Rock wall size determining method suitable for large-section tunnel steel frame rock wall combination construction

Abstract

The invention relates to the technical field of tunnel engineering, in particular to a rock wall size determining method suitable for large-section tunnel steel frame rock wall combination construction. Comprising the steps that all size elements of a rock wall are preliminarily prepared; presetting the size of the rock wall according to the prepared size element, and building a numerical model of the large-section tunnel steel frame rock wall combined construction excavation according to the preset size of the rock wall; if the middle partition wall-main arch ring stress structure system excavated through the steel frame rock wall method meets the strength and rigidity requirements and the middle partition wall-rock wall combined supporting system meets the stability requirement, the preset rock wall size is determined to be the actual construction size; and if the strength and rigidity requirements are not met or the middle partition wall-rock wall combined supporting system does not meet the stability requirement, the size of the rock wall is reset, and the size of the corresponding numerical model is modified. According to the method, the rock wall size suitable for specific large-section tunnel steel frame rock wall combination construction can be determined, and important technical support and safety guarantee are provided for tunnel construction.

Description

Technical Field

[0001] The invention relates to the technical field of tunnel engineering, and in particular to a method for determining rock wall dimensions suitable for steel frame and rock wall combined construction of large-section tunnels. Background Art

[0002] In the construction of large-section highway tunnels, due to the large net cross-sectional area of ​​the tunnel, it is difficult to excavate it at one time, so it is necessary to excavate the pilot tunnel in sections. In the construction of large-section tunnels, steel frame rock wall combination construction is a special construction method, which uses pilot tunnel excavation in sections, adopts the "middle partition wall-core wall" combined support structure to replace the traditional middle partition wall, and retains the core wall as the lower support of the middle partition wall of the upper step. At the same time, the rock wall itself can also be used as a path for construction machinery to pass through. This method can greatly improve the construction quality and efficiency of large-section tunnels. However, the determination of the core wall size, especially the height, width and slope angle of the rock wall, is an urgent problem to be solved by the steel frame rock wall combination construction method.

[0003] At present, in order to ensure the stability of the tunnel section and the middle partition wall excavated by the large-section tunnel steel frame rock wall combination construction method, wider and larger rock wall sizes are often used in the design. Such a design is not conducive to the subsequent construction processes such as excavation of rock walls and excavation of inverts, which increases construction costs and increases the project cost.

[0004] Therefore, in order to simply and effectively determine the size of the core wall, give full play to the bearing capacity of the core wall itself, and facilitate subsequent construction steps such as excavating the rock wall and excavating the invert arch, the present invention mainly uses numerical simulation and adopts multiple criteria to quickly formulate the size of the rock wall, improve construction efficiency, and ensure construction safety. Summary of the invention

[0005] The purpose of the present invention includes providing a method for determining the size of a rock wall suitable for the steel frame and rock wall combination construction of a large-section tunnel, which takes into account the determination of dimensional factors such as the rock wall height, width and slope angle, and can determine the size of the rock wall suitable for the steel frame and rock wall combination construction of a specific large-section tunnel, so that it can not only meet the requirements of construction safety, but also reduce the engineering cost of tunnel construction to a certain extent, providing important technical support and safety guarantee for tunnel construction.

[0006] The embodiments of the present invention can be implemented as follows:

[0007] The present invention provides a method for determining rock wall dimensions applicable to large-section tunnel steel frame rock wall combined construction, comprising:

[0008] In order to ensure the traffic demand of vehicles and the stability requirements of the middle partition-rock wall combined support structure, the rock wall dimension elements are initially formulated. The rock wall dimension elements include the top width of the rock wall, the bottom width of the rock wall, the height of the rock wall and the slope angle of the rock wall;

[0009] The preset rock wall dimensions of the rock wall are set, including the preset rock wall top width, the preset rock wall bottom width, the preset rock wall height and the preset rock wall slope angle, and a numerical model of the steel frame rock wall method construction excavation of a large-section tunnel is established accordingly;

[0010] Extract the internal forces and deformations of the septum and main arch ring. If the septum-main arch ring stress structure system meets the strength and stiffness requirements, the preset rock wall size is appropriate in terms of the septum-main arch ring stress.

[0011] According to the distribution of the plastic zone of the rock wall, it is judged whether the rock wall is crushed and whether there is any block falling in the rock wall, so as to determine the stability of the rock wall; according to the internal force and slip at the bottom of the middle partition wall, it is judged whether the force at the bottom of the middle partition wall is reasonable; if the stability of the rock wall and the force at the bottom of the middle partition wall meet the requirements, it means that the stability of the middle partition wall-rock wall combined support system meets the requirements, that is, the preset rock wall size is appropriate in terms of the stability of the middle partition wall-rock wall;

[0012] If the middle partition wall-main arch ring force-bearing structure system meets the strength and stiffness requirements, and the middle partition wall-rock wall combined support system meets the stability requirements, the preset rock wall top width, preset rock wall bottom width, preset rock wall height and preset rock wall slope angle are the actual construction rock wall dimensions; if the middle partition wall-main arch ring force-bearing structure system does not meet the strength and stiffness requirements, or the middle partition wall-rock wall combined support system does not meet the stability requirements, the preset rock wall top width, preset rock wall bottom width, preset rock wall height and preset rock wall slope angle should be adjusted until they are met.

[0013] In an optional embodiment, the step of preliminarily formulating rock wall dimension elements, which include rock wall top width, rock wall bottom width, rock wall height, and rock wall slope angle, comprises:

[0014] Investigate the traffic demand of construction machinery vehicles, and comprehensively consider the stability requirements of the middle partition wall-rock wall combined supporting structure, such as the collapse and instability of the core wall, the instability and damage of the middle partition wall, and the failure of the locking anchor rods at the bottom of the middle partition wall, and preliminarily formulate the rock wall size elements such as the top width of the rock wall, the bottom width of the rock wall, the height of the rock wall and the slope angle of the rock wall.

[0015] In an optional embodiment, the step of establishing a numerical model for large-section tunnel excavation using a steel frame rock wall method includes:

[0016] The numerical model size is set based on the preset rock wall size preliminarily proposed for the rock wall. The surrounding rock is simulated by solid units that satisfy the Mohr-Coulomb yield criterion. The primary support, secondary lining and middle partition are all elastic solid units. The advanced support is achieved by modifying the mechanical parameters of the reinforcement ring. The system anchor is simulated by Cab le unit, and the locking anchor is simulated by Pi le unit.

[0017] In the numerical simulation, excavation and support operations were carried out according to the steel frame rock wall combined construction method. In order to eliminate the influence of boundary effect, the middle longitudinal section of the numerical model was selected as the research section. The stress and deformation characteristics of the initial support structure of the middle partition wall-main arch ring and the stability of the middle partition wall-rock wall combined support system in the numerical simulation were studied.

[0018] In an optional embodiment, the step of extracting the deformation of the middle septum and the main arch ring includes:

[0019] Take determining the width of the top of a rock wall as an example;

[0020] According to the initially proposed rock wall top width, different rock wall top widths were set, and a large-section steel frame rock wall method combined construction numerical model was established accordingly. By recording the vertical and horizontal displacements of the selected sections at each excavation stage, the tunnel vault settlement and tunnel perimeter convergence that changed with the construction stage under different working conditions were obtained.

[0021] The maximum circumference convergence and the maximum arch settlement are compared with the limit values ​​required by the code. If the code requirements are met, the preset rock wall top width can meet the stiffness requirements of the middle partition wall-main arch ring load-bearing structure system.

[0022] In an optional embodiment, the step of extracting the internal forces of the middle partition wall and the main arch ring includes:

[0023] Take determining the width of the top of a rock wall as an example;

[0024] The stress of the selected tunnel section at each stage is extracted. Based on the plane section assumption, the shotcrete axial force and steel frame bending moment of the selected tunnel section at each construction stage under different working conditions are calculated, and its safety is judged by the value of the safety factor.

[0025] In an optional implementation manner, the step of judging whether it is safe by the value of the safety factor includes:

[0026] Take determining the width of the top of a rock wall as an example;

[0027] According to the highway tunnel design specification, the damage stage method is used to verify the safety factor of the initial tunnel support. The compressive strength of the eccentrically compressed concrete structure should be verified according to the following formula:

[0028]

[0029] In the formula: K is the safety factor; N is the axial force; is the longitudinal bending coefficient of the component. For the tunnel lining, open hole arch ring and side wall with tight backfill, α is the eccentricity influence coefficient of the axial force; R ais the ultimate compressive strength of concrete or masonry; b is the section width (m); h is the section height (m);

[0030] The initial support of the tunnel at each stage is verified according to the above verification formula to obtain the calculated safety factor of concrete at each construction stage and the calculated safety factor of the steel arch frame at each construction stage; if the safety factor is greater than the minimum safety factor required by the code, it is safe, that is, the preset rock wall top width can meet the strength requirements of the intermediate partition wall-main arch ring force structure system.

[0031] In an optional embodiment, the step of determining the stability of the rock wall comprises:

[0032] Take determining the width of the top of a rock wall as an example;

[0033] Based on the established numerical model of large-section tunnel excavation using the steel frame rock wall method under different working conditions, if the plastic zone develops beyond the area of ​​the rock wall itself, the rock wall has become unstable and damaged.

[0034] In an optional embodiment, the step of determining the rationality of the force on the bottom of the middle partition wall includes:

[0035] Take determining the width of the top of a rock wall as an example;

[0036] Based on the numerical model of large-section tunnel steel frame rock wall construction under different working conditions, the instability relationship of the bottom of the middle partition wall in the most unfavorable situation is determined, and the friction coefficient μ1<μ is calculated when the bottom of the middle partition wall does not slide. max ;

[0037] By comparing the shear force and pressure at the junction of the middle partition wall and the rock wall, the calculated friction coefficient at the junction of the middle partition wall and the rock wall is obtained, thereby judging the stability of the bottom of the middle partition wall.

[0038] In an alternative embodiment, the bolt length in a large cross-section tunnel is within the width of the rock wall.

[0039] In an optional embodiment, the clear cross-sectional area of ​​the excavated tunnel of the large cross-section tunnel is greater than 100m 2 .

[0040] The beneficial effects of the rock wall size determination method applicable to the combined construction of steel frame and rock wall in large-section tunnels provided by the embodiment of the present invention include:

[0041] The rock wall size determination method applicable to the steel frame rock wall combined construction of large-section tunnels includes:

[0042] In order to ensure the traffic demand of vehicles and the stability requirements of the intermediate partition-rock wall combined support structure, the rock wall size elements (i.e. the top and bottom width of the rock wall, the rock wall height, and the rock wall slope angle) were initially formulated;

[0043] The size of the rock wall is set (i.e., the preset rock wall top and bottom widths, the preset rock wall height, and the preset rock wall slope angle), and a numerical model of the steel frame rock wall method for large-section tunnel excavation is established accordingly;

[0044] Extract the internal forces and deformations of the septum and main arch ring. If the septum-main arch ring stress structure system meets the strength and stiffness requirements, it means that the preset rock wall size elements are appropriate in terms of the septum-main arch ring stress.

[0045] According to the distribution of the plastic zone of the rock wall, it is judged whether the rock wall is crushed and whether there is any block falling in the rock wall, so as to determine the stability of the rock wall; according to the internal force and slip at the bottom of the middle partition wall, it is judged whether the force at the bottom of the middle partition wall is reasonable; if the stability of the rock wall and the force at the bottom of the middle partition wall meet the requirements, it means that the stability of the middle partition wall-rock wall combined support system meets the requirements, that is, the preset rock wall size elements are appropriate in terms of the stability of the middle partition wall-rock wall;

[0046] If the middle partition wall-main arch ring force-bearing structure system meets the strength and stiffness requirements, and the middle partition wall-rock wall combined support system meets the stability requirements, it means that the preset rock wall size elements (i.e., the preset rock wall top and bottom widths, the preset rock wall height, and the preset rock wall slope angle) are the actual construction rock wall sizes; if the middle partition wall-main arch ring force-bearing structure system does not meet the strength and stiffness requirements, or the middle partition wall-rock wall combined support system does not meet the stability requirements, the preset rock wall size elements (i.e., the preset rock wall top and bottom widths, the preset rock wall height, and the preset rock wall slope angle) should be adjusted until they are met.

[0047] The rock wall size determination method applicable to the steel frame rock wall combination construction of large-section tunnels takes into account the determination of dimensional factors such as rock wall height, width and slope angle, and can determine the rock wall size applicable to the steel frame rock wall combination construction of a specific large-section tunnel, so that it can not only meet the requirements of construction safety, but also reduce the engineering cost of tunnel construction to a certain extent, providing important technical support and safety guarantee for tunnel construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0049] Figure 1 A flow chart of a method for determining rock wall dimensions for steel frame rock wall combined construction of a large-section tunnel provided in this embodiment;

[0050] Figure 2The numerical model diagram of the large-section tunnel steel frame rock wall combined construction method provided in this embodiment, wherein a is the overall model diagram and b is the local model diagram;

[0051] Figure 3 A typical construction stage diagram in the numerical simulation formed according to the actual on-site construction provided in this embodiment, wherein a is the upper excavation support of the subsequent pilot tunnel, b is the upper excavation support of the subsequent pilot tunnel, c is the upper excavation support of the subsequent pilot tunnel, d is the lower excavation support of the subsequent pilot tunnel, e is the removal of the middle partition wall, f is the removal of the rock wall and the excavation of the invert, g is the construction of the invert and the secondary lining, and h is an overview of the tunnel excavation;

[0052] Figure 4 The tunnel vault settlement and tunnel perimeter convergence diagram under different rock wall top widths provided in this embodiment, where a is the vault settlement and b is the tunnel perimeter convergence;

[0053] Figure 5 The axial force diagram of shotcrete at each typical construction stage under different rock wall top widths provided in this embodiment, wherein a is the excavation support of the upper part of the subsequent pilot tunnel, b is the excavation support of the lower part of the subsequent pilot tunnel, c is the removal of the middle partition wall, d is the excavation of the rock wall and the excavation of the invert, and e is the initial support of the invert;

[0054] Figure 6 The bending moment diagrams of steel frames at typical construction stages under different rock wall top widths provided in this embodiment, wherein a is the excavation support of the upper part of the subsequent pilot tunnel, b is the excavation support of the lower part of the subsequent pilot tunnel, c is the removal of the middle partition wall, d is the excavation of the rock wall and the excavation of the invert, and e is the initial support of the invert;

[0055] Figure 7 The safety factor of concrete calculation for each construction stage provided in this embodiment, wherein a is the upper excavation support of the subsequent pilot tunnel, b is the lower excavation support of the subsequent pilot tunnel, c is the removal of the middle partition wall, d is the removal of the rock wall and the excavation of the invert, and e is the initial support of the invert;

[0056] Figure 8 The calculated safety factor of the steel arch frame at each construction stage provided in this embodiment, wherein a is the upper excavation support of the subsequent pilot tunnel, b is the lower excavation support of the subsequent pilot tunnel, c is the removal of the middle partition wall, d is the excavation of the rock wall and the excavation of the invert, and e is the initial support of the invert;

[0057] Fig. 9 A schematic diagram of the anchor provided in this embodiment being driven into the primary support;

[0058] Fig.10 The distribution map of the plastic zone of the rock wall provided for this embodiment;

[0059] Fig.11The maximum and minimum principal stresses of the rock wall at different rock wall top widths provided in this embodiment, where a is the maximum principal stress at 3m, b is the minimum principal stress at 3m, c is the maximum principal stress at 4m, d is the minimum principal stress at 4m, e is the maximum principal stress at 5m, and f is the minimum principal stress at 5m;

[0060] Fig.12 The schematic diagram of the stability of the bottom of the middle partition provided in this embodiment, wherein a is a schematic diagram of the instability of the surrounding rock section of level IV, and b is a schematic diagram of the detailed force; DETAILED DESCRIPTION

[0061] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0062] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0063] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0064] In the description of the present invention, it should be noted that if the terms "upper", "lower", "inside", "outside", etc. appear to indicate an orientation or position relationship, they are based on the orientation or position relationship shown in the accompanying drawings, or are the orientation or position relationship in which the product of the invention is usually placed when used. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0065] In addition, the terms “first”, “second”, etc., if used, are merely used to distinguish between the descriptions and should not be understood as indicating or implying relative importance.

[0066] It should be noted that, in the absence of conflict, the features in the embodiments of the present invention may be combined with each other.

[0067] Please refer to Figure 1 This embodiment provides a method for determining rock wall dimensions applicable to large-section tunnel steel frame rock wall combination construction, including:

[0068] In order to ensure the traffic demand of vehicles and the stability requirements of the middle partition-rock wall combined support structure, the rock wall dimension elements are initially formulated. The rock wall dimension elements include the top width of the rock wall, the bottom width of the rock wall, the height of the rock wall and the slope angle of the rock wall;

[0069] The preset rock wall dimensions of the rock wall are set, including the preset rock wall top width, the preset rock wall bottom width, the preset rock wall height and the preset rock wall slope angle, and a numerical model of the steel frame rock wall method construction excavation of a large-section tunnel is established accordingly;

[0070] Extract the internal forces and deformations of the septum and main arch ring. If the septum-main arch ring stress structure system meets the strength and stiffness requirements, the preset rock wall size is appropriate in terms of the septum-main arch ring stress.

[0071] According to the distribution of the plastic zone of the rock wall, it is judged whether the rock wall is crushed and whether there is any block falling in the rock wall, so as to determine the stability of the rock wall; according to the internal force and slip at the bottom of the middle partition wall, it is judged whether the force at the bottom of the middle partition wall is reasonable; if the stability of the rock wall and the force at the bottom of the middle partition wall meet the requirements, it means that the stability of the middle partition wall-rock wall combined support system meets the requirements, that is, the preset rock wall size is appropriate in terms of the stability of the middle partition wall-rock wall;

[0072] If the middle partition wall-main arch ring force-bearing structure system meets the strength and stiffness requirements, and the middle partition wall-rock wall combined support system meets the stability requirements, the preset rock wall top width, preset rock wall bottom width, preset rock wall height and preset rock wall slope angle are the actual construction rock wall dimensions; if the middle partition wall-main arch ring force-bearing structure system does not meet the strength and stiffness requirements, or the middle partition wall-rock wall combined support system does not meet the stability requirements, the preset rock wall top width, preset rock wall bottom width, preset rock wall height and preset rock wall slope angle should be adjusted until they are met.

[0073] The rock wall size determination method applicable to the steel frame rock wall combination construction of large-section tunnels takes into account the determination of dimensional factors such as rock wall height, width and slope angle, and can determine the rock wall size applicable to the steel frame rock wall combination construction of a specific large-section tunnel, so that it can not only meet the requirements of construction safety, but also reduce the engineering cost of tunnel construction to a certain extent, providing important technical support and safety guarantee for tunnel construction.

[0074] Furthermore, in this embodiment, the steps of preliminarily formulating the rock wall dimension elements (i.e., the rock wall top and bottom widths, the rock wall height, and the rock wall slope angle) include:

[0075] Investigate the traffic demand of construction machinery vehicles, and comprehensively consider the stability requirements of the middle partition wall-rock wall combined supporting structure, such as the crushing instability of the core wall, the instability and damage of the middle partition wall, and the failure of the locking anchor rods at the bottom of the middle partition wall, and preliminarily formulate the rock wall dimensional elements such as the top and bottom width of the rock wall, the rock wall height, and the rock wall slope angle.

[0076] From the above content, it can be seen that after the preset size of the rock wall is proposed and before the internal force and deformation of the middle partition wall and the main arch ring are extracted, it is necessary to establish a numerical model for the construction and excavation of a large-section tunnel using the steel frame rock wall method. The specific steps include:

[0077] The size of the numerical model is set based on the preliminary proposed rock wall size elements (i.e., the top and bottom widths of the rock wall, the rock wall height, and the rock wall slope angle). The surrounding rock is simulated by solid units that satisfy the Mohr-Coulomb yield criterion. The primary support, secondary lining, and intermediate partition are all elastic solid units. The advanced support is achieved by modifying the mechanical parameters of the reinforcement ring. The system anchor is simulated by the Cab le unit, and the locking anchor is simulated by the Pi le unit.

[0078] In the numerical simulation, excavation and support operations were carried out according to the steel frame rock wall combined construction method. In order to eliminate the influence of boundary effect, the middle longitudinal section of the numerical model was selected as the research section. The stress and deformation characteristics of the initial support structure of the middle partition wall-main arch ring and the stability of the middle partition wall-rock wall combined support system in the numerical simulation were studied.

[0079] Therefore, according to the established numerical model of large-section tunnel excavation by steel frame rock wall method, the deformation and internal force of the middle partition wall and main arch ring can be extracted. The specific steps include:

[0080] Take determining the width of the top of a rock wall as an example;

[0081] By recording the vertical and horizontal displacements of the selected sections at each excavation stage, the tunnel crown settlement and tunnel perimeter convergence that change with the construction stage under different working conditions are obtained;

[0082] The maximum circumference convergence and the maximum arch settlement are compared with the limit values ​​required by the code. If they are met, the preset rock wall top width can meet the stiffness requirements of the middle partition wall-main arch ring load-bearing structure system.

[0083] The stress of the selected tunnel section at each stage is extracted. Based on the plane section assumption, the shotcrete axial force and steel frame bending moment of the selected tunnel section at each construction stage under different working conditions are calculated, and its safety is judged by the value of the safety factor.

[0084] According to the highway tunnel design specification, the damage stage method is used to verify the safety factor of the initial tunnel support. The compressive strength of the eccentrically compressed concrete structure should be verified according to the following formula:

[0085]

[0086] Where: K is the safety factor; N is the axial force; is the longitudinal bending coefficient of the component. For the tunnel lining, open hole arch ring and side wall with tight backfill, α is the eccentricity influence coefficient of the axial force; R a is the ultimate compressive strength of concrete or masonry; b is the section width (m); h is the section height (m);

[0087] The initial support of the tunnel at each stage is verified according to the above verification formula to obtain the calculated safety factor of the concrete at each construction stage and the calculated safety factor of the steel arch frame at each construction stage; if the safety factor is greater than the minimum safety factor required by the code, it is safe, and the preset rock wall top width can meet the strength requirements of the intermediate partition wall-main arch ring force structure system.

[0088] After considering the stress and deformation characteristics of the bulkhead-main arch ring structure, it is necessary to determine whether the proposed rock wall preset size meets the stability requirements of the bulkhead-rock wall combined support system. The specific steps include:

[0089] Take determining the width of the top of a rock wall as an example;

[0090] Based on the established numerical model of large-section tunnel steel frame rock wall method construction excavation, if the plastic zone develops beyond the area of ​​the rock wall itself, the rock wall has been unstable and damaged; at the same time, based on the established numerical model of large-section tunnel steel frame rock wall method construction excavation, the instability relationship of the bottom of the middle partition wall in the most unfavorable situation is determined to calculate the friction coefficient μ1<μ when the bottom of the middle partition wall does not slide max ; Compare the shear force and pressure at the junction of the middle partition wall and the rock wall to obtain the calculated friction coefficient at the junction of the middle partition wall and the rock wall, so as to judge the stability of the bottom of the middle partition wall; when the above two requirements are met, it can be judged that the preset rock wall top width meets the stability requirements of the middle partition wall-rock wall combined support system.

[0091] When the deformation and internal force requirements of the bulkhead-main arch ring load-bearing structure are met, and the stability requirements of the bulkhead-rock wall combined support system are met at the same time, the preset top width of the rock wall can be stated as the top width of the rock wall, and then the remaining dimensional elements of the rock wall (rock wall bottom width, rock wall corner, rock wall height) can be gradually determined according to the same operating steps.

[0092] It should be noted that, in this embodiment, the length of the anchor rod in the large-section tunnel is within the width of the rock wall. This setting method is intended to ensure that the length of the anchor rod is within the width of the rock wall to avoid penetrating the rock wall and causing a load-bearing failure. In addition, in this embodiment, the rock wall size determination method applicable to the steel frame rock wall combined construction of a large-section tunnel is applicable to a large-section tunnel with a clear cross-sectional area of ​​more than 100m. 2 .

[0093] In summary, based on the above content, it can be seen that the rock wall size determination method applicable to the large-section tunnel steel frame rock wall combination construction includes the determination of four size elements during the implementation process, including the top and bottom width of the rock wall, the rock wall height, and the rock wall slope angle;

[0094] Among them, the steel frame rock wall combined support method mentioned in this embodiment uses steel support and shotcrete as temporary middle partition wall support, uses core wall as the bottom support of the middle partition wall, forms a middle partition wall-rock wall combined support system, and carries out a construction method of partial excavation of the pilot tunnel; and the core wall has two main functions, one is to support the bottom soil of the middle partition wall and form a middle partition wall-core wall combined support system, and the second is to provide construction machinery represented by rock drilling rigs to enter the site for work.

[0095] The rock wall size determination method applicable to the steel frame rock wall combination construction of large-section tunnels includes the determination of the top and bottom widths of the rock wall, the rock wall height, and the rock wall slope angle during implementation;

[0096] Based on this, the steps for determining the rock wall size elements are as follows:

[0097] S1. Preliminary preparation of rock wall dimension elements (i.e. rock wall top and bottom width, rock wall height, rock wall slope angle);

[0098] S2. Establish a numerical model for the construction and excavation of large-section tunnels using the steel frame rock wall method;

[0099] Numerical model of steel frame rock wall method for large cross-section tunnels Figure 2 As shown in the figure. The size of the numerical model is about 150m×72m×125m. The surrounding rock is simulated by solid units that meet the Mohr-Coulomb yield criterion. The primary support, secondary lining and middle partition are all elastic solid units. The advanced support is achieved by modifying the mechanical parameters of the reinforcement ring. The system anchor is simulated by Cable units, and the locking anchor is simulated by Pile units.

[0100] According to the support parameters, combined with the "Highway Tunnel Design Code", and converting the steel frame to concrete in a stiffness equivalent manner, the physical and mechanical parameters of the surrounding rock and support are shown in Table 1-1.

[0101]

[0102]

[0103] Table 1-1 Physical and mechanical parameters of Class IV surrounding rock and support

[0104] In the numerical simulation, the excavation support operation was carried out according to the steel frame rock wall combined construction method. The excavation depth was taken as 3m according to the on-site construction. In order to eliminate the influence of the boundary on the calculation, the section at y=36m in the middle of the longitudinal direction of the numerical model was taken as the research section. The deformation and stress of the support under the corresponding step sequence were studied based on the arrival of each step sequence at this section. Figure 3 It is a typical construction stage diagram in the numerical simulation formed according to the actual construction on site.

[0105] S3. Change the value of one of the dimensional elements (i.e. rock wall height, rock wall top and bottom width, rock wall slope angle), taking the rock wall top width as an example;

[0106] S4. Extract the internal forces and deformations of the middle partition wall and the main arch ring; S5. If the middle partition wall-primary support combined force system meets the strength and stiffness requirements, it means that the top width of the rock wall is appropriate.

[0107] Deformation criterion: Taking the determination of the top width of the rock wall as an example:

[0108] By recording the vertical and horizontal displacements of the selected sections at each excavation stage, we can obtain Figure 4 The tunnel crown settlement and tunnel perimeter convergence under different working conditions are shown as the construction stages change.

[0109] From the above displacement diagram we can see that:

[0110] During the excavation of the tunnel, the crown settlement and the tunnel perimeter convergence gradually increase and eventually stabilize. It should be noted that the maximum tunnel perimeter convergence and the maximum crown settlement are compared with the limit values ​​required by the specification. If they meet the requirements, the assumed rock wall height meets the requirements.

[0111] Internal force and strength criterion: By extracting the stress of the selected tunnel section at each stage, the following can be obtained by calculation based on the assumption of a flat cross section: Figure 5 and Figure 6 The shotcrete axial force and steel frame bending moment diagrams of the selected tunnel sections in each typical construction stage under different working conditions are shown.

[0112] According to the "Highway Tunnel Design Code", the damage stage method is used to verify the safety factor of the initial support of Lihuashan Tunnel. The compressive strength verification of the eccentrically compressed concrete structure should be calculated according to the following formula:

[0113]

[0114] Where: K is the safety factor, adopted according to Table 1-2; N is the axial force; is the longitudinal bending coefficient of the member. For the tunnel lining, open hole arch ring and side wall with tight backfill, α is the eccentricity influence coefficient of axial force; Ra is the ultimate compressive strength of concrete or masonry; b is the section width (m); h is the section height (m).

[0115]

[0116] Note: The steel structure in the table refers to supporting structures such as anchor rods, steel arch frames and other hanging structures.

[0117] Table 1-2 Comprehensive safety factor values

[0118] According to the above calculation formula, the initial support of the tunnel in each stage is calculated and obtained. Figure 7 Safety factor and Figure 8 Calculation safety factor of steel arch frame at each construction stage.

[0119] It should be noted that if the safety factor is greater than the minimum safety factor required by the code, it is safe, which proves that there is no problem with the proposed rock wall top width.

[0120] S6. According to the distribution of the plastic zone of the rock wall, determine whether the rock wall is crushed and whether there is any block falling in the rock wall, and judge the stability of the middle partition wall-rock wall combined support system according to the internal force and slip at the bottom of the middle partition wall. If the stability requirements are met, it means that the top width of the rock wall is appropriate.

[0121] Please note that, please refer to Fig. 9 The relationship between the length of the anchor rod and the width of the rock wall is that the length of the anchor rod must be within the width of the rock wall. If the rock wall is penetrated, it will not be able to bear the load.

[0122] Please refer to Fig.10 , according to the distribution of the plastic zone of the rock wall, it is judged whether the rock wall is crushed, whether there is block falling in the part of the rock wall, and thus the stability of the rock wall is determined;

[0123] The stability criterion of the rock wall is that if the plastic zone develops completely beyond the area of ​​the rock wall itself (the green block (shear-p) fills the blue block (none)), the rock wall has become unstable and damaged.

[0124] In order to explore the influence of different rock wall top widths on the stress of the core wall, Fig.11 The maximum and minimum principal stresses of the rock wall with different rock wall top widths are given.

[0125] It can be seen from the above rock wall force diagram that: in the most dangerous stage, the maximum principal stress on the rock wall is less than 0, the uniaxial compressive strength of the rock is 10.14MPa, and the minimum principal stress is less than the uniaxial compressive strength of the rock; and with the increase of the width of the rock wall, the force on the rock wall tends to increase, but the change is not very obvious. Therefore, with the change of the width of the rock wall, the force on the rock wall will not change much. However, for the sake of construction efficiency, construction machinery entry, construction safety, construction quality, etc., when using the steel frame rock wall combined construction method, it is also necessary to combine on-site construction to maintain a certain rock wall width.

[0126] The rationality of the force at the bottom of the middle partition wall is determined based on the internal force and slip at the bottom of the middle partition wall;

[0127] Fig.12 The schematic diagram of the instability of the bottom of the middle partition in the most unfavorable situation is given. When the calculated friction coefficient μ1<μ max It won't slide.

[0128] By comparing the shear force and pressure at the junction of the middle partition wall and the rock wall, we can obtain the calculated friction coefficient table at the junction of the middle partition wall and the rock wall in Table 2-1, thereby judging the stability of the bottom of the middle partition wall.

[0129]

[0130] Table 2-1 Stability analysis of the junction between the partition wall and the rock wall

[0131] If the above two requirements of rock wall stability and the stability of the bottom of the middle partition wall are met at the same time, it means that the stability of the middle partition wall-rock wall combined support system is guaranteed.

[0132] S7. If S5 and S6 are satisfied at the same time, it means that the top width of the rock wall is the actual top width of the rock wall. If they cannot be satisfied at the same time, the top width of the rock wall should be continuously adjusted until it is satisfied.

[0133] S8. Repeat S3, S4, S5, S6, and S7 until each rock wall dimension element is determined. The above is only a specific implementation of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for determining rock wall dimensions suitable for large-section tunnel steel frame rock wall combined construction, characterized in that: include: In order to ensure the traffic demand of vehicles and the stability requirements of the intermediate partition wall-rock wall combined support structure, the rock wall dimension elements are initially formulated, including the rock wall top width, rock wall bottom width, rock wall height and rock wall slope angle; The preset rock wall dimensions of the rock wall are set, including the preset rock wall top width, the preset rock wall bottom width, the preset rock wall height and the preset rock wall slope angle, and a numerical model of the steel frame rock wall method construction excavation of a large-section tunnel is established accordingly; Extract the internal forces and deformations of the middle partition wall and the main arch ring. If the middle partition wall-main arch ring force-bearing structure system meets the strength and stiffness requirements, then the preset rock wall size is appropriate in terms of the middle partition wall-main arch ring force; According to the distribution of the plastic zone of the rock wall, it is judged whether the rock wall is crushed and whether there is a block falling locally, so as to determine the stability of the rock wall; according to the internal force and slip at the bottom of the middle partition wall, it is judged whether the force at the bottom of the middle partition wall is reasonable; if the stability of the rock wall and the force at the bottom of the middle partition wall meet the requirements, it means that the stability of the middle partition wall-rock wall combined support system meets the requirements, that is, the preset rock wall size is appropriate in terms of the stability of the middle partition wall-rock wall; If the middle partition wall-main arch ring force-bearing structure system meets the strength and stiffness requirements, and the middle partition wall-rock wall combined support system meets the stability requirements, then the preset rock wall top width, the preset rock wall bottom width, the preset rock wall height and the preset rock wall slope angle are the actual construction rock wall dimensions; if the middle partition wall-main arch ring force-bearing structure system does not meet the strength and stiffness requirements, or the middle partition wall-rock wall combined support system does not meet the stability requirements, then the preset rock wall top width, the preset rock wall bottom width, the preset rock wall height and the preset rock wall slope angle should be adjusted until they are met.

2. The method for determining rock wall dimensions applicable to large-section tunnel steel frame rock wall combined construction according to claim 1, characterized in that: The step of preliminarily formulating rock wall dimension elements, wherein the rock wall dimension elements include rock wall top width, rock wall bottom width, rock wall height and rock wall slope angle, comprises: The traffic demand of engineering machinery vehicles was investigated, and the stability requirements of the middle partition wall-rock wall combined supporting structure, such as the crushing instability of the core wall, the instability and damage of the middle partition wall, and the failure of the locking anchor rods at the bottom of the middle partition wall, were comprehensively considered. Preliminary dimensional elements of the rock wall, such as the top width of the rock wall, the bottom width of the rock wall, the height of the rock wall and the slope angle of the rock wall, were preliminarily formulated.

3. The method for determining rock wall dimensions applicable to large-section tunnel steel frame rock wall combined construction according to claim 1, characterized in that: The steps of establishing a numerical model for large-section tunnel excavation by steel frame rock wall method include: The numerical model size is set based on the preset rock wall size preliminarily proposed for the rock wall, the surrounding rock is simulated by a solid unit that satisfies the Mohr-Coulomb yield criterion, the primary support, the secondary lining and the intermediate partition are all elastic solid units, the advanced support is achieved by modifying the mechanical parameters of the reinforcement ring, the system anchor is simulated by the Cable unit, and the locking anchor is simulated by the Pile unit. In the numerical simulation, excavation and support operations were carried out according to the steel frame rock wall combined construction method. In order to eliminate the influence of boundary effect, the middle longitudinal section of the numerical model was selected as the research section. The stress and deformation characteristics of the initial support structure of the middle partition wall-main arch ring and the stability of the middle partition wall-rock wall combined support system described in the numerical simulation were studied.

4. The method for determining rock wall dimensions applicable to large-section tunnel steel frame rock wall combined construction according to claim 1, characterized in that: The step of extracting the deformation of the middle septum and the main arch ring includes: Taking the determination of the width of the top of the rock wall as an example; According to the initially proposed rock wall top width, different rock wall top widths were set, and a large-section steel frame rock wall method combined construction numerical model was established accordingly. By recording the vertical and horizontal displacements of the selected sections at each excavation stage, the tunnel vault settlement and tunnel perimeter convergence that changed with the construction stage under different working conditions were obtained. The maximum cave circumference convergence and the maximum arch settlement are compared with the limit values ​​required by the code. If the code requirements are met, the preset rock wall top width can meet the stiffness requirements of the middle partition wall-main arch ring force structure system.

5. The method for determining rock wall dimensions applicable to large-section tunnel steel frame rock wall combined construction according to claim 4, characterized in that: The step of extracting the internal forces of the middle partition wall and the main arch ring includes: Taking the determination of the width of the top of the rock wall as an example; The stress of the selected tunnel section at each stage is extracted. Based on the plane section assumption, the shotcrete axial force and steel frame bending moment of the selected tunnel section at each construction stage under different working conditions are calculated, and its safety is judged by the value of the safety factor.

6. The method for determining rock wall dimensions applicable to large-section tunnel steel frame rock wall combined construction according to claim 5, characterized in that: The step of judging whether it is safe by the value of the safety factor comprises: Taking the determination of the width of the top of the rock wall as an example; According to the highway tunnel design specification, the damage stage method is used to verify the safety factor of the initial tunnel support. The compressive strength of the eccentrically compressed concrete structure should be verified according to the following formula: In the formula: K is the safety factor; N is the axial force; is the longitudinal bending coefficient of the component. For the tunnel lining, open hole arch ring and side wall with tight backfill, α is the eccentricity influence coefficient of the axial force; R a is the ultimate compressive strength of concrete or masonry; b is the section width (m); h is the section height (m); The initial support of the tunnel at each stage is verified according to the above verification formula to obtain the calculated safety factor of the concrete at each construction stage and the calculated safety factor of the steel arch frame at each construction stage; if the safety factor is greater than the minimum safety factor required by the specification, it is safe, that is, the preset rock wall top width can meet the strength requirements of the middle partition wall-main arch ring force structure system.

7. The method for determining rock wall dimensions applicable to large-section tunnel steel frame rock wall combined construction according to claim 1, characterized in that: The step of determining the stability of the rock wall comprises: Taking the determination of the width of the top of the rock wall as an example; Based on the established numerical model of large-section tunnel excavation by steel frame rock wall method under different working conditions, if the plastic zone develops beyond the area of ​​the rock wall itself, the rock wall has become unstable and damaged.

8. The method for determining rock wall dimensions applicable to large-section tunnel steel frame rock wall combined construction according to claim 1, characterized in that: The step of judging the rationality of the force on the bottom of the middle partition wall comprises: Taking the determination of the width of the top of the rock wall as an example; Based on the numerical model of large-section tunnel steel frame rock wall construction under different working conditions, the instability relationship of the bottom of the middle partition wall in the most unfavorable situation is determined, and the friction coefficient μ1<μ is calculated when the bottom of the middle partition wall does not slide. max ; The shear force and pressure at the junction of the middle partition wall and the rock wall are compared to obtain the calculated friction coefficient at the junction of the middle partition wall and the rock wall, so as to judge the stability of the bottom of the middle partition wall.

9. The method for determining rock wall dimensions for large-section tunnel steel frame rock wall combined construction according to any one of claims 1 to 8, characterized in that: The bolt length in large-section tunnels is within the width of the rock wall.

10. The method for determining rock wall dimensions for large-section tunnel steel frame rock wall combined construction according to any one of claims 1 to 8, characterized in that: The clear cross-sectional area of ​​the excavated tunnel of a large cross-section tunnel is greater than 100m 2 .

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