A method for determining local reinforcement parameters of tunnel faces

Abstract

The present invention relates to the technical field of tunnel construction data calculation technology, and more specifically, to a method for determining local reinforcement parameters for a tunnel face. This method uses theoretical analysis to determine reinforcement parameters, such as the reinforcement range for advance support. Performing advance reinforcement within this reinforcement range can reduce the amount of reinforcement material used, lower construction costs, and achieve excellent advance reinforcement results in weak strata.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel construction data calculation, and in particular to a method for determining local reinforcement parameters of a tunnel face. Background Art

[0002] With the continuous expansion and improvement of the domestic railway network, the number of tunnel construction projects is increasing. Tunnel construction often encounters complex and changing geological conditions. When tunnels pass through weak strata, the surrounding rock mass is often loose and fragmented, with well-developed joints and fissures, resulting in poor stability. This significantly reduces bearing capacity when exposed to water, making excavation prone to engineering geological hazards such as water inrush, landslides, and mudslides. These hazards not only slow construction progress and increase project investment, but also pose a serious threat to the safety of on-site workers. Existing advance reinforcement measures typically involve a large, one-time reinforcement of the soil ahead of excavation. This can be difficult to control, requires extended operation time, and incurs high construction costs.

[0003] Current tunnel face pre-reinforcement technologies include surface grouting, horizontal jet jetting, and freezing. Surface grouting is the most widely used method. As described in Chinese invention patent application number 202110250136.8, surface grouting involves the following steps: first, determining the target grouting reinforcement area and setting monitoring points within the target grouting reinforcement area; then, pouring a grouting wall, implementing pre-grouting and pre-pipe-roof drilling, and then, sequentially, carrying out pre-grouting and pre-pipe-roof construction.

[0004] However, in actual construction, existing advance reinforcement measures are affected by the construction environment and conditions. This results in a lack of control over the scope of reinforcement when implementing large-scale advance reinforcement of the soil behind the face. This not only increases construction time and material consumption, but also fails to guarantee reinforcement quality. Furthermore, most existing research focuses on optimizing and improving existing advance reinforcement measures to adapt to complex and changing construction environments. However, there is limited research on methods for determining local reinforcement parameters for tunnel faces in soft strata.

[0005] Therefore, since the current tunnel face advance reinforcement measures cannot effectively solve the demand for advance reinforcement of local weak surrounding rock at the tunnel face, the research on determining the local reinforcement parameters of the tunnel face has practical significance and engineering value. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for determining local reinforcement parameters of a tunnel face.

[0007] In order to solve the above technical problems, the present invention adopts a technical solution: a method for determining local reinforcement parameters of a tunnel face, comprising the following steps:

[0008] S1: Solve the ultimate support force of the tunnel face using the Horm tunnel face wedge sliding body analysis model;

[0009] S2: Calculate the maximum tensile stress value of the fixed end beam model based on the results of S1 and the fixed end beam calculation model, and use the maximum tensile stress value as the reinforcement parameter;

[0010] S3: Substitute the S2 calculation formula into , the calculation formula for the local advance reinforcement range is obtained:

[0011] ;

[0012] Where D is the height of the local reinforced rock mass, h is the height of the rock mass, B is the span of the tunnel face, l is the calculated length of the fixed end beam, γ is the weight of the rock mass, t is the range of local advance reinforcement, σ tmax is the maximum tensile stress value of the fixed-end beam model, [σ t ] is the ultimate tensile stress value of the reinforced soil.

[0013] The beneficial effects of the present invention are as follows: the method for determining the local reinforcement parameters of the tunnel face of the present invention calculates the reinforcement range of the advance support through theoretical analysis, and performs advance reinforcement within the reinforcement range, which can reduce the amount of reinforcement materials used, reduce construction costs, and achieve a good advance reinforcement effect for soft strata. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a flow chart of a method for determining local reinforcement parameters of a tunnel face according to an embodiment of the present invention;

[0015] Figure 2 A diagram of a wedge-shaped model according to an embodiment of the present invention;

[0016] Figure 3 This is a force analysis diagram of a wedge-shaped body according to an embodiment of the present invention;

[0017] Figure 4 This is a calculation model diagram of a fixed-end beam according to an embodiment of the present invention;

[0018] Figure 5 This is a schematic diagram of local advance reinforcement construction according to an embodiment of the present invention. DETAILED DESCRIPTION

[0019] To illustrate the technical content, achieved objectives and effects of the present invention in detail, the following description is given in conjunction with the embodiments and accompanying drawings.

[0020] Please refer to Figures 1 to 5 A method for determining local reinforcement parameters of a tunnel face comprises the following steps:

[0021] S1: Solve the ultimate support force of the tunnel face using the Horm tunnel face wedge sliding body analysis model;

[0022] S2: Calculate the maximum tensile stress value of the fixed end beam model based on the results of S1 and the fixed end beam calculation model, and use the maximum tensile stress value as the reinforcement parameter;

[0023] S3: Substitute the S2 calculation formula into , the calculation formula for the local advance reinforcement range is obtained:

[0024] ;

[0025] Where D is the height of the local reinforced rock mass, h is the height of the rock mass, B is the span of the tunnel face, l is the calculated length of the fixed end beam, γ is the weight of the rock mass, t is the range of local advance reinforcement, σ tmax is the maximum tensile stress value of the fixed-end beam model, [σ t ] is the ultimate tensile stress value of the reinforced soil.

[0026] As can be seen from the above description, the beneficial effect of the present invention is that, to ensure the safety of tunnel construction in soft strata, advance reinforcement measures must be taken on the tunnel face to ensure the stability of the soil behind the face and avoid problems such as sudden mud and water gushing, instability and collapse at the face. Based on the fixed-end beam model, the present invention uses theoretical analysis to determine the reinforcement range of advance support. Combined with the local advance reinforcement method selected for the specific construction section, advance reinforcement can be accurately performed within the designed reinforcement range. This reduces the amount of reinforcement material used and construction costs, achieving excellent advance reinforcement results in soft strata.

[0027] The present invention solves the reinforcement range based on the fixed-end beam model, which has the following advantages:

[0028] 1. The unstable rock mass behind the tunnel face in soft strata and the surrounding stable rock mass form a stable "solid-end beam" advance support structure, ensuring the stability of the tunnel excavation working face;

[0029] 2. It can be used for advanced support conditions of tunnels in different soft strata.

[0030] Furthermore, the calculation method of the ultimate support force of the tunnel face in S1 is:

[0031] ;

[0032] Where q2 is the ultimate support force of the tunnel face, α is the angle of the fracture surface, B is the span of the tunnel face, D is the height of the locally reinforced rock mass, G is the deadweight of the wedge, and q1 is the weight of the overlying soil.

[0033] Furthermore, the calculation method of the wedge's deadweight is:

[0034] ;

[0035] Where G is the deadweight of the wedge, γ is the weight of the rock mass, B is the span of the tunnel face, D is the height of the locally reinforced rock mass, and α is the angle of the fracture surface.

[0036] Furthermore, the calculation method of the overlying soil weight is:

[0037] q 1 =γh ;

[0038] Where q1 is the weight of the overlying soil, γ is the density of the rock mass, and h is the height of the rock mass.

[0039] Further, By combining the following formulas:

[0040] ;

[0041] ;

[0042] Among them, F x is the force in the x-axis direction, F y is the force in the y-axis direction, q2 is the ultimate support force of the tunnel face, N is the support force of the stable rock mass on the wedge-shaped sliding body, α is the angle of the fracture surface, B is the span of the tunnel face, D is the height of the locally reinforced rock mass, G is the deadweight of the wedge-shaped body, and q1 is the weight of the overlying soil.

[0043] Furthermore, the calculation method for the maximum tensile stress value of the fixed-end beam model in S2 is:

[0044] ;

[0045] Among them, σ tmax is the maximum tensile stress value of the fixed end beam model, D is the height of the locally reinforced rock mass, h is the height of the rock mass, B is the span of the tunnel face, l is the calculated length of the fixed end beam, γ is the weight of the rock mass, and t is the range of local advance reinforcement.

[0046] Further, Obtained by the following formula:

[0047] ;

[0048] ;

[0049] ;

[0050] Where q is the uniformly distributed load acting on the fixed end beam, B is the span of the tunnel face, q2 is the ultimate support force of the tunnel face, l is the calculated length of the fixed end beam, M + max is the maximum positive bending moment in the fixed end beam, M - maxis the maximum negative bending moment in the fixed end beam, σ cmax is the maximum compressive stress value of the fixed-end beam model, σ tmax is the maximum tensile stress value of the fixed-end beam model, M max is the maximum bending moment in the fixed end beam, y max is the position of the fixed end beam farthest from the neutral axis, I z is the moment of inertia of the cross section of the fixed end beam, t is the range of local advance reinforcement, h is the height of the rock mass, and γ is the density of the rock mass.

[0051] Furthermore, [σ t ]Confirmed through geotechnical tests and literature research.

[0052] Furthermore, [σ t ]Confirmed through geotechnical tests or literature research.

[0053] Furthermore, the calculation method for the height of the locally reinforced rock mass is:

[0054] ;

[0055] Where D is the height of the locally reinforced rock mass, S is the cross-sectional area of the tunnel, and B is the span of the tunnel face, which has the same value as the width of the locally reinforced rock mass.

[0056] Please refer to Figures 1 to 5 The first embodiment of the present invention is a method for determining local reinforcement parameters of a tunnel face, comprising the following steps:

[0057] S1: The Horm wedge sliding body analysis model is used to solve the ultimate support force q2 of the tunnel face.

[0058] S11: Consider the fractured rock mass as a wedge-shaped body ABIJCD, such as Figure 2 The size of the rectangle ABCD in the wedge model is determined according to the height and span of the tunnel section and the area equivalence principle: the width B of the rectangle ABCD is the span of the tunnel section, and the height D is determined by dividing the tunnel section area by the width of the rectangle, that is:

[0059] ;

[0060] Where D is the height of the locally reinforced rock mass, S is the cross-sectional area of the tunnel, and B is the span of the tunnel face, which has the same value as the width of the locally reinforced rock mass.

[0061] S12: The wedge ABIJCD is subjected to a force analysis. It is subjected to the vertical pressure of the upper sinking soil, gravity, the support force of the inclined plane CDJI, and friction resistance. Figure 3To ensure construction safety, when solving the ultimate bearing capacity of the tunnel face according to the static equilibrium condition, a conservative approach is adopted and the frictional resistance of the inclined plane CDJI on the wedge is not considered. The static equilibrium equations in the x and y directions are thus listed:

[0062] ;

[0063] ;

[0064] Among them, F x is the force in the x-axis direction, F y is the force in the y-axis direction, q2 is the ultimate support force of the tunnel face, N is the support force of the stable rock mass on the wedge-shaped sliding body, α is the angle of the fracture surface, B is the span of the tunnel face, D is the height of the locally reinforced rock mass, G is the deadweight of the wedge-shaped body, and q1 is the weight of the overlying soil.

[0065] S13: By combining the static equilibrium equations in S12, we obtain:

[0066] ;

[0067] q2 is the ultimate support force of the tunnel face, α is the angle of the fracture surface, B is the span of the tunnel face, D is the height of the local reinforced rock mass, G is the deadweight of the wedge, and q1 is the weight of the overlying soil;

[0068] The calculation method of the wedge's deadweight is:

[0069] ;

[0070] G is the deadweight of the wedge, γ is the weight of the rock mass, B is the span of the tunnel face, D is the height of the locally reinforced rock mass, and α is the angle of the fracture surface;

[0071] The calculation method of overlying soil weight is:

[0072] q 1 =γh ;

[0073] q1 is the weight of the overlying soil, γ is the density of the rock mass, and h is the height of the rock mass.

[0074] S2: Calculate the maximum tensile stress value of the fixed end beam model based on the results of S1 and the fixed end beam calculation model, and use the maximum tensile stress value as the reinforcement parameter;

[0075] S21: Since the tensile strength of soil is much smaller than its compressive strength, the soil is more susceptible to tensile cracking failure. Therefore, the reinforced soil is approximated by an elastic model. The reinforced soil is simulated using a fixed-end beam model. The uniformly distributed load q acting on the beam is determined based on the ultimate support force q2 at the tunnel face. The size of the fixed-end beam model is determined based on the size of the wedge model, resulting in:

[0076] ;

[0077] ;

[0078] ;

[0079] Where q is the uniformly distributed load acting on the fixed end beam, B is the span of the tunnel face, q2 is the ultimate support force of the tunnel face; l is the calculated length of the fixed end beam, which is the larger value of the width B and height D of the rectangle ABCD;

[0080] S22: Based on the fixed end beam calculation model, see Figure 4 , substitute the uniformly distributed load q and the dimensions of the fixed-end beam model, and calculate the maximum bending moment and the corresponding maximum tensile stress value of the fixed-end beam model:

[0081] ;

[0082] ;

[0083] Among them, M + max is the maximum positive bending moment in the fixed end beam, M - max is the maximum negative bending moment in the fixed end beam, σ cmax is the maximum compressive stress value of the fixed-end beam model, σ tmax is the maximum tensile stress value of the fixed-end beam model, M max is the maximum bending moment in the fixed end beam, y max is the position of the fixed end beam farthest from the neutral axis, I z is the moment of inertia of the fixed end beam cross section, q is the uniformly distributed load acting on the fixed end beam, l is the calculated length of the fixed end beam, t is the local advance reinforcement range, D is the height of the locally reinforced rock mass, h is the height of the rock mass, B is the span of the tunnel face, l is the calculated length of the fixed end beam, and γ is the weight of the rock mass. S3: To ensure that the tunnel face does not lose stability, the fixed end beam model must not exceed its ultimate strength when subjected to the ultimate support force of the tunnel face; that is, the maximum stress value calculated by the fixed end beam model should be less than the ultimate strength of the reinforced soil:

[0084] ;

[0085] ;

[0086] Among them, σ cmax is the maximum compressive stress value of the fixed-end beam model, σ tmax is the maximum tensile stress value of the fixed-end beam model, [σ c ] is the ultimate compressive stress value of the reinforced soil, [σ t ] is the ultimate tensile stress value of the reinforced soil.

[0087] For general rock and soil, ;

[0088] Therefore, the local advance reinforcement range and the ultimate strength of the reinforced soil must satisfy the following relationship:

[0089] ;

[0090] Where D is the height of the local reinforced rock mass, h is the height of the rock mass, B is the span of the tunnel face, l is the calculated length of the fixed end beam, γ is the weight of the rock mass, t is the range of local advance reinforcement, σ tmax is the maximum tensile stress value of the fixed-end beam model, [σ t ] is the ultimate tensile stress value of the reinforced soil.

[0091] S4: From S3, we can derive the strength σ (t) that the rock mass should have after reinforcement. max The following relationship should be satisfied with the local advance reinforcement range t:

[0092] ;

[0093] Where, σ(t) max is the maximum tensile stress value under a certain t value.

[0094] S5: According to the specific local advance reinforcement method, determine the ultimate tensile stress value of the reinforced soil [σ t ], then combine the following two formulas to determine the final reinforcement parameters, and perform local advance reinforcement on the soil to be reinforced to ensure construction safety. The reinforcement diagram is shown in Figure 5 ; The local advance reinforcement method adopts surface grouting or freezing method;

[0095] ;

[0096] .

[0097] In summary, the method for determining the local reinforcement parameters of the tunnel face provided by the present invention and the local advance reinforcement method of the tunnel face based on the fixed end beam model determine the local reinforcement parameters in multiple steps through theoretical calculations combined with geotechnical tests or literature research, and form a stable "fixed end beam" advance support structure with the unstable rock mass behind the tunnel face in soft strata and the surrounding stable rock mass, providing a new technical idea for the advance support construction of the tunnel face in soft strata. Through theoretical analysis, the parameters for advance support reinforcement of tunnel faces in soft strata are determined, including the scope of local advance reinforcement and the strength that the rock mass should have after reinforcement. Combined with geotechnical tests or literature research, the reinforcement parameters are accurately determined in multiple steps, reducing the time of advance support operations while lowering project expenses. In addition, the appropriate local reinforcement method is selected from the two advance reinforcement measures, surface grouting and freezing, based on the specific construction section. Before excavation of the tunnel face in soft strata, a stable "solid end beam" advance support structure is formed, which has a good displacement and deformation restraining effect on the unstable rock mass behind the face.

[0098] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent transformations made using the contents of the present invention's description and drawings, or directly or indirectly applied in related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for determining local reinforcement parameters of a tunnel face, characterized in that: The following steps are involved: S1: The Horm wedge sliding body analysis model is used to solve the ultimate support force of the tunnel face. The calculation method is as follows: ； Where q2 is the ultimate support force of the tunnel face, α is the angle of the fracture surface, B is the span of the tunnel face, D is the height of the local reinforced rock mass, G is the deadweight of the wedge, and q1 is the weight of the overlying soil; S2: Calculate the maximum tensile stress value of the fixed end beam model based on the results of S1 and the fixed end beam calculation model, and use the maximum tensile stress value as the reinforcement parameter. The calculation method of the maximum tensile stress value of the fixed end beam model is: ； Among them, σ tmax is the maximum tensile stress value of the fixed end beam model, D is the height of the locally reinforced rock mass, h is the height of the rock mass, B is the span of the tunnel face, l is the calculated length of the fixed end beam, γ is the weight of the rock mass, and t is the range of the local advance reinforcement; S3: Substitute the S2 calculation formula into , the calculation formula for the local advance reinforcement range is obtained: ； Where D is the height of the local reinforced rock mass, h is the height of the rock mass, B is the span of the tunnel face, l is the calculated length of the fixed end beam, γ is the weight of the rock mass, t is the range of local advance reinforcement, σ tmax is the maximum tensile stress value of the fixed-end beam model, [σ t ] is the ultimate tensile stress value of the reinforced soil; Determine the ultimate tensile stress value [σ t ], confirm the scope of local advance reinforcement, carry out local advance reinforcement on the soil to be reinforced to ensure construction safety. The local advance reinforcement method adopts surface grouting or freezing method.

2. The method for determining local reinforcement parameters of a tunnel face according to claim 1, characterized in that: The calculation method of the wedge-shaped body's deadweight is: ； Where G is the deadweight of the wedge, γ is the weight of the rock mass, B is the span of the tunnel face, D is the height of the locally reinforced rock mass, and α is the angle of the fracture surface.

3. The method for determining local reinforcement parameters of a tunnel face according to claim 1, characterized in that: The calculation method of the overburden weight is: q1=γh; Where q1 is the weight of the overlying soil, γ is the density of the rock mass, and h is the height of the rock mass.

4. The method for determining local reinforcement parameters of a tunnel face according to claim 1, characterized in that: By combining the following formulas: ； ； Among them, F x is the force in the x-axis direction, F y is the force in the y-axis direction, q2 is the ultimate support force of the tunnel face, N is the support force of the stable rock mass on the wedge-shaped sliding body, α is the angle of the fracture surface, B is the span of the tunnel face, D is the height of the locally reinforced rock mass, G is the deadweight of the wedge-shaped body, and q1 is the weight of the overlying soil.

5. The method for determining local reinforcement parameters of a tunnel face according to claim 1, characterized in that: Obtained by the following formula: ; ； ； Where q is the uniformly distributed load acting on the fixed end beam, B is the span of the tunnel face, q2 is the ultimate support force of the tunnel face, l is the calculated length of the fixed end beam, M + max is the maximum positive bending moment in the fixed end beam, M - max is the maximum negative bending moment in the fixed end beam, σ cmax is the maximum compressive stress value of the fixed-end beam model, σ tmax is the maximum tensile stress value of the fixed-end beam model, M max is the maximum bending moment in the fixed end beam, y max is the position of the fixed end beam farthest from the neutral axis, I z is the moment of inertia of the cross section of the fixed end beam, t is the range of local advance reinforcement, h is the height of the rock mass, and γ is the density of the rock mass.

6. The method for determining local reinforcement parameters of a tunnel face according to claim 1, characterized in that: The calculation method for the height of the locally reinforced rock mass is: ； Where D is the height of the locally reinforced rock mass, S is the cross-sectional area of the tunnel, and B is the span of the tunnel face, which has the same value as the width of the locally reinforced rock mass.

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