Rock wall size determination method suitable for large-section tunnel steel frame rock wall combined construction

Abstract

The present application relates to the technical field of tunnel engineering, and particularly relates to a rock wall size determination method suitable for large-section tunnel steel frame rock wall combined construction. The method comprises the following steps: initially determining each size element of the rock wall; presetting the rock wall size according to the size element and establishing a numerical model of the large-section tunnel steel frame rock wall combined construction excavation; if the stress structure system of the mid-parting wall-main arch ring satisfies the strength and stiffness requirements and the mid-parting wall-rock wall combined support system satisfies the stability requirements, the preset rock wall size is determined as the actual construction size; if the strength and stiffness requirements are not satisfied or the mid-parting wall-rock wall combined support system does not satisfy the stability requirements, the rock wall size is reset and the corresponding numerical model size is modified. The method can determine the rock wall size suitable for the specific large-section tunnel steel frame rock wall combined construction, and provides important technical support and safety guarantee for the tunnel construction.

Description

Technical Field

[0001] The present 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, the sheer size of the tunnel makes a single excavation difficult, necessitating segmented pilot tunnel excavation. Steel-framed rock wall construction is a unique construction method for large-section tunnels. This utilizes segmented pilot tunnel excavation, replacing the traditional middle wall with a combined "middle wall-core wall" support structure. The core wall remains as the lower support for the middle wall of the upper step, while the rock wall itself serves as a path for construction machinery. This method can significantly improve the construction quality and efficiency of large-section tunnels. However, determining the core wall dimensions, particularly its height, width, and slope angle, is a pressing issue for the steel-framed rock wall 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 rock wall excavation and invert arch excavation, which increases construction costs and raises the project price.

[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 rock wall size, improve construction efficiency, and ensure construction safety. Summary of the Invention

[0005] The purpose of the present invention includes providing a method for determining rock wall dimensions suitable for steel frame and rock wall combination construction of large-section tunnels. The method takes into account the determination of dimensional factors such as rock wall height, width and slope angle, and can determine the rock wall dimensions suitable for 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 steel frame and rock wall combined construction of large-section tunnels, comprising:

[0008] To ensure the traffic flow and the stability of the bulkhead-rock wall support structure, the rock wall dimension elements were initially formulated. These elements include the rock wall top width, rock wall bottom width, rock wall height, and rock wall slope angle.

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

[0010] The internal force and deformation of the mid-partition wall and the main arch ring are extracted, and if the mid-partition wall-main arch ring stress structure system meets the strength and stiffness requirements, the preset rock wall size is appropriate in terms of the stress of the mid-partition wall-main arch ring;

[0011] According to the distribution of the rock wall plastic zone, it is judged whether the rock wall is crushed and whether there are local rockfalls of the rock wall, so as to determine the stability of the rock wall; according to the bottom internal force and slip of the mid-partition wall, the stress rationality of the bottom of the mid-partition wall is judged; if the stability of the rock wall and the stress of the bottom of the mid-partition wall meet the requirements, it means that the stability of the mid-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 mid-partition wall-rock wall;

[0012] If the mid-partition wall-main arch ring stress structure system meets the strength and stiffness requirements, and the mid-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 size; if the mid-partition wall-main arch ring stress structure system does not meet the strength and stiffness requirements, or the mid-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 the requirements are met.

[0013] In an optional embodiment, the step of initially drafting the rock wall size elements, including the rock wall top width, rock wall bottom width, rock wall height and rock wall slope angle, includes:

[0014] The engineering mechanical vehicle traffic demand is investigated, and the stability requirements of the mid-partition wall-rock wall combined support structure, such as the core wall crushing instability, the mid-partition wall instability and damage, and the failure of the mid-partition wall bottom locking anchor, are comprehensively considered, and the rock wall size elements such as the rock wall top width, rock wall bottom width, rock wall height and rock wall slope angle are initially drafted.

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

[0016] The numerical model size is set based on the initially drafted preset rock wall size of the rock wall, the surrounding rock is simulated by solid elements meeting the Mohr-Coulomb yield criterion, the primary support, secondary lining and mid-partition wall are all elastic solid elements, the advanced support is realized by modifying the mechanical parameters of the reinforcement ring, the system anchor is simulated by Cable element, and the locking anchor is simulated by Pile element.

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

[0018] In the optional implementation, the step of extracting the deformation of the mid-partition wall and the main arch ring comprises:

[0019] Taking the width of the top of the rock wall as an example;

[0020] According to the initially determined width of the top of the rock wall, different widths of the top of the rock wall are set, and a large-section steel frame rock wall combined construction numerical model is established accordingly, the vertical displacement and the horizontal displacement of the selected section at each excavation stage are recorded, and the tunnel arch top settlement and the tunnel peripheral convergence varying with the construction stage under different working conditions are obtained;

[0021] The maximum tunnel peripheral convergence and the maximum arch top settlement are compared with the limit values required by the specification, if the specification requirement is met, the preset width of the top of the rock wall can meet the stiffness requirement of the mid-partition wall-main arch ring stress structure system.

[0022] In the optional implementation, the step of extracting the internal force of the mid-partition wall and the main arch ring comprises:

[0023] Taking the width of the top of the rock wall as an example;

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

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

[0026] Taking the width of the top of the rock wall as an example;

[0027] According to the highway tunnel design specification, the safety factor of the tunnel initial support in the damage stage method is calculated, the compressive strength calculation of the eccentrically compressed concrete structure should be calculated 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, for the tunnel lining, the arch ring of the open cut tunnel and the wall back tight backfill side wall, α is the eccentric influence coefficient of the axial force; R af is the compressive ultimate strength of the concrete or masonry;b is the cross-sectional width (m);h is the cross-sectional height (m);

[0030] According to the checking formula, the initial support of the tunnel in each stage is checked, and the calculation safety factor of the concrete in each construction stage and the calculation safety factor of the steel arch in each construction stage are obtained; the safety factor is greater than the minimum safety factor required by the specification, that is, safe, that is, the width of the top of the rock wall can meet the strength requirement of the structure system of the middle partition wall-main arch.

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

[0032] Taking the width of the top of the rock wall as an example;

[0033] Based on the numerical model of the large-section tunnel steel frame rock wall method construction excavation under different working conditions, if the plastic zone development exceeds the area of the rock wall itself, that is, the rock wall has been destabilized and destroyed.

[0034] In an optional embodiment, the step of determining the stress rationality of the bottom of the middle partition wall comprises:

[0035] Taking the width of the top of the rock wall as an example;

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

[0037] The shear force and pressure at the intersection of the middle partition wall and the rock wall are compared to obtain the calculation friction coefficient of the intersection of the middle partition wall and the rock wall, so as to determine the stability of the bottom of the middle partition wall.

[0038] In an optional embodiment, the length of the anchor rod in the large-section tunnel is within the width of the rock wall.

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

[0040] The beneficial effects of the rock wall size determination method suitable for large-section tunnel steel frame rock wall combined construction provided by the embodiments of the present application include:

[0041] The rock wall size determination method suitable for large-section tunnel steel frame rock wall combined construction comprises:

[0042] To ensure the vehicle traffic demand and the stability requirement of the middle partition wall-rock wall combined support structure, the rock wall size elements (i.e. the width of the top and bottom of the rock wall, the height of the rock wall, and the slope angle of the rock wall) are preliminarily determined;

[0043] Set the size of the dike (i.e. preset dike top and bottom width, preset dike height, preset dike slope angle), and establish a numerical model of large cross-section tunnel steel frame dike construction excavation accordingly;

[0044] Extract the internal force and deformation of the intermediate wall and the main arch, and if the intermediate wall-main arch stress structure system meets the strength and stiffness requirements, it means that the preset dike size elements are appropriate in terms of intermediate wall-main arch stress;

[0045] According to the distribution of the plastic zone of the dike, it is determined whether the dike is crushed and whether there are local falling pieces, so as to determine the stability of the dike; according to the bottom internal force and slip of the intermediate wall, it is determined whether the stress of the bottom of the intermediate wall is reasonable; if the stability of the dike and the stress of the bottom of the intermediate wall meet the requirements, it means that the stability of the intermediate wall-dike combined support system meets the requirements, that is, the preset dike size elements are appropriate in terms of intermediate wall-dike stability;

[0046] If the intermediate wall-main arch stress structure system meets the strength and stiffness requirements, and the intermediate wall-dike combined support system meets the stability requirements, it means that the preset dike size elements (i.e. preset dike top and bottom width, preset dike height, preset dike slope angle) are the actual construction dike size; if the intermediate wall-main arch stress structure system does not meet the strength and stiffness requirements, or the intermediate wall-dike combined support system does not meet the stability requirements, the preset dike size elements (i.e. preset dike top and bottom width, preset dike height, preset dike slope angle) should be adjusted until they meet the requirements.

[0047] The dike size determination method suitable for large cross-section tunnel steel frame dike combined construction considers the determination of dike height, width and slope angle and other size elements, can determine the dike size suitable for the construction of a specific large cross-section tunnel steel frame dike combined construction, so as to meet the requirements of construction safety and reduce the engineering cost of tunnel construction to a certain extent, and provides important technical support and safety guarantee for tunnel construction. BRIEF DESCRIPTION OF DRAWINGS

[0048] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor.

[0049] Figure 1 The flow chart of the dike size determination method suitable for large cross-section tunnel steel frame dike combined construction provided by the present embodiment;

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

[0051] Figure 3 This is a diagram of typical construction stages in a numerical simulation based on actual on-site construction provided in this embodiment, wherein a represents the upper excavation and support of the subsequent pilot tunnel, b represents the upper excavation and support of the subsequent pilot tunnel, c represents the upper excavation and support of the subsequent pilot tunnel, d represents the lower excavation and support of the subsequent pilot tunnel, e represents the removal of the intermediate partition wall, f represents the removal of the rock wall and the excavation of the invert, g represents the construction of the invert and secondary lining, and h represents an overview of the tunnel excavation.

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

[0053] Figure 5 The axial force diagrams of shotcrete at various typical construction stages for different rockwall top widths provided in this embodiment, where a represents the upper excavation and support of the subsequent pilot tunnel, b represents the lower excavation and support of the subsequent pilot tunnel, c represents the removal of the intermediate partition wall, d represents the removal of the rockwall and the excavation of the inverted arch, and e represents the initial support of the inverted arch.

[0054] Figure 6 The steel frame bending moment diagrams for each typical construction stage under different rock wall top widths provided in this embodiment, where a represents the upper excavation and support of the subsequent pilot tunnel, b represents the lower excavation and support of the subsequent pilot tunnel, c represents the removal of the middle partition wall, d represents the removal of the rock wall and the excavation of the inverted arch, and e represents the initial support of the inverted arch.

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

[0056] Figure 8 The calculated safety factors for the steel arch at each construction stage provided in this embodiment, where a represents the upper excavation and support of the subsequent pilot tunnel, b represents the lower excavation and support of the subsequent pilot tunnel, c represents the removal of the middle partition wall, d represents the removal of the rock wall and the excavation of the inverted arch, and e represents the initial support of the inverted arch.

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

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

[0059] Figure 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 3 m, b is the minimum principal stress at 3 m, c is the maximum principal stress at 4 m, d is the minimum principal stress at 4 m, e is the maximum principal stress at 5 m, and f is the minimum principal stress at 5 m;

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

[0061] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only 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 herein 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 as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are intended to fall 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, it does not need to be further defined or explained 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, the orientation or position relationship indicated is based on the orientation or position relationship shown in the accompanying drawings, or is the orientation or position relationship in which the product of the invention is usually placed when in use. It is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be understood as a limitation on the present invention.

[0065] In addition, the terms "first", "second", etc., if used, are merely used to distinguish and describe, 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 the combined construction of steel frame and rock wall in large-section tunnels, including:

[0068] To guarantee the vehicle passing demand and the stability requirement of the diaphragm wall-rock wall combined support structure, the rock wall size elements including the rock wall top width, the rock wall bottom width, the rock wall height and the rock wall slope angle are preliminarily determined;

[0069] The preset rock wall size 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 is set, and a numerical model of the large cross-section tunnel steel frame rock wall method construction excavation is established according to the preset rock wall size;

[0070] The internal force and deformation of the diaphragm wall and the main arch ring are extracted, and if the diaphragm wall-main arch ring stress structure system meets the strength and stiffness requirements, the preset rock wall size is appropriate in terms of the diaphragm wall-main arch ring stress;

[0071] According to the rock wall plastic zone distribution, it is judged whether the rock wall is crushed and whether the rock wall has local spalling, so as to determine the stability of the rock wall; according to the bottom internal force and slip of the diaphragm wall, the stress rationality of the bottom of the diaphragm wall is judged; if the stability of the rock wall and the stress of the bottom of the diaphragm wall meet the requirements, it means that the stability of the diaphragm 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 diaphragm wall-rock wall;

[0072] If the diaphragm wall-main arch ring stress structure system meets the strength and stiffness requirements, and the diaphragm wall-rock wall combined support system meets the stability requirements, 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 size; if the diaphragm wall-main arch ring stress structure system does not meet the strength and stiffness requirements, or the diaphragm wall-rock wall combined support system does not meet the stability requirements, 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 meet the requirements.

[0073] The rock wall size determination method suitable for the large cross-section tunnel steel frame rock wall combined construction considers the determination of the rock wall height, width and slope angle and other size elements, can determine the rock wall size suitable for the large cross-section tunnel steel frame rock wall combined construction, can meet the requirements of construction safety, and can reduce the engineering cost of tunnel construction to a certain extent, thereby providing important technical support and safety guarantee for tunnel construction.

[0074] Further, in the embodiment, the steps of preliminarily determining the rock wall size elements (i.e. the rock wall top and bottom width, the rock wall height, the rock wall slope angle) include:

[0075] The rock wall top and bottom width, the rock wall height, the rock wall slope angle and other rock wall size elements are preliminarily determined by investigating the engineering mechanical vehicle passing demand and comprehensively considering the stability requirements of the diaphragm wall-rock wall combined support structure such as the core wall crushing instability, the diaphragm wall instability damage and the diaphragm wall bottom anchor failure.

[0076] From the above, after the preset size of the rock wall is determined, and before the internal force and deformation of the mid-partition wall and the main arch ring are extracted, a numerical model of the large cross-section tunnel steel frame rock wall method construction excavation needs to be established, and the specific steps include:

[0077] Based on the rock wall size elements (i.e. the rock wall top and bottom width, rock wall height, rock wall slope angle) preliminarily determined for the rock wall, the numerical model size is set, the surrounding rock is simulated by solid elements satisfying the Mohr-Coulomb yield criterion, the primary support, secondary lining and mid-partition wall are all elastic solid elements, the advanced support is realized by modifying the mechanical parameters of the reinforcement ring, the system anchor is simulated by Cable element, and the lock foot anchor is simulated by Pile element.

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

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

[0080] Taking the determination of the rock wall top width as an example;

[0081] By recording the vertical displacement and horizontal displacement of the selected section at each excavation stage, the tunnel vault settlement and hole convergence under different working conditions changing with the construction stage are obtained;

[0082] The maximum hole convergence and the maximum vault settlement are compared with the limit value required by the specification, and if it meets the requirements, the preset rock wall top width can meet the stiffness requirements of the mid-partition wall-main arch ring stress structure system.

[0083] The stress of the selected tunnel section at each stage is extracted, and by 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 whether it is safe is judged by the value of the safety factor.

[0084] According to the highway tunnel design specification, the safety factor of the tunnel initial support is calculated by the damage stage method, and the compressive strength calculation of the eccentrically compressed concrete structure should be calculated according to the following formula:

[0085]

[0086] In the formula: K is the safety factor; N is the axial force; is the longitudinal bending coefficient, and for the tunnel lining, the arch ring and the closely backfilled side wall, take a is the eccentricity influence coefficient of the axial force; R a f'c is the compressive strength of concrete or masonry; b is the width of the cross section (m); h is the height of the cross section (m);

[0087] According to the above checking formula, the initial support of the tunnel at each stage is checked, and the calculation safety factor of the concrete at each construction stage and the calculation safety factor of the steel arch at each construction stage are obtained; the safety factor is greater than the minimum safety factor required by the specification, that is, it is safe, and the preset width of the top of the rock wall can meet the strength requirements of the middle partition wall-main arch ring stress structure system.

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

[0089] Taking the width of the top of the rock wall as an example;

[0090] Based on the numerical model of the large-section tunnel steel frame rock wall construction excavation, if the plastic zone develops beyond the area of the rock wall, that is, the rock wall has been destabilized and destroyed; at the same time, based on the numerical model of the large-section tunnel steel frame rock wall construction excavation, the friction coefficient μ1<μ max is determined when the bottom of the middle partition wall does not slide, the shear and pressure at the intersection of the middle partition wall and the rock wall are compared to obtain the calculation friction coefficient at the intersection of the middle partition wall and the rock wall, so as to determine the stability of the bottom of the middle partition wall; when the above two requirements are met, it can be determined that the preset width of the top of the rock wall meets the stability requirements of the middle partition wall-rock wall combined support system.

[0091] When the deformation and internal force requirements of the middle partition wall-main arch ring structure are met, and at the same time the stability requirements of the middle partition wall-rock wall combined support system are met, it can be explained that the preset width of the top of the rock wall is the width of the top of the rock wall, and then the remaining size elements of the rock wall (the width of the bottom of the rock wall, the corner of the rock wall, and the height of the rock wall) are determined step by step according to the same operation 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, and such a setting mode is to ensure that the length of the anchor rod is within the width of the rock wall, so as to avoid the situation that the anchor rod penetrates the rock wall and cannot bear the load; in addition, in this embodiment, the rock wall size determination method suitable for the large-section tunnel steel frame rock wall combined construction is applicable to large-section tunnels with a net section area of the excavation tunnel of greater 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 steel frame rock wall combination construction of large-section tunnels includes the determination of four dimensional elements during implementation, namely the rock wall top and bottom width, rock wall height, and rock wall slope angle;

[0094] Among them, the steel frame rock wall combined support method mentioned in this embodiment uses steel support and sprayed concrete 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 partial excavation of the pilot tunnel. 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. The second is to provide construction machinery represented by drilling rigs to enter the site for work.

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

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

[0097] S1. Preliminary design of rockwall dimensional elements (i.e. rockwall top and bottom widths, rockwall height, rockwall slope angle);

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

[0099] Numerical model of large-section tunnel steel frame rock wall method Figure 2 The numerical model dimensions are approximately 150 m × 72 m × 125 m. The surrounding rock is simulated using solid elements that meet the Mohr-Coulomb yield criterion. The primary support, secondary lining, and intermediate partition are all elastic solid elements. Advanced support is achieved by modifying the mechanical parameters of the reinforcement ring. System anchors are simulated using Cable elements, and locking anchors are simulated using Pile elements.

[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, excavation and support operations were carried out according to the steel frame rock wall combined construction method. The excavation footage 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 longitudinal middle of the numerical model was used as the research section. The deformation and stress of the support in the corresponding step sequence were studied based on the arrival of each step 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., rockwall height, rockwall top and bottom widths, rockwall slope angle), taking rockwall top width as an example;

[0106] S4. Extract the internal forces and deformations of the septum and main arch ring. S5. If the combined septum-primary support load-bearing system meets the strength and stiffness requirements, the top width of the rockwall is appropriate.

[0107] Deformation criterion: Take the determination of the width of the top 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 Figure 2 shows the tunnel crown settlement and tunnel perimeter convergence as the construction stages change under different working conditions.

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

[0110] During tunnel excavation, the crown settlement and perimeter convergence gradually increase and eventually stabilize. It is important to note that the maximum perimeter convergence and the maximum crown settlement should be compared with the code limits. If these limits are met, the assumed rockwall height meets the requirements.

[0111] Internal force and strength criterion: By extracting the stress of the selected tunnel section at each stage and assuming the plane section, the following can be obtained through calculation: Figure 5 and Figure 6 The shotcrete axial force and steel frame bending moment diagrams of 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 of the eccentrically compressed concrete structure should be verified 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 component. For 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 suspended structures.

[0117] Table 1-2 Comprehensive safety factor values

[0118] According to the above calculation formula, the initial support of the tunnel at each stage is verified 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 rockwall top width.

[0120] S6. Based on the distribution of the rockwall's plastic zone, determine whether the rockwall has collapsed and whether there has been any localized block loss. Furthermore, the stability of the combined bulkhead-rockwall support system can be determined based on the internal forces and slip at the bottom of the bulkhead. If stability requirements are met, the rockwall's top width is appropriate.

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

[0122] Please refer to Figure 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 rock wall, and thus the stability of the rock wall is determined;

[0123] The stability criterion for the rockwall is that if the plastic zone develops completely beyond the area of ​​the rockwall itself (the green block (shear-p) fills the blue block (none)), the rockwall 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, Figure 11 The maximum and minimum principal stresses of the rockwall with different rockwall top widths are given.

[0125] The above rock wall stress diagram shows 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 10.14 MPa, and the minimum principal stress is less than the uniaxial compressive strength of the rock; and as the rock wall width increases, the force on the rock wall tends to increase, but the change is not very obvious. Therefore, with the change of rock wall width, the force on the rock wall will not change much. However, for the sake of construction efficiency, construction machinery access, construction safety, construction quality, etc., when using the steel frame rock wall combination construction method, it is also necessary to maintain a certain rock wall width in combination with on-site construction.

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

[0127] Figure 12 The schematic diagram of the instability of the bottom of the middle partition wall in the most unfavorable situation is given. When the friction coefficient μ1<μ max It will not slide when you touch it.

[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 rock wall stability requirements and the stability requirements of the bottom of the intermediate partition wall are met at the same time, it means that the stability of the intermediate partition wall-rock wall combined support system is guaranteed.

[0132] S7. If both S5 and S6 are satisfied, it means that the top width of the rock wall is the actual top width of the rock wall. If both S5 and S6 are not satisfied, 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 rockwall dimension element is determined. The above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be covered by the scope of protection of the present invention.

Claims

1. A method for determining rock wall dimensions for large-section tunnel steel frame and rock wall assembly construction, characterized in that: include: To ensure vehicle traffic and the stability of the bulkhead-rock wall combined support structure, rock wall dimensional elements were initially formulated. These dimensional elements include rock wall top width, rock wall bottom width, rock wall height, and rock wall slope angle. Setting the preset rock wall dimensions, including the preset rock wall top width, preset rock wall bottom width, preset rock wall height, and preset rock wall slope angle, and establishing a numerical model for the excavation of a large-section tunnel using the steel frame rock wall method based on these dimensions; Extract the internal forces and deformations of the septum and main arch ring. If the septum-main arch ring load-bearing structural system meets the strength and stiffness requirements, then the preset rock wall size is appropriate in terms of the septum-main arch ring load-bearing system. Based on the distribution of the rockwall's plastic zone, determine whether the rockwall has been crushed and whether there has been any localized blockage, thereby determining the rockwall's stability. Based on the internal force and slippage at the bottom of the septum, determine the rationality of the force applied to the bottom of the septum. If the rockwall's stability and the force applied to the bottom of the septum meet the requirements, then the stability of the septum-rockwall combined support system meets the requirements, meaning that the preset rockwall dimensions are appropriate for the stability of the septum-rockwall combination. If the intermediate partition wall-main arch ring load-bearing structure system meets the strength and stiffness requirements, and the intermediate 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 intermediate partition wall-main arch ring load-bearing structure system does not meet the strength and stiffness requirements, or the intermediate 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; the step of preliminarily formulating rock wall size elements, wherein the rock wall size 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 demand of the bulkhead-rock wall combined supporting structure caused by 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. The rock wall top width, the rock wall bottom width, the rock wall height and the rock wall slope angle rock wall size elements were preliminarily formulated.

2. The rock wall size determination method for large-section tunnel steel frame rock wall combination construction according to claim 1 is characterized in that: The steps of establishing a numerical model for large-section tunnel excavation using the steel frame rock wall method include: The numerical model size is set based on the pre-defined rock wall size. The surrounding rock is simulated by solid elements that meet the Mohr-Coulomb yield criterion. The primary support, secondary lining, and the intermediate partition are all elastic solid elements. The advanced support is achieved by modifying the mechanical parameters of the reinforcement ring. The system anchor rods are simulated by cable elements, and the locking anchor rods are simulated by pile elements. In the numerical simulation, excavation and support operations were carried out according to the steel frame rock wall combined construction method. To eliminate the influence of boundary effects, the longitudinal middle 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 described in the numerical simulation and the stability of the middle partition wall-rock wall combined support system were studied.

3. The rock wall size determination method applicable to the combined construction of steel frame and rock wall in large-section tunnels 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; Based on the initially proposed rockwall top width, different rockwall top widths were set, and a numerical model of the large-section steel frame rockwall method combined construction was established. By recording the vertical and horizontal displacements of selected sections at each excavation stage, the tunnel vault settlement and tunnel perimeter convergence under different working conditions and with the construction stage were obtained. The maximum circumference convergence and the maximum arch crown settlement are compared with the code requirements. If the code requirements are met, the preset rock wall top width can meet the stiffness requirements of the intermediate partition wall-main arch ring load-bearing structure system.

4. The rock wall size determination method applicable to the combined construction of steel frame and rock wall in large-section tunnels according to claim 3, 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 assumption of a flat section, the axial force of the shotcrete and the bending moment of the steel frame 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.

5. The rock wall size determination method applicable to the combined construction of steel frame and rock wall in large-section tunnels according to claim 4, characterized in that: The step of judging whether it is safe by the value of the safety factor includes: Taking the determination of the width of the top of the rock wall as an example; According to the highway tunnel design specifications, 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: Where: is the safety factor; 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, ; is the eccentricity influence coefficient of the axial force; is the ultimate compressive strength of concrete or masonry; is the section width (m); 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 intermediate partition wall-main arch ring load-bearing structure system.

6. The rock wall size determination method applicable to the combined construction of steel frame and rock wall in large-section tunnels 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 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 failed.

7. The rock wall size determination method applicable to the combined construction of steel frame and rock wall in large-section tunnels according to claim 1, characterized in that: The step of determining the rationality of the force applied to 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 established numerical model of large-section tunnel excavation using the steel frame rock wall method under different working conditions, the instability relationship of the bottom of the middle partition wall under the most unfavorable conditions is determined, and the friction coefficient when the bottom of the middle partition wall does not slide is calculated. ; The shear force and pressure at the intersection of the middle partition wall and the rock wall are compared to obtain the calculated friction coefficient at the intersection of the middle partition wall and the rock wall, thereby judging the stability of the bottom of the middle partition wall.

8. The method for determining rock wall dimensions for steel frame and rock wall assembly construction in large-section tunnels according to any one of claims 1 to 7, characterized in that: The length of the anchor rods in large-section tunnels is within the width of the rock wall.

9. The method for determining rock wall dimensions for steel frame and rock wall assembly construction in large-section tunnels according to any one of claims 1 to 7, characterized in that: The clear cross-sectional area of ​​the excavated tunnel of a large cross-section is greater than 100m 2 .

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