An initial support design method for deep-buried tunnels based on active control of surrounding rock deformation

Abstract

The present invention discloses a preliminary support design method for deep-buried tunnels based on active control of surrounding rock deformation, which solves the problem that the existing preliminary support design methods are only simply combined with bolts or supports. It has the beneficial effects of designing the preliminary support of the tunnel based on the deformation of the surrounding rock, combining bolts and supports, and enabling a relatively high accuracy in the design of the preliminary support structure of the tunnel. The specific scheme is as follows: It includes determining the surrounding rock deformation control value; determining the initial pre-design parameters of the preliminary support structure, and determining the equivalent support force of the anchoring bearing layer and the support reaction force of the support bearing layer according to the initial pre-design parameters of the preliminary support structure; establishing a mechanical calculation model of the interaction between the surrounding rock and the support based on the equivalent support force of the anchoring bearing layer and the support reaction force of the support bearing layer, solving the whole process of the deformation of the surrounding rock around the tunnel hole, and obtaining the final deformation value of the surrounding rock around the tunnel hole; judging whether the surrounding rock deformation meets the control requirements according to the determined surrounding rock deformation control value.

Description

Technical Field

[0001] The present invention relates to the technical field of mountain tunnel engineering, and in particular to an initial support design method for deep-buried tunnels based on active control of surrounding rock deformation. Background Technique

[0002] The statements in this part only provide background technical information related to the present invention, and do not necessarily constitute prior art.

[0003] The support structure of tunnel engineering is an important part of the tunnel structure system, which can effectively guarantee the stability of the tunnel surrounding rock. At present, according to the design and construction requirements, the tunnel support structures mainly include integral lining, shotcrete lining, precast lining, and composite lining, etc. In China, the composite lining is often used in traffic tunnels constructed by the drill-and-blast method, which is generally composed of initial support, waterproof layer, and secondary lining. Among them, the initial support, as the support structure constructed in time after tunnel excavation, is generally composed of shotcrete, bolts, steel mesh, steel frames, etc., and plays an important role in ensuring the safety of the tunnel construction period. Therefore, the reasonable design of the parameters of the initial support structure is particularly important. The determination of the corresponding parameters of the tunnel initial support has a great correlation with the mechanics of the surrounding rock. At present, relatively mature research results have been obtained for the surrounding rock-support interaction model and the anchoring mechanical effect respectively, but the relevant research results have not deeply combined the two, nor have they involved the research on the related initial support design method.

[0004] For example, Chinese Patent Application CN202011384891.7, a design method and system for the stiffness of a tunnel support structure system, obtains the standard deformation amounts of the surrounding rock at each stage of surrounding rock deformation, and adjusts the stiffness value of the support structure. It does not fully consider the influence of bolts and the support structure on the established model, and only simply considers that the support stiffness of the bolt layer needs to be adjusted, resulting in a relatively low accuracy of the final formed design method. Summary of the Invention

[0005] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide an initial support design method for deep-buried tunnels based on active control of surrounding rock deformation.

[0006] In order to achieve the above purpose, the present invention is realized through the following technical solutions:

[0007] An initial support design method for deep-buried tunnels based on active control of surrounding rock deformation includes the following contents:

[0008] Determine the surrounding rock deformation control value;

[0009] Determine the initial pre-design parameters of the initial support structure, and determine the equivalent support force of the anchoring bearing layer and the support reaction force of the support bearing layer according to the initial pre-design parameters of the initial support structure;

[0010] Based on the equivalent support force of the anchoring bearing layer and the support reaction force of the support bearing layer, a mechanical calculation model of the surrounding rock-support interaction is established to solve the whole process of the deformation of the surrounding rock of the tunnel hole, and the final deformation value of the surrounding rock of the tunnel hole is obtained;

[0011] According to the determined surrounding rock deformation control value, judge whether the surrounding rock deformation meets the control requirements: if the final deformation value of the surrounding rock of the tunnel hole < the surrounding rock deformation control value, it meets the design requirements; if the final deformation value of the surrounding rock of the tunnel hole > the surrounding rock deformation control value, it is necessary to adjust the initial pre-designed parameters of the primary support structure, re-obtain the final deformation value of the surrounding rock of the tunnel hole, and compare it with the surrounding rock deformation control value until the requirements are met. At this time, the initial pre-designed parameters of the primary support structure are the finally determined design parameters of the primary support structure.

[0012] An initial support design method for deep-buried tunnels based on active control of surrounding rock deformation as described above, the surrounding rock deformation control value is calculated according to the following content:

[0013] Determine the surrounding rock grade and mechanical parameters of the tunnel;

[0014] According to the surrounding rock grade of the tunnel, determine the deformation grade of the surrounding rock, and combine the mechanical parameters of the surrounding rock and the geometric parameters of the tunnel to determine the surrounding rock deformation control value.

[0015] An initial support design method for deep-buried tunnels based on active control of surrounding rock deformation as described above, the process of obtaining the equivalent support force of the anchoring bearing layer includes the following content:

[0016] According to the mechanical calculation model of the anchoring bearing layer, obtain the vertical load on the tunnel cross-section;

[0017] According to the vertical load on the tunnel cross-section, the elastic-plastic analytical solution and combined with the limit equilibrium theory, obtain the support strength that the outer boundary of the anchoring bearing layer can provide, that is, the equivalent support force of the anchoring bearing layer.

[0018] An initial support design method for deep-buried tunnels based on active control of surrounding rock deformation as described above, the process of obtaining the equivalent support force of the anchoring bearing layer is as follows:

[0019] According to the tunnel radius and the circumferential spacing of the bolts, obtain the number of bolts in the semi-cross-section;

[0020] According to the bolt length, the tunnel radius and the number of bolts in the semi-cross-section, obtain the thickness of the anchoring composite bearing body;

[0021] According to the pre-tightening force of the bolts, the axial spacing of the bolts and the circumferential spacing of the bolts, obtain the equivalent support force provided by the prestressed bolts;

[0022] Based on the elastoplastic analytical solution, the tangential stress of the anchoring bearing layer is obtained according to the equivalent support force provided by the prestressed anchor rod, the distance of the anchoring bearing layer from the tunnel center, the equivalent cohesive force of the anchoring bearing layer, the equivalent internal friction angle, and the tunnel radius.

[0023] The equivalent support force of the anchoring bearing layer is obtained according to the tangential stress of the anchoring bearing layer, the tunnel radius, the equivalent support force provided by the prestressed anchor rod, and the thickness of the anchoring composite support body.

[0024] For the initial support design method of a deep-buried tunnel based on the active control of surrounding rock deformation as described above, the process of obtaining the equivalent cohesive force of the anchoring bearing layer and the equivalent internal friction angle includes the following:

[0025] Determine the bolt density factor according to the friction resistance coefficient between the bolt and the surrounding rock, the axial spacing of the bolts, the circumferential spacing of the bolts, the tunnel radius, and the bolt diameter.

[0026] Determine the equivalent cohesive force of the anchoring bearing layer according to the bolt density factor and the angle of bolt installation.

[0027] Determine the equivalent internal friction angle according to the bolt density factor, the angle of bolt installation, and the equivalent cohesive force of the anchoring bearing layer.

[0028] For the initial support design method of a deep-buried tunnel based on the active control of surrounding rock deformation as described above, the process of obtaining the equivalent radial support force of the support bearing layer includes the following:

[0029] Obtain the support stiffness of the support bearing layer according to the mechanical calculation model of the support bearing layer combined with the thick-walled cylinder theory.

[0030] Obtain the support reaction force of the support bearing layer according to the support stiffness of the support bearing layer and the deformation value of the support bearing layer.

[0031] For the initial support design method of a deep-buried tunnel based on the active control of surrounding rock deformation as described above, the support stiffness of the support bearing layer is obtained according to the shear stiffness of the support bearing layer, the Poisson's ratio of the support bearing layer, the tunnel radius, and the tunnel radius after the support bearing layer is constructed.

[0032] The shear stiffness of the support bearing layer is obtained according to the elastic modulus of the support bearing layer and the Poisson's ratio of the support bearing layer.

[0033] For the initial support design method of a deep-buried tunnel based on the active control of surrounding rock deformation as described above, determine the sectional bending stiffness of the support bearing layer according to the sectional bending stiffness of the concrete part and the sectional bending stiffness of the steel section, and then determine the elastic modulus of the support bearing layer.

[0034] Determine the equivalent compressive strength of the support bearing layer according to the compressive strength of the steel frame, the compressive strength of the concrete, the compressive strength of the concrete, the concrete area and the cross-sectional area of the support bearing layer;

[0035] Determine the ultimate bearing capacity of the support layer according to the tunnel radius, the tunnel radius after the construction of the support bearing layer and the equivalent compressive strength of the support bearing layer;

[0036] Determine the age of the shotcrete according to the ultimate bearing capacity of the support layer and the elastic modulus of the support bearing layer.

[0037] For an initial support design method for deep-buried tunnels based on active control of surrounding rock deformation as described above, establish an equivalent mechanical calculation model according to the equivalent support force of the anchoring bearing layer and the support reaction force of the support bearing layer to obtain a homogeneous isotropic continuous medium surrounding rock;

[0038] Obtain the equivalent mechanical calculation model of the tunnel under the set hydrostatic stress;

[0039] Based on the condition of consistent deformation around the tunnel hole, through equivalent transformation, transform the equivalent support force acting on the equivalent tunnel radius of the anchoring bearing layer into the equivalent support force acting on the tunnel radius, and thus establish the mechanical calculation model of the interaction between the surrounding rock and the support.

[0040] For an initial support design method for deep-buried tunnels based on active control of surrounding rock deformation as described above, the process of obtaining the final deformation value of the surrounding rock around the tunnel hole includes the following contents:

[0041] Determine the equivalent tunnel radius and the change value of the tunnel hole perimeter displacement after the support of the anchoring bearing layer according to the hydrostatic pressure, the cohesion of the surrounding rock, the anchoring angle of the bolt and the equivalent support force of the anchoring bearing layer;

[0042] Convert the equivalent tunnel radius after the support of the anchoring bearing layer into the equivalent support force acting on the tunnel radius;

[0043] The change value of the tunnel hole perimeter displacement is equal to the change value of the displacement at the tunnel radius, obtain the equivalent support force at the tunnel radius, and then obtain the tunnel hole perimeter displacement deformation expression at the tunnel radius;

[0044] Obtain the elastic-plastic deformation of the tunnel hole perimeter under the action of the virtual support force generated by the spatial effect of the excavation surface and the passive reaction force of the support structure.

[0045] The beneficial effects of the present invention are as follows:

[0046] 1) The design method of the present invention first determines the surrounding rock deformation control value, determines the equivalent support force of the anchoring bearing layer and the support reaction force of the support bearing layer according to the initial pre-design parameters of the primary support structure, establishes a mechanical calculation model of the interaction between the surrounding rock and the support based on the two, and obtains the final deformation value of the surrounding rock of the tunnel hole. According to the comparison between the final deformation value of the surrounding rock of the tunnel hole and the surrounding rock deformation control value, it is judged whether the initial pre-design parameters of the primary support structure meet the requirements, realizing the provision of a design method for the primary support of deep-buried tunnels based on the active control of surrounding rock deformation.

[0047] 2) In the present invention, according to the vertical load, elastic-plastic analytical solution and combined with the limit equilibrium theory on the tunnel cross-section, the support strength that the outer boundary of the anchoring bearing layer can provide, that is, the equivalent support force of the anchoring bearing layer, is obtained. In the process of obtaining the equivalent support force of the anchoring bearing layer, based on the elastic-plastic analytical solution, multiple factors are fully considered, including the pre-tightening force of the bolt, the axial spacing of the bolt, the circumferential spacing of the bolt, the equivalent cohesive force of the anchoring bearing layer, the equivalent internal friction angle and other factors, ensuring the accuracy of obtaining the equivalent support force of the anchoring bearing layer.

[0048] 3) In the present invention, according to the mechanical calculation model of the support bearing layer and combined with the thick-walled cylinder theory, the support stiffness of the support bearing layer is obtained; according to the support stiffness of the support bearing layer and the deformation value of the support bearing layer, the support reaction force of the support bearing layer is obtained. The support reaction force of the support bearing layer is the support reaction force of the shotcrete and the arch frame. In the process of calculating the support reaction force of the support bearing layer, the shear stiffness of the support bearing layer, the Poisson's ratio of the support bearing layer, the tunnel radius and the tunnel radius after the support bearing layer is constructed are fully considered for obtaining, ensuring the accuracy of obtaining the support reaction force of the support bearing layer.

[0049] 4) The present invention as a whole adopts the ideal elastic-plastic analytical solution, combines the mechanical calculation model of the anchoring bearing layer, and considers the surrounding rock deformation, and proposes a mechanical calculation model of the interaction between the surrounding rock and the support considering the bearing effect of the anchoring bearing layer; deduces the analytical calculation expression of the whole process of the deformation of the deep-buried circular tunnel hole; finally, based on the mechanical calculation model of the interaction between the surrounding rock and the support, with the goal of controlling the deformation value of the surrounding rock of the tunnel hole, a design method for the active control of the deformation of the primary support of deep-buried tunnels is established, realizing the quantitative and accurate design of the primary support structures such as prestressed bolts, shotcrete and arch frames, forming a design method for the active control of the deformation of the primary support with the goal of controlling deformation, overcoming the defects of the design of the support structure in tunnel engineering, and enriching the relevant theories of the refined design of the support structure in tunnel engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The specification drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0051] Figure 1 It is a flowchart of a primary support design method for deep-buried tunnels based on active control of surrounding rock deformation according to one or more embodiments of the present invention.

[0052] Figure 2 It is a mechanical calculation model of the anchoring bearing layer in a primary support design method for deep-buried tunnels based on active control of surrounding rock deformation according to one or more embodiments of the present invention.

[0053] Figure 3 It is a mechanical calculation model of the support bearing layer in a primary support design method for deep-buried tunnels based on active control of surrounding rock deformation according to one or more embodiments of the present invention.

[0054] Figure 4 It is an equivalent mechanical calculation model of a tunnel considering the effects of the anchoring bearing layer and the support bearing layer in a primary support design method for deep-buried tunnels based on active control of surrounding rock deformation according to one or more embodiments of the present invention.

[0055] In the figure: The distances or sizes between each part are exaggerated for showing the positions of each part, and the schematic diagram is only for illustration. Specific Embodiments

[0056] It should be noted that the following detailed description is exemplary and intended to provide further illustration of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0057] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the present invention clearly states otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof;

[0058] As introduced in the background art, for the problems in the prior art, in order to solve the above technical problems, the present invention proposes a primary support design method for deep-buried tunnels based on active control of surrounding rock deformation.

[0059] Example 1

[0060] In a typical embodiment of the present invention, referring to Figure 1 as shown, a primary support design method for deep-buried tunnels based on active control of surrounding rock deformation includes the following contents:

[0061] Determine the surrounding rock deformation control value;

[0062] Determine the initial pre - design parameters of the primary support structure, and determine the equivalent support force of the anchoring bearing layer and the support reaction force of the support bearing layer according to the initial pre - design parameters of the primary support structure;

[0063] Establish a mechanical calculation model of the surrounding rock - support interaction based on the equivalent support force of the anchoring bearing layer and the support reaction force of the support bearing layer, solve the whole - process deformation of the surrounding rock around the tunnel, and obtain the final deformation value of the surrounding rock around the tunnel;

[0064] According to the determined surrounding - rock deformation control value, judge whether the surrounding - rock deformation meets the control requirements: If the final deformation value of the surrounding rock around the tunnel < the surrounding - rock deformation control value, it meets the design requirements; if the final deformation value of the surrounding rock around the tunnel > the surrounding - rock deformation control value, it does not meet the design requirements, and the initial pre - design parameters of the primary support structure need to be adjusted, re - obtain the final deformation value of the surrounding rock around the tunnel, and compare it with the surrounding - rock deformation control value until the requirements are met. At this time, the initial pre - design parameters of the primary support structure are the finally determined design parameters of the primary support structure.

[0065] Among them, it should be explained that the anchoring bearing layer refers to the anchor - rock complex formed by the bolt and the surrounding rock, and the support effect is realized through the support force provided by the anchor - rock complex. The support bearing layer refers to the shotcrete and arch support layer, and the support effect of the support bearing layer is considered as the support force acting on the inner surface of the tunnel;

[0066] It is easy to understand that the surrounding - rock deformation control value is calculated according to the following content:

[0067] According to the geological exploration data of the actual tunnel project, determine the surrounding - rock grade and surrounding - rock mechanical parameters;

[0068] According to the surrounding - rock grade of the tunnel, determine the deformation grade of the surrounding rock, and combine the surrounding - rock mechanical parameters and tunnel geometric parameters to determine the surrounding - rock deformation control value.

[0069] The surrounding - rock mechanical parameters include the strength and deformation properties of the surrounding rock. The surrounding - rock mechanical parameters include compressive strength, shear strength, etc. The deformation property refers to the deformation characteristics of the surrounding rock when it is subjected to external stress.

[0070] Regarding the anchoring bearing layer, after the tunnel excavation and the installation of bolts, due to the interaction between the bolts and the surrounding rock, a conical compaction zone is formed between adjacent bolts. The compaction zones of the surrounding rock under the action of the bolt group are connected and penetrated to form a continuous and stable layered anchoring structure. The process of obtaining the equivalent support force of the anchoring bearing layer includes the following content:

[0071] Refer to Figure 2 As shown, according to the existing mature mechanical calculation model of the anchoring bearing layer, obtain the vertical load F acting on the tunnel cross - section nis the vertical load acting on the tunnel cross-section and is axially symmetric about the tunnel axis;

[0072] According to the vertical load on the tunnel cross-section, the elastoplastic analytical solution, and in combination with the limit equilibrium theory, the support strength that the outer boundary of the anchoring bearing layer can provide is obtained, that is, the equivalent support force of the anchoring bearing layer.

[0073] In this embodiment, the process of obtaining the equivalent support force of the anchoring bearing layer is as follows:

[0074] According to the tunnel radius and the circumferential spacing of the bolts, the number of bolts in the semi-cross-section is obtained;

[0075] According to the bolt length, the tunnel radius, and the number of bolts in the semi-cross-section, the thickness of the anchoring composite carrier is obtained;

[0076] According to the pre-tightening force of the bolts, the axial spacing of the bolts, and the circumferential spacing of the bolts, the equivalent support force provided by the prestressed bolts is obtained;

[0077] Based on the elastoplastic analytical solution, according to the equivalent support force provided by the prestressed bolts, the distance from the anchoring bearing layer to the tunnel center, the equivalent cohesive force of the anchoring bearing layer, the equivalent internal friction angle, and the tunnel radius, the tangential stress of the anchoring bearing layer is obtained;

[0078] According to the tangential stress of the anchoring bearing layer, the tunnel radius, the equivalent support force provided by the prestressed bolts, and the thickness of the anchoring composite carrier, the equivalent support force of the anchoring bearing layer is obtained;

[0079] Specifically, according to the tangential stress of the anchoring bearing layer It can be seen that when the thickness of the anchoring bearing layer is b, F n can be expressed as

[0080]

[0081] According to the Mohr-Coulomb yield criterion (abbreviated as the M-C yield criterion) and in combination with the limit equilibrium theory, the support strength that the outer boundary of the anchoring bearing layer can provide, that is, the equivalent support force P of the anchoring bearing layer b The calculation formula is:

[0082]

[0083] Assume that the surrounding rock of the anchoring bearing layer obeys the Mohr-Coulomb yield criterion. Based on the classical elastoplastic analytical solution (Fenner solution), the radial stress σ of the anchoring bearing layer is obtained m rp and the tangential stress σ m θp The expression is:

[0084]

[0085] Where: r is the distance from the anchoring bearing layer to the tunnel center, R0 is the tunnel radius, and P y is the equivalent support force provided by the prestressed anchor bolt; c*, are the equivalent cohesive force and equivalent internal friction angle of the anchoring bearing layer respectively, c is the cohesive force of the anchoring bearing layer, is the internal friction angle of the anchoring bearing layer;

[0086] The expression for the thickness b of the anchoring composite carrier is:

[0087]

[0088] The number N of bolts in the semi - cross - section is

[0089]

[0090] The prestressed anchor bolt provides an equivalent support force;

[0091]

[0092] Where, Q is the pre - tightening force of the anchor bolt; L is the length of the anchor bolt; S L is the axial spacing of the anchor bolts, and S T is the circumferential spacing of the anchor bolts.

[0093] It should be noted that the process of obtaining the equivalent cohesive force and equivalent internal friction angle of the anchoring bearing layer includes the following content:

[0094] Determine the bolt density factor according to the friction resistance coefficient between the bolt and the surrounding rock, the axial spacing of the bolts, the circumferential spacing of the bolts, the tunnel radius and the bolt diameter;

[0095] Determine the equivalent cohesive force of the anchoring bearing layer according to the bolt density factor and the setting angle of the bolts;

[0096] Determine the equivalent internal friction angle according to the bolt density factor, the setting angle of the bolts and the equivalent cohesive force of the anchoring bearing layer;

[0097] Specifically, after bolt support, the bolt itself can not only effectively improve the stability of the tunnel surrounding rock, but also due to the coupling effect between the bolt and the tunnel surrounding rock, the self - bearing capacity of the tunnel surrounding rock can be fully exerted. By using the homogenization method, the surrounding rock affected by the bolts is regarded as a homogeneous and continuous composite material, and the bolt density factor β is defined as:

[0098]

[0099] Where: λ is the friction resistance coefficient between the bolt and the surrounding rock, and in the deformed steel bolt support system, λ = tanφ, Db is the bolt diameter.

[0100] Based on the assumption that the composite material of the bolt and surrounding rock still satisfies the M-C yield criterion, the expressions for the equivalent internal friction angle φ* and equivalent cohesion c* of the anchoring structure are derived:

[0101]

[0102] The equivalent elastic modulus of the anchoring structure is affected by both the elastic modulus of the bolt and the elastic modulus of the surrounding rock. According to the area equivalence principle, the equivalent elastic modulus E * of the anchoring structure is expressed as:

[0103]

[0104] In the formula, E b is the elastic modulus of the bolt, E is the elastic modulus of the surrounding rock, c is the cohesion, and φ is the internal friction angle.

[0105] In addition to bolt support, the shotcrete + arch (steel arch, lattice arch) structure is also an important part of the initial support. This structure is called the support bearing layer. The process of obtaining the equivalent radial support force of the support bearing layer includes the following:

[0106] Referring to Figure 3 as shown, based on the mechanical calculation model of the support bearing layer and the existing thick-walled cylinder theory, the support stiffness of the support bearing layer is obtained;

[0107] The support reaction force of the support bearing layer is obtained according to the support stiffness of the support bearing layer and the deformation value of the support bearing layer.

[0108] Among them, the support stiffness of the support bearing layer is obtained according to the shear stiffness of the support bearing layer, the Poisson's ratio of the support bearing layer, the tunnel radius, and the tunnel radius after the support bearing layer is constructed;

[0109] The shear stiffness of the support bearing layer is obtained according to the elastic modulus of the support bearing layer and the Poisson's ratio of the support bearing layer;

[0110] According to the sectional bending stiffness of the concrete part and the sectional bending stiffness of the steel section, the sectional bending stiffness of the support bearing layer is determined, and then the elastic modulus of the support bearing layer is determined;

[0111] According to the compressive strength of the steel frame, the compressive strength of the concrete, the compressive strength of the concrete, the concrete area, and the sectional area of the support bearing layer, the equivalent compressive strength of the support bearing layer is determined;

[0112] According to the tunnel radius, the tunnel radius after the support bearing layer is constructed, and the equivalent compressive strength of the support bearing layer, the ultimate bearing capacity of the support layer is determined;

[0113] Determine the shotcrete age according to the ultimate bearing capacity of the support layer and the elastic modulus of the support bearing layer.

[0114] Specifically, according to the thick-walled cylinder theory, the support stiffness K of the support bearing layer c is:

[0115]

[0116] Therefore, the support reaction force P of the support bearing layer c is:

[0117] P c = K c u0 (12)

[0118] In the formula, R 0l is the tunnel radius after the construction of the support bearing layer; u0 is the deformation value of the support bearing layer; G is the shear stiffness of the support bearing layer, G = E c / (2(1 - v c )); v c is the Poisson's ratio of the support bearing layer; E c is the elastic modulus of the support bearing layer.

[0119] Among them, the mechanical parameters of the support layer are jointly determined by the shotcrete and the arch structure. Due to the hardening characteristics of the shotcrete, its mechanical properties have a certain timeliness. Many existing scholars have analyzed its mechanical properties. Using the relationship between the shotcrete strength and the elastic modulus E c1 and the age t proposed in the existing technology, it is as follows:

[0120]

[0121] In the formula: E c1,0 , σ c1,0 are the final strength and elastic modulus of the shotcrete; t is the age of the shotcrete; α, β are time constants, and α = β can be taken.

[0122] Regarding the stiffness calculation of the arch structure, it is calculated according to the shotcrete stiffness calculation formula (formula (11)), and only the elastic modulus needs to be replaced. Similarly, it can be known that if the equivalent elastic modulus of the shotcrete structure and the arch structure is brought into formula (11), it can be considered as the support stiffness of the support layer. The Poisson's ratio of the support layer can be assumed to be the Poisson's ratio of the shotcrete. Therefore, according to the principle of equivalent cross-section bending stiffness, the equivalent elastic modulus E c of the support layer can be obtained, and the calculation expression is:

[0123] E c I = E c1 I c1 + E c2 I c2(14)

[0124] In the formula, E c is the flexural rigidity of the I-section member; E c1 I c1 is the flexural rigidity of the concrete part; E c2 I c2 is the flexural rigidity of the steel section.

[0125] Similarly, the calculation expression for the ultimate bearing capacity of the support layer is:

[0126]

[0127] According to the principle of equivalent area, the calculation expression for the equivalent compressive strength of the support layer is derived as:

[0128] σ c A = σ c1 A c1 + σ c2 A c2 (16)

[0129] In the formula, σ c is the equivalent compressive strength of the support layer; σ c1 is the compressive strength of the steel frame; σ c2 is the compressive strength of the concrete; A c1 is the cross-sectional area of the steel frame; A c2 is the area of the concrete; A is the cross-sectional area, A = A c1 + A c2 .

[0130] After the bolts are installed, the bolts and the surrounding rock form an anchor-rock complex (anchoring bearing layer). Based on the mechanical calculation model of the anchoring bearing layer and the classical elastic-plastic analytical solution (Fenner solution), the equivalent support force of the anchoring bearing layer is obtained, and considering the role of the support bearing layer, an equivalent mechanical calculation model is established (as shown in Figure 4 ), that is, an equivalent mechanical calculation model is established according to the equivalent support force of the anchoring bearing layer and the support reaction force of the support bearing layer, and a homogeneous isotropic continuous medium surrounding rock is obtained;

[0131] When the hydrostatic stress is P₀, the calculation expressions for the radius R p of the plastic zone of the tunnel and the displacement u b0 around the tunnel perimeter are as follows:

[0132]

[0133] In the formula, R b is the equivalent tunnel radius after the support of the anchoring bearing layer;

[0134] Based on the condition of consistent deformation around the tunnel hole, through equivalent transformation, the equivalent support force acting on the equivalent tunnel radius by the anchoring bearing layer is transformed into the equivalent support force acting on the tunnel radius, and thus a mechanical calculation model of the interaction between the surrounding rock and the support is established;

[0135] It can be analyzed from the mechanical calculation model of the support layer bearing that the equivalent support force provided by the support bearing layer is related to its own deformation, that is, there is an interaction relationship between the support bearing layer and the deformation of the surrounding rock. Therefore, in order to consider the support effect of the support bearing layer, a mechanical calculation model of the interaction between the surrounding rock and the support needs to be established. Since the equivalent radius of the tunnel in the above tunnel equivalent mechanical calculation model considering the action of the anchoring bearing layer is R b , it is impossible to directly establish a relationship with the support bearing layer. Therefore, based on the condition of consistent deformation around the tunnel hole in this application, through equivalent transformation, the equivalent support force P b acting on the equivalent tunnel radius R b is transformed into the equivalent support force P ib acting on the tunnel radius R0, and the specific transformation is as follows:

[0136] Based on the condition of consistent deformation around the tunnel hole, it can be obtained that

[0137]

[0138] That is

[0139]

[0140] After simplifying the formula, the equivalent support force P ib when the tunnel radius is R0 is obtained as:

[0141]

[0142] Therefore, the calculation expression of the deformation of the surrounding rock around the tunnel under the action of the anchoring bearing layer is obtained as:

[0143]

[0144] The generation and development of the deformation of the tunnel surrounding rock are affected by various force fields, mainly including the in-situ stress, the virtual support force generated by the spatial effect of the excavation surface the passive reaction force of the support structure Pc and so on. Therefore, based on the spatial effect of the excavation surface and the analytical solution of the elastic-plastic displacement of the surrounding rock under the action of the above-established anchoring bearing layer, a new mechanical calculation model of the surrounding rock-support considering the action effect of the anchoring bearing layer is established, as described below.

[0145] It can be seen from formula (20) that the calculation expression of the elastic-plastic deformation of the tunnel hole perimeter under the action of force on the tunnel hole perimeter is:

[0146]

[0147] The elastic displacement corresponding to the outer diameter of the support bearing layer The support reaction force P c is as follows:

[0148]

[0149] In the formula,

[0150] Corresponding to The virtual support force is;

[0151]

[0152] According to the Hoek fitting formula, it can be obtained that:

[0153]

[0154] Among them, It is calculated by the classical elastic-plastic displacement formula (Fenner solution) of the tunnel based on the M-C criterion.

[0155] Corresponding to The virtual support force is

[0156]

[0157] In the formula: is the radial displacement of the surrounding rock at point A when the support starts; x[[ID=5I]] A is the distance from point A to the excavation face when the support starts.

[0158] Substitute equations (22) and (23) into equation (21), and the real-time analytical equation of the whole process deformation of the surrounding rock-support interaction can be obtained when the surrounding rock undergoes radial elastic-plastic displacement for support

[0159]

[0160] Among them,

[0161]

[0162] It is easy to understand that according to the mechanical calculation model of the surrounding rock-support interaction, the longitudinal deformation curve of the tunnel is obtained to determine the support construction time.

[0163] The design method provided by this application generally adopts the analytical solution of ideal elastoplasticity, combines the mechanical calculation model of the anchoring bearing layer, and considers the surrounding rock deformation, and proposes a mechanical calculation model for the interaction between the surrounding rock and the support considering the bearing effect of the anchoring bearing layer; deduces the analytical calculation expression for the whole process of the deformation around the perimeter of a deeply buried circular tunnel; finally, based on the mechanical calculation model of the interaction between the surrounding rock and the support, with the goal of controlling the deformation value of the surrounding rock around the tunnel, an active control design method for the deformation of the initial support of a deeply buried tunnel is established, realizing the quantitative and accurate design of the initial support structures such as prestressed anchor bolts, shotcrete, and steel arches, forming an active control design method for the deformation of the initial support with the goal of controlling deformation, and overcoming the defects in the design of the support structure for tunnel engineering.

[0164] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for designing initial support for deep tunnels based on active control of surrounding rock deformation, characterized in that: Includes the following: Determine the surrounding rock deformation control value; Determine the initial pre-design parameters of the initial support structure, and determine the equivalent support force of the anchor bearing layer and the support reaction force of the support bearing layer based on the initial pre-design parameters of the initial support structure; Based on the equivalent support force of the anchor bearing layer and the support reaction force of the support bearing layer, a mechanical calculation model of the surrounding rock-support interaction is established to solve the deformation of the rock around the tunnel hole in the whole process and obtain the final deformation value of the rock around the tunnel hole. Based on the determined surrounding rock deformation control value, determine whether the surrounding rock deformation meets the control requirements: if the final deformation value of the rock around the tunnel is less than the surrounding rock deformation control value, the design requirements are met; If the final deformation value of the rock around the tunnel is greater than the surrounding rock deformation control value, the initial pre-design parameters of the initial support structure need to be adjusted, and the final deformation value of the rock around the tunnel needs to be re-obtained and compared with the surrounding rock deformation control value until the requirements are met. The initial pre-design parameters of the initial support structure at this time are the finalized initial support structure design parameters; An equivalent mechanical calculation model is established based on the equivalent support force of the anchor bearing layer and the support reaction force of the support bearing layer to obtain a homogeneous isotropic continuous medium surrounding rock; Obtain the equivalent mechanical calculation model of the tunnel under the set hydrostatic stress; Based on the uniform deformation condition around the tunnel, the equivalent support force of the anchor bearing layer at the equivalent tunnel radius is converted into the equivalent support force at the tunnel radius through equivalent transformation, thereby establishing the surrounding rock-support interaction mechanical calculation model.

2. The method for designing initial support for deep tunnels based on active control of surrounding rock deformation according to claim 1, characterized in that: The surrounding rock deformation control value is calculated according to the following: Determine the tunnel surrounding rock grade and surrounding rock mechanical parameters; The deformation grade of the surrounding rock is determined according to the grade of the tunnel surrounding rock, and the surrounding rock deformation control value is determined in combination with the surrounding rock mechanical parameters and the tunnel geometric parameters.

3. The method for designing initial support for deep tunnels based on active control of surrounding rock deformation according to claim 1, characterized in that: The process of obtaining the equivalent support force of the anchor bearing layer includes the following: According to the mechanical calculation model of the anchor bearing layer, the vertical load on the tunnel cross section is obtained; Based on the vertical load on the tunnel cross section, the elastic-plastic analytical solution and the limit equilibrium theory, the support strength that can be provided by the outer boundary of the anchor bearing layer is obtained, that is, the equivalent support force of the anchor bearing layer.

4. The method for designing initial support for deep tunnels based on active control of surrounding rock deformation according to claim 3 is characterized in that: The process of obtaining the equivalent support force of the anchor bearing layer is as follows: Obtain the number of anchor bolts in the half cross section according to the tunnel radius and the circumferential spacing of anchor bolts; The thickness of the anchoring composite bearing body is obtained according to the anchor length, tunnel radius and the number of anchors in the half cross section; The equivalent support force provided by the prestressed anchor rods is obtained based on the anchor rod preload, anchor rod axial spacing, and anchor rod circumferential spacing; Based on the elastoplastic analytical solution, the tangential stress of the anchor bearing layer is obtained according to the equivalent support force provided by the prestressed anchor, the distance between the anchor bearing layer and the tunnel center, the equivalent cohesion of the anchor bearing layer, the equivalent internal friction angle and the tunnel radius. The equivalent support force of the anchor bearing layer is obtained according to the tangential stress of the anchor bearing layer, the tunnel radius, the equivalent support force provided by the prestressed anchor rods and the thickness of the anchor composite bearing body.

5. The method for designing initial support for deep tunnels based on active control of surrounding rock deformation according to claim 4 is characterized in that: The process of obtaining the equivalent cohesion of the anchor bearing layer and the equivalent internal friction angle includes the following: The anchor density factor is determined based on the friction coefficient between the anchor and the surrounding rock, the axial spacing of the anchor, the circumferential spacing of the anchor, the tunnel radius and the anchor diameter; Determine the equivalent cohesion of the anchor bearing layer according to the anchor density factor and the anchor angle of the anchor; The equivalent internal friction angle is determined based on the anchor density factor, the anchor angle and the equivalent cohesion of the anchor bearing layer.

6. The method for designing initial support for deep tunnels based on active control of surrounding rock deformation according to claim 1, characterized in that: The process of obtaining the support reaction force of the support bearing layer includes the following: Based on the mechanical calculation model of the support bearing layer and the thick-walled cylinder theory, the support stiffness of the support bearing layer is obtained; The support reaction force of the support bearing layer is obtained according to the support stiffness and deformation value of the support bearing layer.

7. The method for designing initial support for deep tunnels based on active control of surrounding rock deformation according to claim 6, characterized in that: The support stiffness of the support bearing layer is obtained according to the shear stiffness of the support bearing layer, the Poisson's ratio of the support bearing layer, the tunnel radius and the tunnel radius after the support bearing layer is constructed; The shear stiffness of the support bearing layer is obtained based on the elastic modulus and Poisson's ratio of the support bearing layer.

8. The method for designing initial support for deep tunnels based on active control of surrounding rock deformation according to claim 7, characterized in that: Determine the cross-sectional bending stiffness of the support bearing layer according to the cross-sectional bending stiffness of the concrete part and the cross-sectional bending stiffness of the steel section, and then determine the elastic modulus of the support bearing layer; Determine the equivalent compressive strength of the support bearing layer based on the compressive strength of the steel frame, the compressive strength of the concrete, the cross-sectional area of the steel frame, the concrete area and the cross-sectional area of the support bearing layer; The ultimate bearing capacity of the support layer is determined based on the tunnel radius, the tunnel radius after the support bearing layer is constructed, and the equivalent compressive strength of the support bearing layer.

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