A safety checking method for a mine method excavated arch wall assembled tunnel structure

Abstract

The present invention provides a safety calculation method for an arch-wall prefabricated tunnel structure excavated using the mining method. The method first determines the tunnel surrounding rock pressure and the load sharing ratio, establishes a beam-spring load structure model, determines the load combination for the beam-spring load structure model, calculates the load results under different load combinations, and finally performs a safety calculation on the lining structure. The present invention analyzes prefabricated composite linings based on the New Austrian Tunneling Method (NATM). It simulates the stresses on the lining structure using a summarized empirical formula, resolving the principle of the load sharing ratio between primary support and secondary lining. It also simulates the bending stiffness of the lining sheet joints and proposes an empirical formula for the lining sheet joints. This method achieves a calculation method that is closer to the mining method prefabricated tunnel lining, is more valuable as a reference, and ensures project safety.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of tunnel lining secondary lining structure internal force calculation, and particularly relates to a mine method excavation arch wall assembled tunnel structure safety checking method. BACKGROUND

[0002] At present, there are two main construction methods for mountain tunnel construction in China, namely, drilling and blasting method and tunneling machine method (shield and TBM (Tunnel Boring Machine, full-face hard rock tunnel boring machine)). The drilling and blasting method (New Austrian Tunneling Method) is commonly used in mountain highway tunnel construction. When the assembled lining is used to replace the cast-in-place concrete secondary lining, the construction timing of the assembled secondary lining can be roughly divided into three cases:

[0003] I. Lagging assembly, consistent with the traditional New Austrian Tunneling Method, the secondary lining is assembled after the displacement and convergence of the surrounding rock are stable, which is similar to the stress of the composite lining;

[0004] II. Synchronous assembly, similar to the immediate assembly of the shield segment, the secondary lining is assembled immediately after excavation, and the secondary lining is assembled immediately after the surrounding rock is excavated to bear the load;

[0005] III. Through assembly, consistent with the current TBM construction tunnel, the secondary lining is assembled after the tunnel is penetrated.

[0006] In the three cases, the proportion of the load shared by the secondary lining is different. The size of the load sharing ratio of the secondary lining has a significant impact on the selection of the optimal support parameters in tunnel construction. In-depth study of the load sharing ratio of the secondary lining is of great practical significance for the reasonable selection of the assembled lining structure, the optimization of the design parameters and the standardization of the design parameters.

[0007] The existing internal force calculation of the assembled secondary lining structure generally refers to the internal force calculation of the shield lining segment structure and uses the modified conventional method. The modified conventional method assumes that the structure is an elastic homogeneous body, considers the existence of the ring joint, reduces the bending stiffness of the ring as a whole, and introduces the ring stiffness reduction coefficient η and the segment moment transfer coefficient ζ to simulate the reduction of the segment stiffness caused by the multiple joints of the segment and the influence of the segment joint assembly. This method is too simplified and does not conform to the actual situation, often causing large errors, and the safety checking result is difficult to reference, which can easily form a safety hazard in actual engineering. SUMMARY

[0008] In order to solve the prior art, the present application provides a mine method excavation arch wall assembly type tunnel structure safety checking calculation method, which is based on the "New Austrian Tunneling Method" for analyzing the assembly type composite lining, simulates the stress of the lining structure through the summarized empirical formula, can solve the problem of the initial support and secondary lining load sharing ratio principle, and determine the lining piece structure numerical calculation and the value of the lining piece joint stiffness, and is based on the actual stress condition of the "mine method" tunnel composite lining, continues to use the concept of the composite lining load sharing ratio, combines the "beam-spring" model closer to the actual secondary lining, simulates the bending stiffness of the lining piece joint, and proposes an empirical formula for the lining piece joint, so as to achieve the checking calculation purpose closer to the mine method assembly type tunnel lining, has higher reference value, and ensures the engineering safety.

[0009] The technical scheme adopted by the present application to solve the technical problems is as follows: a mine method excavation arch wall assembly type tunnel structure safety checking calculation method is provided, comprising the following steps:

[0010] S1, determining the tunnel surrounding rock pressure;

[0011] S2, determining the load sharing ratio;

[0012] S3, establishing a beam-spring load structure model;

[0013] S4, determining the load combination of the beam-spring load structure model;

[0014] S5, calculating the load result under different load combinations;

[0015] S6, performing safety checking calculation on the lining structure.

[0016] The step S1 determines the tunnel surrounding rock pressure, and specifically includes the following processes:

[0017] S1.1, dividing the tunnel deep and shallow burying:

[0018] The tunnel deep and shallow burying dividing depth H is determined through the following formula: p :

[0019] H p =m·h q (1)

[0020] Wherein m is an empirical coefficient, which is determined comprehensively according to the geological conditions and construction method factors, and the value range is 2-2.5, h q represents the loose confining pressure load height, which is calculated through the following formula:

[0021] h q =0.33×2.72 0.6s ω (2)

[0022] where s represents the surrounding rock grade, ω represents the width influence coefficient, ω = 0.2 + 0.1B, and B is the maximum excavation span of the tunnel;

[0023] S1.2, calculating the surrounding rock pressure under the condition of shallow burial:

[0024] When calculating the internal force of the lining of a shallow-buried tunnel, the surrounding rock pressure is considered as loose pressure, and the vertical and horizontal uniform pressure thereof is determined respectively:

[0025] a. The vertical uniform pressure q is calculated by the following formula:

[0026]

[0027]

[0028]

[0029] where γ represents the bulk density of the overlying surrounding rock of the tunnel, H represents the vertical distance from the tunnel arch to the ground under the condition of shallow burial of the tunnel, θ represents the friction angle of the broken surface on both sides of the roof soil column, λ represents the lateral pressure coefficient, represents the calculated friction angle of the surrounding rock, and β represents the broken angle when the maximum thrust is generated;

[0030] b. The horizontal uniform pressure is directly determined according to the surrounding rock grade;

[0031] S1.3, calculating the surrounding rock pressure under the condition of deep burial:

[0032] For a deep-buried tunnel with a basically horizontal ground, the load acting thereon is symmetrical, and the vertical and horizontal uniform pressure thereof is determined by the following methods:

[0033] a. The vertical pressure under the condition of deep burial is calculated by formula (4);

[0034] b. The horizontal pressure under the condition of deep burial is calculated by the following formula:

[0035] e i = γh i λ (6)

[0036] where e i represents the horizontal pressure at any point i under the condition of deep burial, h i represents the distance from any point i on the inside and outside to the ground; when h i < h a , take θ = 0, which belongs to an ultra-deep-buried tunnel, and h a is the calculation height of the vertical load of the deep-buried tunnel.

[0037] In step S2, according to the New Austrian Tunneling Method principle, the lining piece is assembled in lag, the secondary lining is assembled after the convergence of the surrounding rock displacement is stable, and in the IV and V surrounding rock, the secondary lining sharing ratio value range is 35% to 20% and 70% to 50% respectively.

[0038] The step S3 of establishing the beam-spring load structure model includes the following processes:

[0039] S3.1, establishing a beam-spring load structure model:

[0040] A prefabricated tunnel model surrounded by lining pieces is established, the lining pieces include an arch top precast block, a right arch wall precast block, a curved foundation and a left arch wall precast block connected in sequence; the load borne by the secondary lining is calculated according to the load sharing ratio in step S2, and is loaded on the prefabricated tunnel model;

[0041] S3.2, determining the equivalent stiffness of the lining piece:

[0042] The parameters of the steel and the concrete are equivalent according to the stiffness equivalence principle, and the elastic modulus of the lining piece is represented as:

[0043]

[0044] Wherein E c represents the cross-sectional elastic modulus, E0 represents the deformation modulus of the concrete, S g represents the total cross-sectional area of the main reinforcement, E g represents the deformation modulus of the reinforcement, S c represents the cross-sectional area of the concrete;

[0045] S3.3, determining the joint stiffness of the lining piece:

[0046] The elastic bending stiffness of the lining piece joint is represented as:

[0047]

[0048] Wherein EI represents the elastic bending stiffness of the bolt between the segments of the beam-spring model method, I c represents the cross-sectional moment of inertia, L represents the ring width, K θ represents the ring joint rotational stiffness, which is determined by the following empirical formula:

[0049] K θ = γ(εN+μM+C) (9)

[0050] Wherein γ represents the block reduction coefficient of the lining piece, ε represents the axial force influence coefficient, μ represents the bending moment influence coefficient, N represents the axial force of the lining piece, M represents the bending moment of the lining piece, and C represents the initial stiffness;

[0051] S3.4, Establishing boundary conditions:

[0052] Except for the bolt connection of lining piece, the lining piece and the cast-in-place concrete construction joint, the lining piece in the assembled tunnel model is provided with an elastic curved foundation spring as a constraint boundary, forming a beam-spring load structure model;

[0053] The lining piece and the cast-in-place concrete construction joint, and the lining piece bolt connection are connected by an elastic spring, and the spring modulus of the bolt between the lining pieces is valued according to formula (8).

[0054] The load combination of the beam-spring load structure model determined in step S4 includes the combination mode of the structure dead weight, active earth pressure, surrounding rock pressure and surrounding rock elastic resistance under the permanent load and constant load classification, considering the normal use limit state and the bearing capacity limit state.

[0055] Step S6 performs safety checking on the lining structure, specifically including the following processes:

[0056] S6.1, For the lining structure of the beam-spring load structure model, according to the material and eccentricity of the lining structure, safety checking is performed according to the following conditions:

[0057] a. For plain concrete regarded as a compression-bending member, when the eccentricity e0 of the rectangular section is ≤0.2h, the compressive strength controls the bearing capacity, h represents the lining section thickness, and the safety factor K is calculated by the following formula:

[0058]

[0059] Wherein represents the longitudinal bending coefficient of the member, a represents the eccentricity influence coefficient of the axial force, R a represents the compressive ultimate strength of concrete or masonry, b represents the section width, h represents the section thickness, and N represents the axial force.

[0060] b. For plain concrete regarded as a compression-bending member, when the eccentricity e0 of the rectangular section is >0.2h0, the tensile strength controls the bearing capacity, and the safety factor K is calculated by the following formula:

[0061]

[0062] Wherein R l represents the tensile ultimate strength of concrete, e0 represents the eccentricity of the axial force, and h represents the section thickness.

[0063] c. For reinforced concrete regarded as a compression-bending member, when the eccentricity e0 of the rectangular section is ≤0.55h0, safety checking is performed according to the following conditions:

[0064] When the concrete compression zone height x is less than or equal to 0.55h0, the safety factor K is calculated by the following formula:

[0065] K=R w bx(h0-x / 2)+R g A′ g (h0-a′) (12)

[0066] wherein R w represents the flexural compressive ultimate strength of the concrete, R g represents the tensile or compressive calculated strength of the steel, A′ g represents the cross-sectional area of the longitudinal compression steel, and a′ represents the distance from the resultant point of the longitudinal compression steel to the near edge of the section.

[0067] When x is greater than 0.55h0, the safety factor K is calculated by the following formula:

[0068] K=0.5R a bh0 2 +R g A′ g (h0-a′) (13)

[0069] S6.2, judging whether the lining structure safety factor meets the requirements according to the railway tunnel design specification.

[0070] The present application has the beneficial effects of the technical scheme in that:

[0071] (1) The mine method excavation arch wall fabricated tunnel structure safety checking method provided by the present application is based on the "New Austrian Tunneling Method" for analyzing the fabricated composite lining, establishing a calculation model, and simulating the stress of the lining structure through the summarized empirical formula. The key to the calculation using the method is to solve the initial support and secondary lining load sharing ratio principle, as well as the lining piece structure numerical calculation and the lining piece joint stiffness value. The traditional "modified conventional method" considers that the reduction of the bending stiffness of the tunnel joint part is the reduction of the bending stiffness of the ring as a whole, and introduces the circular ring stiffness reduction coefficient η and the pipe piece bending moment transmission coefficient ζ to simulate the influence of the pipe piece joint stiffness reduction and the pipe piece joint assembly caused by the pipe piece multiple joints. This method is too simplified and does not conform to the actual situation. The present application is based on the actual stress condition of the "mine method" tunnel composite lining, continues to use the concept of composite lining load sharing ratio, combines the "beam-spring" model which is closer to the actual secondary lining, simulates the bending stiffness of the lining piece joint, and at the same time puts forward a new empirical formula for the lining piece joint, so as to realize the purpose of more close to the mine method fabricated tunnel lining calculation.

[0072] (2) The rigidity calculation formula proposed by the mine method excavation arch wall assembled tunnel structure safety checking and calculating method for lining piece joint can obtain the functional relationship of joint rigidity and lining axial force, bending moment and block quantity. The lining piece block reduction coefficient γ, axial force influence coefficient ε and bending moment influence coefficient μ are introduced, which can be more in line with the actual stress condition.

[0073] (3) The current "Highway Tunnel Design Specification" (JTG 3370.1-2018) has a recommended value for the secondary lining load sharing ratio of two-lane tunnels under the conditions of class IV and class V surrounding rock, that is, in class IV and class V surrounding rock, the secondary lining load sharing ratio is recommended to be in the range of 40% to 20% and 80% to 60%, respectively. In actual engineering, the recommended value of the specification is often too conservative, and the research on the secondary lining load sharing ratio in the academic field lacks more accurate values, which directly leads to the experience-based design of the secondary lining, inevitably causing material waste and directly increasing the engineering cost. On the other hand, the construction time load sharing ratio of the lining has an important influence. According to the principle of "New Austrian Tunneling Method", the lining piece is assembled in lag, and the secondary lining is assembled after the surrounding rock displacement convergence is stable. According to the surrounding rock condition and the monitoring measurement data, the secondary lining load sharing ratio is recommended to be in the range of 35% to 20% and 70% to 50% in class IV and class V surrounding rock, respectively, which is closer to the true value and can greatly reduce the engineering cost. BRIEF DESCRIPTION OF DRAWINGS

[0074] Figure 1 is a flowchart of the mine method excavation arch wall assembled tunnel structure safety checking and calculating method provided by the present application.

[0075] Figure 2 is a schematic diagram of the main load action under shallow buried conditions.

[0076] Figure 3 is a schematic diagram of the main load action under deep buried conditions.

[0077] Figure 4 is a schematic diagram of the assembled tunnel model.

[0078] Wherein: 1 - arch top precast block, 2 - right arch wall precast block, 3 - curved foundation, 4 - left arch wall precast block, 5 - elastic spring. DETAILED DESCRIPTION

[0079] The present application will be further described below in conjunction with the drawings and examples.

[0080] The present application provides a mine method excavation arch wall assembled tunnel structure safety checking and calculating method, referring to Figure 1 , comprising the following steps:

[0081] S1, determining the tunnel surrounding rock pressure, specifically including the following process:

[0082] S1.1, divide tunnel deep and shallow bury:

[0083] The tunnel deep and shallow bury demarcation depth H is determined by the following formula p :

[0084] H p = m·h q (1)

[0085] Wherein m is an empirical coefficient, which is determined comprehensively in combination with geological conditions and construction method factors, and the value range is 2-2.5. Under the condition of new Austrian tunnel construction, H p = 2.5h q is taken for Ⅳ-Ⅵ grade surrounding rock; H p = 2h q is taken for Ⅰ-Ⅲ grade surrounding rock.

[0086] h q Indicates the loose confining pressure load height (m), which is calculated by the following formula:

[0087] h q = 0.33×2.72 0.6s ω (2)

[0088] Wherein s indicates the surrounding rock grade, and ω indicates the width influence coefficient, ω = 0.2 + 0.1B, and B is the maximum excavation span of the tunnel (m).

[0089] S1.2, calculate the surrounding rock pressure under shallow bury condition:

[0090] Referring to p , for the case where the buried depth is less than H Figure 2 , when calculating the internal force of the lining of the shallow buried tunnel, the surrounding rock pressure is considered as loose pressure, and the vertical and horizontal uniform pressure is determined respectively:

[0091] a, the vertical uniform pressure q is calculated by the following formula:

[0092]

[0093]

[0094]

[0095] Wherein γ indicates the unit weight of the overlying surrounding rock of the tunnel, H indicates the vertical distance from the tunnel arch to the ground when the tunnel is shallow buried, θ indicates the friction angle of the broken surface on both sides of the roof soil column, λ indicates the lateral pressure coefficient, indicates the calculated friction angle of the surrounding rock, and β indicates the broken angle when the maximum thrust is generated.

[0096] When there is no measured data, θ can be taken according to the following table:

[0097]

[0098] Table 1 θ values ​​of surrounding rock at various levels

[0099] The mechanical indices of surrounding rocks are given in the following table:

[0100]

[0101] Table 2 Mechanical indexes of surrounding rock

[0102] b. The horizontal average pressure can be directly determined according to the surrounding rock grade, as shown in the following table:

[0103] Surrounding rock class Ⅰ～Ⅱ Ⅲ Ⅳ Ⅴ Water level distribution pressure 0 <0.25q (0.25～0.5)q (0.3～0.5)q

[0104] Table 3 Average pressure distribution of surrounding rock

[0105] S1.3. Calculate the surrounding rock pressure under deep burial conditions:

[0106] Reference Figure 3 , for burial depth greater than H p In the case of a deep tunnel with a substantially horizontal ground surface, the loads it bears are symmetrical, and the vertical and horizontal pressure distributions are determined as follows:

[0107] a. Calculate the vertical pressure under deep burial conditions using formula (4);

[0108] b. Calculate the horizontal pressure under deep burial conditions using the following formula:

[0109] e i =γh i λ (6)

[0110] where e i represents the horizontal pressure at any point i under deep burial conditions, h i Indicates the distance from any point i inside or outside to the ground; when h i <h a When θ=0, it is an ultra-deep tunnel, h a Calculate height for vertical loads in deep tunnels.

[0111] S2. Determine the load sharing ratio. Specifically, according to the New Austrian Tunneling Method (NATM), the lining segments should be assembled lagging, and the secondary lining should be installed after the surrounding rock displacement converges and stabilizes. For Grade IV and Grade V surrounding rock, the secondary lining sharing ratio should be in the range of 35% to 20% and 70% to 50%, respectively.

[0112] S3. Establishing a beam-spring load structure model, including the following steps:

[0113] S3.1. Establish beam-spring load structure model:

[0114] Reference Figure 4 In the Midas software, the assembled tunnel model surrounded by the lining piece is established, the lining piece includes the vault prefabricated block 1, the right arch wall prefabricated block 2, the curved foundation 3 and the left arch wall prefabricated block 4 connected in sequence. The load borne by the secondary lining calculated according to the load sharing ratio of step S2 is shared according to the load sharing ratio of step S1, and the load borne by the secondary lining is calculated and loaded on the assembled tunnel model.

[0115] S3.2, determine the equivalent stiffness of the lining piece:

[0116] The parameters of the steel and the concrete are equivalent by using the stiffness equivalent principle, and the elastic modulus of the lining piece is represented as:

[0117]

[0118] Wherein E c represents the cross-section elastic modulus, E0 represents the deformation modulus of the concrete, S g represents the total cross-sectional area of the main reinforcement, E g represents the deformation modulus of the reinforcement, S c represents the cross-sectional area of the concrete;

[0119] S3.3, determine the joint stiffness of the lining piece:

[0120] The elastic bending stiffness of the lining piece joint is represented as:

[0121]

[0122] Wherein EI represents the elastic bending stiffness of the bolt between the segments of the beam-spring model method, I c represents the cross-sectional moment of inertia, L represents the ring width, K θ represents the rotational stiffness of the ring joint, which is determined by the following empirical formula:

[0123] K θ = γ(εN+μM+C) (9)

[0124] Wherein γ represents the block reduction coefficient of the lining piece, ε represents the axial force influence coefficient, μ represents the bending moment influence coefficient, N represents the axial force of the lining piece, M represents the bending moment of the lining piece, and C represents the initial stiffness;

[0125] S3.4, establish the boundary condition:

[0126] Except for the bolt connection of the lining piece, the lining piece and the cast-in-place concrete construction joint, the lining piece in the assembled tunnel model is provided with an elastic curved foundation spring as a constraint boundary, forming a beam-spring load structure model;

[0127] The elastic spring is arranged at the lining piece and cast-in-place concrete construction joint and the lining piece bolt connection, and the spring modulus of the bolt between the lining pieces is valued according to formula (8).

[0128] S4, determine the load combination of the beam-spring load structure model, including the structure dead weight, active earth pressure, surrounding rock pressure and surrounding rock elastic resistance under the permanent load and constant load classification, considering the combination mode under the normal use limit state and the bearing capacity limit state, as shown in the following table:

[0129]

[0130] Table 4 Load and combination form

[0131] S5, calculate the load result under different load combinations, that is, combine the deep and shallow buried surrounding rock pressure calculation method and the checking working condition. Taking Panxing railway Panzhou tunnel engineering as an example, the deep and shallow buried surrounding rock pressure results are shown in the following table:

[0132] Surrounding rock class Ⅳ Ⅴ Vertical wall pressure q (kN / m 2 )]]> 157.29 264.02 Horizontal surrounding rock pressure e (kN / m 2 )]]> 31.46 105.61

[0133] Table 5 Deep buried surrounding rock pressure

[0134] Surrounding rock class Ⅳ Ⅴ Vertical wall pressure q (kN / m 2 )]]> 338.51 470.97 horizontal surrounding rock pressure e1 (kN / m 2 )]]> 47.77 144.48 horizontal surrounding rock pressure e2 (kN / m 2 )]]> 83.01 195.47

[0135] Table 6 Shallow buried surrounding rock pressure

[0136] S6, safety checking calculation of lining structure.

[0137] Step S6, safety checking calculation of lining structure, specifically including the following processes:

[0138] S6.1, for the lining structure of the beam-spring load structure model, according to the material and eccentricity of the lining structure, the safety checking calculation is carried out according to the following conditions:

[0139] a, for the plain concrete regarded as a compression bending member, when the rectangular cross section eccentricity e0≤0.2h, the compressive strength controls the bearing capacity, h represents the lining section thickness, the safety factor K of the plain concrete structure is calculated by the following formula:

[0140]

[0141] Wherein represents the longitudinal bending coefficient of the member, α represents the eccentricity influence coefficient of the axial force, R a represents the compressive ultimate strength of concrete or masonry, b represents the section width, h represents the section thickness, and N represents the axial force.

[0142] b. For plain concrete structures that are considered as compression-bending members, when the eccentricity of the rectangular section e0>0.2h0, the tensile strength controls the bearing capacity. The tensile strength of the plain concrete structure is checked and the safety factor K is calculated using the following formula:

[0143]

[0144] where R l represents the ultimate tensile strength of concrete, e0 represents the eccentricity of the axial force, and h represents the section thickness;

[0145] c. For reinforced concrete members that are considered as compression-bending members, when the eccentricity of the rectangular section e0 ≤ 0.55h0, safety calculations are performed according to the following conditions:

[0146] When the height of the concrete compression zone x≤0.55h0, the safety factor K is calculated by the following formula:

[0147] K=R w bx(h0-x / 2)+R g A′ g (h0-a′) (12)

[0148] where R w The ultimate compressive strength of concrete, R g Indicates the calculated tensile or compressive strength of the steel bar, A′ g represents the cross-sectional area of ​​the longitudinal compressive reinforcement, and a′ represents the distance from the resultant force point of the longitudinal compressive reinforcement to the near side of the cross section;

[0149] When x>0.55h0, the safety factor K is calculated by the following formula:

[0150] K=0.5R a bh0 2 +R g A′ g (h0-a′) (13)

[0151] S6.2. Determine whether the lining structure safety factor meets the standards based on the Railway Tunnel Design Code. According to Article 8.5.2 of the Railway Tunnel Design Code (TB 10003-2016), the strength safety factors for concrete and reinforced concrete structures are as shown in the following table:

[0152]

[0153]

[0154] Table 7 Strength safety factors of concrete and masonry structures

[0155]

[0156] Table 8 strength safety factor of reinforced concrete structure

[0157] When the tunnel lining is calculated according to the damage stage, the lining strength safety factor is selected according to the following criteria: for plain concrete, when the concrete is controlled according to the compressive strength, the safety factor is greater than or equal to 2.4; when the concrete is controlled according to the tensile strength, the safety factor is greater than or equal to 3.6. For reinforced concrete structure, when the concrete reaches the compressive ultimate strength, the safety factor is greater than or equal to 2.0.

[0158] Based on the safety calculation results of the commonly used modified conventional design method, the recommended lining thickness configuration is as follows:

[0159]

[0160] Table 9 recommended reinforcement of different lining thicknesses for deep buried section of IV surrounding rock using commonly used "modified conventional design method"

[0161] Based on the safety calculation method of the mine method excavation arch wall assembly type tunnel structure provided by the application, the recommended lining thickness configuration is as follows:

[0162]

[0163] Table 10 lining reinforcement of different thicknesses for deep buried section of IV surrounding rock using the application method

[0164] As can be seen from the above table, since the commonly used "modified conventional design method" is too simplified, the reinforcement amount is conservative during calculation. The scheme calculation model is relatively complex, but is closer to the actual stress condition, and the reinforcement of the lining structure is more optimized, and has more practical reference value.

[0165] The safety calculation method of the mine method excavation arch wall assembly type tunnel structure provided by the application is based on the "New Austrian Tunneling Method" for analysis of the assembly type composite lining, simulates the stress of the lining structure through the summarized empirical formula, can solve the problem of load sharing ratio principle of primary support and secondary lining, is based on the actual stress condition of the composite lining of the "mine method" tunnel, continues to use the concept of load sharing ratio of composite lining, combines the "beam-spring" model which is closer to the actual secondary lining, simulates the bending stiffness of the lining piece joint, and proposes an empirical formula for the lining piece joint, achieves the purpose of more close to the calculation of the mine method assembly type tunnel lining, has more reference value, and ensures the engineering safety.

Claims

1. A method for checking the safety of an arch-wall assembled tunnel structure excavated by a mining method, characterized in that The following steps are involved: S1. Determine the tunnel surrounding rock pressure; S2. Determine the load sharing ratio. According to the New Austrian Tunneling Method (NATM), the lining segments are assembled with a delay, and the secondary lining is assembled after the surrounding rock displacement converges and stabilizes. In Grade IV and Grade V surrounding rock, the load sharing ratio of the secondary lining is in the range of 35% to 20% and 70% to 50%, respectively. S3. Establishing a beam-spring load structure model, including the following steps: S3.

1. Establish beam-spring load structure model: Establishing an assembled tunnel model surrounded by lining segments, wherein the lining segments include a vault precast block, a right vault wall precast block, a curved foundation, and a left vault wall precast block connected end to end; sharing the various pressures calculated in step S1 according to the load sharing ratio obtained in step S2, calculating the load on the secondary lining, and applying the load to the assembled tunnel model; S3.

2. Determine the equivalent stiffness of the lining: The stiffness equivalence principle is used to make the parameters of steel and concrete equivalent, and the elastic modulus of the lining is expressed as: Among them E c represents the section elastic modulus, E0 represents the deformation modulus of concrete, S g Indicates the total cross-sectional area of ​​the main reinforcement, E g represents the deformation modulus of the steel bar, S c Indicates the cross-sectional area of ​​concrete; S3.

3. Determine the lining joint stiffness: The elastic bending stiffness of the lining sheet joint is expressed as: Where EI represents the elastic bending stiffness of the bolts between segments in the beam-spring model method, I C represents the section inertia moment, L represents the ring width, K θ It represents the rotational stiffness of the annular gap and is determined by the following empirical formula: K θ =γ(εN+μM+C) (9), Where γ represents the lining segment reduction coefficient, ε represents the axial force influence coefficient, μ represents the bending moment influence coefficient, N represents the lining segment axial force, M represents the lining segment bending moment, and C represents the initial stiffness; S3.

4. Establish boundary conditions: Except for the bolted connections between the lining segments and the construction joints between the lining segments and cast-in-place concrete, all lining segments in the prefabricated tunnel model are set with elastic curved foundation springs that are only subjected to compression as constraint boundaries, forming a beam-spring load structure model. Elastic springs are set at the construction joints between the lining pieces and the cast-in-place concrete, as well as at the bolt connections of the lining pieces. The spring modulus of the bolts between the lining pieces is determined according to formula (8); S4. Determine the load combination of the beam-spring load structure model; S5. Calculate the load results under different load combinations; S6. Carry out safety check calculation on the lining structure.

2. The method for checking the safety of an arch-wall assembled tunnel structure excavated by a mining method according to claim 1, characterized in that: The determination of the tunnel surrounding rock pressure in step S1 specifically includes the following process: S1.

1. Classification of tunnel depth and shallowness: The tunnel depth H is determined by the following formula p : H p =m·h q (1), Where m is the empirical coefficient, which is determined by combining geological conditions and construction methods, and the value range is 2 to 2.

5. q It represents the height of the loose confining pressure effective load and is calculated by the following formula: h q =0.33×2.72 0.6s oh (2), Where s represents the surrounding rock grade, ω represents the width influence coefficient, ω = 0.2 + 0.1B, B is the maximum excavation span of the tunnel; S1.

2. Calculate the surrounding rock pressure under shallow burial conditions: When calculating the internal forces of shallow tunnel linings, the surrounding rock pressure is considered as loose pressure, and its vertical and horizontal distributed pressures are determined separately: a. The vertical uniform pressure q is calculated by the following formula: Where γ represents the density of the surrounding rock above the tunnel, H represents the vertical distance from the tunnel arch to the ground when the tunnel is shallowly buried, θ represents the friction angle of the fracture surface on both sides of the top soil column, and λ represents the lateral pressure coefficient. represents the calculated friction angle of the surrounding rock, and β represents the fracture angle when the maximum thrust is generated; b. The horizontal average pressure is directly determined according to the surrounding rock grade; S1.

3. Calculate the surrounding rock pressure under deep burial conditions: For a deep tunnel with a substantially horizontal surface, the loads it bears are symmetrical. The vertical and horizontal pressure distributions are determined as follows: a. Calculate the vertical pressure under deep burial conditions using formula (4); b. Calculate the horizontal pressure under deep burial conditions using the following formula: e i =γh i λ (6), where e i represents the horizontal pressure at any point i under deep burial conditions, h i Indicates the distance from any point i inside or outside to the ground; when h i <h a When θ=0, it is an ultra-deep tunnel, h a Calculate height for vertical loads in deep tunnels.

3. The method for safety calculation of an arch-wall assembled tunnel structure excavated by a mining method according to claim 1, characterized in that: The load combination for the beam-spring load structure model determined in step S4 includes the combination of the structure's deadweight, active earth pressure, surrounding rock pressure, and surrounding rock elastic resistance under the classifications of permanent load and dead load, respectively, taking into account the serviceability limit state and the ultimate bearing capacity limit state.

4. The method for checking the safety of an arch-wall assembled tunnel structure excavated by a mining method according to claim 1, characterized in that: Step S6 performs safety check calculation on the lining structure, specifically The following processes are included: S6.1 For the lining structure of the beam-spring load structure model, safety checks shall be performed according to the following conditions, based on the material and eccentricity of the lining structure: a. For plain concrete structures that are considered as compression-bending members, when the eccentricity of the rectangular section e0 ≤ 0.2h, the compressive strength controls the bearing capacity. h represents the thickness of the lining section. The compressive strength of the plain concrete structure is checked and the safety factor K is calculated using the following formula: in represents the longitudinal bending coefficient of the component, α represents the eccentricity influence coefficient of the axial force, R a represents the ultimate compressive strength of concrete or masonry, b represents the section width, h represents the lining section thickness, and N represents the axial force; b. For plain concrete members that are considered as compression-bending members, when the eccentricity e0 of the rectangular section is greater than 0.2h, the tensile strength controls the bearing capacity. The tensile strength of the plain concrete structure is checked and the safety factor K is calculated using the following formula: where R l represents the ultimate tensile strength of concrete, e0 represents the axial force eccentricity, and h represents the thickness of the lining section; c. For reinforced concrete members regarded as compression-bending members, when the eccentricity of the rectangular section e0 ≤ 0.55h, safety check calculations are performed according to the following conditions: When the height of the concrete compression zone x≤0.55h, the safety factor K is calculated by the following formula: K=R w bx(h-x / 2)+R g A′ g (h-a′) (12), where R w The ultimate compressive strength of concrete, R g Indicates the calculated tensile or compressive strength of the steel bar, A′ g represents the cross-sectional area of ​​the longitudinal compressive reinforcement, and a′ represents the distance from the resultant force point of the longitudinal compressive reinforcement to the near side of the cross section; When x>0.55h, the safety factor K is calculated by the following formula: K=0.5R a bh 2 +R g A′ g (h-a′) (13), S6.

2. Determine whether the safety factor of the lining structure meets the standard according to the railway tunnel design specifications.

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