Method for designing safety thickness of rock clamping body in construction period of oblique crossing over-crossing tunnel

Abstract

The invention provides a method for designing the safety thickness of a rock clamping body in the construction period of an oblique crossing tunnel, and belongs to the technical field of tunnel construction, and the method comprises the following steps: S1, calculating the stress of a rock clamping infinitesimal body in the oblique crossing tunnel; s2, calculating an included angle theta between the position of the infinitesimal body and the axis of the new tunnel; s3, simulating stress distribution of a tunnel bottom surrounding rock plane; s4, determining a shear stress range of an infinitesimal body of the interlaced rock mass; s5, calculating the stress extreme value of the infinitesimal body of the interlaced rock mass; s6, setting basic conditions of the safety thickness of the interlayer rock; and S7, calculating the safety thickness of the sandwiched rock mass by adopting an iteration method. According to the design method for the safety thickness of the rock clamping mass in the construction period of the oblique crossing overpass tunnel, stable operation safety of the existing line tunnel is guaranteed, and meanwhile it is guaranteed that the construction activity of a newly-built tunnel is efficiently promoted in a safe environment.

Description

Technical Field

[0001] This invention relates to the field of tunnel construction technology, and in particular to a method for designing the safe thickness of interbedded rock mass during the construction of skew-crossing tunnels. Background Technology

[0002] With the rapid expansion and deepening of my country's railway and highway transportation network, tunnel engineering design inevitably encounters special structural forms such as parallel tunnels with small clearance, tunnels crossing small clearance, and tunnels passing under small clearance, due to the dual constraints of line planning and layout and complex and variable geological conditions. These special tunnel layouts pose more stringent safety standards and challenges to the continuous safe operation of existing tunnels and the smooth construction of new tunnels.

[0003] Through extensive and in-depth scientific research and rich engineering practice, the current railway tunnel design specifications and highway tunnel design specifications have provided relatively clear thickness definition standards for parallel tunnels with small clearances, and have specifically proposed reinforcement strategies and specific construction requirements for rock walls in small clearances, providing important technical support for the industry.

[0004] However, the mechanical mechanisms involved in the excavation and unloading of newly constructed skewed tunnels with small clearances are particularly complex. This process not only triggers the formation of a loosened zone in the surrounding rock of the new tunnel but also profoundly affects the readjustment of the mechanical equilibrium between the existing tunnel and the surrounding rock, making the mechanical behavior of the interbedded rock mass even more intricate. Therefore, ensuring that the structural stress and deformation of the existing tunnel remain below its structural failure stress and within a safe deformation range that does not affect normal operation during the construction of the new skewed tunnel with small clearances becomes crucial to guaranteeing project safety.

[0005] Therefore, there is an urgent need for a method to accurately calculate and assess the safe thickness of interbedded rock masses during construction. Summary of the Invention

[0006] The purpose of this invention is to provide a method for designing the safe thickness of interbedded rock mass during the construction of skew-crossing tunnels, ensuring the stable and safe operation of existing tunnels, while ensuring that the construction activities of new tunnels can be carried out efficiently in a safe environment.

[0007] To achieve the above objectives, this invention provides a method for designing the safe thickness of interbedded rock mass during the construction of an oblique overpass tunnel, comprising the following steps:

[0008] S1. Calculate the stress of the interlocking rock micro-element in the oblique overpass tunnel: Determine the geometric parameters of the oblique overpass tunnel, and calculate the stress state of any selected micro-element in the interlocking rock mass according to the stress function expression;

[0009] S2. Calculate the angle θ between the position of the micro-element and the axis of the newly built tunnel: Based on the geometric layout of the tunnel and the positional relationship of the interbedded rock mass, calculate the specific value of the angle θ through geometric relationship analysis;

[0010] S3. Simulate the stress distribution of the surrounding rock plane at the bottom of the new tunnel: Based on the basic assumptions of elasticity, the gravity of the upper rock mass is simplified into the distributed load of the surrounding rock plane at the bottom of the new tunnel. The specific form of stress distribution of the surrounding rock plane at the bottom of the new tunnel is obtained through the natural exponential distribution model.

[0011] S4. Determine the range of shear stress in the interlocking rock mass micro-elements: Based on the stress state and geometric parameters in S1, and combined with the calculation formula of shear stress, determine the range of shear stress in the interlocking rock mass micro-elements during the construction of the skew-crossing tunnel.

[0012] S5. Calculate the stress extreme values ​​of the micro-elements in the interbedded rock mass: After determining the range of shear stress, use the extreme value theory to further calculate the stress extreme values ​​of the micro-elements in the interbedded rock mass.

[0013] S6. Set the basic conditions for the safe thickness of the interbedded rock: Based on the shear strength index of the rock mass and the comparative analysis of the shear stress value, set a basic condition that requires that the shear stress of the interbedded rock mass at a certain depth must not exceed its shear strength.

[0014] S7. Calculate the safe thickness of the interbedded rock mass using an iterative method: Adjust the thickness value of the interbedded rock mass in each iteration and recalculate the shear stress until the minimum thickness value of the interbedded rock mass that satisfies the condition that the shear stress is less than the shear strength is found.

[0015] Preferably, the stress function expression is:

[0016]

[0017] Where, σ x σ is the horizontal normal stress along the x-axis; z τ is the vertical normal stress along the z-axis; xz denoted as xoz plane shear stress; A is the coefficient of the natural exponential load function; Q is the distribution function of unloading in the newly constructed tunnel; x is the x-axis coordinate value of the infinitesimal element; z is the z-axis coordinate value of the infinitesimal element.

[0018] Preferably, the expression for calculating the angle θ between the position of the infinitesimal element and the axis of the newly constructed tunnel is as follows:

[0019]

[0020] Where θ is the angle between the position of the infinitesimal element and the axis of the newly built tunnel.

[0021] Preferably, the expression for the shear stress range of the micro-element within the interbedded rock mass is:

[0022]

[0023] Where p is the weight of the overlying rock mass of the new tunnel; g is the gravitational acceleration; H is the thickness of the overlying rock mass of the new tunnel; and t is the sin 2 θ.

[0024] Preferably, the expression for the stress extremum of the micro-element within the interbedded rock mass is as follows:

[0025]

[0026] Preferably, the expression for the safe thickness of the interbedded rock mass in the iterative method calculation is:

[0027] τ xz ≤[τ xz ];

[0028]

[0029] Among them, [τ xz [ ] represents the shear strength of the existing tunnel roof slab.

[0030] Therefore, the present invention adopts the above-mentioned design method for the safe thickness of interbedded rock mass during the construction period of oblique overpass tunnels, and the technical effects are as follows:

[0031] 1. Improve construction safety: By calculating in detail the safe thickness of the interlocking rock mass during the construction of the skewed overpass tunnel, the stress and deformation of the existing tunnel structure are effectively guaranteed to be less than the stress that causes structural failure and the deformation that affects operational safety. This reduces the risk of safety accidents caused by rock instability during construction and protects the lives of construction personnel.

[0032] 2. Optimize construction plan: Based on the calculation results of the safe thickness of the interbedded rock mass, this technology can guide the optimization of the construction plan, including the determination of key parameters such as tunneling speed and support method.

[0033] 3. Scientific guidance and standard formulation: It provides a scientific theoretical basis and calculation method for the construction of skew-crossing tunnels, which helps to promote the improvement and formulation of relevant construction standards. This is of great significance for improving the overall level and quality of tunnel construction in my country. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the calculation model for the stress of interlocking rock micro-elements in the oblique overpass tunnel of the present invention;

[0035] Figure 2 This is a schematic diagram illustrating the transformation relationship between the rectangular coordinate system and the polar coordinate system of this invention. Detailed Implementation

[0036] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0037] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0038] Example 1

[0039] This invention provides a method for designing the safe thickness of interlocking rock mass during the construction of skew-crossing tunnels. Combining the theories of elasticity and rock mechanics, a dynamic equilibrium relationship between the stress and shear strength of the interlocking rock mass is established. The specific steps are as follows:

[0040] S1. Calculate the stress of the interlocking rock micro-element in the oblique overpass tunnel: Determine the geometric parameters of the oblique overpass tunnel, and calculate the stress state of any selected micro-element in the interlocking rock mass according to the stress function expression;

[0041] like Figure 1 As shown, based on the plane strain problem in elasticity, a coordinate system for an oblique tunnel is established, and the stress state of the micro-element is described by a stress function. The stress function must satisfy the compatibility equation. Combined with boundary conditions, the normal stress and shear stress of the micro-element are solved, accurately quantifying the stress distribution inside the interlocking rock mass during construction, and providing basic data for subsequent safe thickness calculations.

[0042] The stress function expression is:

[0043]

[0044] Where, σ x σ is the horizontal normal stress along the x-axis; z τ is the vertical normal stress along the z-axis; xz denoted as xoz plane shear stress; A is the coefficient of the natural exponential load function; Q is the distribution function of unloading in the newly constructed tunnel; x is the x-axis coordinate value of the infinitesimal element; z is the z-axis coordinate value of the infinitesimal element.

[0045] S2. Calculate the angle θ between the position of the infinitesimal element and the axis of the newly built tunnel: (e.g., ...) Figure 2 As shown, based on the geometric layout of the tunnel and the positional relationship of the interbedded rock masses, the specific value of angle θ is calculated through geometric relationship analysis;

[0046] The stress components in the Cartesian coordinate system are converted into radial stress σ in the polar coordinate system. r and tangential stress σ θ Through geometric relationships:

[0047] σ r =σ x cos 2 θ+σ y sin 2 θ+τxy sin2θ;

[0048] σ θ =σ x sin 2 θ+σ y cos 2 θ-τ xy sin2θ;

[0049] The coordinate system transformation is achieved, and the polar coordinate system is more in line with the geometric characteristics of the circular cross-section of the tunnel, which facilitates the analysis of the stress distribution around the tunnel.

[0050] The expression for calculating angle θ is:

[0051]

[0052] Where θ is the angle between the position of the infinitesimal element and the axis of the newly built tunnel.

[0053] S3. Simulate the stress distribution of the surrounding rock plane at the bottom of the new tunnel: Based on the basic assumptions of elasticity, the gravity of the upper rock mass is simplified into a distributed load on the surrounding rock plane at the bottom of the tunnel. The specific form of stress distribution on the surrounding rock plane at the bottom of the new tunnel is obtained through the natural exponential distribution model.

[0054] Due to the excavation of the new tunnel, the gravity field of the original rock mass changes. Assuming that the distributed load on the surrounding rock plane at the tunnel bottom is caused by the gravity of the upper rock mass and distributed according to the natural exponential distribution, based on the assumptions of elasticity:

[0055] Q = PgH;

[0056] S4. Determine the range of shear stress in the interlocking rock mass micro-elements: Based on the stress state and geometric parameters in S1, and combined with the calculation formula of shear stress, determine the range of shear stress in the interlocking rock mass micro-elements during the construction of the skew-crossing tunnel.

[0057] The expression for the shear stress range of a micro-element within a medium-sized rock mass is:

[0058]

[0059] Where P is the weight of the overlying rock mass of the new tunnel; g is the gravitational acceleration; H is the thickness of the overlying rock mass of the new tunnel; and t is the sin 2 θ.

[0060] S5. Calculate the stress extreme values ​​of the micro-elements in the interbedded rock mass: After determining the range of shear stress, use the extreme value theory to further calculate the stress extreme values ​​of the micro-elements in the interbedded rock mass.

[0061] The expression for the stress extremum of the micro-element within the interbedded rock mass is as follows:

[0062]

[0063] S6. Establish basic conditions for the safe thickness of the interbedded rock mass: Based on the shear strength index of the rock mass (i.e., the rock mass's ability to resist shear failure), and in conjunction with the shear stress values ​​calculated in the previous steps, conduct a comparative analysis. Set a basic condition that, at a certain depth, the shear stress of the interbedded rock mass must not exceed its shear strength to ensure the stability of the rock mass.

[0064] τ xz ≤[τ xz ];

[0065] S7. Calculate the safe thickness of the interbedded rock mass using an iterative method: Based on the data and conditions obtained in the previous steps, perform multiple iterative calculations using the formula or related iterative algorithm from S6. In each iteration, adjust the thickness value of the interbedded rock mass and recalculate the shear stress until the minimum interbedded rock mass thickness that meets the safety conditions is found. This value is the desired safe thickness of the interbedded rock mass, providing a scientific basis for optimizing the construction plan.

[0066]

[0067] Among them, [τ xz [ ] represents the shear strength of the existing tunnel roof slab.

[0068] If the shear stress of the interbedded rock mass satisfies the formula in S7 during the unloading of the newly constructed tunnel, then z in the formula is the minimum safe thickness of the interbedded rock mass.

[0069] Taking a newly built oblique overpass tunnel on the Chongqing-Kunming Railway as an example:

[0070] In the construction of a new oblique overpass tunnel on the Chongqing-Kunming Railway, the new tunnel crosses over the existing tunnel at an oblique angle of 34.1°. The engineering geological conditions are complex, with the surrounding rock being Class V rock, possessing a shear strength of 400 kPa and a unit weight of 27 kN / m³. 3 The maximum excavation width of the tunnel is 14.96m, and the burial depth is 33m. The impact of the new tunnel construction on the existing tunnel below needs to be quantified by the unloading length (x), where x is defined as the horizontal projection length from the axis of the new tunnel to the axis of the existing tunnel below. By designing the safety thickness of the interbedded rock mass, the stress and deformation of the existing tunnel structure during construction are ensured to be controlled within a safe range, while the construction plan and monitoring strategy are optimized.

[0071] A rectangular coordinate system is established with the axis of the newly constructed tunnel as the reference, and the origin is located at the center of the tunnel. Considering an oblique angle of 34.1°, the existing tunnel position is converted into a relative coordinate system. Based on the plane strain theory of elasticity, assuming that the stress state of the infinitesimal element satisfies the compatibility equation, the normal stress and shear stress are solved using stress functions. Combining the tunnel geometric parameters and rock mechanics parameters, the stress distribution on the surface of the intercalary rock mass is preliminarily estimated, providing input for subsequent polar coordinate transformation.

[0072] The angle θ is calculated based on the conversion relationship between rectangular and polar coordinates. θ is defined as the angle between the position of the infinitesimal element and the axis of the newly built tunnel, taking into account the correction for the oblique angle. The stress components in the rectangular coordinate system are converted into radial and tangential stresses in the polar coordinate system. The stress components in the polar coordinate system better reflect the characteristics of the tunnel cross-section, making it easier to analyze the stress distribution around the tunnel.

[0073] Assuming the plane stress in the surrounding rock at the tunnel bottom is caused by the gravity of the upper rock mass, it can be described using a natural exponential distribution model:

[0074] Q = pgH;

[0075] Based on the polar coordinate stress transformation results and the gravity field distribution model, the shear stress expression was derived, the shear stress time history curves of key sections of the interlocking rock mass were extracted, and the range of maximum shear stress was determined. In this project, the maximum shear stress on the surface of the interlocking rock mass is 230.44 kPa, located at the junction of the sidewall of the new tunnel and the roof of the existing tunnel.

[0076] Differentiate the shear stress expression and set the derivative to zero to obtain the coordinates of the extreme points. Substitute these coordinates into the shear stress expression to calculate the maximum shear stress value. In this project, the maximum shear stress occurs in the middle of the interbedded rock mass, with a value of 230.44 kPa. Locate the high-risk area of ​​the interbedded rock mass to guide the implementation of local reinforcement measures.

[0077] A balance relationship between shear stress and rock mass shear strength was established. In this project, the shear strength of the interbedded rock mass is 400 kPa, compared to a maximum shear stress of 230.44 kPa, which meets the safety requirements.

[0078] The thickness z of the interbedded rock mass was gradually adjusted using a bisection method until the safety conditions were met. After five iterations, the minimum safe thickness was determined to be 15m. At this point, the shear stress of the interbedded rock mass was 230.44kPa, which was less than the shear strength of 400kPa, thus meeting the safety requirements. The distance from the working face to the section where the safe thickness was calculated must exceed 1.5 times the safe thickness (i.e., 22.5m) to avoid instability caused by dynamic construction disturbances.

[0079] Using steps S1-S5 of this method, the shear stress of the interstitial rock mass was calculated to be 230.44 kPa. Iterative calculations determined the minimum safe thickness to be 15 m. Construction control requirements stipulated that the distance from the tunnel face to the calculated safe thickness section should exceed 1.5 times the safe thickness, i.e., 22.5 m. Field monitoring showed that the deformation of the interstitial rock mass was controlled within 1.19 mm, and the stress increase in the existing tunnel structure was less than 15%, verifying the effectiveness of the method.

[0080] Therefore, the present invention adopts the above-mentioned design method for the safe thickness of the interbedded rock mass during the construction period of the oblique overpass tunnel. By calculating the stress of the interbedded rock micro-elements, simulating the stress distribution of the surrounding rock at the bottom of the new tunnel, determining the range and extreme value of shear stress, and setting safety conditions, the minimum thickness of the interbedded rock mass that meets the safety requirements is obtained by iterative calculation, so as to ensure the stable operation of the existing tunnel and the construction safety of the new tunnel.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for designing the safe thickness of interbedded rock mass during the construction of an oblique overpass tunnel, characterized in that, Includes the following steps: S1. Calculate the stress of the interlocking rock micro-element in the oblique overpass tunnel: Determine the geometric parameters of the oblique overpass tunnel, and calculate the stress state of any selected micro-element in the interlocking rock mass according to the stress function expression; S2. Calculate the angle θ between the position of the micro-element and the axis of the newly built tunnel: Based on the geometric layout of the tunnel and the positional relationship of the interbedded rock mass, calculate the specific value of the angle θ through geometric relationship analysis; S3. Simulate the stress distribution of the surrounding rock plane at the bottom of the new tunnel: Based on the basic assumptions of elasticity, the gravity of the upper rock mass is simplified into the distributed load of the surrounding rock plane at the bottom of the new tunnel. The specific form of stress distribution of the surrounding rock plane at the bottom of the new tunnel is obtained through the natural exponential distribution model. S4. Determine the range of shear stress in the interlocking rock mass micro-elements: Based on the stress state and geometric parameters in S1, and combined with the calculation formula of shear stress, determine the range of shear stress in the interlocking rock mass micro-elements during the construction of the skew-crossing tunnel. S5. Calculate the stress extreme values ​​of the micro-elements in the interbedded rock mass: After determining the range of shear stress, use the extreme value theory to further calculate the stress extreme values ​​of the micro-elements in the interbedded rock mass. S6. Set the basic conditions for the safe thickness of the interbedded rock: Based on the shear strength index of the rock mass and the comparative analysis of the shear stress value, set a basic condition that requires that the shear stress of the interbedded rock mass at a certain depth must not exceed its shear strength. S7. Calculate the safe thickness of the interbedded rock mass using an iterative method: Adjust the thickness value of the interbedded rock mass in each iteration and recalculate the shear stress until the minimum thickness value of the interbedded rock mass that satisfies the condition that the shear stress is less than the shear strength is found.

2. The method for designing the safe thickness of interbedded rock mass during the construction of an oblique overpass tunnel according to claim 1, characterized in that, The stress function expression is: Where, σ x σ is the horizontal normal stress along the x-axis; z τ is the vertical normal stress along the z-axis; xz denoted as xoz plane shear stress; A is the coefficient of the natural exponential load function; Q is the distribution function of unloading in the newly constructed tunnel; x is the x-axis coordinate value of the infinitesimal element; z is the z-axis coordinate value of the infinitesimal element.

3. The method for designing the safe thickness of interbedded rock mass during the construction of an oblique overpass tunnel according to claim 1, characterized in that, The expression for calculating the angle θ between the position of the infinitesimal element and the axis of the newly built tunnel is as follows: Where θ is the angle between the position of the infinitesimal element and the axis of the newly built tunnel.

4. The method for designing the safe thickness of interbedded rock mass during the construction of an oblique overpass tunnel according to claim 1, characterized in that, The expression for the shear stress range of a micro-element within a medium-sized rock mass is: Where p is the weight of the overlying rock mass of the new tunnel; g is the gravitational acceleration; H is the thickness of the overlying rock mass of the new tunnel; and t is the sin 2 θ.

5. The method for designing the safe thickness of interbedded rock mass during the construction of an oblique overpass tunnel according to claim 1, characterized in that, The expression for the stress extremum of the micro-element within the interbedded rock mass is as follows:

6. The method for designing the safe thickness of interbedded rock mass during the construction of an oblique overpass tunnel according to claim 1, characterized in that, The expression for the safe thickness of the interbedded rock mass in the iterative method calculation is: t xz ≤[τ xz ]; Among them, [τ xz [ ] represents the shear strength of the existing tunnel roof slab.

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