracy of modeling. Theoretical calculation mainly adopts two paths: limit analysis and limit equilibrium. Limit analysis mainly adopts the upper limit method, and the calculated advance is small and conservative, resulting in engineering waste. There are studies on limit equilibrium at present, which mainly establishes the relationship between the advance and the internal friction angle, cohesion, support pressure, excavation height and other parameters based on the Jansen silo theory. The defect of this type of model is that the soil pressure above the face is greatly affected by the burial depth. When it is shallowly buried, the error of the result is large. The advance calculation based on the earth pressure arch theory essentially assumes that the face is stable and only calculates the stability of the tunnel arch, which is inconsistent with the actual situation. Therefore, there is an urgent need for a calculation method for the safe advance of full-section excavation, which is beneficial to engineering safety and improving excavation efficiency. Summary of the invention

[0004] The purpose of the present invention is to provide a method for calculating the safe advance of full-section excavation of a shallow tunnel, so as to solve the problems existing in the prior art of complex analysis parameters, large result errors and slow analysis process.

[0005] The technical solution of the present invention to solve the above technical problems is as follows: a method for calculating the safe advance of full-section excavation of a shallow tunnel, characterized in that the calculation method comprises:

[0006] S1: Model parameter setting, statistical summary of relevant parameters, and construction of calculation model; the relevant parameters include tunnel height H1, tunnel top burial depth H, and surface load q;

[0007] S2: Set model assumptions to simplify the calculation process;

[0008] S3: Fracture surface integral calculation;

[0009] S4: Calculation of earth pressure at any height on the vertical wall AB:

[0010] S5: Calculation of coordinates of point D, the dividing point between plane segment CD and arc segment AD;

[0011] S6: Calculate the static balance of soil block ABCD to obtain the safe advance length.

[0012] In step S1, the model assumes that the ground surface is horizontal, and the soil block ABCD is divided into two areas a and b, and the fracture surface is assumed to be a plane to arc-shaped failure surface, and the slope of the surface AD ​​is h′ b , the slope of surface CD is h′ a The plane-arc type failure surface is characterized in that the failure surface is an arc near the bottom of the tunnel face and then continues to extend upward to the top of the tunnel in a plane.

[0013] In step S3, the rupture surface integral is calculated, that is, in plane segment CD: have is the internal friction angle of soil, h′ a is the slope of the fracture surface CD in area a; in the arc segment AD: (hz R )(h′-λ)+(1+λh′)(xx R )=0, x is the X coordinate value of any point on the entire fracture surface; h is the Z coordinate value of any point on the entire fracture surface, x R , z R is the coordinate of the center of the arc, h′ is the slope of the damaged arc segment AD, so:

[0014]

[0015] In the formula, l1 is the width of the damage zone at the top of the tunnel. Further, after integral operation, we get:

[0016]

[0017] in

[0018] In step S4, the soil pressure at any height h on the vertical wall AB is calculated. That is, it can be known from the calculation that the soil pressure e at any height h on the vertical wall AB h For: e h =γhK γ -2cK c +qK q

[0019] Where:

[0020]

[0021]

[0022] In the formula, K q is the load earth pressure coefficient, Kc is the cohesive earth pressure coefficient, K γ is the gravity earth pressure coefficient, γ is the gravity of the soil, q is the surface load of the soil, c is the cohesion of the soil, is the internal friction angle of the soil, and h is any height on the straight wall AB; according to the above formula, the soil pressure coefficient can be obtained when the failure surface is in the form of a plane ~ arc surface.

[0023] In step S5, the coordinates of the dividing point D between the plane segment CD and the arc segment AD are calculated as follows:

[0024]

[0025] x1 and z1 are the x- and z-coordinates of D respectively. is the internal friction angle of soil;

[0026] Furthermore, the length of l1 is:

[0027] l1=-2x1

[0028] Where: l1 is the width of the damage zone at the top of the tunnel, x1 and z1 are the x-coordinate and z-coordinate of D respectively.

[0029] In step S6, the soil pressure on the BC surface above the tunnel face is first calculated as:

[0030]

[0031] Where l1 is the width of the damage zone at the top of the tunnel, l is the excavation depth, q1 is the overburden pressure on the BC surface, H is the thickness of the overburden on the tunnel, and K is q is the load earth pressure coefficient, K c is the cohesive earth pressure coefficient, K γ is the gravity earth pressure coefficient, γ is the gravity of the soil, q is the surface load of the soil, c is the cohesion of the soil, is the internal friction angle of soil;

[0032] Then the soil block ABCD is subjected to static balance calculation, and the safe advance of the tunnel face when EAB=0 is calculated according to the following formula:

[0033]

[0034] In the formula, E AB is the total earth pressure on the AB surface, H1 is the height of the tunnel excavation, K q is the load earth pressure coefficient, K c is the cohesive earth pressure coefficient, K γ is the gravity earth pressure coefficient, γ is the density of soil, q1 is the overlying soil pressure on the BC surface, and c is the soil cohesion.

[0035] The present invention assumes that the ground surface is horizontal and divides the potential failure surface into plane and arc failure surfaces. By calculating the earth pressure system, the maximum length of the tunnel when the tunnel face is stable can be obtained. Compared with the prior art, the present invention has the following beneficial effects: (1) It can solve the problem of calculating the safe length of the tunnel during the construction of shallow buried tunnels; (2) It can solve the problems of complex parameters and cumbersome modeling in the traditional calculation process; (3) The present invention has the advantages of accurate calculation, accurate results and high reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a model calculation diagram of a safe advance calculation method for full-section excavation of a shallow buried tunnel according to the present invention;

[0037] Figure 2 The present invention is a flow chart of a method for calculating safe advance for full-section excavation of a shallow tunnel. DETAILED DESCRIPTION

[0038] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0039] Example

[0040] like Figure 2 A method for calculating safe advance of full-section excavation of a shallow tunnel is shown, comprising the following steps:

[0041] S1: Model parameter settings, tunnel depth H = 10m, tunnel height H1 = 10m, soil layer weight 20kN / m 3 , surface level, surface load q = 200 kPa, soil cohesion C = 10 kPa / 50 kPa / 100 kPa, internal friction angle Calculate the safe advance of the tunnel face;

[0042] S2: Model assumptions, such as Figure 1 Assuming the ground surface is horizontal, a detailed analysis is conducted on block ABCD. Block ABCD is divided into two areas, a and b, and the fracture surface is assumed to be a plane ~ arc-shaped failure surface, and the slope of surface AD ​​is h′ b The slope of surface CD is h′ a ;

[0043] S3: Fracture surface integral calculation, that is, in the plane segment CD: have On the arc segment AD: (hz R )(h′-λ)+(1+λh′)(xx R )=0, so:

[0044]

[0045] Furthermore, after integral operation, we get:

[0046]

[0047] in

[0048] S4: Solve the integral equation in S3 to obtain the soil pressure at any height h on the vertical wall AB:

[0049] e h =γhK γ -2cK c +qK a

[0050] Where:

[0051]

[0052] From this, the earth pressure coefficient can be obtained when the failure surface is a plane ~ arc surface;

[0053] S5: Calculation of coordinates of point D. The coordinates of point D, the dividing point between plane segment CD and arc segment AD, are calculated as follows:

[0054]

[0055] Furthermore, the length of l1 is:

[0056] l1=-2x1:

[0057] S6: Static balance calculation of soil block ABCD. The soil pressure on the BC surface above the tunnel face is:

[0058]

[0059] Then perform static balance calculation on soil block ABCD to obtain the value of E AB = 0: Tunnel face safe advance:

[0060]

[0061] In the above calculation process, the calculation results of each parameter are shown in Table 1:

[0062] Table 1 Calculation of safe penetration of the tunnel face by this patent algorithm

[0063]

[0064] Through the above calculation, when q1≥0 and l≥0, it means that the surrounding rock is self-stable, otherwise it means that the surrounding rock is not self-stable and collapses as soon as it is excavated. Pre-reinforcement measures such as grouting are required to improve the surrounding rock strength parameters.

Claims

1. A method for calculating safe advance of full-section excavation of shallow tunnels, characterized in that: The calculation method includes: S1: setting model parameters, summarizing relevant parameters, and building a calculation model; the relevant parameters include tunnel height H1, tunnel top burial depth H, and surface load q; S2: Set model assumptions to simplify the calculation process; S3: Fracture surface integral calculation; S4: Calculation of earth pressure at any height on the vertical wall AB: S5: Calculation of coordinates of point D, the dividing point between plane segment CD and arc segment AD; S6: Calculate the static balance of soil block ABCD to obtain the safe advance length.

2. A method for calculating safe advance of full-section excavation of shallow tunnel according to claim 1, characterized in that: In step S1, the model assumes that the ground surface is horizontal, and the soil block ABCD is divided into two areas a and b, and the fracture surface is assumed to be a plane to arc-shaped failure surface, and the slope of the surface AD ​​is h′ b , the slope of surface CD is h′ a The plane-arc type failure surface is characterized in that the failure surface is an arc near the bottom of the tunnel face and then continues to extend upward to the top of the tunnel in a plane.

3. The method for calculating safe advance of full-section excavation of shallow tunnel according to claim 1 is characterized in that: In step S3, the rupture surface integral is calculated, that is, in plane segment CD: have is the internal friction angle of soil, h′ a is the slope of the fracture surface CD in area a; in the arc segment AD: (hz R )(h′-λ)+(1+λh′)(xx R )=0, x is the X coordinate value of any point on the entire fracture surface; h is the Z coordinate value of any point on the entire fracture surface, x R , z R is the coordinate of the center of the arc, h′ is the slope of the damaged arc segment AD, so: In the formula, l1 is the width of the damage zone at the top of the tunnel. Further, after integral operation, we get: in 4. The method for calculating safe advance of full-section excavation of shallow tunnel according to claim 1 is characterized in that: In step S4, the soil pressure at any height h on the vertical wall AB is calculated. That is, it can be known from the calculation that the soil pressure e at any height h on the vertical wall AB h for: yes h =γhK γ -2cK c +qK q , Where: In the formula, K q is the load earth pressure coefficient, K c is the cohesive earth pressure coefficient, K γ is the gravity earth pressure coefficient, γ is the gravity of the soil, q is the surface load of the soil, c is the cohesion of the soil, is the internal friction angle of the soil, and h is any height on the straight wall AB; according to the above formula, the soil pressure coefficient can be obtained when the failure surface is in the form of a plane ~ arc surface.

5. The method for calculating safe advance of full-section excavation of shallow tunnel according to claim 1 is characterized in that: In step S5, the coordinates of the dividing point D between the plane segment CD and the arc segment AD are calculated as follows: x1 and z1 are the x- and z-coordinates of D respectively. is the internal friction angle of soil; Furthermore, the length of l1 is: l1＝-2x1， Where: l1 is the width of the damage zone at the top of the tunnel, x1 and z1 are the x-coordinate and z-coordinate of D respectively.

6. A method for calculating safe advance of full-section excavation of shallow tunnel according to claim 1, characterized in that: In step S6, the soil pressure on the BC surface above the tunnel face is first calculated as: Where l1 is the width of the damage zone at the top of the tunnel, l is the excavation depth, q1 is the overburden pressure on the BC surface, H is the thickness of the overburden on the tunnel, and K is q is the load earth pressure coefficient, K c is the cohesive earth pressure coefficient, K γ is the gravity earth pressure coefficient, γ is the gravity of the soil, q is the surface load of the soil, c is the cohesion of the soil, is the internal friction angle of soil; Then the soil block ABCD is subjected to static balance calculation, and the following formula is used to calculate when E AB = 0: Tunnel face safe advance: In the formula, E AB is the total earth pressure on the AB surface, H1 is the height of the tunnel excavation, K q is the load earth pressure coefficient, K c is the cohesive earth pressure coefficient, K γ is the gravity earth pressure coefficient, γ is the density of soil, q1 is the overlying soil pressure on the BC surface, and c is the soil cohesion.

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