Shallow-buried tunnel face surrounding rock stability quantitative judgment method and application

Abstract

The invention provides a shallow-buried tunnel face surrounding rock stability quantitative discrimination method and device, and the method comprises the steps: determining the supporting force needed by the stability of a tunnel face according to a wedge-shaped body model of a soil body in front of the tunnel face when a shallow-buried tunnel is excavated; determining the stability coefficient of the reinforced tunnel face under the action of considering different support measures; and comparing the stability coefficient of the tunnel face with the critical stability coefficient of the tunnel face, judging the stability of the tunnel face according to a comparison result, and evaluating the effect of the current support measure. According to the provided calculation formula of the stability coefficient of the tunnel face, quantitative analysis of the initial stability of the tunnel face and the stability of the tunnel face under four supporting measures of pipe sheds, tunnel face anchor rods, tunnel face grouting and reserved core soil can be achieved.

Description

Technical Field

[0001] This application relates to the fields of tunnel engineering and geotechnical mechanics, and in particular to a quantitative method and application for determining the stability of the surrounding rock mass at the working face of a shallow tunnel. Background Technology

[0002] Tunnel face stability is crucial for ensuring safe tunnel construction. Unlike deep-buried tunnels, the instability and collapse of shallow-buried tunnels are mainly caused by pre-deformation of the soil ahead and extrusion deformation of the tunnel face. To ensure the stability of the tunnel face in shallow-buried tunnels, existing technologies often employ comprehensive pre-reinforcement measures to achieve safe tunnel construction. However, the selection of pre-reinforcement measures is often determined based on engineering experience, resulting in a lack of reasonable and effective design criteria, which frequently leads to safety accidents.

[0003] To evaluate tunnel face stability, Broms et al. proposed the concept of a stability coefficient; Atkinson et al. derived the minimum support pressure required for the stability of non-cohesive soil tunnel faces using plastic limit analysis; Horn proposed a wedge-shaped model with soil chamber loading based on a 3D model; Anagnostou et al. calculated the ultimate support pressure of homogeneous strata using a wedge-shaped model; Lecu et al., assuming the slip surface consists of one or two cones, proposed an upper limit solution for the support pressure of tunnel face stability; Zhang et al. proposed a three-dimensional failure mechanism composed of four truncated cones; Zheng Yingren et al. explored the advantages of using the safety factor as a criterion for tunnel stability judgment compared to criteria such as tunnel convergence and plastic zone; Jiang Wujun and Zhao et al. analyzed the sensitivity of the influence parameters of the upper limit solution for tunnel face stability. Gu Boyuan et al. proposed a calculation model and engineering examples of horizontally segmenting the wedge-shaped body. Wang Guofu et al. established a trapezoidal limit equilibrium model under abrupt geological interface conditions. Wei Xiaohang et al. studied the influence of surrounding rock parameters on tunnel face stability. Meanwhile, in the research on tunnel face support measures, Song Zhanping et al. proposed a stress analysis model for pipe roof considering the overall integrity of grouting reinforcement, derived the deflection and internal forces of the pipe roof, and verified its rationality. Wang Zhijian, Wang Mingnian et al. introduced calculation methods for tunnel face anchors and tunnel face grouting. Cao Aiwu et al. provided a quantitative analysis method for tunnel face glass fiber anchor reinforcement. Wang Xiuying et al. analyzed the influence of glass fiber anchor parameters on tunnel face stability based on the Taoshuping Tunnel of the Lanzhou-Chongqing Railway. Huang Weixin et al. optimized the excavation sequence of the pre-reserved core soil method for tunnels with biased soft surrounding rock. Lai Hongpeng et al.'s research showed that after grouting, the cohesion and internal friction angle of the tunnel face soil increased, and the shear strength and unconfined compressive strength were significantly improved. The above-mentioned existing results provide analytical methods for studying tunnel face stability and reveal the influence law of different advanced pre-reinforcement measures on tunnel face stability. However, there are few reports on the quantitative judgment of the stability of shallow-buried tunnel faces under different support measures. Therefore, it is of great significance to achieve a quantitative evaluation of the contribution of different advanced reinforcement measures to the stability of the tunnel face, and thus to determine the stability state of the tunnel face. This is crucial for the safe, rapid and economical construction of shallow tunnels.

[0004] This invention derives a method for calculating the initial stability coefficient of the tunnel face based on the limit equilibrium model of a wedge, and obtains the stability coefficients of the tunnel face under four support measures: pipe roof, face anchor bolts, face grouting, and reserved core soil. Finally, based on a tunnel excavation project of Chongqing Rail Transit passing under the Ring Expressway, this method is used to evaluate and optimize the stability of the tunnel face. The rationality of the optimization scheme is verified through on-site monitoring, ensuring safe tunnel construction. Summary of the Invention

[0005] In view of the above problems, this application provides a method and device for quantitatively judging the stability of the surrounding rock mass at the tunnel face, which is used to comprehensively and quantitatively evaluate the effect of four reinforcement measures—pipe roof, tunnel face grouting, anchor bolts, and reserved core soil—on improving the stability of the tunnel face, so as to overcome or at least partially solve the above problems.

[0006] In a first aspect, embodiments of this application provide a method for quantitatively determining the stability of the surrounding rock mass at the working face of a shallow-buried tunnel, the method comprising: Based on the wedge-shaped model of the soil in front of the tunnel face during shallow tunnel excavation, determine the support force required for tunnel face stability. Considering the effects of different support measures, determine the stability coefficient of the tunnel face after reinforcement with applied support measures; The stability coefficient of the working face under the current support measures is compared with the boundary stability coefficient of the working face. The stability of the working face is judged based on the comparison results, and the effectiveness of the current support measures is evaluated.

[0007] Optionally, the support force P required for face stability is: in, The width of the equivalent excavation face of the wedge-shaped sliding body. Let β be the height of the equivalent excavation face of the wedge-shaped sliding body, φ be the slip angle of the slip surface of the wedge-shaped sliding body, φ be the internal friction angle of the surrounding rock, γ be the unit weight of the wedge-shaped sliding body, H be the depth of the soil above the tunnel face, σv be the normal stress on the upper surface of the micro-element, z be the depth of the soil micro-element, F be the compressive stress of the prism acting on the wedge-shaped body, G be the self-weight of the wedge-shaped sliding body, T2 be the shear stress on the side of the wedge-shaped sliding body, and c be the cohesion. This represents the lateral pressure coefficient of a shallow-buried tunnel.

[0008] Optionally, considering the effects of different support measures, the stability coefficient of the tunnel face after reinforcement with applied support measures is determined, including: Determine the vertical pressure on the soil in front of the tunnel face during the excavation of a shallow tunnel supported by pipe roof; Determine the cohesion of the surrounding rock in the reinforced area after grouting reinforcement at the tunnel face; Determine the resultant force of the anchor bolt support at the tunnel face under the action of anchor bolt support; Determine the combined support force provided by the reserved core soil support; Based on the vertical pressure provided by the pipe roof, the cohesion of the surrounding rock in the reinforced area, the combined force of the anchor bolt support at the working face, and the combined force of the reserved core soil support at the working face, the stability coefficient of the reinforced working face is determined.

[0009] Optionally, the formula for calculating the resultant force of the reserved core soil support is as follows: in, Here, h is the Rankine passive earth pressure coefficient, and h is the core soil height. The width of the bottom of the core soil.

[0010] Optionally, the formula for calculating the stability coefficient of the reinforced tunnel face is: Where K is the stability coefficient of the reinforced tunnel face; and These are the shear stresses on the two sides of the wedge-shaped sliding body after grouting reinforcement; The support force provided to the anchor bolt; The supporting force provided for the reserved core soil; α1 is the surrounding rock pressure reduction coefficient; G is the self-weight of the soil in front of the tunnel face; β is the slip angle of the soil in front of the tunnel face.

[0011] Optionally, the stability coefficient of the tunnel face under the current support measures is compared with the critical stability coefficient of the tunnel face. Based on the comparison results, the stability of the tunnel face is determined, and the effectiveness of the current support measures is evaluated, including: (1) Determine whether the support stress of the soil face in front of the tunnel face is greater than 0 during the current shallow tunnel excavation: If so, it means the initial working face is unstable and proceeds to the next step; If not, calculate the initial stability coefficient and determine whether the initial stability coefficient is greater than the working face boundary stability coefficient. If yes, it means that the initial working face is stable; if not, it means that the safety reserve is insufficient, and proceed to the next step. (2) Apply face support measures, including pipe roof support, grouting support, anchor bolt support and reserved core soil; (3) Determine the stability coefficient of the face under the current support measures according to the calculation formula of the face stability coefficient, and determine whether the face stability coefficient is greater than the face boundary stability coefficient: If so, it indicates that the working face is stable and the current support measures are effective; If not, it indicates that the working face is unstable and the current support measures are ineffective. Return to the previous step and continue to increase the strength of the current support measures.

[0012] Secondly, embodiments of this application provide a quantitative determination device for the stability of the surrounding rock mass at the working face of a shallow-buried tunnel, the device comprising: The support force determination module is used to determine the support force required for the stability of the tunnel face based on the wedge-shaped model of the soil in front of the tunnel face during shallow tunnel excavation. The stability coefficient determination module is used to determine the stability coefficient of the reinforced tunnel face considering different support measures. The discrimination module is used to compare the stability coefficient of the working face with the critical stability coefficient of the working face, and to judge the stability of the working face based on the comparison results, thereby evaluating the effectiveness of the current support measures.

[0013] Thirdly, embodiments of this application provide an electronic device, including a memory, a processor, and a computer program stored in the memory, wherein the processor executes the computer program to implement a quantitative determination method for the stability of the surrounding rock mass at the working face of a shallow tunnel as described above.

[0014] Fourthly, embodiments of this application provide a readable storage medium storing a program or instructions, which, when executed by a processor, implements the method for quantitatively determining the stability of the surrounding rock mass at the face of a shallow-buried tunnel as described above.

[0015] The specific beneficial effects are as follows: First, this invention transforms the mechanical effects of various reinforcement measures (such as the beam effect of pipe roofs, the reinforcement effect of grouting, the anchoring force of anchor bolts, and the retaining effect of core soil) into parameters that can be calculated in this model, thereby expanding the applicable boundaries and practicality of the classic model.

[0016] Second, this invention evaluates the stability of the tunnel face through the tunnel face stability coefficient and systematically incorporates the calculation of various reinforcement measures (such as the beam effect of pipe roof, the reinforcement effect of grouting, the anchoring force of anchor bolts, and the retaining effect of core soil), thus constructing a new evaluation system.

[0017] Third, this invention establishes a quantitative analysis model for tunnel face stability. Based on this model, a new formula for calculating the tunnel face stability coefficient K is derived. By using this formula to calculate the tunnel face stability coefficient K, it is possible to quantitatively describe the initial stability of the tunnel face and its stability under four support measures: pipe roof, tunnel face anchor bolt, tunnel face grouting, and reserved core soil. This guides the optimization of tunnel support structures and ensures the safe construction of tunnel sections passing under highways. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 (a)-(b) are schematic diagrams of the limit equilibrium model; where, Figure 1 (a) is the three-dimensional computational model of the wedge-shaped sliding body. Figure 1 (b) is a planar schematic diagram of the wedge-shaped sliding body; Figure 2 This is a schematic diagram of the forces acting on a wedge-shaped body; Figure 3 It is a model for calculating loosened earth pressure; Figure 4 Schematic diagram of the reserved core soil section; Figure 5 This is a flowchart of a method for determining the stability of the tunnel face. Figure 6 The stability coefficient (K) and vertical pressure reduction coefficient under pipe roof support are given. The relationship between ) Figure 7 The stability coefficient (K) of the working face is related to the grouting depth ( ) The relationship between ) Figure 8 (a) represents the relationship between the face stability coefficient (K), grouting filling rate (ζ), and grout cohesion ( The three-dimensional distribution cloud map of ) Figure 8 (b) shows the relationship curve between the stability coefficient (K) and the grouting filling rate (ζ). Figure 8 (c) represents the relationship between the stability coefficient (K) and the slurry cohesion ( The relationship curve; Figure 9 The stability coefficient (K) is related to the bottom width of the core soil ( ), and a three-dimensional cloud map showing the relationship between the core soil height (h); Figure 10 This is a graph showing the trend of the tunnel face stability coefficient as the anchor bolt density increases; Figure 11 (a) is a satellite topographic map of an underground rail transit tunnel in a certain city. Figure 11 (b) is a schematic diagram of the cross-section of an underground rail transit tunnel in a certain city.

[0020] Figure 12 For the stability coefficient and the vertical deformation pressure reduction coefficient ( The relationship curve; Figure 13 (a) shows the relationship curve between the stability coefficient of the tunnel face and the cohesion of the mortar. Figure 13 (b) is the curve showing the relationship between the stability coefficient of the tunnel face and the grouting filling rate; Figure 14 A schematic diagram showing the layout of on-site measuring points for the highway in the study section; Figure 15 The cumulative displacement trend of characteristic measuring points JC-1 to JC-9 is shown. Detailed Implementation

[0021] Exemplary embodiments of this application will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of this application are shown in the drawings, it should be understood that this application may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of this application and to fully convey the scope of this application to those skilled in the art.

[0022] The stability of the tunnel face and the rationality of support measures are crucial for safe tunnel construction and also significantly impact project cost and schedule. To quantitatively evaluate the stability of the tunnel face and the effectiveness of support measures, this invention proposes a method for quantitatively determining the stability of the surrounding rock mass at the tunnel face of shallow-buried tunnels. The method includes the following steps: Step 1: Determine the support force required for the stability of the tunnel face based on the wedge-shaped model of the soil in front of the tunnel face during shallow tunnel excavation; In the embodiments of this application, the focus is on the surrounding rock mass of the tunnel face in shallow-buried tunnels. During the excavation of shallow-buried tunnels, the soil in front of the tunnel face has a tendency to slide, which may cause instability at the tunnel face, leading to the formation of a wedge-shaped sliding body, such as... Figure 1 As shown in (a), the triangular prism ABC-abc is the wedge-shaped sliding body at the working face; the quadrangular prism DCcd-EFfe is the soil above, buried at a depth of H; AaBb is the equivalent excavation face of the wedge-shaped sliding body, with a height of The equivalent width is When using full-face excavation, the excavation area is the cross-sectional area of ​​the tunnel; when using the bench method, the excavation area is the area of ​​the upper bench. EeFf represents the surface area of ​​the prism-shaped soil mass. BbDd represents the unsupported section, its length... (DB, such as) Figure 1 (b) is related to the actual excavation progress of the project. Figure 1 In (a), AaCc is the slip surface of the wedge-shaped sliding body, and its slip angle (β) is related to the internal friction angle (φ) of the surrounding rock as follows: (1) Based on the following assumptions ①-④, a limit equilibrium model for the wedge-shaped body can be established: ① The soil is a homogeneous, isotropic, rigid-plastic material. For multi-layered soils, a weighted average method can be used. The soil material obeys the Mohr-Coulomb failure criterion (…). ① Where c is cohesion and σ is normal stress, and the influence of groundwater is not considered. ② The failure range of the excavation section is composed of a wedge (ABC-abc) and a prism (DCcd-EFfe). ③ Based on the principle of area equivalence, the tunnel face is equivalent to a rectangle (ABba) with the same area for calculation. ④ The vertical stress on the side of the wedge increases linearly with depth, while the stress on the top surface and the inclined sliding surface is uniformly distributed.

[0023] Figure 2 This is a schematic diagram of the forces acting on the wedge, where P is the active force ensuring the stability of the working face, F is the compressive stress exerted by the prism on the wedge, and G is the self-weight of the wedge (with a unit weight of γ). and These represent the compressive stress and shear stress on the slip surfaces A(a) and C(c), respectively. and These are the compressive stress and shear stress acting on the side ABC of the wedge, respectively. It should be noted that... Perpendicular to side ABC. The forces on side abc are the same as those on side ABC. Based on the limit equilibrium model of the wedge, the following conditions apply to the wedge's self-weight (G), compressive stress (F), and shear stress on the slip surface (G). ) and shear stress on the side of the wedge ( Solve for the compressive stress (P) exerted by the prism on the wedge: When the wedge is in a state of limit equilibrium, its force equilibrium equation can be expressed as: (2) Therefore, the compressive stress on the slip surface A(a)C(c) is ( The active force (P) can be expressed as: (3) The soil element (DCcd-EFfe) at the top is selected as the analysis object. The stress analysis of the soil micro-element at a depth of z is as follows: Figure 3 As shown, Figure 3 In the equation, q represents the uniformly distributed load on the ground, w represents the self-weight of the soil element, σv represents the normal stress on the upper surface of the soil element, and σh and Let be the normal stress and shear stress on the side of the infinitesimal soil element, respectively. Then the vertical force equilibrium equation of the infinitesimal soil element is: (4) Where S is the upper surface area of ​​the infinitesimal element, and λ is the lateral pressure coefficient of the soil. Based on the characteristics of the vertical force equilibrium equation, equation (4) can be rewritten as: (5) Among them, equation parameters and They are represented as follows: Therefore, the equation relating the normal stress (σv) on the upper surface of the infinitesimal element to the burial depth (z) can be obtained: (6) If we assume that the compressive stress (F) exerted by the soil above (DCcd-EFfe) on the top of the wedge-shaped sliding body is: (7) At this point, the equation relating the soil normal stress (σv) at the tunnel arch to the burial depth (z) can be expressed as: (8) Combining equations (8) and (7), we can obtain the expression for the compressive stress (F): (9) Based on the above assumption ④, the shear stress on the slip surface (AaCc) of the wedge-shaped sliding body ( )for: (10) By combining equations (8), (9), and (10), we can obtain: (11) Based on assumption ③, the shear stress at a depth of z on the slip surface ( )for: (12) Based on the above analysis, equations (2), (9), (11), and (12) can be substituted into equation (3) to obtain the support force P required for the stability of the tunnel face: (13) Step 2: Considering the effects of different support measures, determine the stability coefficient of the shallow tunnel face after reinforcement with applied support measures; Existing research indicates that increasing the anti-sliding force and reducing the sliding force are the main ways to improve the stability of the tunnel face. To improve the stability of the tunnel face, several reinforcement measures (support measures) are commonly used in surrounding rock engineering to reinforce the tunnel excavation section, such as pipe roof, tunnel face grouting, tunnel face anchor bolts, and reserved core soil.

[0024] Regarding the quantification of support effects, Wang Zhijian, Wang Mingnian, and others conducted quantitative analyses of pipe roof support, face grouting, and face anchor bolts. The pressure reduction factor was used to quantify the effect of pipe roof support. Quantitative evaluation of the vertical deformation pressure of the disturbed section. The grouting effect at the working face is assessed by improving the cohesion of the surrounding rock (…). The method of evaluating the support effect is as follows: First, the minimum bearing capacity of each anchor bolt under five failure modes is calculated. Then, the bearing capacities of each anchor bolt are summed to obtain the total support force provided by the anchor bolts. ).

[0025] The steps for calculating the stability coefficient (K) of the tunnel face based on the reinforcement effects of pipe roof, face grouting, anchor bolts, and reserved core soil are as follows: Step 2.1: Determine the vertical pressure on the soil in front of the tunnel face during the excavation of a shallow tunnel under pipe roof support; Specifically, the vertical pressure exerted on the soil (wedge-shaped sliding body) in front of the tunnel face during shallow tunnel excavation after the support structure is installed. Represented as: (14) in, This is the surrounding rock pressure reduction factor; Step 2.2: Determine the cohesion of the surrounding rock in the reinforced area after grouting reinforcement at the working face; Specifically, after grouting reinforcement is adopted at the tunnel face, the cohesion of the surrounding rock in the reinforced area... for: (15) (16) in, It is the cohesive force of the mortar; V is the volume of the mortar; ζ is the volume of the wedge-shaped sliding body; and ζ is the mortar filling rate. is the grouting depth; n is the porosity of the surrounding rock; c is the initial cohesion of the surrounding rock; This is the strengthening coefficient of cohesion after grouting. The height of the working face. It is the slip angle.

[0026] The cohesion after grouting reinforcement Substituting these values ​​into equations (11) and (12), the shear stress on the slip surface after grouting reinforcement can be obtained. ) and shear stress on the side of the wedge ( ).

[0027] Step 2.3: Determine the resultant force of the anchor bolt support at the tunnel face under the action of anchor bolt support; Fiberglass anchors are a commonly used and typical type of anchor for tunnel face reinforcement. Their failure modes include tensile failure of the anchor rod body. The non-anchored section of the rod slipped and failed. The mortar in the non-anchored section slides and fails against the borehole wall. The anchoring section of the rod slipped and failed due to the mortar. The anchoring section mortar slipped and failed due to the hole wall. Considering construction safety, the anchoring force of a single anchor bolt is taken as the minimum value among the five failure modes. The formula for calculating the anchoring force is: (17) (18) (19) (20) (twenty one)

[0028] in, This represents the anchoring force of the i-th row of anchor bolts corresponding to the first failure mode. The anchoring force of the i-th row of anchor bolts corresponding to the second failure mode; The anchoring force of the i-th row of anchor bolts corresponding to the third failure mode; The anchoring force of the i-th row of anchor bolts corresponding to the fourth failure mode; The anchoring force of the i-th row of anchor bolts corresponding to the fifth failure mode; The tensile strength of the anchor bolt; The diameter of the anchor bolt; This is the design value for the tensile strength of the mortar; is the length of the i-th row of anchors in the non-anchored zone; is the length of the i-th row of anchors in the anchorage zone; Where λ is the borehole diameter; λ is the lateral pressure coefficient of the soil. Based on the anchoring force of a single anchor bolt, the resultant support force of the anchor bolts at the tunnel face can be obtained. for: (twenty two) in, Let n be the number of horizontal anchor bolts in the i-th row; n is the number of anchor bolt rows. Step 2.4: Determine the combined support force provided by the reserved core soil support; Reserving core soil is another effective measure to ensure the stability of the tunnel face. This invention introduces a quantitative method for the supporting effect of reserved core soil, based on existing research. A simplified schematic diagram of reserved core soil is shown below. Figure 4 As shown, The width of the core soil base. Let h be the width of the top of the core soil and h be the height of the core soil. Assuming the mechanical action of the wedge-shaped sliding body on the reserved core soil causes it to reach a critical state of imminent sliding, then the support force reaches its maximum at this point. This maximum support force can be determined by the passive earth pressure on the core soil. Therefore, the resultant support force provided by the reserved core soil ( This can be represented as: (twenty three) in, Rankine's passive earth pressure coefficient; Assuming the slope toe angle of the reserved core soil is equal to the slip angle (β) of the surrounding rock, then the top width of the core soil ( ) can be represented as: (twenty four) By combining equations (23) and (24), the combined support force provided by the reserved core soil can be obtained. for: (25).

[0029] Step 2.5: Determine the stability coefficient of the tunnel face based on the vertical pressure provided by the pipe roof, the cohesion of the surrounding rock in the reinforced area, the combined force of the anchor bolt support at the tunnel face, and the combined force of the reserved core soil support at the tunnel face; From the stability conditions of a wedge, it is known that when the sliding force generated by the wedge's weight (G) and compressive stress (F) exceeds the anti-sliding force generated by the surrounding rock, the surrounding rock will undergo sliding failure. To quantitatively describe the stability of the tunnel face, the ratio of the anti-sliding force to the sliding force acting on the wedge can be defined as the tunnel face stability coefficient (K). (26) based on Figure 1 The stress characteristics of the wedge-shaped body in the tunnel, and the initial stability coefficient of the tunnel face ( This can be represented as: (27) Considering the reinforcement effects of pipe roof, face grouting, face anchors, and reserved core soil, the stability coefficient (K) of the reinforced face can be expressed as: (28) In the formula: and These are the shear stresses on the two sides of the wedge-shaped sliding body after grouting reinforcement; Support force provided by anchor bolts The combined support force provided for the reserved core soil.

[0030] Step 3: Compare the stability coefficient of the working face under the current support measures with the critical stability coefficient of the working face, determine the stability of the working face based on the comparison results, and evaluate the effectiveness of the current support measures; To reasonably determine the stability of the tunnel face, this invention introduces a critical stability coefficient for the tunnel face. The critical stability coefficient is the minimum stability coefficient required to ensure the tunnel face remains stable. By comparing the currently calculated tunnel face stability coefficient with this coefficient, the effectiveness of four reinforcement measures—pipe roof, tunnel face grouting, anchor bolts, and reserved core soil—in improving tunnel face stability can be comprehensively and quantitatively evaluated. Then, based on the initial stability assessment of the tunnel face, it can be determined whether reinforcement of the excavation face is necessary.

[0031] Existing studies typically use rigid body limit equilibrium conditions to analyze the stability of rock slopes or soil-rock slopes. Based on the silo model, it can be seen that the failure mode of the tunnel face of a shallow-buried tunnel is the overall sliding failure of the wedge-shaped body, and the slip surface is usually planar, which is the same as the collapse mode of rock slopes and soil-rock combined slopes. Therefore, the instability judgment of the tunnel face of a shallow-buried tunnel can refer to the judgment criteria for slope slippage. Combining existing specifications (references [1], [2]), the sliding wedge-shaped body in front of the tunnel face is regarded as a secondary temporary slope, and the boundary stability coefficient of the tunnel face ( The value can be determined to be 1.20.

[0032] Optionally, step 3 may include the following sub-steps: Step 3.1: Determine the support stress P (resultant support force) of the soil in front of the tunnel face during the current shallow tunnel excavation. If the value is greater than 0, it indicates that the initial working face is in an unstable state, and proceed to step 3.2; Otherwise, when P≤0, the initial stability coefficient is calculated according to equation (27). And determine whether the initial stability coefficient is greater than the boundary stability coefficient of the tunnel face. ,Right now If not, it means that the current safety reserve is insufficient and proceed to step 3.2; otherwise, it means that the initial working face is in a stable state and no support is required. Step 3.2: Apply different face support measures, including pipe roof support, grouting support, anchor bolt support, and reserved core soil; Step 3.3: Determine the stability coefficient of the tunnel face after applying different support measures according to equation (28). Then, the stability coefficient of the working face under the current support measures is calculated. Boundary stability coefficient of the tunnel face By comparing the current support measures, we can determine their effectiveness.

[0033] Specifically, after the face support is applied, its stability can be reassessed based on the reinforced face stability coefficient (K) described in equation (28). For example, if the applied support measure is face grouting, then the stability coefficient (K) can be calculated. and Then and Substituting into equation (28), we can obtain the stability coefficient (K) of the working face under the grouting measures.

[0034] Based on stability coefficient The specific steps for determining stability are: ① When If this occurs, it indicates that the support measures cannot meet the stability requirements of the working face, and the support strength needs to be increased until the stability coefficient meets the requirements. ② When This indicates that the support measures can ensure the stability of the working face and have a certain safety reserve.

[0035] The stability assessment process for the working face, such as... Figure 5 As shown. In practical applications, the contribution of different reinforcement measures to the stability of the tunnel face can be further evaluated by combining the geometric parameters of existing shallow-buried tunnels. For example, if the burial depth (H) is 10m and the tunnel clearance ( The length of the unsupported section is 10m. The depth is 1m; the rock mass parameters are: cohesion (c) is 7.50 kPa, internal friction angle (φ) is 28.60°, and unit weight (γ) is... The lateral pressure coefficient (λ) is 0.5217, the porosity (n) is 40%, and the top overload (q) is 0 kPa. Applications include... Figure 5 The discriminant method shown below evaluates the stability effect after implementing different support measures: (1) Reinforcement effect of pipe shed Figure 6 The stability coefficient (K) and vertical pressure reduction factor of the tunnel face under pipe roof support. The relationship between ) and ). When =0 indicates that the pipe roof bears all the pressure above the arch, when =1 indicates that the pipe roof does not bear the pressure from above. Figure 7 It can be seen that the stability coefficient (K) of the tunnel face in shallow tunnels ranges from 0.85 to 1.64. After the pipe roof support is installed, the stability coefficient of the tunnel face increases negatively with the increase of the vertical deformation pressure reduction coefficient. When the vertical pressure reduction coefficient is less than 0.40, the stability coefficient is significantly greater than the critical stability coefficient. When the vertical pressure reduction factor is greater than 0.40, the stability coefficient is significantly smaller than the critical stability coefficient. Wang Mingnian et al., based on the classic prism-wedge model, have shown that the safety pressure reduction coefficient of rock mass in actual tunnel engineering is generally between 0.60 and 0.90. However, due to... Figure 7This indicates that the stability coefficient corresponding to the calculated safe pressure reduction factor is 0.90~1.06, which is significantly smaller than the critical stability coefficient. Therefore, it can be concluded that simply using pipe roof reinforcement to strengthen the surrounding rock cannot meet the stability requirements of the working face.

[0036] (2) Grouting reinforcement of the working face Grouting reinforcement effect at the working face and cohesion after grout solidification ( ), Grouting filling rate (ζ), Grouting depth ( Closely related to ). Figure 7 This demonstrates the relationship between the face stability coefficient (K) and the grouting depth ( The relationship between ) and ). Figure 7 It can be concluded that the grouting depth at the tunnel face caused the stability coefficient to undergo two stages: linear growth and steady development, with the stage dividing point at 5.94 m. The stage evolution characteristics of the stability coefficient indicate that before grouting reinforcement at the tunnel face ( =0), and the stability coefficient of 0.86 is significantly smaller than the critical indeterminate coefficient (1.20), indicating that the tunnel face cannot reach a self-stable state. When the grouting depth increases from 0 to 6 m, the stability coefficient of the tunnel face increases linearly, and the reinforcement effect of the tunnel face significantly improves when the grouting depth is greater than 2.40 m. When the grouting depth reaches 6 m, the stability coefficient reaches its maximum of 1.75, indicating that the tunnel face has the best reinforcement effect. However, when the grouting depth exceeds 6 m, the stability coefficient remains around 1.75, indicating that the grouting reinforcement effect no longer improves.

[0037] The reason is that grouting at the tunnel face primarily improves the stability and load-bearing capacity of the face by increasing the cohesion of the slip surface of the wedge. When the grouting depth exceeds the slip surface of the wedge, the grouting effect cannot be fully utilized by the wedge and slip surface. Further increasing the grouting depth will not significantly improve the stability of the tunnel face; instead, it will reduce the utilization rate of the grouting material. Therefore, when reinforcing the tunnel face with grouting, the location of the slip surface of the wedge must be considered, and the grouting depth must be determined comprehensively based on factors such as the excavation progress and the performance of the grouting equipment.

[0038] Considering the potential instability of the tunnel face and reserving sufficient grouting depth, the grouting depth here is... =8 m. Figure 8 The stability coefficient (K) of the tunnel face, the grouting filling rate (ζ), and the grout cohesion (ζ) are given. The three-dimensional distribution cloud map and relationship curve of ( ). From Figure 8 (a) It can be seen that the stability coefficient of the tunnel face has spatial zoning characteristics, indicating that there are differences in the grouting reinforcement effect. Figure 8(b) shows the relationship between the stability coefficient and the grouting filling rate when the grout cohesion is between 1000 and 4000 kPa. It can be seen that when the grout cohesion is fixed, the stability coefficient increases linearly with the increase of the grouting filling rate. When the grout cohesion is 1000 kPa, as the grouting filling rate increases from 0 to 0.075, the stability coefficient increases from 0.86 to 1.20, eventually reaching the critical stability coefficient (1.20). Existing research indicates that the grout filling rate of surrounding rock in actual engineering is generally between 0.15 and 0.20. Therefore, as the grouting filling rate continues to increase to 0.20, the stability coefficient can be increased to 1.75, significantly improving the reinforcement effect.

[0039] Figure 8 (c) indicates that when the grouting filling rate is determined, the stability coefficient and the grout cohesion have a good linear correlation. When the grouting filling rate is 0.15, the stability coefficient increases from 0.86 to 1.22 as the grout cohesion increases from 0 to 550 kPa; when the grout cohesion continues to increase to 4000 kPa, the stability coefficient reaches 3.52, which is 4.09 times higher than the initial face stability coefficient. When the grouting filling rate is 0.20, the stability coefficients corresponding to grout cohesions of 1000 kPa, 2000 kPa, 3000 kPa, and 4000 kPa are 1.75, 2.63, 3.52, and 4.41, respectively, which are 103%, 206%, 309%, and 413% higher than the initial stability coefficient. Although a higher stability coefficient (K) can significantly improve the safety of the face, it also increases engineering costs and excavation difficulty. Therefore, in actual engineering projects, parameters such as grout type, grouting pressure, and grouting time should be reasonably determined based on soil properties, groundwater environment, and other conditions to achieve both safety and economy.

[0040] (3) Reserving core soil for reinforcement Figure 9 When using pre-reserved core soil to reinforce the tunnel face, the stability coefficient (K) and the bottom width of the core soil are considered. The three-dimensional relationship cloud diagram of the core soil height (h) is shown. It can be seen that when using reserved core soil to reinforce the tunnel face, the stability coefficient (K) of the shallow-buried tunnel face exhibits a typical spatial distribution characteristic. The projection of the stability coefficient on the horizontal plane is triangular, and its variation range is 0.85~1.225. When the bottom width of the reserved core soil (h) When the height (h) reaches 6.60m, the stability coefficient can be basically stabilized at 1.225, which is slightly greater than the critical stability coefficient. ).

[0041] Formula (25) shows that the support force provided by the reserved core soil is equal to... The relationship between h and the stability coefficient is linear, while the relationship between h and h is a cubic nonlinear function. This shows that h has a significantly greater influence on the stability coefficient of the tunnel face than h. Relevant specifications indicate that the reserved core soil area should generally be no less than 50% of the excavation face area. However, in actual construction, the size of the reserved core soil is often limited by factors such as tunnel dimensions, cycle advance, its own stability, and ease of construction. Therefore, when the tunnel is excavated using the full-face method, a larger excavation height will reduce the proportion of the reserved core soil area to the excavation cross-sectional area, ultimately resulting in limited support effect. In contrast, the bench excavation method allows for a larger reserved core soil height, leading to better support effect, which aligns with the understanding that reserved core soil is often used in bench excavation. From the above analysis, it can be seen that, under the premise of ensuring the stability of the reserved core soil itself and sufficient construction space, appropriately increasing the core soil height and bottom width can improve the stability of the tunnel face. However, excessively increasing the core soil size will adversely affect the ease of construction.

[0042] (4) Anchor bolt reinforcement at the working face Fiberglass anchors are mainly composed of fiberglass-reinforced polymers and are widely used in tunnel face reinforcement due to their high tensile strength, low shear strength, and ease of removal. To analyze the reinforcement effect of anchors on the tunnel face, the bearing capacity of a single anchor under five failure modes was calculated. Referring to existing research, the anchor parameters were set as follows: Based on equations (31) to (36), the anchoring forces of a single anchor rod are calculated as follows: , , , , The combined support force of anchor bolts Therefore, the anchoring effect at the tunnel face can be studied by increasing the anchor bolt density. Figure 10 The trend of the face stability coefficient (K) with the increase of anchor bolt density is shown.

[0043] Depend on Figure 10 It can be seen that the stability coefficient of the tunnel face increases linearly with the increase of anchor bolt density. When the anchor bolt density is less than... At that time, the stability of the working face clearly could not meet the requirements for safe construction; when the anchor bolt density was greater than As the tunnel face stability coefficient gradually exceeds the critical stability coefficient (1.20), it indicates that the tunnel face stability gradually improves, and the anchoring effect of the anchor bolts becomes increasingly prominent. In actual engineering projects, the anchor bolt density is generally... (As shown in the shaded area in the figure), the stability coefficient calculated based on the data in this paper is 1.17~2.09. Therefore, it can be seen that, given a fixed anchor bolt anchoring force, the improvement in tunnel face stability depends on the anchor bolt density. However, considering practical working conditions, the anchor bolt density should not be increased indiscriminately while ignoring engineering economics.

[0044] Engineering Cases To verify the effectiveness of the present invention, a quantitative assessment of the stability of the surrounding rock mass at the tunnel face of a shallow-buried tunnel under a ring expressway in a certain city was conducted.

[0045] (1) Project Overview Figure 11 This is a schematic diagram of an underground rail transit tunnel passing under a ring expressway in a certain city. Figure 11 The satellite topographic map in (a) shows that the left, right, and central tunnels all cross the existing ring expressway obliquely using the cut-and-cover method. The study section's left tunnel mileage is from K17+665.000 to K17+739.000, the right tunnel mileage is from K17+659.500 to K17+733.500, and the central tunnel mileage is from YCK0+600.000 to YCK0+674.000. The tunnel length under the ring expressway is approximately 74m. The left and right tunnels are symmetrically distributed about the central tunnel, with a width of 7.06m, a height of 7.11m, and a burial depth of 16.136m. The central tunnel has a width of 7.06m, a height of 7.56m, and a burial depth of 7.252m. Geological survey data indicates that the burial depth of all three tunnels is less than 2.50 times the height of the surrounding rock pressure arch, classifying them as shallow tunnels. Length of the unsupported section of the excavation cross section ( The spacing between the grid arch frames is 0.50m. The tunnel geometry and excavation parameters are statistically analyzed and shown in Table 1.

[0046] Table 1 Tunnel geometry and excavation parameters Above the tunnel arch, the main strata consist of artificial fill and silty clay, classified as Grade V. The bedrock is primarily composed of Middle Jurassic Shaximiao Formation sandstone and sandy mudstone, classified as Grade IV. The exposed strata, from top to bottom, consist of Quaternary Holocene artificial fill (…). ), residual slope deposits of silty clay ( ), Middle Jurassic Shaximiao Formation ( Sedimentary rock strata. Since the ring expressway is a two-way four-lane expressway, according to the "General Specifications for Highway Bridge and Culvert Design," the standard value (q) of the uniformly distributed load for a Class I lane is 10.50 kN / m. Geological survey data indicates that the strata on the left tunnel are poor silty clay, which is prone to landslides and instability at the tunnel face during excavation. Therefore, it is necessary to optimize the reinforcement scheme for the tunnel face.

[0047] (2) Initial stability analysis of the tunnel face Based on the geological conditions and surrounding rock mechanics parameters of the left tunnel, the initial stability of the tunnel face is analyzed using the method proposed in this invention. According to equations (13) and (27), the required support force (P) to reach a stable state is calculated to be 289.90 kN, and the initial stability coefficient (P) is calculated to be... The value is 0.733, which is only the critical stability coefficient. 61.83%. Therefore, without reinforcement measures, the tunnel face cannot reach a stable state.

[0048] According to the original design scheme, the tunnel in the study section adopted double-layer grouting pipe roof and reserved core soil measures to support the tunnel face. According to the original design scheme, the tunnel in the study section adopted double-layer grouting pipe roof and reserved core soil to support the tunnel face. According to equations (13) and (27), the support force required for the tunnel face to reach stability in the original design scheme is 0 kN and the stability coefficient is 1.13, which is slightly less than the critical stability coefficient of 1.20. This shows that although the original design scheme can initially stabilize the tunnel face, it cannot guarantee the safe construction of the tunnel due to insufficient safety reserve, and there is a large construction risk. On-site monitoring shows that the surface of the auxiliary road of the left tunnel underwent excessive settlement on October 7, 2019 when the original design scheme was adopted, which further confirms the reliability of the calculation results.

[0049] (3) Optimization analysis of support measures Figure 12 The relationship curve between the stability coefficient and the vertical deformation pressure reduction coefficient under pipe roof action is given. It can be found that only when the value of the vertical deformation pressure reduction coefficient is adjusted from 0.80 to 0.60 can the stability coefficient (K) of the tunnel face increase from 1.13 to 1.23, barely approaching the critical stability coefficient. Therefore, optimizing the pipe roof parameters to reduce the vertical deformation pressure reduction coefficient does not effectively guarantee the stability of the tunnel face. On the contrary, forcibly increasing the pipe roof parameters will greatly increase the difficulty of operation and construction costs. Furthermore, the pipe roof serves to bear the crushed stone at the arch to ensure construction safety; therefore, the pipe roof support cannot be removed. In summary, it is recommended to abandon the optimization of the original design parameters and instead adopt an additional grouting reinforcement at the tunnel face based on the original support measures to improve tunnel face stability.

[0050] The specification indicates that when the grout cohesion is 1000~4000 kPa, the grouting filling rate of the surrounding rock is approximately 0.15~0.20. The calculation for this project shows that the distance from the slip surface to the working face is 2.60m; therefore, the selected grouting depth is (…). The thickness is 3m and the slurry cohesion is 1000 kPa. Figure 13 The curve and distribution cloud map showing the relationship between the stability coefficient of the working face and the grout filling rate are shown. Figure 13(b) It can be seen that when the grouting filling rate increases from 0 to 0.035, the stability coefficient increases from 0.733 to 1.208. When the grouting filling rate continues to increase, the stability coefficient continues to increase linearly; when the grouting filling rate increases to 0.15, the stability coefficient reaches 2.769, which is significantly greater than the critical stability coefficient, indicating that under the condition that the grouting cohesion is certain, the reinforcement effect can be effectively improved by appropriately increasing the grouting filling rate.

[0051] Therefore, it can be concluded that the reserved core soil in the original design scheme (reserved core soil + pipe roof support) does not meet the conditions for optimization, and the reinforcement effect after optimizing the pipe roof parameters is not significant. However, the stability of the working face can be greatly improved by grouting reinforcement. Therefore, considering the effects of reinforcement measures, construction difficulty, and cost factors, the optimized scheme of pipe roof + reserved core soil + working face grouting was finally formed.

[0052] Finally, to verify the rationality and superiority of the optimized support measures, on-site monitoring of surface settlement of the highway in the study section was conducted to reveal the stability of the tunnel face. A schematic diagram of the on-site monitoring point layout is shown below. Figure 14 As shown, the monitoring points are arranged longitudinally along the highway surface at 2m intervals. The distance between the tunnel face and the monitoring point is approximately three times the tunnel diameter (21-24m). The daily excavation advance of the tunnel is approximately 2m. After 4 days of excavation, the next monitoring point begins to enter the settlement influence range. Figure 14 JC-1 to JC-9 are characteristic measuring points spaced 8 m apart, with three measuring points arranged between every two characteristic measuring points.

[0053] Figure 15 The surface settlement time history curves for characteristic monitoring points JC-1 to JC-9 show that the cumulative settlement displacement at all monitoring points gradually increases with monitoring time. The further away from the tunnel face, the slower the increase in cumulative settlement displacement, and the smaller the maximum cumulative settlement value. Comparing the settlement characteristics of different monitoring points reveals that at a distance of approximately 3.4 times the tunnel dimension from the tunnel face, the cumulative deformation and rate of change at monitoring point JC-1 continuously increase. When the tunnel face is excavated to below the monitoring point, the cumulative settlement displacement reaches 34.50 mm, exceeding the settlement warning value (30 mm). This poses a significant safety risk to the ring expressway, necessitating the cessation of tunnel excavation and optimization of the original plan.

[0054] To ensure the stability of the excavation face and suppress surface settlement along the ring expressway, a reinforcement scheme of "pipe roof + reserved core soil + grouting at the excavation face" was adopted. Reinforcement was carried out on the excavation face from day 12 to day 16, as shown in the shaded area. During the four days of grouting at the excavation face, the cumulative settlement displacement monitored at points JC-2 and JC-3 showed a gradually converging trend. After the grouting was completed, the settlement at points JC-2 and JC-3 continued to increase, but the maximum cumulative settlement displacement was only 61.45% and 53.94% of that at point JC-1, respectively, indicating a significant reduction in settlement. As the excavation face continued to advance, the trends at points JC-4 to JC-9 were basically the same, with the maximum cumulative settlement displacement being approximately 15.50 mm, only 44.93% of that at point JC-1. After optimization of the reinforcement scheme, the settlement deformation at points JC-2 to JC-9 all met the settlement deformation control values. This requirement indicates that the optimized scheme of "pipe roof + reserved core soil + tunnel face grouting" has a significant effect on controlling surface deformation and ensures the safe and rapid construction of the tunnel section passing under the highway.

[0055] This application embodiment also provides a quantitative determination device for the stability of the surrounding rock mass at the working face of a shallow-buried tunnel, the device including: The support force determination module is used to determine the support force required for the stability of the tunnel face based on the wedge-shaped model of the soil in front of the tunnel face during shallow tunnel excavation. The stability coefficient determination module is used to determine the stability coefficient of the reinforced tunnel face considering different support measures. The discrimination module is used to compare the stability coefficient of the working face with the critical stability coefficient of the working face, and to judge the stability of the working face based on the comparison results, thereby evaluating the effectiveness of the current support measures.

[0056] References: Reference [1]: Ministry of Housing and Urban-Rural Development of the People's Republic of China. Technical Specification for Building Slope Engineering (with Explanatory Notes) [S]. GB 50330-2013. Beijing: China Architecture & Building Press, 2013. Reference [2]: Ministry of Housing and Urban-Rural Development of the People's Republic of China. Technical Specification for Appraisal and Reinforcement of Building Slope Engineering [S]. GB 50843-2013. Beijing: China Architecture & Building Press, 2013. The device in this application embodiment can be an electronic device or a component within an electronic device, such as an integrated circuit or a chip. The electronic device can be a terminal or other devices besides a terminal. For example, the electronic device can be a GPU BOX, mobile phone, tablet computer, laptop computer, PDA, in-vehicle electronic device, mobile internet device (MID), augmented reality (AR) / virtual reality (VR) device, robot, wearable device, ultra-mobile personal computer (UMPC), netbook, or personal digital assistant (PDA), etc. It can also be a server, network attached storage (NAS), personal computer (PC), television (TV), ATM, or self-service machine, etc. This application embodiment does not specifically limit the device.

[0057] The device in this application embodiment can be a device with an operating system. The operating system can be Android, Linux, Windows, or other possible operating systems; this application embodiment does not specifically limit it.

[0058] The tunnel face advanced core soil stability analysis device provided in this application embodiment can achieve... Figure 1 The various processes implemented in the method implementation examples will not be described again here to avoid repetition.

[0059] This application also provides a computer-readable storage medium storing a computer program / instruction thereon, which, when executed by a processor, implements the steps in the quantitative determination method for the stability of the surrounding rock mass at the working face of a shallow tunnel considering spatial effects disclosed in this application.

[0060] This application also provides a computer program product that, when run on an electronic device, enables the processor to execute the steps in the quantitative determination method for the stability of the surrounding rock mass at the working face of a shallow tunnel, considering spatial effects, as disclosed in this application.

[0061] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0062] This application describes embodiments with reference to flowchart illustrations and / or block diagrams of methods, apparatuses, electronic devices, and computer program products according to embodiments of this application. It should be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing terminal device to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing terminal device, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0063] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing terminal device to operate in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0064] These computer program instructions can also be loaded onto a computer or other programmable data processing terminal equipment, causing a series of operational steps to be performed on the computer or other programmable terminal equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable terminal equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0065] Although preferred embodiments of the present application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the embodiments of the present application.

[0066] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or terminal device. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or terminal device that includes said element.

[0067] The above provides a detailed description of the quantitative determination method and application of the stability of the surrounding rock mass at the working face of a shallow tunnel considering spatial effects, as provided in this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the method and its core ideas. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for quantitatively determining the stability of surrounding rock mass at the working face of a shallow-buried tunnel, characterized in that, The method includes: Based on the wedge-shaped model of the soil in front of the tunnel face during shallow tunnel excavation, determine the support force required for tunnel face stability. Considering the effects of different support measures, determine the stability coefficient of the tunnel face after reinforcement with applied support measures; The stability coefficient of the working face under the current support measures is compared with the boundary stability coefficient of the working face. The stability of the working face is judged based on the comparison results, and the effectiveness of the current support measures is evaluated.

2. The method according to claim 1, characterized in that, The support force P required for the stability of the tunnel face is: in, The width of the equivalent excavation face of the wedge-shaped sliding body. Let β be the height of the equivalent excavation face of the wedge-shaped sliding body, φ be the slip angle of the slip surface of the wedge-shaped sliding body, φ be the internal friction angle of the surrounding rock, γ be the unit weight of the wedge-shaped sliding body, H be the depth of the soil above the tunnel face, σv be the normal stress on the upper surface of the micro-element, z be the depth of the soil micro-element, F be the compressive stress of the prism acting on the wedge-shaped body, G be the self-weight of the wedge-shaped sliding body, T2 be the shear stress on the side of the wedge-shaped sliding body, and c be the cohesion. This represents the lateral pressure coefficient of a shallow-buried tunnel.

3. The method according to claim 1, characterized in that, Considering the effects of different support measures, determine the face stability coefficient of shallow-buried tunnels after reinforcement with applied support measures, including: Determine the vertical pressure on the soil in front of the tunnel face during the excavation of a shallow tunnel supported by pipe roof; Determine the cohesion of the surrounding rock in the reinforced area after grouting reinforcement at the tunnel face; Determine the resultant force of the anchor bolt support at the tunnel face under the action of anchor bolt support; Determine the combined support force provided by the reserved core soil support; Based on the vertical pressure provided by the pipe roof, the cohesion of the surrounding rock in the reinforced area, the combined force of the anchor bolt support at the working face, and the combined force of the reserved core soil support at the working face, the stability coefficient of the reinforced working face is determined.

4. The method according to claim 3, characterized in that, The formula for calculating the resultant force of the support provided by the reserved core soil support is as follows: in, denoted as Rankine's passive earth pressure coefficient, h as the core soil height, and b1 as the core soil bottom width.

5. The method according to claim 4, characterized in that, The formula for calculating the stability coefficient of the reinforced tunnel face is: Where K is the stability coefficient of the reinforced tunnel face; and P1 represents the shear stress on the two sides of the wedge-shaped sliding body after grouting reinforcement; P2 represents the support force provided by the anchor bolt; P3 represents the combined support force provided by the reserved core soil; α1 represents the surrounding rock pressure reduction coefficient; G represents the self-weight of the soil in front of the tunnel face; and β represents the slip angle of the soil in front of the tunnel face.

6. The method according to claim 1, characterized in that, The stability coefficient of the tunnel face under the current support measures is compared with the critical stability coefficient of the tunnel face. Based on the comparison results, the stability of the tunnel face is determined, and the effectiveness of the current support measures is evaluated, including: (1) Determine whether the support stress of the soil face in front of the tunnel face is greater than 0 during the current shallow tunnel excavation: If so, it means the initial working face is unstable and proceeds to the next step; If not, calculate the initial stability coefficient and determine whether the initial stability coefficient is greater than the working face boundary stability coefficient. If yes, it means that the initial working face is stable; if not, it means that the safety reserve is insufficient, and proceed to the next step. (2) Apply face support measures, including pipe roof support, grouting support, anchor bolt support and reserved core soil; (3) Determine the stability coefficient of the face under the current support measures according to the calculation formula of the face stability coefficient, and determine whether the face stability coefficient is greater than the face boundary stability coefficient: If so, it indicates that the working face is stable and the current support measures are effective; If not, it indicates that the working face is unstable and the current support measures are ineffective. Return to the previous step and continue to increase the strength of the current support measures.

7. A quantitative determination device for the stability of surrounding rock mass at the working face of a shallow-buried tunnel, characterized in that, The device includes: The support force determination module is used to determine the support force required for the stability of the tunnel face based on the wedge-shaped model of the soil in front of the tunnel face during shallow tunnel excavation. The stability coefficient determination module is used to determine the stability coefficient of the working face after reinforcement by considering the effects of different support measures. The discrimination module is used to compare the stability coefficient of the face under the current support measures with the boundary stability coefficient of the face, and to judge the stability of the face based on the comparison results, thereby evaluating the effectiveness of the current support measures.

8. An electronic device, characterized in that, The method includes a memory, a processor, and a computer program stored in the memory, wherein the processor executes the computer program to implement a quantitative method for determining the stability of the surrounding rock mass at the working face of a shallow tunnel as described in any of the above-mentioned methods.

9. A readable storage medium, characterized in that, The readable storage medium stores a program or instructions, which, when executed by a processor, implement a quantitative method for determining the stability of the surrounding rock mass at the face of a shallow-buried tunnel as described above.

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