A method and system for evaluating the reinforcement effect of a soft rock tunnel face

Abstract

The application discloses a soft rock tunnel face pre-reinforcement effect evaluation method and system, relates to the technical field of tunnel and underground engineering surrounding rock stability evaluation, and has the technical scheme as follows: tunnel engineering geological parameters, face section parameters and pre-reinforcement design parameters are acquired; the type is determined according to the pre-reinforcement design parameters, and equivalent reinforcement parameters and effective far-field stress are calculated according to the pre-reinforcement type; three-dimensional unloading in front of the soft rock face is equivalent to spherical cavity unloading, and the equivalent reinforcement parameters, effective far-field stress, original rock mechanical parameters and original rock initial stress are substituted respectively, so that the extrusion displacement of the face center and the elastic-plastic interface radius before and after reinforcement are solved; according to the extrusion displacement of the face center and the elastic-plastic interface radius before and after reinforcement, the equivalent reinforcement parameters, the original rock mechanical parameters and the effective far-field stress, the extrusion deformation reduction rate, the comprehensive strength improvement coefficient and the safety coefficient are calculated, and the pre-reinforcement effect of the soft rock tunnel face is determined by adopting two-step grading judgment.

Description

Technical Field

[0001] This invention relates to the field of stability evaluation technology for surrounding rock in tunnels and underground engineering projects, and more specifically, to a method and system for evaluating the pre-reinforcement effect of soft rock tunnel faces. Background Technology

[0002] As tunnel construction in my country progresses into areas with high ground stress and complex geological conditions, large deformation of soft rock and instability of the tunnel face have become the primary engineering challenges faced by mining methods. Soft rock has low strength and a small deformation modulus, and its plastic zone expands rapidly after excavation. Under three-dimensional unloading, the pre-core soil is prone to progressive failure, leading to excessive extrusion deformation or even instability and collapse of the tunnel face. To address this challenge, advanced pre-reinforcement technologies (including grouting, GFRP anchors, and pipe roof support) have become key technical means to control tunnel face stability.

[0003] The Geotechnical Deformation Control Analysis (ADECO-RS) method positions the pre-reinforced core soil as a fourth-dimensional support structure and classifies the surrounding rock behavior into three states (A, B, and C) based on deformation response, providing a classification framework for pre-reinforcement design. However, while this theory has been successfully applied in design, it lacks a corresponding quantitative standard system for evaluation, resulting in the following core problems:

[0004] First, ADECO-RS uses deformation magnitude as a guide for selection during the design phase, but lacks corresponding quantitative grading standards during the post-construction effect evaluation phase, resulting in a clear disconnect between the design and evaluation phases.

[0005] Second, the mechanical action paths of the three types of measures—anchor bolts, pipe roofs, and grouting—are completely different. They act on the core soil through reinforcement constraint, stress transfer, and cementation improvement, respectively. Their design parameters are incompatible with each other, making it impossible to compare the reinforcement effects of various construction methods on the same scale. The selection of schemes lacks a unified quantitative basis.

[0006] Third, most existing assessments use a single deformation index for grading, failing to integrate deformation control effect, degree of improvement of mechanical parameters and safety margin level into an organic multi-dimensional assessment framework, and also lack supporting analytical calculation and judgment methods.

[0007] In summary, existing technologies cannot meet the engineering needs of shifting from empirical qualitative judgment to theoretical quantitative evaluation of pre-reinforcement effects. Summary of the Invention

[0008] The purpose of this invention is to provide a method and system for evaluating the pre-reinforcement effect of soft rock tunnel faces. This method unifies different types of pre-reinforcement methods into equivalent reinforcement parameters and calculates multi-dimensional evaluation indicators under a unified mechanical model, thereby achieving a quantitative evaluation of the pre-reinforcement effect of soft rock tunnel faces.

[0009] The above-mentioned technical objective of the present invention is achieved through the following technical solution:

[0010] In a first aspect, the present invention provides a method for evaluating the pre-reinforcement effect of soft rock tunnel faces, the method comprising:

[0011] Obtain the tunnel engineering geological parameters, tunnel face cross-sectional parameters, and design parameters for pre-reinforcement measures for soft rock tunnels; among which, the tunnel engineering geological parameters include the original rock mechanical parameters and the original rock initial stress, and the tunnel face cross-sectional parameters include the tunnel excavation radius;

[0012] Calculate the equivalent reinforcement parameters and effective far-field stress based on the design parameters of the pre-reinforcement measures;

[0013] The geometric boundary of the spherical cavity is determined based on the tunnel excavation radius. The three-dimensional unloading problem in front of the tunnel face of soft rock tunnel is equivalent to the unloading problem of the spherical cavity. The equivalent reinforcement parameters and effective far-field stress are substituted into the unloading problem of the spherical cavity to solve for the extrusion displacement of the center of the tunnel face after reinforcement and the radius of the elastic-plastic interface after reinforcement. At the same time, the original rock mechanical parameters and the original rock initial stress are substituted into the unloading problem of the spherical cavity to solve for the extrusion displacement of the center of the tunnel face before reinforcement and the radius of the elastic-plastic interface before reinforcement.

[0014] Based on the extrusion displacement at the center of the tunnel face before reinforcement, the extrusion displacement at the center of the tunnel face after reinforcement, the radius of the elastic-plastic interface before reinforcement, the radius of the elastic-plastic interface after reinforcement, the equivalent reinforcement parameters, the original rock mechanical parameters, and the effective far-field stress, the extrusion deformation reduction rate, the comprehensive strength improvement coefficient, and the safety factor are calculated.

[0015] Based on the extrusion deformation reduction rate, comprehensive strength improvement coefficient, and safety factor, a two-step classification judgment method is adopted to determine the pre-reinforcement effect of the tunnel face in soft rock.

[0016] A second aspect of the present invention provides a system for evaluating the pre-reinforcement effect of soft rock tunnel faces, comprising:

[0017] The parameter acquisition module is used to acquire the tunnel engineering geological parameters, tunnel face cross-sectional parameters, and design parameters of pre-reinforcement measures for soft rock tunnels. Among them, the tunnel engineering geological parameters include the original rock mechanical parameters and the original rock initial stress, and the tunnel face cross-sectional parameters include the tunnel excavation radius.

[0018] The equivalent parameter calculation module is used to calculate the equivalent reinforcement parameters and effective far-field stress based on the design parameters of the pre-reinforcement measures.

[0019] The spherical cavity solution module is used to determine the geometric boundary of the spherical cavity based on the tunnel excavation radius. It transforms the three-dimensional unloading problem in front of the tunnel face in soft rock into a spherical cavity unloading problem. It substitutes the equivalent reinforcement parameters and effective far-field stress into the spherical cavity unloading problem to solve for the extrusion displacement at the center of the tunnel face after reinforcement and the radius of the elastic-plastic interface after reinforcement. At the same time, it substitutes the original rock mechanical parameters and the original rock initial stress into the spherical cavity unloading problem to solve for the extrusion displacement at the center of the tunnel face before reinforcement and the radius of the elastic-plastic interface before reinforcement.

[0020] The index calculation module is used to calculate the extrusion deformation reduction rate, comprehensive strength improvement coefficient and safety factor based on the extrusion displacement of the center of the tunnel face before reinforcement, the extrusion displacement of the center of the tunnel face after reinforcement, the radius of the elastic-plastic interface before reinforcement, the radius of the elastic-plastic interface after reinforcement, the equivalent reinforcement parameters, the original rock mechanical parameters and the effective far-field stress.

[0021] The comprehensive grading and judgment module is used to determine the pre-reinforcement effect of the tunnel face in soft rock by adopting a two-step grading and judgment method based on the extrusion deformation reduction rate, comprehensive strength improvement coefficient and safety factor.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. This invention maps the design parameters of different pre-reinforcement measures into equivalent reinforcement parameters and effective far-field stresses by exploring the mechanical action paths of these measures. This unifies heterogeneous reinforcement measures such as grouting, anchor bolts, and pipe roofs into a single mechanical characterization system, solving the problem of cross-method quantitative comparison caused by incompatible design parameters. Based on this, the obtained equivalent reinforcement parameters and effective far-field stresses are substituted into the spherical cavity unloading problem equivalent to the equivalent advanced core soil model to solve for the extrusion displacement at the center of the working face after reinforcement and the radius of the elastic-plastic interface after reinforcement. Simultaneously, the original rock mechanical parameters and the initial stress of the original rock are also considered. By substituting the force into the unloading problem of the spherical cavity, the extrusion displacement at the center of the tunnel face before reinforcement and the radius of the elastic-plastic interface before reinforcement are obtained. Subsequently, based on the extrusion displacement and the radius of the elastic-plastic interface before and after reinforcement, as well as the geological parameters of the tunnel, the extrusion deformation reduction rate, the comprehensive strength improvement coefficient, and the safety factor are calculated. This overcomes the limitation of existing technologies that rely on only a single deformation index. Finally, based on the extrusion deformation reduction rate, the comprehensive strength improvement coefficient, and the safety factor, a two-step graded judgment method is used to determine the pre-reinforcement effect of the tunnel face in soft rock, realizing quantitative comparison and effect judgment across construction methods.

[0024] 2. This invention establishes an evaluation system covering three dimensions: deformation control effect, mechanical parameter improvement, and safety margin. The comprehensive strength improvement coefficient unifies cohesion and internal friction angle into a single strength index, avoiding inconsistencies when evaluating the two parameters separately. The multi-dimensional evaluation system can reflect the reinforcement effect of pre-reinforcement measures and provide a more complete basis for engineering decisions.

[0025] 3. This invention employs a two-step grading method. The first step determines the basic grade based on the extrusion deformation reduction rate and the comprehensive strength improvement coefficient. The second step uses a safety factor for limit correction. When the safety factor is below the threshold, even if the deformation index meets the requirements, the effect grade will be limited to below the grade corresponding to the safety factor, thereby identifying the risk of false convergence where deformation has converged but the safety reserve is insufficient.

[0026] 4. This invention equates the three-dimensional unloading problem of the core soil in front of the tunnel face to a spherical cavity unloading problem, and adopts a spherical cavity unloading elastoplastic semi-analytical solution method. It uses the expansion of the plastic zone and extrusion deformation as the basis for stability control, which is more in line with the evolution mechanism of deformation instability of the tunnel face in soft rock tunnels.

[0027] 5. In forward modeling mode, the present invention can predict the pre-reinforcement effect based on design parameters. In inverse modeling mode, it can inverse the comprehensive reinforcement effectiveness coefficient based on the on-site measured extrusion displacement, correct the equivalent reinforcement parameters, and re-evaluate, thereby realizing the engineering closed loop of pre-reinforcement measures design, construction, and effect evaluation. Attached Figure Description

[0028] 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:

[0029] Figure 1 A flowchart of a method for evaluating the pre-reinforcement effect of a soft rock tunnel face, provided in an embodiment of the present invention;

[0030] Figure 2 A schematic diagram illustrating the classification of pre-reinforcement measures and the principles for establishing an equivalent advanced core soil model as provided in embodiments of the present invention;

[0031] Figure 3 A framework diagram of a three-dimensional, five-indicator evaluation system provided in this embodiment of the invention;

[0032] Figure 4 This is a schematic diagram of the mechanical model of the spherical cavity provided in an embodiment of the present invention;

[0033] Figure 5 The distribution curve of the pre-convergence displacement in front of the tunnel face as a function of longitudinal distance is provided for an embodiment of the present invention;

[0034] Figure 6 The flowchart for the two-step comprehensive classification determination provided in the embodiments of the present invention is shown. Detailed Implementation

[0035] 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.

[0036] It should be noted that the terms that may be used in the various embodiments of this application include or may include indications of the presence of the claimed function, operation, or element, and do not limit the addition of one or more functions, operations, or elements. Furthermore, as used in the various embodiments of this application, the terms "including," "having," and their cognates are intended only to indicate a specific feature, number, step, operation, element, component, or combination of the foregoing, and should not be construed as primarily excluding the presence of one or more other features, numbers, steps, operations, elements, components, or combinations of the foregoing, or adding one or more combinations of the foregoing.

[0037] It should be understood that terms such as "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "multiple" means two or more, unless otherwise explicitly specified.

[0038] The technical terms used in this embodiment are described below.

[0039] Equivalent Advanced Core Soil Model: This model simplifies the advanced core soil ahead of the tunnel face into a mechanical model of a spherical cavity unloading problem. In this model, the cavity wall represents the free surface of the tunnel face, the radial displacement of the cavity wall represents the extrusion displacement at the center of the tunnel face, and the outer boundary of the spherical cavity is subjected to far-field stress. Using this model, the three-dimensional unloading problem ahead of the tunnel face can be transformed into a spherically symmetric problem for solution.

[0040] Equivalent reinforcement parameters: The improvement effects of different types of pre-reinforcement measures (grouting, anchor bolts, pipe roof) on the mechanical parameters of surrounding rock are uniformly converted into equivalent elastic modulus, equivalent cohesion and equivalent internal friction angle, so that the effects of different reinforcement methods can be compared under the same mechanical scale.

[0041] Effective far-field stress: The stress after reducing the initial stress of the original rock by the pipe roof load transfer factor, which is used as the outer boundary stress of the spherical cavity unloading problem. Without pipe roof reinforcement, the pipe roof load transfer factor is 1.0, and the effective far-field stress is equal to the initial stress of the original rock.

[0042] Elastic-plastic interface radius: In a spherical cavity unloading problem, the distance from the interface between the elastic and plastic zones to the cavity center. When the elastic-plastic interface radius equals the tunnel excavation radius, it indicates that the plastic zone has disappeared and the core soil is in a fully elastic state.

[0043] Extrusion deformation reduction rate: The ratio of the difference between the extrusion displacement of the center of the face before reinforcement and the extrusion displacement of the center of the face after reinforcement to the extrusion displacement of the center of the face before reinforcement, is used to characterize the control effect of pre-reinforcement on deformation.

[0044] Comprehensive strength improvement coefficient: The ratio of the shear strength after reinforcement to the shear strength before reinforcement. The shear strength before and after reinforcement is calculated based on the Mohr-Coulomb shear strength criterion under a unified reference normal stress, and is used to characterize the improvement effect of pre-reinforcement on the mechanical parameters of the surrounding rock.

[0045] Safety factor: The ratio of critical load to effective far-field stress, used to characterize the safety reserve level of the core soil at the preset limit state.

[0046] False convergence risk: The risk that the deformation index meets the requirements but the safety reserve is insufficient, that is, the extrusion deformation at the working face has converged but the core soil still has the potential risk of gradual instability.

[0047] Figure 1 This document presents a flowchart illustrating a method for evaluating the pre-reinforcement effect of a soft rock tunnel face, as provided in an embodiment of the present invention. The following detailed description uses a highway tunnel traversing a Class V soft rock stratum as an example. In this embodiment, the tunnel depth is approximately 300m, and the tunnel excavation radius R = 5m. The original rock mechanical parameters are: elastic modulus E0 = 800MPa, cohesion c0 = 0.30MPa, internal friction angle φ0 = 25°, initial stress P0 = 7.0MPa (taking γ≈23.5kN / m³, lateral pressure coefficient K0 = 1), and Poisson's ratio ν = 0.32. A combined pre-reinforcement scheme is adopted: full-section pre-grouting, with an improved elastic modulus E0 = 800MPa. g0 =2000MPa, cohesion c g0 =0.80MPa, internal friction angle φ g0 =35°; GFRP anchor bolts are 55 in number, with a diameter d b =25mm, effective anchorage length L b =6m, elastic modulus E b =40GPa, pull-out strength τ at the anchor-soil interface b =0.2MPa. The extrusion displacement u at the working face was measured on-site after construction was completed. e,field =13.5mm. Semi-analytical solution parameters: shear dilatation angle ψ=0, geometric correction factor χ=1, allowable extrusion displacement u at the working face. e,lim =50mm, allowable plastic zone radius R p,lim =8m. The method includes the following steps:

[0048] S101, obtain the tunnel engineering geological parameters, tunnel face cross-sectional parameters, and design parameters of pre-reinforcement measures for the soft rock tunnel face; among which, the tunnel engineering geological parameters include the original rock mechanical parameters and the original rock initial stress, and the tunnel face cross-sectional parameters include the tunnel excavation radius.

[0049] Specifically, the original rock mechanical parameters include the original rock elastic modulus E0, the original rock cohesion c0, and the original rock internal friction angle φ0, with the original rock initial stress being P0. The tunnel face cross-sectional parameters include the tunnel excavation radius R. The pre-reinforcement design parameters include grouting parameters, anchor bolt parameters, and pipe roof parameters.

[0050] The design parameters of pre-reinforcement measures refer to the original data describing the physical properties, geometric dimensions, and layout of the pre-reinforcement measures, such as the grouting reinforcement range, anchor length and spacing, pipe roof diameter and circumferential layout angle, etc. These parameters are usually derived from engineering design drawings or construction plans, and do not directly reflect the mechanical state of the surrounding rock after reinforcement.

[0051] S102, calculate the equivalent reinforcement parameters and effective far-field stress based on the design parameters of the pre-reinforcement measures.

[0052] Specifically, pre-reinforcement measures, including grouting reinforcement, anchor bolt reinforcement, and pipe roof reinforcement, are common knowledge in this technical field. However, different pre-reinforcement measures have fundamentally different mechanisms of action on the tunnel face. For example, grouting mainly alters the physical and mechanical properties of the soil and rock through cementation, belonging to the material improvement path; anchor bolts mainly provide radial confining pressure through axial constraint, belonging to the reinforcement path; while pipe roofs and other support structures mainly share the overburden load through the arch effect, belonging to the stress transfer path. To evaluate the effectiveness of these heterogeneous measures at the same scale, this embodiment converts the physical design parameters of each measure into unified mechanical model inputs based on their specific mechanical action paths. The equivalent reinforcement parameters characterize the overall constitutive relationship of the core soil after reinforcement, such as the equivalent elastic modulus, equivalent cohesion, and equivalent internal friction angle; the effective far-field stress characterizes the reduction or adjustment effect of external loads transferred to the core soil, such as the load transfer coefficient. Through this mapping mechanism, regardless of the actual reinforcement method or its combination, they are ultimately normalized to material properties and boundary conditions that the model can recognize, thus solving the problem of incompatibility between cross-method parameters.

[0053] In this embodiment, in actual reinforcement projects, pre-reinforcement measures include a combination of grouting reinforcement and pipe roof reinforcement, a combination of grouting reinforcement and anchor reinforcement, a combination of anchor reinforcement and pipe roof reinforcement, and a combination of grouting reinforcement, anchor reinforcement, and pipe roof reinforcement.

[0054] In practical engineering, pre-reinforcement of soft rock tunnel faces typically employs a combination of two or three measures. This embodiment uses four typical combination schemes as examples to illustrate the calculation process of equivalent reinforcement parameters and effective far-field stress. For the combination of grouting reinforcement and pipe roof reinforcement, grouting directly improves the physical and mechanical properties of the surrounding rock through grout bonding, while pipe roofing transfers part of the load to the supported section ahead through the beam effect. Both measures act on the core soil through material parameter improvement and load boundary condition reduction, respectively. The equivalent reinforcement parameters are contributed only by grouting reinforcement, while pipe roofing only contributes to the effective far-field stress reduction. For the combination of grouting reinforcement and anchor reinforcement, grouting improves the overall mechanical parameters of the surrounding rock, while anchors provide radial constraint through axial tension and interface shear stress. Both measures act on the core soil through material parameter improvement, following a step-by-step superposition sequence of first improving and then reinforcing.

[0055] For the combined measures of anchor reinforcement and pipe roof reinforcement, the anchors enhance the mechanical parameters of the surrounding rock through reinforcement and constraint, while the pipe roof reduces the effective far-field stress through load transfer. The two measures act on the core soil through material parameter improvement and load boundary condition reduction, respectively. The equivalent reinforcement parameters are contributed only by the anchor reinforcement, while the pipe roof only contributes to the reduction of effective far-field stress.

[0056] For combined reinforcement measures involving grouting, anchor bolts, and pipe roofs, the three measures are applied in a step-by-step, superimposed order: first improvement, then reinforcement, and finally stress reduction. The equivalent parameters after grouting improvement serve as the basis for anchor bolt reinforcement, while the pipe roof only contributes to effective far-field stress reduction.

[0057] In a combined pre-reinforcement scheme of grouting and anchor bolt reinforcement, the equivalent reinforcement parameters and effective far-field stress are calculated based on the corresponding design parameters of the pre-reinforcement measures. It is understood that the equivalent reinforcement parameters described in this embodiment include the equivalent elastic modulus E. * Equivalent cohesion c * and equivalent internal friction angle φ * The effective far-field stress is the stress after the original rock initial stress P0 is reduced by the load transfer coefficient β of the pipe roof.

[0058] Specifically, in the case of pipe-free roof reinforcement, the load transfer factor β=1.0, and the effective far-field stress P eff =β·P0=1.0×7.0=7.0MPa, in other words, the effective far-field stress is equal to the initial stress of the original rock.

[0059] like Figure 2 As shown, grouting reinforcement directly improves the physical and mechanical properties of the surrounding rock through grout bonding, and its equivalent parameters are calculated using the area-weighted method. The first design parameters of the grouting reinforcement measure are obtained, including the area A of the grouting improvement zone. g Area A of the unimproved zone uMechanical parameters of the grouting improvement zone (including the elastic modulus E of the grouting improvement zone) g0 , Cohesion of the grouting improvement zone c g0 φ, the friction angle within the grouting improvement zone g0 ) and the original rock mechanical parameters (including the original rock elastic modulus E0, the original rock cohesion c0, and the original rock internal friction angle φ0).

[0060] Based on the area of ​​the grouting-improved zone, the area of ​​the unimproved zone, the mechanical parameters of the grouting-improved zone, and the mechanical parameters of the original rock, the equivalent elastic modulus E is calculated using the area-weighted method. g Equivalent cohesion c g and equivalent internal friction angle φ g .

[0061] The equivalent elastic modulus is calculated by direct area weighting: E g =(A g ·E g0 +A u ·E0) / (A g +A u ).

[0062] Equivalent cohesion is calculated directly by area weighting: c g =( A g ·c g0 + A u ·c0) / (A g +A u The equivalent internal friction angle is obtained by inverse switching the area weighted value of the friction parameter tanφ, i.e., first calculate: tanφ g =(A g ·tanφ g0 +A u ·tanφ0) / (A g +A u ), and then by φ g =arctan(tanφ g ) Obtained when full-section grouting A u =0, at this time E g =E g0 c g =c g0 φ g =φ g0 In this embodiment, if advanced grouting reinforcement (modified type) is used alone, the area A of the grouting improvement zone is taken as... g =78.54m², unmodified area Au=0 (full cross-section grouting), elastic modulus E of grouting modified area g0 =2000MPa, cohesion of the grouting improvement zone c g0 =0.80MPa, friction angle φ in the grouting improvement zone g0=35°, original rock elastic modulus E0=800MPa, original rock cohesion c0=0.30MPa, original rock internal friction angle φ0=25°. Due to A u =0, the equivalent reinforcement parameter is the parameter of the grouting improvement zone: E g =2000MPa, c g =0.80MPa, φ g =35°.

[0063] like Figure 2 As shown, anchor bolt reinforcement refers to forming a reinforced composite by applying longitudinal constraints through high-strength members. Its stiffness parameter is directly equivalent using a parallel hybrid law, and its strength parameter is equivalent through the anchor bolt reinforcement amount. The second design parameters for the anchor bolt reinforcement measure are obtained, including anchor bolt arrangement parameters (including the number of anchor bolts N). b Anchor bolt diameter d b Effective anchorage length L of anchor bolt b Equivalent core soil cross-sectional area A c Equivalent influence length L of core soil c ) and anchor bolt interface mechanical parameters (including anchor bolt cross-sectional area A) b Elastic modulus E of anchor bolt b τ, the pull-out strength of the anchor bolt interface b ).

[0064] Calculate the equivalent volume fraction η of anchor bolts based on anchor bolt arrangement parameters. b =(N b ·A b ·L b ) / (A c ·L c Based on the equivalent volume fraction η of the anchor bolt b And the elastic modulus E of the anchor bolt b The equivalent elastic modulus increment ΔE is calculated using the parallel hybrid law. b =η b ·(E b -E0)·λ E , where λ E The comprehensive correction coefficient is determined by experiments, numerical calculations, or field monitoring inversion.

[0065] The equivalent anchorage constraint stress q is calculated based on anchor bolt arrangement parameters and anchor bolt interface mechanical parameters. b =(N b ·π·d b ·L b ·τ b ) / A c Based on the equivalent anchorage constraint stress q b and calibration factors (including cohesion calibration factor k) c and friction parameter calibration coefficient k φCalculate the cohesion increment Δc b =k c ·q b and the friction parameter increment Δ(tanφ)b=k φ ·q b / σ ref , where σ ref To unify the reference normal stress.

[0066] The equivalent elastic modulus increment ΔE b Cohesion increment Δc b And the friction parameter increment Δ(tanφ) b The equivalent reinforcement parameters are obtained by superimposing them onto the original rock mechanical parameters: E * =E0+ΔE b c * =c0+Δc b tanφ * =tanφ0+Δ(tanφ) b .

[0067] In this embodiment, if anchor bolt reinforcement (reinforced type) is used alone, the number of anchor bolts N is taken as follows. b =55, Anchor bolt diameter d b =25mm, effective anchorage length L of anchor bolt b =6m, equivalent core soil cross-sectional area A c =78.54m², Anchor bolt interface pull-out strength τ b =0.2MPa, calibration coefficient k c =1.5, k φ =0. Calculate the equivalent anchorage constraint stress q. b =55×π×0.025×6×0.2 / 78.54=0.066MPa, cohesion increment Δc b =1.5×0.066=0.10MPa, friction parameter increment Δ(tanφ) b =0.

[0068] like Figure 2 As shown, when the pre-reinforcement measures are a combination of grouting reinforcement, anchor bolt reinforcement, and pipe roof reinforcement, the equivalent reinforcement parameters are calculated using a step-by-step superposition rule. First, the equivalent parameters after grouting reinforcement are calculated. Then, the equivalent parameters after anchor bolt reinforcement are superimposed on the equivalent parameters after grouting reinforcement to obtain the equivalent reinforcement parameters of the combined pre-reinforcement measures of grouting reinforcement, anchor bolt reinforcement, and pipe roof reinforcement.

[0069] For example, the first step is to calculate the equivalent parameters after grouting reinforcement according to the mechanical path of grouting reinforcement: due to full-section grouting (A u =0), the equivalent parameter is the parameter of the grouting improvement zone, Eg =2000MPa, c g =0.80MPa, φ g =35°. The second step is to superimpose the equivalent parameters of the anchor bolt reinforcement onto the equivalent parameters of the grouting reinforcement: equivalent anchorage constraint stress q. b =0.066MPa, cohesion increment Δc b =0.10MPa, elastic modulus increment ΔE b Calculated according to the parallel mixed law:

[0070] Take the equivalent influence length L of the core soil c =6m, equivalent volume fraction of anchor bolt η b =(N b ·A b ·L b ) / (A c ·L c ) = 55 × 4.91 × 10 -4 ×6 / (78.54×6)≈3.44×10 -4 ;

[0071] Therefore, the elastic modulus increment ΔE b =η b ·(E b −E0)·λ E =3.44×10 -4 ×(40000−800)×1.0≈13.5MPa, thus obtaining the design equivalent reinforcement parameter E. d * =E g +ΔE b =2000+13.5≈2014MPa.

[0072] The equivalent reinforcement parameter c is obtained after superposition. d * =c g +Δc b =0.90MPa, φ d * =φ g =35°.

[0073] The load transfer coefficient β of the pipe roof is calculated based on the pipe roof parameters. The product of the initial stress P0 of the original rock and the load transfer coefficient β of the pipe roof is taken as the effective far-field stress P. eff =β·P0. When there is no pipe roof reinforcement, the load transfer coefficient of the pipe roof is taken as 1. When there is pipe roof reinforcement, the load transfer coefficient of the pipe roof is calculated or calibrated by pipe roof parameters such as pipe roof stiffness, circumferential spacing, and effective length. At this time, the load transfer coefficient of the pipe roof is less than 1.

[0074] Since the combined grouting and anchor reinforcement measures do not include pipe roof reinforcement, and the pipe roof load transfer coefficient β=1.0, the initial stress of the original rock is taken as the effective far-field stress, i.e., P. eff =P0.

[0075] S103. Based on the tunnel excavation radius, the geometric boundary of the spherical cavity is determined. The three-dimensional unloading problem in front of the tunnel face of the soft rock tunnel is equivalent to the unloading problem of the spherical cavity. The equivalent reinforcement parameters and effective far-field stress are substituted into the unloading problem of the spherical cavity to solve for the extrusion displacement of the center of the tunnel face after reinforcement and the radius of the elastic-plastic interface after reinforcement. At the same time, the original rock mechanical parameters and the original rock initial stress are substituted into the unloading problem of the spherical cavity to solve for the extrusion displacement of the center of the tunnel face before reinforcement and the radius of the elastic-plastic interface before reinforcement.

[0076] Specifically, the equivalent advanced core soil model simplifies the advanced core soil in front of the tunnel face into a spherical cavity unloading problem. The geometric boundary of the spherical cavity is determined based on the tunnel excavation radius, and the inner radius of the spherical cavity is the tunnel excavation radius. The three-dimensional unloading problem in front of the soft rock tunnel face is equivalent to the spherical cavity unloading problem. The cavity wall of the spherical cavity represents the free surface of the tunnel face, and the radial displacement of the cavity wall represents the extrusion displacement at the center of the tunnel face.

[0077] like Figure 4 As shown, the spherical cavity mechanical model simplifies the advanced core soil in front of the tunnel face into a spherical cavity. The inner boundary of the spherical cavity is the free surface of the tunnel face, and the outer boundary is subjected to far-field stress. The elastoplastic interface divides the surrounding rock region into elastic and plastic zones. The specific process of solving the spherical cavity unloading problem is as follows:

[0078] S1031, Establish a spherical symmetric equilibrium differential equation and set the boundary conditions of the spherical cavity; wherein, the spherical symmetric equilibrium differential equation describes the radial stress and tangential stress of the spherical cavity along the radial direction, and the boundary conditions include an inner boundary with zero radial stress and an outer boundary subjected to effective far-field stress.

[0079] Specifically, the spherically symmetric equilibrium differential equation describes the radial stress σ of the spherical cavity. r and tangential stress σ θ Equilibrium relationship along radial r: dσ r / dr +2(σ r -σ θ ) / r=0. Set the boundary conditions for the spherical cavity, including that the inner boundary is a free surface of the face and the radial stress of the inner boundary is zero (σ when r=R). r =0), the outer boundary is subjected to far-field stress (σr=P when r→∞). eff or σ r =P0)

[0080] S1032, using the Mohr-Coulomb yield criterion and the non-associated flow law to describe the plastic region, and solving the spherically symmetric equilibrium differential equations, the Mohr-Coulomb yield criterion, and the non-associated flow law simultaneously, yields the radial stress σ at the elastoplastic interface. r,fp .

[0081] Specifically, the radial stress σ at the elastic-plastic interface is calculated by simultaneously applying the spherically symmetric Lame solution in the elastic region and the Mohr-Coulomb yield criterion. r,fp =[3·P eff ·(1-sinφ)-4·c·cosφ] / (3+sinφ).

[0082] The plastic region adopts the Mohr-Coulomb yield criterion and the non-associated flow law, with a shear dilatation angle of _____. When experimental data is lacking, take Related flows are a special case of this method, namely... When the calculated yield condition is not triggered, take... The equivalent core soil is in a fully elastic state; when hour, This is the plastic region, and its thickness is... .

[0083] S1033, when the radial stress at the elastoplastic interface is less than or equal to zero, the radius of the elastoplastic interface is set to be equal to the tunnel excavation radius, and the extrusion displacement at the center of the tunnel face is calculated based on the radial displacement of the cavity wall and the geometric correction coefficient; wherein, the geometric correction coefficient is the conversion coefficient between the radial displacement of the spherical cavity wall and the extrusion displacement at the center of the tunnel face.

[0084] Specifically, when the radial stress σ at the elastoplastic interface r,fp When the value is less than or equal to zero, it indicates that the radial stress of the cavity wall has not reached the yield condition, and the equivalent core soil is in a fully elastic state. At this time, let the radius R of the elastoplastic interface be... fp Equal to the tunnel excavation radius R, and calculate the extrusion displacement u at the center of the tunnel face. e Specifically, the formula for calculating the extrusion displacement at the center of the tunnel face is u. e =χ·u R The geometric correction factor χ is the conversion factor between the radial displacement of the spherical cavity wall and the extrusion displacement of the center of the face. In the basic calculation mode, χ=1.

[0085] S1034, when the radial stress at the elastoplastic interface is greater than zero, the lower limit of the search interval is taken as the tunnel excavation radius, and the upper limit of the search interval is calculated based on the radial stress at the elastoplastic interface, the tunnel excavation radius, the cohesion and the internal friction angle. The midpoint of the search interval is taken as the trial value, and the stress field of the plastic zone is integrated from the cavity wall of the spherical cavity outward with a set step size to obtain the radial stress of the plastic zone at the midpoint.

[0086] Specifically, when the radial stress at the elastoplastic interface is greater than zero, the bisection method is used to search for the radius R of the elastoplastic interface. fp The specific process is as follows:

[0087] (a) Initialize the search interval [r L ,r U ]:rL=R; ; where r L r is the lower bound of the search interval. U The upper limit of the search interval is given by c, which represents the cohesion. This represents the angle of internal friction.

[0088] (b) Take the midpoint r of the search interval M =(r L +r U ) / 2;

[0089] (c) The stress field in the plastic region is determined by integrating outward from the cavity wall r=R with dr as the numerical step size, as shown in the following expression.

[0090] ;in, Indicates the outer boundary of the spherical cavity. This represents the stress field in the plastic region.

[0091] , will σ r Updated to ,r updated to Repeat until r ≥ r M The radial stress σ in the plastic zone is obtained. r,pl (rM);

[0092] (d) Calculate the residual f = σ between the radial stress in the plastic zone and the radial stress at the elastoplastic interface at the midpoint of the search interval. r,pl (rM)-σ r,fp Update the search interval based on the sign of the residual (if f > 0, let r). U =r M Otherwise let r L =r M );

[0093] (e) Repeat (b) to (d) until the residual |f| converges to less than the set tolerance tol, and obtain the radius R of the elastoplastic interface. fp .

[0094] (f) If the binary iteration fails to converge within the set search interval to obtain a result that satisfies the residual condition, it will indicate that the input parameters are abnormal and the surrounding rock mechanical parameters and boundary conditions need to be checked.

[0095] The process of solving the displacement field in the plastic region is as follows: Based on the radial stress σ at the elastic-plastic interface r,fp Calculation of elastic displacement u(R) at the elastoplastic interface for far-field stress fp )=(P eff -σ r,fp )·R fp / (4G) (the displacement is based on the distance to infinity in the far field, i.e., relative displacement), where G is the shear modulus. Self-elastic-plastic interface (r=R) fp Numerical integration along the radial direction inward with a set step size dr reveals the non-associated flow law and strain-displacement relationship (ε). r =du / dr,ε θ =u / r), gradually update the displacement of the plastic region until it reaches the cavity wall of the spherical cavity (r=R), and obtain the radial displacement u of the cavity wall. R .

[0096] Based on the implementation method described above, the radius R of the elastoplastic interface before reinforcement is obtained by solving (substituting E0=800MPa, c0=0.30MPa, φ0=25°, P0=7.0MPa). fp0 ≈9.23m, reinforcement of the center extrusion displacement u of the front face e0 ≈52.3mm. Solve (substitute into E) * =1771MPa, c * =0.78MPa, φ * =35°, P eff =7.0MPa) to obtain the radius R of the reinforced elastoplastic interface. fp * ≈5.98m, extrusion displacement u at the center of the reinforced working face e * ≈13.5mm.

[0097] S104, based on the extrusion displacement of the center of the tunnel face before reinforcement, the extrusion displacement of the center of the tunnel face after reinforcement, the radius of the elastic-plastic interface before reinforcement, the radius of the elastic-plastic interface after reinforcement, the equivalent reinforcement parameters, the original rock mechanical parameters, and the effective far-field stress, calculate the extrusion deformation reduction rate, the comprehensive strength improvement coefficient, and the safety factor.

[0098] like Figure 3 As shown, based on the extrusion displacement u at the center of the reinforced front face...e0 and the extrusion displacement u at the center of the reinforced face e * Calculate the extrusion deformation reduction rate η e =(u e0 -u e * ) / u e0 ×100%. In this embodiment, η e =(52.3-13.5) / 52.3×100%=74.2%. Extrusion deformation reduction rate η e The ratio of the difference between the center extrusion displacement of the front face and the center extrusion displacement of the rear face to the center extrusion displacement of the front face.

[0099] Based on equivalent cohesion c * Equivalent internal friction angle φ * The original rock cohesion c0, the original rock internal friction angle φ0, and the unified reference normal stress σ ref Calculate the overall strength improvement coefficient I c Overall strength improvement coefficient I c The ratio of the shear strength after reinforcement to the shear strength before reinforcement is given. Both the shear strength after reinforcement and the shear strength before reinforcement are calculated based on the Mohr-Coulomb shear strength criterion: Shear strength after reinforcement τ * =c * +σ ref ·tanφ * Before reinforcement, the shear strength τ0 = c0 + σ ref ·tanφ0,I c =τ * / τ0. In this embodiment, σ is taken. ref =P0=7.0MPa, I c =(0.78+7.0×tan35°) / (0.3+7.0×tan25°)=(0.78+4.9) / (0.3+3.26)≈1.59.

[0100] The process of calculating the safety factor is as follows:

[0101] Obtain the allowable extrusion displacement u at the working face e,lim And the allowable elastoplastic interface radius R p,lim Allowable extrusion displacement u at the working face e,lim And the allowable elastoplastic interface radius R p,lim The determination is based on the surrounding rock grade, tunnel dimensions, construction risk level, or historical engineering data. In this embodiment, u e,lim =50mm, R p,lim =8m.

[0102] With effective far-field stress P effBased on this, the outer boundary load of the spherical cavity unloading problem is gradually increased. Specifically, the outer boundary stress is set to the load factor λ. load With effective far-field stress P eff The product of , i.e., P = λ load ·P eff , from λ load =1, and gradually increase λload. For each level of external load P, calculate the corresponding extrusion displacement u at the center of the working face using the spherical cavity unloading elastoplastic method described in claim 5. e (P) and the radius R of the elastoplastic interface fp (P).

[0103] When the center of the tunnel face is squeezed out, displacement u e (P) Achieve the allowable extrusion displacement u at the working face. e,lim At that time, record the corresponding first critical load P. cr,u When the radius R of the elastoplastic interface fp (P) Reaching the allowable elastoplastic interface radius R p,lim At that time, record the corresponding second critical load P. cr,R Take the first critical load P. cr,u Second critical load P cr,R The minimum value in the range is taken as the critical load P. cr =min(P cr,u ,P cr,R ).

[0104] Based on the critical load P cr and effective far-field stress P eff The ratio is used to calculate the safety factor F. s =P cr / P eff When the extrusion displacement at the center of the tunnel face under the current load is greater than or equal to the allowable extrusion displacement u... e,lim Or the radius of the elastoplastic interface under the current load is greater than or equal to the allowable elastoplastic interface radius R. p,lim When determining the safety factor F s No greater than 1.

[0105] In this embodiment, the search is performed by progressively increasing the outer boundary load to obtain the result when u e =u e,lim The critical load P corresponding to =50mm cr,u ≈18.84MPa, at this time R fp ≈7.06m has not yet reached R p,lim =8m, therefore P cr =P cr,u =18.84 MPa, correspondingly, the safety factor F s =P cr / P eff=18.84 / 7.0=2.69.

[0106] In one embodiment, the method further includes: calculating the pre-convergence deformation reduction rate and the stiffness improvement coefficient; and outputting a risk status prompt when the difference between the level corresponding to the pre-convergence deformation reduction rate and the level corresponding to the extrusion deformation reduction rate is greater than or equal to a preset level difference, or the difference between the level corresponding to the stiffness improvement coefficient and the level corresponding to the comprehensive strength improvement coefficient is greater than or equal to a preset level difference.

[0107] Specifically, such as Figure 5 As shown, Figure 5 The distribution curve of the pre-convergence displacement in front of the tunnel face as a function of longitudinal distance is shown to illustrate the deformation comparison before and after reinforcement. First, the process of calculating the pre-convergence deformation reduction rate is as follows:

[0108] Based on the radius R of the elastic-plastic interface before reinforcement fp0 And the radius R of the reinforced elastoplastic interface fp * The pre-convergence displacement u before reinforcement was calculated using a Panet-type longitudinal deformation correction mapping function. p0 and the pre-convergence displacement u after reinforcement p * The Panet-type longitudinal deformation correction mapping function establishes the mapping relationship between the extrusion displacement at the center of the face and the forward pre-convergence displacement: u p =K(x)·u e Where K(x) is the comprehensive mapping function, which can be determined based on the range R of the plastic region. fp / R, Poisson's ratio ν, and longitudinal influence range L p Calculation or calibration. The comprehensive mapping function is represented in Panet-type exponential decay form, which is K0(x) = κ before hardening. 0,0 ·e^(−x / ξ0), after reinforcement, becomes K * (x)=κ *,0 ·e^(−x / ξ * ), where x is the dimensionless distance in front of the face of the tunnel (x = x' / R, x' is the longitudinal distance from the face of the tunnel), x ≥ 0; κ 0,0 κ *,0 is the initial mapping coefficient at the face of the tunnel (x=0).

[0109] Based on the equivalent advanced core soil model, the pre-convergence displacement at the tunnel face and the extrusion displacement at the center of the tunnel face adopt the same conversion benchmark (χ=1). Therefore, in this embodiment, κ is taken as χ. 0,0 =κ *,0 =1; ξ0、ξ * The length of the longitudinal influence feature (a multiple of R, L) p =ξ·R), and the range of the plastic region R fp / R and Poisson's ratio ν are related and can be determined by on-site monitoring or based on the radius R of the plastic zone. fp Calculation. Due to the different ranges of the plastic zone before and after reinforcement, the comprehensive mapping functions K0(x) and K... * (x) are different.

[0110] Stiffness improvement factor I E The calculation process is as follows: Stiffness improvement coefficient I E Let I be the ratio of the shear modulus after reinforcement to the shear modulus before reinforcement. If the Poisson's ratio ν* after reinforcement is equal to the Poisson's ratio ν0 before reinforcement, then it simplifies to I. E =E * / E0. In this embodiment, the stiffness improvement factor I E =1771 / 800=2.21. Stiffness improvement factor I E Used to verify the coordination of deformation control mechanisms, it does not participate in the direct determination of the basic grade. Specifically, the shear modulus is calculated according to... Calculate, where, The ratio is Poisson's ratio, and is taken as 0.3 to 0.35 for soft rocks.

[0111] Specifically, the pre-convergence deformation reduction rate and stiffness improvement coefficient defined in this embodiment are used as auxiliary verification indicators. Their role is to verify the physical coordination between the extrusion deformation reduction rate, the comprehensive strength improvement coefficient, and the safety factor, rather than directly participating in the assessment of the foundation grade. The pre-convergence deformation reduction rate reflects the degree of pre-convergence of the surrounding rock within a certain range ahead of the tunnel face before excavation. Its calculation relies on the longitudinal deformation correction mapping function, which considers factors such as the plastic zone range, Poisson's ratio, and longitudinal influence length, and can characterize the constraint effect of reinforcement measures on the deformation of deep surrounding rock. The stiffness improvement coefficient is defined as the ratio of the equivalent shear modulus after reinforcement to the original rock shear modulus. When the Poisson's ratio does not change significantly, it can be simplified to the ratio of the equivalent elastic modulus to the original rock elastic modulus, used to characterize the improvement in the overall stiffness of the surrounding rock. These two auxiliary indicators cross-validate the main evaluation system composed of the extrusion deformation reduction rate and the comprehensive strength improvement coefficient from two aspects: longitudinal deformation distribution and material stiffness properties.

[0112] For example, when the auxiliary verification index deviates significantly from the corresponding index in terms of grade assessment, i.e., the grade difference reaches or exceeds the preset grade difference (e.g., 2 grades), a risk status warning will be output. For instance, if the extrusion deformation reduction rate is rated as excellent, but the pre-convergence deformation reduction rate is only average or insufficient, it may mean that the reinforcement measures only control the apparent extrusion in the local area of ​​the tunnel face, but the constraint on the deep surrounding rock ahead is insufficient, posing a risk of the reinforcement range being too short or the longitudinal effect decaying too quickly. Another example is if the stiffness improvement coefficient is significantly higher than the comprehensive strength improvement coefficient, indicating that the surrounding rock stiffness has been significantly improved but the strength reserve is insufficient. This state of strong stiffness and weak strength is highly likely to lead to brittle failure or gradual instability under long-term loads. By setting this trigger mechanism, the assessment method can effectively cover marginal cases where the main indicators seem normal but the internal mechanical mechanisms are inconsistent, preventing hidden dangers from being masked by meeting the standards of a single dimension.

[0113] S105, based on the extrusion deformation reduction rate, comprehensive strength improvement coefficient and safety factor, a two-step classification judgment method is used to determine the pre-reinforcement effect of the tunnel face in soft rock.

[0114] Specifically, the two-step classification method includes two stages: determining the basic level and setting a safety factor limit. This is based on the extrusion deformation reduction rate η. e =74.2%, Comprehensive strength improvement coefficient I c =1.59 and safety factor F s =2.69, a two-step graded judgment method was used to determine the pre-reinforcement effect. The first step, based on η... e and I c The basic level is determined to be good; the second step is to use a safety factor F. s Limit correction is applied to the basic level, if the safety factor F s =2.69 is greater than the third preset threshold of 1.5, so there is no level limit and the pre-reinforcement effect remains good.

[0115] In this embodiment, the first step of the two-step grading method is the basic grade determination stage. A grading threshold library is obtained, which includes the extrusion deformation reduction rate η. e The first preset threshold and the comprehensive strength improvement coefficient I c The second preset threshold. The graded threshold library supports the establishment of multiple threshold systems based on surrounding rock grade, tunnel cross-sectional dimensions, and regional geological conditions.

[0116] In this embodiment, as Figure 6 As shown, the first preset threshold includes: η e ≥75% is considered excellent, 50%≤η e <75% is considered good, 30% ≤η e <50% is considered normal, η e <30% is insufficient; the second preset threshold includes: Ic ≥2.0 is excellent, 1.5≤I c <2.0 is good, 1.0≤I c <1.5 is considered normal, I c <1.0 is insufficient. The extrusion deformation reduction rate η e The deformation control level is determined by comparing it with the first preset threshold.

[0117] In this embodiment, η e =74.2% is between 50% and 75%, indicating a good deformation control level. The overall strength improvement factor I... c The parameter improvement level is determined by comparing it with a second preset threshold. In this embodiment, I... c =1.59 is between 1.5 and 2.0, indicating a good parameter improvement level. The minimum value between the deformation control level and the parameter improvement level is determined as the basic level. In this embodiment, the deformation control level is good, the parameter improvement level is good, and the basic level is good. When the basic level is the lowest level (insufficient), the pre-reinforcement effect is determined to be the lowest level (insufficient), and the second step is not executed. That is, when η e <30% or I c When the value is less than 1.0, the pre-reinforcement effect is directly judged as insufficient.

[0118] like Figure 6 As shown, the second step of the two-step classification method is the safety factor limit stage. The safety factor F is obtained. s The third preset threshold. In this embodiment, the third preset threshold includes: F s There is no limit to the number of levels when ≥1.5, and 1.2≤F s When the strength is less than 1.5, the pre-reinforcement effect is the best, considered "good"; when it is 1.0... <F s When the value is less than 1.2, the pre-reinforcement effect is at best moderate. s If the pre-reinforcement effect is ≤1.0, it is directly judged as insufficient. If the safety factor F... s If the value is less than the corresponding threshold in the third preset threshold, the pre-reinforcement effect will be limited to a level not exceeding the safety factor. For example, when the basic level is excellent but F... s When =1.3, since 1.2≤F s <1.5, the pre-reinforcement effect is corrected from excellent to good. If the safety factor F s If the value is greater than or equal to the corresponding threshold in the third preset threshold, then the basic level is maintained as the pre-reinforcement effect. In this embodiment, F s =2.69, greater than 1.5, no grade limit, indicating that the pre-reinforcement effect of the soft rock tunnel face remains at a good basic level.

[0119] The two-step comprehensive grading process also includes weakness identification, as detailed below:

[0120] When the pre-reinforcement effect does not reach the highest level (excellent), calculate the normalized shortest board degree D for each evaluation index. j Normalized bottleneck degree D j The target level threshold T for this indicator j With the current value X j The difference relative to the target level threshold T j The ratio, i.e., D j =(T j -X j ) / T j Among them, T j X is the threshold corresponding to the target level (excellent). j This is the current value of the indicator.

[0121] The assessment index with the highest normalized shortness ratio is taken as the shortness index. When the safety factor is a limiting factor, it is also included in the calculation of the normalized shortness ratio. In this embodiment, the pre-reinforcement effect is good, but not excellent. The normalized shortness ratio of each assessment index is calculated as: D ηe =(75-74.2) / 75≈1.1%, D Ic =(2.0-1.594) / 2.0≈20.3%. D Ic >D ηe And the difference exceeds 2%, therefore I c This is a weak point indicator, reflecting that the overall improvement in strength has not yet reached the excellent threshold.

[0122] like Figure 6 The two-step comprehensive grading judgment logic shown eliminates the possibility of a high score on a single indicator masking potential safety hazards, ensuring that the assessment results can truly reflect the stable state of the working face.

[0123] Specifically, the first step is to determine the foundation grade. The foundation grade is determined based on the lower of the individual grades corresponding to the deformation control index and the mechanical parameter improvement index. At this stage, the deformation control index (such as the extrusion deformation reduction rate) reflects the apparent suppression effect of reinforcement measures on the surrounding rock deformation, while the mechanical parameter improvement index (such as the comprehensive strength improvement coefficient) reveals the degree of improvement in the inherent strength of the surrounding rock. The lower grade is used instead of a weighted average or a higher grade because in geotechnical stability evaluation, deformation control and strength improvement are mutually necessary conditions: if only deformation is controlled but strength is not improved, the surrounding rock may be in a critical state of brittle failure; if only strength is improved but deformation is still too large, it indicates that the reinforcement measures have failed to effectively restrain the loosening of the surrounding rock. Therefore, the foundation grade is determined by the weaker of the two, ensuring the robustness of the evaluation benchmark. For example, if the deformation control index is rated as excellent, while the mechanical parameter improvement index is rated as average, the foundation grade is determined to be average.

[0124] The second step is to limit the basic level based on the safety factor. According to the numerical range of the safety factor (e.g., safety factor Fs), mandatory constraints are imposed on the basic level determined in the first step. This step is the core feature that distinguishes this embodiment from the traditional weighted scoring method; it treats the safety factor as an insurmountable threshold indicator, rather than an ordinary evaluation factor. The specific limiting rules are as follows:

[0125] If the safety factor is less than or equal to a first preset threshold, the comprehensive evaluation level is determined to be Level 1. In a preferred embodiment, the first preset threshold can be 1.0. When the safety factor is less than or equal to 1.0, it means that the current load has reached or exceeded the critical load, and the tunnel face is in a state of limit equilibrium or instability. Regardless of its deformation or strength indicators, the comprehensive evaluation result is forcibly determined to be the lowest level (i.e., insufficient) to warn of immediate risks.

[0126] If the safety factor is greater than the first preset threshold and less than or equal to the second preset threshold, the overall assessment level will be limited to no higher than the second level. For example, the second preset threshold can be 1.2. Within this range, although the working face has not yet become unstable, the safety reserve is extremely low, and it is in a barely stable state. At this time, even if the basic level is excellent or good, the overall assessment level is forcibly limited to average or lower to prevent misjudgment of long-term safety due to good short-term monitoring data.

[0127] If the safety factor is greater than the second preset threshold and less than or equal to the third preset threshold, the overall assessment level will be limited to no higher than the third level. For example, the third preset threshold can be 1.5. Within this range, the working face has a certain safety reserve, but it is still not sufficient. If the basic level is excellent, the overall assessment level will be limited to good; if the basic level itself is lower than good, the original basic level will remain unchanged.

[0128] When the safety factor is greater than the third preset threshold, the basic level is used as the comprehensive evaluation level. When the safety factor is greater than 1.5, it indicates that the working face has sufficient safety reserves. At this time, the safety margin no longer constitutes a limiting factor, and the comprehensive evaluation level is directly determined by the basic level, truly reflecting the actual effectiveness of reinforcement measures in deformation control and strength improvement.

[0129] The evaluation results for Level 1, Level 2, and Level 3 increase sequentially. It should be understood that the values ​​of 1.0, 1.2, and 1.5 mentioned above are merely recommended values ​​based on statistical experience in soft rock tunnel engineering. In practical applications, those skilled in the art can adjust the aforementioned preset thresholds according to the surrounding rock level, tunnel importance level, and construction risk tolerance. For example, for extremely high-risk deep-buried soft rock tunnels, the third preset threshold can be increased to 1.8 or 2.0; while for temporary support or low-risk conditions, the threshold can be appropriately relaxed. Any logical framework that maintains a safety margin as a threshold indicator for unidirectionally limiting the basic level falls within the scope of protection of this application.

[0130] Through the above two-step comprehensive grading strategy, this embodiment can effectively identify and avoid the risk of false convergence. False convergence refers to a situation where, under certain specific working conditions, reinforcement measures significantly improve the stiffness of the surrounding rock, resulting in a substantial reduction in extrusion deformation (excellent deformation index). However, due to poor grouting quality or insufficient anchoring force, the strength of the surrounding rock is not substantially improved (strength index is average or even insufficient), leading to a low safety factor. In traditional single deformation index assessment or simple weighted assessment systems, such working conditions are easily misjudged as good or even excellent, thus masking the potential hidden danger of progressive instability of the core soil. Under the grading mechanism of this embodiment, because the safety factor is lower than a preset threshold, the comprehensive assessment level is forcibly downgraded, thereby forcing engineers to focus on the shortcomings in strength and safety reserves, achieving a unity between the assessment results and the actual safety of the project.

[0131] In some embodiments, when the overall assessment level fails to reach the target level, reinforcement parameter adjustment suggestions can be generated based on the overall assessment level and the weakness index. Specifically, when the current overall assessment level is determined to be lower than the preset target level (e.g., excellent or good), optimization suggestions are generated. These generated suggestions do not rely on human experience for judgment, but are automatically generated based on the weakness index determined in the aforementioned embodiments, using preset mechanical mechanism mapping rules to generate targeted reinforcement parameter adjustment suggestion data. It should be understood that the target level can be dynamically set according to the engineering risk level, surrounding rock grade, or construction stage, and this application does not limit this.

[0132] The specific details of the reinforcement parameter adjustment suggestions are generated according to the different types of short board indicators, so as to accurately match the key mechanical factors that restrict stability.

[0133] When the shortest-plate index is used as a deformation control index, suggestions are generated to increase anchor bolt density or improve grouting modification parameters. Specifically, when the extrusion deformation reduction rate becomes the bottleneck restricting the overall grade, it indicates that the overall stiffness of the surrounding rock at the working face is insufficient or the longitudinal restraint effect is weak, resulting in excessive apparent deformation after excavation and unloading. At this time, the generated suggestion data points to measures to enhance the stiffness and restraint capacity of the surrounding rock. For example, it is suggested to increase the anchor bolt density to suppress the expansion of the plastic zone by increasing the equivalent elastic modulus and radial restraint stress of the reinforced composite; or it is suggested to improve the grouting modification parameters (such as expanding the grouting range and increasing the strength of the grout-bound stone body) to directly improve the deformation modulus of the matrix material. In a preferred embodiment, the suggestion data may also include a quantitative adjustment range based on the normalized shortest-plate degree value. For example, when the shortest-plate degree is large, it is suggested to increase the anchor bolt spacing from 1.2m to 0.8m, or increase the grouting diffusion radius by 20%, thereby making the optimization suggestions more operable.

[0134] When the weakest link index is the mechanical parameter improvement index, suggestions are generated to optimize the grouting mix ratio or increase reinforcement measures. Specifically, when the comprehensive strength improvement coefficient becomes the weakest link, it indicates that although the deformation of the surrounding rock may be controlled to some extent, its inherent shear strength is not sufficiently improved, posing a long-term stability hazard or risk of brittle failure. At this time, simply increasing stiffness is no longer sufficient to solve the problem; reinforcement of strength parameters must be addressed. Based on this, suggestions are generated to optimize the grouting mix ratio (such as adjusting the water-cement ratio, adding early-strength agents or ultrafine cement) to improve the cohesion and internal friction angle of the cementitious body; or suggestions are generated to increase reinforcement measures (such as using higher-strength glass fiber anchors or increasing anchor length) to enhance the peak strength and residual strength of the surrounding rock by increasing the equivalent anchorage constraint stress.

[0135] With the safety factor as the weakest link, recommended data is generated to improve the quality of grouting reinforcement, increase reinforcement constraints, or reduce the load-bearing capacity of pipe roofs. Specifically, when the safety factor becomes a weak link or even triggers the limit, it indicates that the tunnel face is in a state of low safety reserve or critical instability, and local adjustments to a single measure may not be sufficient to reverse the overall risk. Therefore, the generated recommended data covers multiple synergistic approaches: improving the quality of grouting reinforcement aims to reduce parameter reductions caused by construction defects and ensure that the design strength is achieved; increasing reinforcement constraints aims to enhance the ultimate bearing capacity of the core soil; and improving the load-bearing capacity of pipe roofs (such as reducing the circumferential spacing of pipe roofs, increasing the pipe diameter, or increasing the overlap length) aims to directly reduce the effective far-field stress acting on the core soil by lowering the load transfer coefficient. This multi-pronged recommendation strategy reflects the special nature of safety margin as a threshold indicator, namely, the safety reserve level must be rapidly improved through comprehensive means.

[0136] It should be noted that the generation process of the above-mentioned reinforcement parameter adjustment suggestions is entirely based on the inherent correlation between the mechanical model and the indicator system, rather than a simple rule lookup. The physical meaning of the short-board indicators is automatically matched with the mechanical action path of the pre-reinforcement measures, ensuring the scientific rigor and relevance of the suggestions. Furthermore, the output suggestion data format is not limited to text prompts; it can also be a structured list of parameter adjustments, recommended design change drawing annotations, or configuration files that can be directly imported into design software, facilitating rapid adoption and implementation by engineers. In this way, this embodiment transforms abstract evaluation levels into concrete engineering action guidelines, significantly enhancing the practical value and engineering guidance significance of the pre-reinforcement effect evaluation method.

[0137] In some embodiments, this embodiment also provides a method for determining the equivalent reinforcement parameters through reverse verification, namely:

[0138] Obtain the extrusion displacement of the tunnel face measured on-site;

[0139] Based on the on-site measured extrusion displacement of the tunnel face and the extrusion displacement of the center of the tunnel face after reinforcement, the comprehensive reinforcement effectiveness coefficient is obtained by using an iterative optimization method.

[0140] The equivalent reinforcement parameters are corrected based on the comprehensive reinforcement effectiveness coefficient to obtain the corrected equivalent reinforcement parameters.

[0141] Specifically, the bisection method is used to iteratively invert and derive the comprehensive reinforcement effectiveness coefficient. The input parameters include: the field-measured extrusion displacement at the center of the tunnel face. Equivalent reinforcement parameters Original rock mechanical parameters and convergence tolerance (1% can be taken as a value; this value is a recommended empirical value for engineering projects. Those skilled in the art can adjust it appropriately according to the required calculation accuracy, and are not limited to this value.) The process of using the bisection method to iteratively invert and calculate the comprehensive reinforcement effectiveness coefficient is as follows:

[0142] 1. Initialize the overall reinforcement effectiveness coefficient search range ,Pick .

[0143] 2. Based on the comprehensive reinforcement effectiveness coefficient Update the equivalent hardening parameters, i.e. , , If a certain equivalent reinforcement parameter has been independently confirmed by core sampling or in-situ testing, this parameter will not be included in the verification, and the confirmed value will be taken directly.

[0144] 3. Update the equivalent reinforcement parameters from step 2 above using the comprehensive reinforcement effectiveness coefficient. , , By substituting the measured load into the unloading problem of the spherical cavity, the extrusion displacement can be calculated. .

[0145] 4. Calculate the extrusion displacement at the center of the working face as measured on-site. and extrusion displacement The relative error between them, i.e. .

[0146] 5. If relative error Less than tolerance Then output the comprehensive reinforcement effectiveness coefficient. and the equivalent reinforcement parameters after reverse verification, otherwise: if (The equivalent reinforcement parameters are too weak), making Otherwise, ;renew Proceed to step 2.

[0147] For example, the equivalent reinforcement parameter E calculated through step S103 above... d * =2014MPa, c d * =0.90MPa, φ d * =35°, the calculated extrusion displacement deviates from the actual measured extrusion displacement on site. Using the bisection method, λ≈0.80 is obtained. The corrected equivalent reinforcement parameter is E. * =800+0.80×(2014-800)=1771MPa, c * =0.30 + 0.80 × (0.90 - 0.30) = 0.78 MPa. Since φ * It has been independently confirmed by core sampling tests, φ * The design value of 35° is taken and is not included in the λ correction.

[0148] The corrected equivalent reinforcement parameters are resubmitted into the spherical cavity unloading problem for solution, and the pre-reinforcement effect evaluation index and pre-reinforcement effect are recalculated. In this embodiment, the extrusion displacement u at the center of the tunnel face after reinforcement is recalculated by substituting the corrected equivalent reinforcement parameters. e * ≈13.5mm, radius R of the reinforced elastoplastic interface fp * ≈5.98m, the recalculated evaluation index is η e =74.2%, I c =1.59, F s =2.69, the pre-reinforcement effect is good.

[0149] When an equivalent reinforcement parameter has been independently verified, that parameter does not participate in the inversion; the comprehensive reinforcement effectiveness coefficient λ only affects the other parameters. For example, when the equivalent internal friction angle φ... * When independently confirmed by core sampling or in-situ testing, the equivalent internal friction angle φ * It does not participate in the inversion of the comprehensive reinforcement effectiveness coefficient λ, which only applies to the equivalent elastic modulus E. * and equivalent cohesion c * This approach ensures the physical reliability of the parameters while guaranteeing the uniqueness of the inversion parameters.

[0150] This invention also provides a system for evaluating the pre-reinforcement effect of soft rock tunnel faces, comprising:

[0151] The parameter acquisition module is used to acquire the tunnel engineering geological parameters, tunnel face cross-sectional parameters, and design parameters of pre-reinforcement measures for soft rock tunnels. Among them, the tunnel engineering geological parameters include the original rock mechanical parameters and the original rock initial stress, and the tunnel face cross-sectional parameters include the tunnel excavation radius.

[0152] The equivalent parameter calculation module is used to calculate the equivalent reinforcement parameters and effective far-field stress based on the design parameters of the pre-reinforcement measures.

[0153] The spherical cavity solution module is used to determine the geometric boundary of the spherical cavity based on the tunnel excavation radius. It transforms the three-dimensional unloading problem in front of the tunnel face in soft rock into a spherical cavity unloading problem. It substitutes the equivalent reinforcement parameters and effective far-field stress into the spherical cavity unloading problem to solve for the extrusion displacement at the center of the tunnel face after reinforcement and the radius of the elastic-plastic interface after reinforcement. At the same time, it substitutes the original rock mechanical parameters and the original rock initial stress into the spherical cavity unloading problem to solve for the extrusion displacement at the center of the tunnel face before reinforcement and the radius of the elastic-plastic interface before reinforcement.

[0154] The index calculation module is used to calculate the extrusion deformation reduction rate, comprehensive strength improvement coefficient and safety factor based on the extrusion displacement of the center of the tunnel face before reinforcement, the extrusion displacement of the center of the tunnel face after reinforcement, the radius of the elastic-plastic interface before reinforcement, the radius of the elastic-plastic interface after reinforcement, the equivalent reinforcement parameters, the original rock mechanical parameters and the effective far-field stress.

[0155] The comprehensive grading and judgment module is used to determine the pre-reinforcement effect of the tunnel face in soft rock by adopting a two-step grading and judgment method based on the extrusion deformation reduction rate, comprehensive strength improvement coefficient and safety factor.

[0156] This application provides an embodiment of a soft rock tunnel face pre-reinforcement effect evaluation system, which is similar to the above-mentioned... Figure 1The method for evaluating the pre-reinforcement effect of soft rock tunnel face shown is a technical solution based on the same inventive concept. Through the detailed description of the method for evaluating the pre-reinforcement effect of soft rock tunnel face provided in the above embodiments, those skilled in the art can clearly understand the implementation process of each module included in the system for evaluating the pre-reinforcement effect of soft rock tunnel face in this embodiment. Therefore, for the sake of brevity, it will not be described in detail here.

[0157] The above specific embodiments further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are merely specific embodiments of the present invention and are 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 evaluating the pre-reinforcement effect of soft rock tunnel faces, characterized in that the method... include: Obtain the tunnel engineering geological parameters, tunnel face cross-sectional parameters, and design parameters for pre-reinforcement measures for soft rock tunnels; among which, the tunnel engineering geological parameters include the original rock mechanical parameters and the original rock initial stress, and the tunnel face cross-sectional parameters include the tunnel excavation radius; Calculate the equivalent reinforcement parameters and effective far-field stress based on the design parameters of the pre-reinforcement measures; The geometric boundary of the spherical cavity is determined based on the tunnel excavation radius. The three-dimensional unloading problem in front of the tunnel face of soft rock tunnel is equivalent to the unloading problem of the spherical cavity. The equivalent reinforcement parameters and effective far-field stress are substituted into the unloading problem of the spherical cavity to solve for the extrusion displacement of the center of the tunnel face after reinforcement and the radius of the elastic-plastic interface after reinforcement. At the same time, the original rock mechanical parameters and the original rock initial stress are substituted into the unloading problem of the spherical cavity to solve for the extrusion displacement of the center of the tunnel face before reinforcement and the radius of the elastic-plastic interface before reinforcement. Based on the extrusion displacement at the center of the tunnel face before reinforcement, the extrusion displacement at the center of the tunnel face after reinforcement, the radius of the elastic-plastic interface before reinforcement, the radius of the elastic-plastic interface after reinforcement, the equivalent reinforcement parameters, the original rock mechanical parameters, and the effective far-field stress, the extrusion deformation reduction rate, the comprehensive strength improvement coefficient, and the safety factor are calculated. Based on the extrusion deformation reduction rate, comprehensive strength improvement coefficient, and safety factor, a two-step classification judgment method is adopted to determine the pre-reinforcement effect of the tunnel face in soft rock.

2. The method for evaluating the pre-reinforcement effect of soft rock tunnel face according to claim 1, characterized in that, Calculate the equivalent reinforcement parameters and effective far-field stress based on the design parameters of the pre-reinforcement measures, including: Pre-reinforcement measures for the tunnel face in soft rock are determined; wherein, the pre-reinforcement measures include a combination of grouting reinforcement and pipe roof reinforcement, a combination of grouting reinforcement and anchor bolt reinforcement, a combination of anchor bolt reinforcement and pipe roof reinforcement, and a combination of grouting reinforcement, anchor bolt reinforcement and pipe roof reinforcement. Calculate the equivalent reinforcement parameters and effective far-field stress of the soft rock tunnel face after reinforcement based on the design parameters corresponding to the pre-reinforcement measures.

3. A method for evaluating the pre-reinforcement effect of soft rock tunnel face according to claim 2, characterized in that, When the pre-reinforcement measure is a combination of grouting reinforcement and pipe roof reinforcement, the first design parameters of the grouting reinforcement measure and the pipe roof parameters of the pipe roof reinforcement are obtained; The equivalent parameters after grouting reinforcement are calculated based on the design parameters of the first sub-pre-reinforcement and used as the equivalent reinforcement parameters of the combined measures of grouting reinforcement and pipe roof reinforcement. The product of the original rock initial stress and the pipe roof load transfer coefficient is taken as the effective far-field stress. When the pre-reinforcement measure is a combination of grouting reinforcement and anchor bolt reinforcement, the second design parameters of the anchor bolt reinforcement measure are obtained. The equivalent parameters after anchor bolt reinforcement are calculated based on the second design parameters and used as the equivalent reinforcement parameters for the combined measures of grouting reinforcement and anchor bolt reinforcement. The initial stress of the original rock is taken as the effective far-field stress; When the pre-reinforcement measure is a combination of anchor bolt reinforcement and pipe roof reinforcement, the equivalent parameters after anchor bolt reinforcement are calculated based on the second design parameters and used as the equivalent reinforcement parameters of the combination of anchor bolt reinforcement and pipe roof reinforcement. The product of the initial stress of the original rock and the load transfer coefficient of the pipe roof is taken as the effective far-field stress.

4. A method for evaluating the pre-reinforcement effect of soft rock tunnel faces according to claim 3, characterized in that, When the pre-reinforcement measures are a combination of grouting reinforcement, anchor bolt reinforcement and pipe roof reinforcement, the equivalent reinforcement parameters of the pre-reinforcement measures are obtained by superimposing the equivalent parameters of the anchor bolt reinforcement on the equivalent parameters of the grouting reinforcement. The product of the initial stress of the original rock and the load transfer coefficient of the pipe roof is taken as the effective far-field stress.

5. A method for evaluating the pre-reinforcement effect of soft rock tunnel face according to claim 1, characterized in that, Solving the unloading problem of a spherical cavity includes: A spherical symmetric equilibrium differential equation is established, and the boundary conditions of the spherical cavity are set. The spherical symmetric equilibrium differential equation describes the radial and tangential stresses of the spherical cavity in equilibrium along the radial direction. The boundary conditions include an inner boundary with zero radial stress and an outer boundary subjected to effective far-field stress. The plastic zone is described by the Mohr-Coulomb yield criterion and the non-associated flow law. The radial stress at the elastoplastic interface is solved by combining the spherically symmetric equilibrium differential equation, the Mohr-Coulomb yield criterion and the non-associated flow law. Using the tunnel excavation radius as the lower limit of the search interval, the upper limit of the search interval is calculated based on the radial stress at the elastoplastic interface, the tunnel excavation radius, the cohesion, and the internal friction angle. The midpoint of the search interval is taken as the trial value. The stress field in the plastic zone is integrated from the cavity wall of the spherical cavity outward with a set step size to obtain the radial stress in the plastic zone at the midpoint. Calculate the residual between the radial stress in the plastic zone and the radial stress at the elastoplastic interface at the midpoint. Update the search interval according to the sign of the residual. Repeat until the residual converges to less than the set tolerance to obtain the radius of the elastoplastic interface. The elastic displacement at the elastoplastic interface is calculated based on the radial stress and effective far-field stress at the elastoplastic interface. The displacement of the plastic region is gradually updated radially inward from the elastoplastic interface with a set step size until the cavity wall of the spherical cavity is reached, and the radial displacement of the cavity wall is obtained. The extrusion displacement at the center of the tunnel face is calculated based on the radial displacement of the cavity wall and the geometric correction factor; wherein, the geometric correction factor is the conversion factor between the radial displacement of the spherical cavity wall and the extrusion displacement at the center of the tunnel face.

6. A method for evaluating the pre-reinforcement effect of soft rock tunnel face according to claim 1, characterized in that, Calculate the extrusion deformation reduction rate and the overall strength improvement coefficient, including: Based on the extrusion displacement at the center of the front and rear face of the reinforced tunnel, the extrusion deformation reduction rate is calculated; wherein, the extrusion deformation reduction rate is the ratio of the difference between the extrusion displacement at the center of the front and rear face of the reinforced tunnel to the extrusion displacement at the center of the front face of the reinforced tunnel. Based on equivalent cohesion, equivalent internal friction angle, original rock cohesion, original rock internal friction angle, and unified reference normal stress, a comprehensive strength improvement coefficient is calculated; wherein, the comprehensive strength improvement coefficient is the ratio of the shear strength after reinforcement to the shear strength before reinforcement, and both the shear strength after reinforcement and the shear strength before reinforcement are calculated based on the Mohr-Coulomb shear strength criterion.

7. A method for evaluating the pre-reinforcement effect of soft rock tunnel faces according to claim 6, characterized in that, The method further includes: Calculate the pre-convergence deformation reduction rate and stiffness improvement coefficient; If the difference between the level corresponding to the pre-convergence deformation reduction rate and the level corresponding to the extrusion deformation reduction rate is greater than or equal to the preset level difference, or if the difference between the level corresponding to the stiffness improvement coefficient and the level corresponding to the comprehensive strength improvement coefficient is greater than or equal to the preset level difference, a risk status warning will be output.

8. A method for evaluating the pre-reinforcement effect of soft rock tunnel face according to claim 1, characterized in that, Calculating the safety factor includes: Obtain the allowable extrusion displacement at the tunnel face and the allowable radius of the elastoplastic interface; Based on the effective far-field stress, the outer boundary load of the spherical cavity unloading problem is gradually increased, and the corresponding extrusion displacement at the center of the working face and the radius of the elastoplastic interface are solved for each level of outer boundary load. When the extrusion displacement at the center of the tunnel face reaches the allowable extrusion displacement, record the corresponding first critical load. When the radius of the elastoplastic interface reaches the allowable radius of the elastoplastic interface, record the corresponding second critical load; The minimum value between the first critical load and the second critical load is taken as the critical load. The safety factor is calculated based on the ratio of the critical load to the effective far-field stress; wherein, the safety factor is not greater than 1 when the extrusion displacement at the center of the tunnel face under the current load is greater than or equal to the allowable extrusion displacement of the tunnel face, or when the radius of the elastoplastic interface under the current load is greater than or equal to the allowable radius of the elastoplastic interface.

9. A method for evaluating the pre-reinforcement effect of soft rock tunnel face according to claim 1, characterized in that, The two-step classification method includes: The first step is to determine the basic grade based on the extrusion deformation reduction rate and the comprehensive strength improvement coefficient; The second step is to adjust the basic level using a safety factor to obtain the pre-reinforcement effect of the tunnel face in soft rock.

10. A method for evaluating the pre-reinforcement effect of a soft rock tunnel face according to claim 9, characterized in that, The first step includes: Obtain a graded threshold library, which includes a first preset threshold for the extrusion deformation reduction rate and a second preset threshold for the comprehensive strength improvement coefficient; The extrusion deformation reduction rate is compared with a first preset threshold to determine the deformation control level; The overall strength improvement coefficient is compared with the second preset threshold to determine the parameter improvement level; The minimum value between the deformation control level and the parameter improvement level is determined as the basic level; when the basic level is the lowest level, the pre-reinforcement effect is determined to be the lowest level, and the second step is not performed. The second step includes: Obtain the third preset threshold for the safety factor; If the safety factor is less than the third preset threshold, the pre-reinforcement effect will be limited to the level corresponding to the safety factor. If the safety factor is greater than or equal to the third preset threshold, the basic level is maintained as the pre-reinforcement effect.

11. A method for evaluating the pre-reinforcement effect of soft rock tunnel face according to claim 10, characterized in that, When the pre-reinforcement effect does not reach the highest level, calculate the normalized short board degree of each of the extrusion deformation reduction rate, comprehensive strength improvement coefficient and safety factor; where, the normalized short board degree is the ratio of the difference between the target level threshold and the current value of each of the extrusion deformation reduction rate, comprehensive strength improvement coefficient and safety factor to the target level threshold. The normalized shortest board degree, which is the largest among the extrusion deformation reduction rate, comprehensive strength improvement coefficient, and safety factor, is taken as the shortest board index.

12. A method for evaluating the pre-reinforcement effect of soft rock tunnel face according to claim 1, characterized in that, The method further includes: Obtain the extrusion displacement of the tunnel face measured on-site; Based on the on-site measured extrusion displacement of the tunnel face and the extrusion displacement of the center of the tunnel face after reinforcement, the comprehensive reinforcement effectiveness coefficient is obtained by using an iterative optimization method. The equivalent reinforcement parameters are corrected based on the comprehensive reinforcement effectiveness coefficient to obtain the corrected equivalent reinforcement parameters.

13. A system for evaluating the pre-reinforcement effect of soft rock tunnel faces, characterized in that, include: The parameter acquisition module is used to acquire the tunnel engineering geological parameters, tunnel face cross-sectional parameters, and design parameters of pre-reinforcement measures for soft rock tunnels. Among them, the tunnel engineering geological parameters include the original rock mechanical parameters and the original rock initial stress, and the tunnel face cross-sectional parameters include the tunnel excavation radius. The equivalent parameter calculation module is used to calculate the equivalent reinforcement parameters and effective far-field stress based on the design parameters of the pre-reinforcement measures. The spherical cavity solution module is used to determine the geometric boundary of the spherical cavity based on the tunnel excavation radius. It transforms the three-dimensional unloading problem in front of the tunnel face in soft rock into a spherical cavity unloading problem. It substitutes the equivalent reinforcement parameters and effective far-field stress into the spherical cavity unloading problem to solve for the extrusion displacement at the center of the tunnel face after reinforcement and the radius of the elastic-plastic interface after reinforcement. At the same time, it substitutes the original rock mechanical parameters and the original rock initial stress into the spherical cavity unloading problem to solve for the extrusion displacement at the center of the tunnel face before reinforcement and the radius of the elastic-plastic interface before reinforcement. The index calculation module is used to calculate the extrusion deformation reduction rate, comprehensive strength improvement coefficient and safety factor based on the extrusion displacement of the center of the tunnel face before reinforcement, the extrusion displacement of the center of the tunnel face after reinforcement, the radius of the elastic-plastic interface before reinforcement, the radius of the elastic-plastic interface after reinforcement, the equivalent reinforcement parameters, the original rock mechanical parameters and the effective far-field stress. The comprehensive grading and judgment module is used to determine the pre-reinforcement effect of the tunnel face in soft rock by adopting a two-step grading and judgment method based on the extrusion deformation reduction rate, comprehensive strength improvement coefficient and safety factor.

Images