A high ground stress water-rich soft rock tunnel double-layer initial support surrounding rock deformation calculation method

Abstract

The application discloses a kind of high ground stress water-rich soft rock tunnel double-layer initial support surrounding rock deformation calculation methods, including setting high ground stress water-rich soft rock tunnel double-layer initial support surrounding rock deformation calculation's assumed condition;Establish soft weak surrounding rock mechanics model, determine plastic surrounding rock dilatancy law;Establish the basic equation of circular tunnel soft weak surrounding rock elastoplasticity analysis;Get the stress distribution of elastic zone surrounding rock, strain distribution;After the first layer initial support is made, the viscoelastic plastic distribution of surrounding rock is calculated;After the second layer initial support is made, the viscoelastic plastic distribution of surrounding rock is calculated;The radius of plastic softening zone of surrounding rock, plastic residual zone radius is calculated.The application is used to solve the problem that double-layer initial support structure cannot be theoretically analyzed and calculated in the prior art, realize the scientific calculation of the surrounding rock deformation of high ground stress water-rich soft rock tunnel double-layer initial support, which is beneficial to the rational design of double-layer initial support technology, and further guides the purpose of on-site engineering construction.

Description

Technical Field

[0001] This invention relates to the field of surrounding rock deformation calculation, specifically to a method for calculating the deformation of surrounding rock in the initial support of a double-layer soft rock tunnel with high ground stress and abundant water. Background Technology

[0002] With the steady progress of infrastructure construction in western my country, an increasing number of underground engineering projects, such as highway and railway tunnels, are encountering large deformations in weak surrounding rock during construction. The construction of tunnels in high-stress, water-rich soft rock is particularly affected by multiple factors, including high ground stress, weak rock lithology, groundwater softening, and insufficient resistance of the initial support structure. Under high ground stress conditions, the surrounding rock maintains good integrity for a short period after excavation, exhibiting large deformation and a rapid deformation rate, primarily characterized by compressive deformation, mainly elastic and plastic deformation. During the construction of high-stress, water-rich soft rock tunnels, as the excavation face continues to advance, the continuous release of ground stress and the softening effect of groundwater cause the surrounding rock near the excavation outline to gradually loosen and fracture.

[0003] Furthermore, under high ground stress conditions, the creep phenomenon of the surrounding rock is obvious, and a certain amount of deformation still occurs in the surrounding rock during the later stages of construction. When the resistance of the initial support structure is insufficient, it cannot effectively control the instantaneous deformation of the surrounding rock in a short period of time, nor can it effectively control the rheological deformation of the surrounding rock over a long period of time.

[0004] In existing technologies, due to the multi-factor influence on the large deformation of surrounding rock in high-stress soft rock tunnels, a double-layer initial support structure is typically used during construction to achieve a "release-resistance combination" support effect. Existing research on double-layer initial support for soft rock tunnels largely focuses on numerical simulation and field monitoring analysis, with few studies elucidating the support mechanism of double-layer initial support from the perspective of large deformation in soft rock, nor has any research theoretically verified the support effect of double-layer initial support. This results in existing technologies being unable to accurately grasp the reserved deformation amount of the double-layer initial support structure and making it difficult to accurately determine the timing of its construction.

[0005] Therefore, when using double-layer initial support to increase the support resistance, it is necessary to combine the actual engineering situation and scientifically calculate the surrounding rock deformation of double-layer initial support for water-rich soft rock tunnels with high ground stress. Summary of the Invention

[0006] The purpose of this invention is to provide a method for calculating the deformation of the surrounding rock in the double-layer initial support of a high-stress, water-rich soft rock tunnel. This method addresses the problem in existing technologies where it is difficult to explain the support mechanism of double-layer initial support from the perspective of large deformation in soft rock, and where it is impossible to perform theoretical analysis and calculation of the double-layer initial support structure. This method enables the scientific calculation of the deformation of the surrounding rock in the double-layer initial support of a high-stress, water-rich soft rock tunnel, which is beneficial for the rational design of the double-layer initial support process and, consequently, for guiding on-site engineering construction.

[0007] This invention is achieved through the following technical solution:

[0008] A method for calculating the deformation of the surrounding rock in the initial double-layer support of a high-stress, water-rich soft rock tunnel includes the following steps:

[0009] S1. Set the assumptions for calculating the deformation of the surrounding rock in the initial double-layer support of a high-stress, water-rich soft rock tunnel.

[0010] S2. Establish a mechanical model for weak surrounding rock and determine the expansion law of plastic surrounding rock;

[0011] S3. Establish the basic equations for the elastic-plastic analysis of weak surrounding rock in circular tunnels;

[0012] S4. Perform elastic analysis of the surrounding rock during tunnel excavation to obtain the stress distribution and strain distribution of the surrounding rock in the elastic zone.

[0013] S5. Calculate the viscoelastic-plastic distribution of the surrounding rock after the first layer of initial support is installed.

[0014] S6. Calculate the viscoelastic-plastic distribution of the surrounding rock after the second layer of initial support is installed.

[0015] S7. Calculate the radius of the plastic softening zone and the radius of the plastic residual zone of the surrounding rock.

[0016] To address the limitations of existing technologies in explaining the support mechanism of double-layer initial support from the perspective of large deformation in soft rock, and the inability to theoretically analyze and calculate the double-layer initial support structure, which leads to difficulties in accurately determining the reserved deformation amount and the timing of its construction, this invention proposes a method for calculating the deformation of the surrounding rock in double-layer initial support for high-stress, water-rich soft rock tunnels. This method first establishes assumptions for calculating the deformation of the surrounding rock in double-layer initial support for high-stress, water-rich soft rock tunnels to facilitate subsequent calculations. Then, a mechanical model of the weak surrounding rock is established, and the expansion law of the plastic surrounding rock is determined through this model. Next, the basic equations for the elastoplastic analysis of the weak surrounding rock in circular tunnels are established. Based on these basic equations, an elastic analysis of the surrounding rock is performed instantaneously during tunnel excavation, thereby obtaining the stress and strain distribution of the surrounding rock in the elastic zone. Then, following the construction sequence, the viscoelastic-plastic distribution of the surrounding rock after the first layer of initial support is constructed is calculated, followed by the viscoelastic-plastic distribution of the surrounding rock after the second layer of initial support is constructed. Finally, based on the surrounding rock displacement data, the radius of the plastic softening zone and the radius of the plastic residual zone of the surrounding rock can be calculated.

[0017] It can be seen that this application has creatively calculated and analyzed the double-layer initial support mechanism under large deformation of the surrounding rock of a water-rich soft rock tunnel with high ground stress. It can verify the support effect of the double-layer initial support structure from a theoretical perspective, and thus guide the construction design and on-site operation of the double-layer initial support technology. It provides a scientific and reasonable reference for the reserved deformation amount and construction timing of the double-layer initial support structure.

[0018] Furthermore, in step S1, the assumed conditions include:

[0019] The tunnel has a circular cross-section; the surrounding rock is homogeneous, isotropic, and incompressible; the lateral pressure coefficient is 1; the permeability coefficient is the same in all directions within the rock mass; the seepage water is a single-phase, incompressible Newtonian fluid, and the seepage direction is radial; the water head at the tunnel wall is 0; the distance from the tunnel is R... E Outside the area, the external water head is the same as the external water head of the original seepage field.

[0020] Furthermore, in step S2:

[0021] The established mechanical model for weak surrounding rock is as follows:

[0022] ;

[0023] In the formula: These are the softening values ​​for cohesion, angle of internal friction, and elastic modulus, respectively. These are the initial values ​​of cohesion, angle of internal friction, and elastic modulus, respectively. c M φ M E These are the softening modulus of cohesion, internal friction angle, and elastic modulus, respectively, where ε is the cumulative strain within the rock. p ε represents the cumulative value of the rock entering a plastic softening state. b This represents the cumulative value of the rock entering the plastic residual state.

[0024] Based on the monitoring data and wave velocity distribution of the surrounding rock during the entire process of large deformation in soft rock tunnels, it can be seen that the surrounding rock of the tunnel entering the plastic residual state is loose and fractured, and its bearing capacity decreases. This part of the surrounding rock deformation is an important component of the large deformation of soft rock. When the rock enters the plastic softening state, both the strength and stiffness parameters decrease with the increase of strain accumulation; when the rock enters the plastic residual state, both the strength and stiffness parameters are residual values. The soft surrounding rock mechanical model established in this scheme can reflect both the compression deformation of the surrounding rock after the excavation of a high-stress soft rock tunnel and the loosening deformation of the surrounding rock in the later stage.

[0025] Furthermore, in step S2, the expansion law of the plastic surrounding rock is as follows:

[0026] ;

[0027] In the formula: β2 is the expansion coefficient of the plastic residual region, β2=1+µ, µ=0.3~0.5; The radial strain is the residual plastic strain of the surrounding rock of the tunnel. The circumferential strain is the residual plastic state of the surrounding rock in the tunnel.

[0028] Furthermore, in step S3, the basic equations for the elastoplastic analysis of the weak surrounding rock of the circular tunnel include: equilibrium differential equations, geometric equations, and physical equations.

[0029] The equilibrium differential equation is:

[0030] ;

[0031] In the formula: r is the radius of the surrounding rock of the circular tunnel; Radial stress in the surrounding rock of the tunnel; For the circumferential stress of the tunnel surrounding rock; The equivalent pore water pressure coefficient of the rock; The specific gravity of water; R0 represents the external water head of the original seepage field; R0 is the excavation radius of the circular tunnel.

[0032] Since the buoyancy component accounts for a relatively small proportion of the seepage water pressure, this scheme does not consider the buoyancy component of the seepage water pressure for the time being; therefore, the equilibrium differential equation given in this scheme is an equilibrium differential equation that considers the seepage volume force.

[0033] The geometric equation is:

[0034] ;

[0035] In the formula: Radial strain of the tunnel surrounding rock; U represents the circumferential strain of the tunnel surrounding rock; u represents the displacement of the tunnel surrounding rock.

[0036] The physical equation is:

[0037] ;

[0038] In the formula: is Poisson's ratio; E represents the elastic modulus.

[0039] Furthermore, in step S4:

[0040] The stress distribution of the surrounding rock in the elastic zone is as follows:

[0041] ;

[0042] ;

[0043] In the formula: Represents the radial stress of the surrounding rock in the elastic zone when it is in an elastic state; P0 represents the circumferential stress of the surrounding rock in the elastic zone under elastic conditions; t is time; V is the tunnel excavation rate; R L To determine the area affected by tunnel excavation, take ;P w Let r be the pore water pressure at radius r;

[0044] The strain distribution of the surrounding rock in the elastic zone is as follows:

[0045] ;

[0046] ;

[0047] In the formula: The radial viscoelastic strain of the surrounding rock in the elastic zone; The circumferential viscoelastic strain represents the surrounding rock in the elastic zone; η is the viscosity modulus. It is Poisson's ratio.

[0048] At the moment of tunnel excavation, the surrounding rock is in an elastic state and has not yet entered the plastic state. The deformation is mainly viscous and elastic. Therefore, the stress and strain distribution of the surrounding rock in the elastic zone can be calculated based on the model provided in this scheme.

[0049] Furthermore, in step S5, after the first layer of initial support is applied, the viscoelastic-plastic distribution of the surrounding rock includes: the stress state of the surrounding rock in the elastic zone, the strain distribution of the surrounding rock in the elastic zone, the radial and circumferential distribution of the surrounding rock in the plastic softening zone, and the displacement equation of the surrounding rock in the plastic softening zone.

[0050] In this scheme, based on the effective elastic solution and considering the action of pore water pressure, combined with stress boundary conditions, the stress state of the surrounding rock in the elastic zone can be obtained. After removing the original rock stress component, the strain distribution of the surrounding rock in the elastic zone can be calculated.

[0051] Furthermore, the stress state of the surrounding rock in the elastic zone is as follows:

[0052] ;

[0053] ;

[0054] In the formula: R represents the radial stress at the elastoplastic interface of the tunnel surrounding rock; p η is the radius of the plastic softening zone; η is the viscous modulus.

[0055] The strain distribution of the surrounding rock in the elastic zone is as follows:

[0056] ;

[0057] ;

[0058] The radial and circumferential distribution of the surrounding rock in the plastic softening zone is as follows:

[0059] ;

[0060] ;

[0061] In the formula: Represents the radial stress of the surrounding rock in the plastic softening zone; Represents the circumferential stress of the surrounding rock in the plastic softening zone;

[0062] ; This represents the cohesion softening value of the surrounding rock in the plastic softening zone. This represents the softening value of the internal friction angle of the surrounding rock in the plastic softening zone.

[0063] The displacement equation for the surrounding rock in the plastic softening zone is:

[0064] ;

[0065] In the formula: This represents the displacement of the surrounding rock in the plastic softening zone; The expansion coefficient of the plastic softening zone; To calculate the coefficients.

[0066] Furthermore, in the displacement equation of the surrounding rock in the plastic softening zone, the expansion coefficient of the plastic softening zone is calculated using the following formula. Calculation coefficients :

[0067] β1 = (1 + sinΨ) / (1 - sinΨ);

[0068] ;

[0069] In the formula: This refers to the dilatation angle of the rock mass.

[0070] Furthermore, in step S6, after the second layer of initial support is constructed, the viscoelastic-plastic distribution of the surrounding rock includes: radial stress distribution and circumferential stress distribution of the surrounding rock in the plastic residual zone, and the displacement calculation equation of the surrounding rock in the plastic residual zone.

[0071] The radial stress distribution and circumferential stress distribution of the surrounding rock in the residual zone of the plastic zone are as follows:

[0072] ;

[0073] ;

[0074] In the formula: Represents the radial stress of the surrounding rock in the plastic residual zone; Represents the circumferential stress of the surrounding rock in the plastic residual zone; ; This represents the cohesion softening value of the surrounding rock in the plastic softening zone. This represents the softening value of the internal friction angle of the surrounding rock in the plastic softening zone. =Support resistance provided by the double-layer initial support structure;

[0075] The equation for calculating the displacement of the surrounding rock in the plastic residual zone is as follows:

[0076] ;

[0077] In the formula: Represents the displacement of the surrounding rock in the plastic residual zone; R b The radius of the plastic residual region; This represents the residual elastic modulus of the surrounding rock in the plastic residual zone.

[0078] Furthermore, in step S7, the radius R of the plastic softening zone is calculated using the following formula. p Radius R of the plastic residual zone b :

[0079] ;

[0080] ;

[0081] In the formula: ; φ0 is the initial value of the cohesion of the tunnel surrounding rock; φ0 is the initial value of the friction angle of the tunnel surrounding rock. This represents the residual cohesion value of the surrounding rock in the tunnel. This is the cohesive softening modulus.

[0082] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0083] 1. This invention provides a method for calculating the deformation of the surrounding rock in the initial double-layer support of a water-rich soft rock tunnel under high ground stress. It creatively establishes a viscoelastic-plastic analytical model for the initial double-layer support of a soft rock tunnel in a water-rich environment. This model can scientifically calculate the deformation of the surrounding rock in the initial double-layer support of a water-rich soft rock tunnel under high ground stress, thereby guiding the construction design and on-site operation of the initial double-layer support process.

[0084] 2. The present invention provides a method for calculating the deformation of the surrounding rock in the initial double-layer support of a high-stress, water-rich soft rock tunnel. This method can provide scientific and reasonable guidance for the reserved deformation amount of the initial double-layer support structure and the timing of its construction, which is of great significance for on-site engineering construction. Attached Figure Description

[0085] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings:

[0086] Figure 1 This is a flowchart illustrating a specific embodiment of the present invention;

[0087] Figure 2 This is a schematic diagram comparing theoretical calculation results with on-site monitoring results in a specific embodiment of the present invention. Detailed Implementation

[0088] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0089] Example 1:

[0090] like Figure 1 The method for calculating the deformation of the surrounding rock in the initial double-layer support of a high-stress, water-rich soft rock tunnel, as shown, includes the following steps:

[0091] Step S1: Set the assumptions for calculating the deformation of the surrounding rock in the initial double-layer support of a high-stress, water-rich soft rock tunnel.

[0092] The assumptions in this embodiment include:

[0093] The tunnel cross-section is circular; the tunnel excavation radius is R0, and the radius of the plastic softening zone is R. p The radius of the plastic residual region is R. b The surrounding rock of the tunnel is a homogeneous, isotropic, and incompressible material. Neglecting body forces, the initial in-situ stress is P0, the lateral pressure coefficient is 1, and the permeability coefficient is uniform throughout the rock mass. The seepage water is a single-phase, incompressible Newtonian fluid, with radial flow predominantly. The water head at the inner wall is 0. The distance from the tunnel is R. E Outside the range, the external water head is the same as the original external water head h0 of the seepage field.

[0094] Step S2: Establish a mechanical model of weak surrounding rock and determine the expansion law of plastic surrounding rock.

[0095] In this embodiment, the established mechanical model for weak surrounding rock is as follows:

[0096] ;

[0097] In the formula: These are the softening values ​​for cohesion, angle of internal friction, and elastic modulus, respectively. These are the initial values ​​of cohesion, angle of internal friction, and elastic modulus, respectively. c M φM E These are the softening modulus of cohesion, internal friction angle, and elastic modulus, respectively, where ε is the cumulative strain within the rock. p ε represents the cumulative value of the rock entering a plastic softening state. b This represents the cumulative value of the rock entering the plastic residual state.

[0098] In this embodiment, the expansion law of the plastic surrounding rock is as follows:

[0099] ;

[0100] In the formula: β2 is the expansion coefficient of the plastic residual region, β2=1+µ, µ=0.3~0.5; The radial strain is the residual plastic strain of the surrounding rock of the tunnel. The circumferential strain is the residual plastic state of the surrounding rock in the tunnel.

[0101] Step S3: Establish the basic equations for the elastic-plastic analysis of weak surrounding rock in a circular tunnel.

[0102] The basic equations for the elastoplastic analysis of weak surrounding rock in a circular tunnel include: equilibrium differential equations, geometric equations, and physical equations.

[0103] The equilibrium differential equation is:

[0104] ;

[0105] In the formula: r is the radius of the surrounding rock of the circular tunnel; Radial stress in the surrounding rock of the tunnel; For the circumferential stress of the tunnel surrounding rock; The equivalent pore water pressure coefficient of the rock; The specific gravity of water; R0 represents the external water head of the original seepage field; R0 is the excavation radius of the circular tunnel.

[0106] The geometric equation is:

[0107] ;

[0108] In the formula: Radial strain of the tunnel surrounding rock; denoted as circumferential strain of the tunnel surrounding rock; u represents the displacement of the tunnel surrounding rock.

[0109] The physical equation is:

[0110] ;

[0111] In the formula: is Poisson's ratio; E represents the elastic modulus.

[0112] Step S4: Perform elastic analysis of the surrounding rock during tunnel excavation to obtain the stress distribution and strain distribution of the surrounding rock in the elastic zone.

[0113] In this embodiment, the stress distribution of the surrounding rock in the elastic zone is as follows:

[0114] ;

[0115] ;

[0116] In the formula: Represents the radial stress of the surrounding rock in the elastic zone when it is in an elastic state; P0 represents the circumferential stress of the surrounding rock in the elastic zone under elastic conditions; t is time; V is the tunnel excavation rate; R L To determine the area affected by tunnel excavation, take ;P w Let be the pore water pressure at a radius of r.

[0117] In this embodiment, the strain distribution of the surrounding rock in the elastic zone is as follows:

[0118] ;

[0119] ;

[0120] In the formula: The radial viscoelastic strain of the surrounding rock in the elastic zone; The circumferential viscoelastic strain represents the surrounding rock in the elastic zone; η is the viscosity modulus. It is Poisson's ratio.

[0121] Step S5: Calculate the viscoelastic-plastic distribution of the surrounding rock after the first layer of initial support is installed. Specifically, this includes: the stress state of the surrounding rock in the elastic zone, the strain distribution of the surrounding rock in the elastic zone, the radial and circumferential distribution of the surrounding rock in the plastic softening zone, and the displacement equation of the surrounding rock in the plastic softening zone after the first layer of initial support is installed.

[0122] In this embodiment, the stress state of the surrounding rock in the elastic zone is as follows:

[0123] ;

[0124] ;

[0125] In the formula: R represents the radial stress at the elastoplastic interface of the tunnel surrounding rock; p η is the radius of the plastic softening zone; η is the viscous modulus.

[0126] In this embodiment, the strain distribution of the surrounding rock in the elastic zone is as follows:

[0127] ;

[0128] .

[0129] In this embodiment, the radial and circumferential distribution of the surrounding rock in the plastic softening zone is as follows:

[0130] ;

[0131] ;

[0132] In the formula: Represents the radial stress of the surrounding rock in the plastic softening zone; Represents the circumferential stress of the surrounding rock in the plastic softening zone; ; This represents the cohesion softening value of the surrounding rock in the plastic softening zone. This represents the softening value of the internal friction angle of the surrounding rock in the plastic softening zone.

[0133] In this embodiment, the displacement equation of the surrounding rock in the plastic softening zone is:

[0134] ;

[0135] In the formula: This represents the displacement of the surrounding rock in the plastic softening zone; The expansion coefficient of the plastic softening zone; To calculate the coefficients.

[0136] in, , Calculated using the following formula:

[0137] ;

[0138] ;

[0139] In the formula: Ψ is the rock mass dilatation angle.

[0140] Step S6: Calculate the viscoelastic-plastic distribution of the surrounding rock after the second layer of initial support is installed. Specifically, this includes: the radial and circumferential stress distribution of the surrounding rock in the plastic residual zone after the second layer of initial support is installed, and the calculation equation for the displacement of the surrounding rock in the plastic residual zone.

[0141] In this embodiment, the radial stress distribution and circumferential stress distribution of the surrounding rock in the residual zone of the plastic zone are as follows:

[0142] ;

[0143] ;

[0144] In the formula: Represents the radial stress of the surrounding rock in the plastic residual zone; Represents the circumferential stress of the surrounding rock in the plastic residual zone; ; This represents the cohesion softening value of the surrounding rock in the plastic softening zone. This represents the softening value of the internal friction angle of the surrounding rock in the plastic softening zone. =Support resistance provided by the double-layer initial support structure.

[0145] In this embodiment, the equation for calculating the displacement of the surrounding rock in the plastic residual zone is:

[0146] ;

[0147] In the formula: Represents the displacement of the surrounding rock in the plastic residual zone; R b The radius of the plastic residual region; This represents the residual elastic modulus of the surrounding rock in the plastic residual zone.

[0148] Step S7: Calculate the radius R of the plastic softening zone of the surrounding rock. p Radius R of the plastic residual zone b .

[0149] ;

[0150] ;

[0151] In the formula: ; φ0 is the initial value of the cohesion of the tunnel surrounding rock; φ0 is the initial value of the friction angle of the tunnel surrounding rock. This represents the residual cohesion value of the surrounding rock in the tunnel. This is the cohesive softening modulus.

[0152] Example 2:

[0153] This embodiment uses the calculation method described in Embodiment 1 to conduct on-site verification for a certain tunnel.

[0154] Located on the eastern side of the Lancang River active fault zone, the tunnel is 13.39 km long. The tunnel site is primarily composed of mudstone, shale, and sandstone, typical of the "Western Yunnan Red Beds." The maximum horizontal principal stress in the traversed area is 12-20 MPa, the minimum is 8-14 MPa, and the vertical principal stress is 13-20 MPa, indicating a high-stress environment. The tunnel frequently traverses complex strata and water-rich areas, characterized by large water inflow and a wide-ranging groundwater influence. Water is present year-round at the tunnel entrances / exits and within the tunnel body. Most of the surface water flow originates from atmospheric precipitation, with a smaller portion originating from groundwater. Groundwater is found in sandstone and fault fracture zones, with a ridge acting as a watershed, branching east and west. Excavation revealed that the tunnel face consists of mudstone interbedded with sandstone, predominantly mudstone. The rock is soft, with well-developed joints and fissures, and is prone to loosening and fracturing. When exposed to groundwater, the rock mass softens, leading to a decrease in its physical and mechanical properties and stability, resulting in deformation and instability.

[0155] The tunnel initially employed single-layer initial support. During the construction of the main tunnel and pilot tunnel, significant deformation occurred in the surrounding rock. Specific on-site monitoring data revealed that the deformation rate of the surrounding rock was highest in the first 30 days of tunnel excavation, and the proportion of deformation to total deformation was significant during this period. The deformation at the arch crown and arch waist was 68.2 cm and 70.3 cm, respectively. By the 70th day, these figures had increased to 70.8 cm and 74.3 cm, respectively. This significant deformation of the tunnel's surrounding rock was accompanied by cracking of the initial support at the sidewalls, peeling and spalling of the initial support at the arch, and bulging and twisting deformation at the steel arch frame connections.

[0156] To effectively control large deformations of the surrounding rock, the tunnel adopted a deformation control measure of "double-layer initial support + subsequent shallow grouting to fill the gaps." The double-layer initial support increased the stiffness of the initial support, providing greater support resistance. Through this deformation control measure, effective control of the surrounding rock deformation was achieved. By the time of the secondary lining construction, the maximum deformation of the surrounding rock in this section was below 20 cm. The construction parameters for the double-layer initial support and secondary lining are shown in Table 1.

[0157] Table 1 Construction parameters for double-layer initial support and secondary lining

[0158]

[0159] The theoretical calculation results obtained using the calculation method described in this application are compared with the surrounding rock displacement data obtained from field monitoring. The comparison results are as follows: Figure 2 As shown, the theoretical calculation results based on this application are in high agreement with the on-site monitoring data of the double-layer initial support of the tunnel, proving that the method of this application can be used for surrounding rock deformation prediction and has practical engineering value.

[0160] It should be noted that, in this document, terms such as “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0161] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for calculating the deformation of surrounding rock in the initial double-layer support of a high-stress, water-rich soft rock tunnel, characterized in that... Includes the following steps: S1. Set the assumptions for calculating the deformation of the surrounding rock in the initial double-layer support of a high-stress, water-rich soft rock tunnel. S2. Establish a mechanical model for weak surrounding rock and determine the expansion law of plastic surrounding rock; S3. Establish the basic equations for the elastic-plastic analysis of weak surrounding rock in circular tunnels; S4. Perform elastic analysis of the surrounding rock during tunnel excavation to obtain the stress distribution and strain distribution of the surrounding rock in the elastic zone. S5. Calculate the viscoelastic-plastic distribution of the surrounding rock after the first layer of initial support is installed. S6. Calculate the viscoelastic-plastic distribution of the surrounding rock after the second layer of initial support is installed. S7. Calculate the radius of the plastic softening zone and the radius of the plastic residual zone of the surrounding rock.

2. The method for calculating the deformation of surrounding rock in the initial double-layer support of a high-stress, water-rich soft rock tunnel according to claim 1, is characterized in that, In step S1, the assumed conditions include: The tunnel has a circular cross-section; the surrounding rock is homogeneous, isotropic, and incompressible; the lateral pressure coefficient is 1; the permeability coefficient is the same in all directions within the rock mass; the seepage water is a single-phase, incompressible Newtonian fluid, and the seepage direction is radial; the water head at the tunnel wall is 0; the distance from the tunnel is R... E Outside the area, the external water head is the same as the external water head of the original seepage field.

3. The method for calculating the deformation of the surrounding rock in the initial double-layer support of a high-stress, water-rich soft rock tunnel according to claim 1, is characterized in that... In step S2: The established mechanical model for weak surrounding rock is as follows: ； In the formula: c′, φ′, and E′ are the softening values ​​of cohesion, internal friction angle, and elastic modulus, respectively; c0, φ0, and E0 are the initial values ​​of cohesion, internal friction angle, and elastic modulus, respectively; M c M φ M E These are the softening modulus of cohesion, internal friction angle, and elastic modulus, respectively, where ε is the cumulative strain within the rock. p ε represents the cumulative value of the rock entering a plastic softening state. b This represents the cumulative value of the rock entering a plastic residual state; The expansion law of the plastic surrounding rock is as follows: ； In the formula: β2 is the expansion coefficient of the plastic residual region, β2=1+µ, µ=0.3~0.5; The radial strain is the residual plastic strain of the surrounding rock of the tunnel. The circumferential strain is the residual plastic state of the surrounding rock in the tunnel.

4. The method for calculating the deformation of the surrounding rock in the initial double-layer support of a high-stress, water-rich soft rock tunnel according to claim 2, is characterized in that... In step S3, the basic equations for the elastic-plastic analysis of the weak surrounding rock of the circular tunnel include: equilibrium differential equations, geometric equations, and physical equations. The equilibrium differential equation is: ； In the formula: r is the radius of the surrounding rock of the circular tunnel; Radial stress in the surrounding rock of the tunnel; For the circumferential stress of the tunnel surrounding rock; The equivalent pore water pressure coefficient of the rock; The specific gravity of water; R0 is the external water head of the original seepage field; R0 is the excavation radius of the circular tunnel. The geometric equation is: ； In the formula: Radial strain of the tunnel surrounding rock; U represents the circumferential strain of the tunnel surrounding rock; u represents the displacement of the tunnel surrounding rock. The physical equation is: ； In the formula: is Poisson's ratio; E represents the elastic modulus.

5. The method for calculating the deformation of the surrounding rock in the double-layer initial support of a high-stress, water-rich soft rock tunnel according to claim 4, is characterized in that... In step S4: The stress distribution of the surrounding rock in the elastic zone is as follows: ； ； In the formula: Represents the radial stress of the surrounding rock in the elastic zone when it is in an elastic state; P0 represents the circumferential stress of the surrounding rock in the elastic zone under elastic conditions; P0 is the initial in-situ stress; t is time. V represents the tunnel excavation rate; R L To determine the area affected by tunnel excavation, take ;P w Let be the pore water pressure at a radius of r; The strain distribution of the surrounding rock in the elastic zone is as follows: ； ； In the formula: The radial viscoelastic strain of the surrounding rock in the elastic zone; The circumferential viscoelastic strain represents the surrounding rock in the elastic zone; η is the viscosity modulus. It is Poisson's ratio.

6. The method for calculating the deformation of the surrounding rock in the initial double-layer support of a high-stress, water-rich soft rock tunnel according to claim 5, is characterized in that... In step S5, after the first layer of initial support is installed, the viscoelastic-plastic distribution of the surrounding rock includes: the stress state of the surrounding rock in the elastic zone, the strain distribution of the surrounding rock in the elastic zone, the radial and circumferential distribution of the surrounding rock in the plastic softening zone, and the displacement equation of the surrounding rock in the plastic softening zone.

7. The method for calculating the deformation of surrounding rock in the initial double-layer support of a high-stress, water-rich soft rock tunnel according to claim 6, is characterized in that... The stress state of the surrounding rock in the elastic zone is as follows: ； ； In the formula: R represents the radial stress at the elastoplastic interface of the tunnel surrounding rock; p η is the radius of the plastic softening zone; η is the viscous modulus. The strain distribution of the surrounding rock in the elastic zone is as follows: ； ； The radial and circumferential distribution of the surrounding rock in the plastic softening zone is as follows: ； ； In the formula: Represents the radial stress of the surrounding rock in the plastic softening zone; Represents the circumferential stress of the surrounding rock in the plastic softening zone; ; This represents the cohesion softening value of the surrounding rock in the plastic softening zone. The internal friction angle softening value of the surrounding rock in the plastic softening zone; The displacement equation for the surrounding rock in the plastic softening zone is: ； In the formula: This represents the displacement of the surrounding rock in the plastic softening zone; The expansion coefficient of the plastic softening zone; To calculate the coefficients.

8. The method for calculating the deformation of the surrounding rock in the initial double-layer support of a high-stress, water-rich soft rock tunnel according to claim 7, is characterized in that... In the displacement equation of the surrounding rock in the plastic softening zone, the following formula is used to calculate... , : β1 = (1 + sinΨ) / (1 - sinΨ); ； In the formula: Ψ is the rock mass dilatation angle.

9. The method for calculating the deformation of the surrounding rock in the initial double-layer support of a high-stress, water-rich soft rock tunnel according to claim 7, is characterized in that... In step S6, after the second layer of initial support is constructed, the viscoelastic-plastic distribution of the surrounding rock includes: radial stress distribution and circumferential stress distribution of the surrounding rock in the plastic residual zone, and the calculation equation for the displacement of the surrounding rock in the plastic residual zone. The radial stress distribution and circumferential stress distribution of the surrounding rock in the residual zone of the plastic zone are as follows: ； ； In the formula: Represents the radial stress of the surrounding rock in the plastic residual zone; Represents the circumferential stress of the surrounding rock in the plastic residual zone; ; This represents the cohesion softening value of the surrounding rock in the plastic softening zone. The internal friction angle softening value of the surrounding rock in the plastic softening zone; =Support resistance provided by the double-layer initial support structure; The equation for calculating the displacement of the surrounding rock in the plastic residual zone is as follows: ； In the formula: Represents the displacement of the surrounding rock in the plastic residual zone; R b The radius of the plastic residual region; This represents the residual elastic modulus of the surrounding rock in the plastic residual zone.

10. The method for calculating the deformation of the surrounding rock in the initial double-layer support of a high-stress, water-rich soft rock tunnel according to claim 9, characterized in that, In step S7, the radius R of the plastic softening zone is calculated using the following formula. p Radius R of the plastic residual zone b : ； ； In the formula: ; φ0 is the initial value of the cohesion of the tunnel surrounding rock; φ0 is the initial value of the friction angle of the tunnel surrounding rock. This represents the residual cohesion value of the surrounding rock in the tunnel. This is the cohesive softening modulus.

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