Tunnel single-layer lining embedded type grating steel frame structure and construction method thereof

Abstract

The invention relates to a tunnel single-layer lining embedded grating steel frame structure and a construction method thereof, and belongs to the technical field of highway engineering. The structure is composed of a primary support, a film spraying waterproof layer, a secondary lining and embedded grating steel frames, the embedded grating steel frames are embedded into the primary support and the secondary lining respectively, the effects of transmitting shear stress and coordinating deformation are achieved, the primary support and the secondary lining form a combined beam stress state, and the overall rigidity and bearing capacity of the lining structure are remarkably improved. During construction, the arrangement distance of the grating steel frames is determined through theoretical calculation, and it is ensured that the anti-shearing requirement is met. The method has the advantages of being convenient and fast to construct, high in safety and good in economical efficiency, the lining thickness and the number of reinforcing bars can be effectively reduced, the engineering cost is reduced, meanwhile, the method adapts to tunnel engineering of different surrounding rock grades, the problem that in traditional single-layer lining, shearing force transmission between a primary support and a secondary lining is insufficient is solved, an innovative solution is provided for tunnel lining structure design, and the method is worthy of popularization and application. The method has important engineering application value and popularization prospect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of highway engineering, and specifically relates to a tunnel single-layer lining embedded grating steel frame structure and a construction method thereof. BACKGROUND

[0002] The tunnel lining structure is a key engineering measure to ensure the safety and stability of the tunnel. At present, the composite lining structure is widely used due to its simple structure form and clear stress mechanism. However, in the composite lining, the primary support and the secondary lining are separated by a waterproof board, which can only transmit radial stress but cannot transmit tangential stress, resulting in the primary support and the secondary lining being in a composite beam stress state, which weakens the overall carrying capacity of the lining structure and increases the engineering cost.

[0003] The single-layer lining, as a new supporting concept, aims to combine the primary support and the secondary lining into a whole, so that the shear force can be fully transmitted between the layers and the deformation can be coordinated, thereby improving the overall stiffness and economy of the structure. However, the core problem of the single-layer lining is how to ensure the effective transmission of shear force and collaborative stress between the primary support and the secondary lining without the waterproof board. The existing solutions mainly include the following two types:

[0004] 1. Using steel fiber sprayed concrete, such as patent document CN115142854A, but there are problems such as poor dispersibility of steel fibers, easy to form clusters, etc., and high cost;

[0005] 2. Directly canceling the primary support steel frame and the steel mesh, and extending the anchor rod end as a shear key, such as patent document CN114776338A, but this method is too simplified and has safety hazards such as arch top spalling and worker injury and anchor rod end piercing.

[0006] Therefore, there is an urgent need for a single-layer lining structure and construction method that is convenient to construct, has low risk, and can significantly enhance the bonding performance between the primary support and the secondary lining, to solve the above technical problems, realize the transmission of shear force and collaborative stress between the primary support and the secondary lining, and improve the overall performance of the tunnel lining structure. SUMMARY

[0007] To solve the above problems, the present application provides a tunnel single-layer lining embedded grating steel frame structure and a construction method thereof, aiming to propose a simple and efficient construction method and structure form, reduce the risk of working face construction, and effectively enhance the bonding strength of the primary support and the secondary lining, so that they can collaboratively bear stress and form a composite beam stress state, thereby reducing the lining thickness and improving the carrying capacity and economy of the lining structure.

[0008] The technical solution adopted by the present application is as follows:

[0009] A tunnel single-layer lining embedded grid steel structure, comprising an initial support located at the outermost layer of the tunnel, a membrane waterproof layer, a secondary lining located at the inner layer of the tunnel and an embedded grid steel structure; the initial support comprises anchor rods, steel mesh and I-beam for initial reinforcement of the surrounding rock; the membrane waterproof layer is made of a high-bonding-performance membrane material and is applied to the surface of the initial support; the secondary lining is composed of cast-in-place concrete and a single-layer steel mesh and is a permanent support structure; the embedded grid steel structure is arranged in a ring along the cross section of the tunnel and is embedded in the initial support and the secondary lining, so that the initial support and the secondary lining form a combined beam in a stress state.

[0010] A construction method of a tunnel single-layer lining embedded grid steel structure, based on the tunnel single-layer lining embedded grid steel structure described above, comprising the following steps:

[0011] Step 1, tunnel excavation and initial spraying closure:

[0012] The tunnel is excavated according to the design requirements to ensure that the excavation contour conforms to the design section; after the excavation is completed, the surface of the surrounding rock is immediately closed by initial spraying of concrete;

[0013] Step 2, application of initial support and embedded grid steel structure:

[0014] The anchor rods, steel mesh and I-beam are installed to form an initial support system; the I-beam, as the main load-bearing component, is arranged uniformly along the longitudinal direction of the tunnel at an interval determined according to the design; the embedded grid steel structure is installed synchronously during the construction of the initial support, part of the embedded grid steel structure is embedded in the initial support, and a certain length of the embedded grid steel structure protrudes into the secondary lining for subsequent connection with the secondary lining;

[0015] Step 3, re-spraying closure of the I-beam:

[0016] The installed I-beam and embedded grid steel structure are re-sprayed with concrete to further close the initial support structure; during the re-spraying process, the protruding part of the embedded grid steel structure is reserved to ensure that it can be connected with the secondary lining;

[0017] Step 4, application of the membrane waterproof layer:

[0018] After the initial support is closed into a ring, the membrane waterproof layer is applied to the surface of the initial support; the membrane waterproof layer is made of a high-bonding-performance material, the thickness of the membrane is controlled to be 1-2 mm, and uniform construction is achieved through automatic spraying equipment;

[0019] Step 5, secondary lining construction:

[0020] Before the construction of the secondary lining, a single layer of steel mesh is laid, the longitudinal steel of which is passed through the protruding outer edge of the embedded grid steel frame and firmly connected therewith to form an integral force system; the longitudinal steel is fixed with the grid steel frame through binding or mechanical connection; cast-in-place concrete is poured to form the secondary lining structure.

[0021] Step 6, arrangement interval control of the embedded grid steel frame:

[0022] The arrangement interval of the embedded grid steel frame is determined through calculation, and the arrangement interval needs to meet the shear resistance requirement; the installation position and protruding length of the embedded grid steel frame need to be accurately controlled to ensure the effective connection thereof with the secondary lining.

[0023] Further, the calculation process of the arrangement interval of the embedded grid steel frame is as follows:

[0024] Step 6.1, calculation of the interface shear flow q:

[0025] The calculation formula of the interface shear flow q is:

[0026]

[0027] In the formula, V is the maximum shear value of the required layout section of the tunnel; S* is the area moment of the combined section at the interface; I is the moment of inertia of the combined section;

[0028] Step 6.2, calculation of the shear flow q2 borne by the concrete at the interface:

[0029] The calculation formula of the shear flow q2 borne by the concrete at the interface is:

[0030] q2 = α cv · f td,min · bh0;

[0031] In the formula, α cv is the contribution coefficient of the concrete, which is 0.7; f td,min is the tensile strength design value of the initial support concrete at the interface; b is the calculation single width, which is 1 m; h0 is the interface height, which refers to the effective height at the interface between the initial support and the secondary lining;

[0032] Step 6.3, calculation of the shear resistance R of a single grid steel frame:

[0033] The calculation formula of the shear resistance R of a single grid steel frame is:

[0034] R = n · f yd · A S · sinθ;

[0035] In the formula, n is the number of the web members and stirrups of the grid steel frame; f yd is the tensile strength design value of the web members and stirrups of the grid steel frame; AS is the interface area of single web and stirrup; θ is the angle between the web of lattice steel frame and the main reinforcement;

[0036] Step 6.4, calculating the arrangement spacing s of lattice steel frame:

[0037] The calculation formula of the arrangement spacing s of lattice steel frame is:

[0038]

[0039] In the formula, R is the shear bearing capacity of single lattice steel frame; q1 is the shear flow required to be borne by the lattice steel frame at the interface; q2 is the shear flow required to be borne by the concrete at the interface.

[0040] Further, in step 6.1, the calculation process of the moment of inertia I of the combined section is as follows:

[0041] The basic parameters of the combined beam are determined, including: the thickness h2 of the initial support and the thickness h1 of the secondary lining; the total height h of the combined beam is represented as: h=h1+h2; the elastic modulus E2 of the initial support and the elastic modulus E1 of the secondary lining are determined;

[0042] According to the deformation compatibility principle, the axial forces of the neutral axis on both sides of the combined beam are equal:

[0043]

[0044] In the formula, ε is the strain, and the strain distribution of the combined beam is usually assumed to be linear; y a is the position of the neutral axis, that is, the position of the combined section at which the strain is zero when bending;

[0045] The expression of the neutral axis y a is obtained as follows:

[0046]

[0047] According to the parallel shift axis theorem, the moment of inertia of the combined beam is calculated:

[0048]

[0049] In the formula, y1 is the distance from the centroid of the initial support to the bottom of the combined section, y2 is the distance from the centroid of the secondary lining to the bottom of the combined section

[0050] Further, in step 6.1, the calculation formula of the area moment S* of the combined section at the interface is as follows:

[0051] S*=bh1|y1-y a |.

[0052] The beneficial effects of the present application are:

[0053] The tunnel single-layer lining embedded grid steel frame structure and its construction method have remarkable beneficial effects in terms of technology, economy and safety through innovative design and optimized construction process, and the specific effects are as follows:

[0054] 1. Technical performance improvement: The embedded grid steel frame, as a connecting piece between the primary support and the secondary lining, can effectively transfer shear stress, solving the problem of insufficient shear force transmission in traditional single-layer lining. The primary support and the secondary lining form a composite beam stress state, significantly improving the overall stiffness and bearing capacity of the lining structure. The spray membrane waterproof layer has high bonding performance, enhancing the bonding strength of the interface between the primary support and the secondary lining, ensuring their cooperative stress. The longitudinal reinforcement passes through the protruding outer edge of the embedded grid steel frame, further strengthening the connection performance of the primary support and the secondary lining. Due to the cooperative stress of the primary support and the secondary lining, the overall thickness and reinforcement quantity of the lining structure can be appropriately reduced, thereby optimizing the material utilization efficiency.

[0055] 2. Significant economic benefits: The reduction of lining thickness and reinforcement quantity reduces the use of concrete and steel reinforcement, directly saving material costs. The construction period is shortened, indirectly reducing labor costs and mechanical equipment rental fees. The overall stiffness and bearing capacity of the lining structure are improved, reducing the possibility of later maintenance and reinforcement, and reducing the whole life cycle cost.

[0056] 3. Construction convenience and safety: The embedded grid steel frame can be prefabricated outside the tunnel and assembled inside the tunnel, simplifying the construction process and greatly shortening the construction period. The spray membrane waterproof layer is constructed using automatic spraying equipment, ensuring quality while improving construction efficiency. The design of the grid steel frame avoids the safety hazards caused by the excessive length of the traditional anchor rod end, such as stabbing the construction personnel. The cooperative stress of the primary support and the secondary lining reduces the risk of arch top spalling, ensuring the safety of the working face construction.

[0057] 4. Environmental adaptability and durability: It is suitable for tunnel projects of different surrounding rock grades, especially for low bearing capacity surrounding rock. The calculation formula is dynamically adjusted, and the layout spacing of the embedded grid steel frame can be optimized according to the specific working conditions. The embedded grid steel frame is corrosion-resistant, suitable for the humid environment of the tunnel, and prolongs the service life. The spray membrane waterproof layer has both waterproof and bonding functions, improving the durability and impermeability of the structure.

[0058] 5. Value of popularization and application: It can be widely applied to highway tunnels, railway tunnels and municipal tunnel projects, especially suitable for projects with high requirements for construction period and cost. The invention solves the core problem of insufficient shear force transmission between the primary support and the secondary lining in single-layer lining, providing an innovative solution for tunnel lining structure design. Through actual engineering case verification and long-term monitoring data accumulation, it provides reliable technical basis for subsequent similar projects.

[0059] The tunnel single-layer lining embedded grid steel frame structure and the construction method thereof improve the overall performance of the tunnel lining structure, and greatly reduce the engineering cost and construction risk. BRIEF DESCRIPTION OF DRAWINGS

[0060] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced. Obviously, the drawings in the following description are only some embodiments described in the present application, and other drawings can be obtained by those skilled in the art based on these drawings.

[0061] Figure 1 It is a schematic diagram of the overall arrangement of the tunnel single-layer lining embedded grid steel frame structure of the present application.

[0062] Figure 2 It is a cross-sectional view of the embedded grid steel frame arrangement of the present application.

[0063] Figure 3 It is a calculation principle diagram of the composite beam lining of the present application.

[0064] Figure 4 It is a shear force distribution cloud chart of the lining structure of the present application.

[0065] In the figure, 1 is the primary support, 2 is the secondary lining, 3 is the waterproof layer of membrane spraying, and 4 is the embedded grid steel frame. DETAILED DESCRIPTION

[0066] The technical solutions in the embodiments of the present application will be described clearly and completely with reference to the drawings of the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0067] In view of the problems of insufficient shear force transmission between the primary support and the secondary lining in the traditional tunnel single-layer lining and the inability to cooperate in force, the present embodiment provides a tunnel single-layer lining embedded grid steel frame structure. The tunnel single-layer lining embedded grid steel frame structure realizes effective connection between the primary support and the secondary lining through the embedded grid steel frame, and improves the overall stiffness and bearing capacity of the structure.

[0068] As shown in Figure 1 and Figure 2 , the tunnel single-layer lining embedded grid steel frame structure comprises the following parts:

[0069] Primary support 1: The primary support 1 is located at the outermost layer of the tunnel section; the primary support includes anchor rods, steel mesh and I-beam frames, and is used for initial reinforcement of the surrounding rock.

[0070] Sprayed membrane waterproof layer 3: The sprayed membrane waterproof layer 3 uses a sprayed membrane material with high bonding performance, such as a polyurethane or epoxy resin base material, and is applied to the surface of the primary support 1, and has the functions of waterproofing and enhancing the bonding between the primary support and the secondary lining.

[0071] Secondary lining 2: The secondary lining 2 is located in the inner layer of the tunnel and is composed of cast-in-place concrete and a single-layer steel mesh, serving as a permanent support structure.

[0072] Embedded grid steel frame 4: The embedded grid steel frame 4 serves as a connecting structure and is arranged in a ring shape along the tunnel section, embedded in the primary support and the secondary lining respectively, and plays a role in transferring shear force and coordinating deformation, so that the primary support and the secondary lining form a composite beam stress state.

[0073] Further, the embedded grid steel frame 4 in the present embodiment is made of high-strength steel material, such as Q345, which has high shear bearing capacity. The steel frame is designed in a four-limbed grid form, with the angle between the web members and the main reinforcement close to 90° to improve the shear efficiency. The surface of the embedded grid steel frame is subjected to corrosion prevention treatment, such as hot-dip galvanizing or epoxy coating, to adapt to the humid environment of the tunnel. The embedded grid steel frame 4 is uniformly arranged along the longitudinal direction of the tunnel, and the spacing thereof is determined according to calculation to meet the shear resistance requirement. The embedded grid steel frame 4 is partially embedded in the primary support 1 and protrudes into the secondary lining 2, ensuring the transfer of shear force between the primary support and the secondary lining.

[0074] Through the embedded grid steel frame 4, the shear force borne by the primary support 1 is effectively transferred to the secondary lining 2, so that the primary support and the secondary lining bear force in coordination. As a connecting piece, the embedded grid steel frame 4 significantly improves the overall stiffness of the primary support and the secondary lining, and improves the stress performance of the lining structure. Since the primary support and the secondary lining form a composite beam stress state, the overall thickness and the amount of reinforcement of the lining structure can be appropriately reduced, thereby reducing the engineering cost. The embedded grid steel frame 4 can be prefabricated outside the tunnel and assembled inside the tunnel, which simplifies the construction process and shortens the construction period.

[0075] For the above-mentioned tunnel single-layer lining embedded grid steel frame structure, the present embodiment further proposes a construction method of a tunnel single-layer lining embedded grid steel frame structure; the construction method of the tunnel single-layer lining embedded grid steel frame structure comprises the following steps:

[0076] Step 1, tunnel excavation and initial spraying sealing:

[0077] Tunnel excavation: The tunnel excavation is performed according to the design requirements to ensure that the excavation contour conforms to the designed section.

[0078] Initial spray sealing rock surface: Immediately after excavation is completed, the surrounding rock surface is initially sprayed with concrete to prevent the surrounding rock from loosening and collapsing. The initial spraying thickness is generally 5-10 cm.

[0079] Step 2, initial support and embedded grid steel frame installation:

[0080] Initial support installation: Install anchor rods, steel mesh, and I-beam frames to form the initial support system. The I-beam frame serves as the main load-bearing component and is uniformly distributed along the tunnel in the longitudinal direction, with the spacing determined according to the design.

[0081] Embedded grid steel frame installation: Install the embedded grid steel frame simultaneously during the initial support construction process to ensure its shear performance. The embedded grid steel frame is partially embedded in the initial support and protrudes a certain length, such as 5-10 cm, into the secondary lining for subsequent connection with the secondary lining. The grid steel frame can be constructed using the method of precast outside the hole and assembled inside the hole, improving construction efficiency.

[0082] Step 3, I-beam frame re-spraying:

[0083] Re-spraying of the installed I-beam frame and embedded grid steel frame with concrete to further seal the initial support structure. During the re-spraying process, pay attention to preserving the protruding part of the embedded grid steel frame to ensure its connection with the secondary lining.

[0084] Step 4, spray membrane waterproof layer installation:

[0085] After the initial support is closed into a ring, install the spray membrane waterproof layer on the surface of the initial support. The spray membrane waterproof layer uses high adhesion materials such as polyurethane or epoxy resin base materials, and is uniformly constructed through automated spraying equipment. The spray membrane thickness is controlled at 1-2 mm to ensure strong interfacial adhesion and also serves as a waterproof function.

[0086] Step 5, secondary lining construction:

[0087] Single-layer steel mesh installation: Before secondary lining construction, lay a single-layer steel mesh, with the longitudinal steel of the steel mesh passing through the protruding outer edge of the embedded grid steel frame and firmly connected to form an integrated load-bearing system. The longitudinal steel and grid steel frame are fixed through binding or mechanical connection such as sleeve connection.

[0088] Secondary lining concrete pouring: Pour the mold injection concrete to form the secondary lining structure; the concrete strength grade is generally C30-C40 to ensure its common load-bearing with the initial support.

[0089] Step 6, embedded grid steel frame arrangement spacing control:

[0090] The arrangement interval of the embedded lattice steel frame is determined by calculation, and the arrangement interval needs to meet the shear resistance requirement; the installation position and protruding length of the embedded lattice steel frame need to be accurately controlled to ensure the effective connection with the secondary lining.

[0091] Further, the embedded lattice steel frame serves as a shear connector and bears the shear force between the primary support and the secondary lining. The arrangement interval of the embedded lattice steel frame needs to meet the shear resistance requirement, and the specific calculation process is as follows:

[0092] Step 6.1, calculate the interface shear flow q:

[0093] The calculation formula of the interface shear flow q is:

[0094]

[0095] In the formula, V is the maximum shear value of the required layout section of the tunnel; as shown in Figure 4 , Figure 4 The left side of the formula is the shear condition at each position of the tunnel section, Figure 4 and the right side is the numerical simulation calculation condition. The maximum shear V is determined by numerical simulation calculation of the shear distribution of different surrounding rock grades. The maximum shear position is the lower right corner, and the maximum shear is 301.80374 kN. S* is the area moment of the combined section at the interface; I is the moment of inertia of the combined section.

[0096] The calculation process of the moment of inertia I of the combined section is as follows:

[0097] As shown in Figure 3 , the basic parameters of the combined beam are determined, including:

[0098] The thickness of the primary support h2;

[0099] The thickness of the secondary lining h1;

[0100] The total height of the combined beam h, which is expressed as: h = h1 + h2;

[0101] The elastic modulus E2 of the primary support is determined;

[0102] The elastic modulus E1 of the secondary lining is determined;

[0103] As shown in Figure 3 , the axial forces on both sides of the neutral axis of the combined beam are equal, and according to the deformation compatibility principle:

[0104]

[0105] In the formula, ε is the strain, and the strain distribution of the combined beam is usually assumed to be linear; y a is the position of the neutral axis, i.e. the position of the combined section where the strain is zero when bending;

[0106] Solve the neutral axis y a The expression is:

[0107]

[0108] According to the parallel shift axis theorem, the inertia moment of the composite beam is calculated:

[0109]

[0110] In the formula, y1 is the distance from the centroid of the initial support to the bottom of the composite section, y2 is the distance from the centroid of the secondary lining to the bottom of the composite section

[0111] Wherein, the calculation formula of the area moment S* of the composite section at the interface is as follows:

[0112] S* = bh1|y1-y a |.

[0113] Step 6.2, calculate the shear flow q2 of the concrete at the interface:

[0114] The calculation formula of the shear flow q2 of the concrete at the interface is:

[0115] q2 = α cv ·f td,min ·bh0;

[0116] In the formula, α cv is the contribution coefficient of concrete, taking 0.7; f td,min is the tensile strength design value of the initial support concrete at the interface; b is the calculation single width, taking 1m; h0 is the interface height, which refers to the effective height at the interface of the initial support and the secondary lining.

[0117] Step 6.3, calculate the shear capacity R of single grid steel frame:

[0118] The calculation formula of the shear capacity of single grid steel frame is:

[0119] R = n·f yd ·A S ·sinθ;

[0120] In the formula, n is the number of grid steel frame web members and stirrups; f yd is the tensile strength design value of the grid steel frame web members and stirrups; A S is the interface area of single web member and stirrup; θ is the angle between the grid steel frame web member and the main reinforcement.

[0121] Step 6.4, calculate the arrangement spacing s of the grid steel frame:

[0122] The formula for calculating the arrangement interval s of the grid steel frame is:

[0123]

[0124] In the formula, R is the shear bearing capacity of a single grid steel frame; q1 is the shear flow required to be borne by the grid steel frame at the interface; and q2 is the shear flow required to be borne by the concrete at the interface.

[0125] Further, in order to verify the feasibility of the construction method of the tunnel single-layer lining embedded grid steel frame structure, the embodiment further provides the following application examples:

[0126] Taking a tunnel project as an example, the shear calculation result of the lining section of the tunnel V-class surrounding rock is as shown in Figure 4 It can be known from Figure 4 that the maximum shear V of the section is 301 kN, the thickness h2 of the primary support is 25 cm, C25 sprayed concrete is adopted, E2 is 28 GPa, the design value of the tensile strength f td is 1.27 MPa, the thickness h1 of the secondary lining is 45 cm, C30 mold injection concrete is adopted, E1 is 30 GPa, the embedded grid steel frame adopts a four-limbed grid steel frame, and the size is 55 cm*40 cm. The calculation process of the arrangement interval of the embedded grid steel frame is as follows:

[0127] 1. The related parameters are brought into the formula:

[0128]

[0129] The neutral axis y a is calculated:

[0130]

[0131] 2. The related parameters are brought into the formula:

[0132]

[0133] The moment of inertia I of the section of the primary support and the secondary lining combined beam is calculated:

[0134]

[0135] 3. The related parameters are brought into the formula:

[0136] S*=bh1|y1-y a |

[0137] The area moment S* of the interface of the primary support and the secondary lining combined beam is calculated:

[0138]

[0139] 4. The calculation results and the related parameters are brought into the formula:

[0140]

[0141] Calculate the interface shear flow q of the lining structure:

[0142]

[0143] 5. Bring the relevant parameters into the formula:

[0144] q2 = a cv · f td,min · bh0

[0145] Calculate the shear flow q2 borne by the concrete at the interface:

[0146] q2 = a cv · f td,min · bh0

[0147] = 0.7 x 1430 x 1 x (45 + 25) x 10 -2

[0148] = 700.7 kN / m

[0149] 6. Bring the relevant parameters into the formula:

[0150] R = n · f yd · A S · sin θ

[0151] Calculate the shear capacity R of the single lattice steel frame:

[0152] R = n · f yd · A S · sin θ

[0153] = 4 x 3600000 x 201.1 x 10 -6 x sin 60 + 2 x 270000 x 50.27 x 10 -6

[0154] = 277.94 kN

[0155] 7. Bring the above calculation results into the formula:

[0156]

[0157] Calculate the arrangement spacing s of the embedded lattice steel frame:

[0158]

[0159] From the above calculation, under the geological conditions and support parameters, when the embedded grating steel frame arrangement spacing is not more than 3.68m, the primary support and secondary lining can form a combined beam stress state, ensuring the safety of tunnel construction and operation.

[0160] In summary, the tunnel single-layer lining embedded grating steel frame structure construction method can be constructed simultaneously with the embedded grating steel frame and the primary support I-beam, can be precast outside the hole and assembled inside the hole, is simple and convenient to construct, can provide shear bearing capacity to connect the primary support and secondary lining as a whole, can form a combined beam stress state, can increase the overall stiffness of the lining structure, can improve the bearing performance, thereby reducing the overall thickness and reinforcement quantity of the lining, ensuring the safety of the structure while greatly reducing the cost of the tunnel.

[0161] The above shows and describes the basic principles, main features and advantages of the present application. Those skilled in the art should understand that the present application is not limited to the above examples, and the above examples and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A tunnel single lining embedded grid steel frame structure, characterized in that: The primary support located at the outermost layer of the tunnel, the waterproof layer, the secondary lining located at the inner layer of the tunnel and the embedded grid steel frame; the primary support includes anchor rods, steel mesh and I-steel frame for initial reinforcement of surrounding rock; the waterproof layer is made of high adhesion performance spraying membrane material and is applied on the surface of the primary support; the secondary lining is composed of cast-in-place concrete and single-layer steel mesh and is a permanent support structure; The embedded grid steel frame is arranged along the tunnel section as a connecting structure and is embedded in the primary support and the secondary lining, so that the primary support and the secondary lining form a combined beam stress state.

2. A construction method of a tunnel single lining embedded grid steel frame structure based on the tunnel single lining embedded grid steel frame structure according to claim 1, characterized in that, The method comprises the following steps: Step 1, tunnel excavation and initial spraying closure: The tunnel is excavated according to the design requirements to ensure that the excavation profile meets the design section; after the excavation is completed, the surface of the surrounding rock is immediately closed by initial spraying concrete; Step 2, application of primary support and embedded grid steel frame: Install anchor rods, steel mesh and I-steel frame to form a primary support system; the I-steel frame is arranged along the tunnel longitudinally as the main load-bearing component with a uniform spacing determined according to the design; the embedded grid steel frame is installed synchronously during the construction of the primary support, part of which is embedded in the primary support and protrudes into the secondary lining with a certain length to facilitate the subsequent connection with the secondary lining; Step 3, re-spraying closure of I-steel frame: Re-spraying concrete is applied to the installed I-steel frame and embedded grid steel frame to further close the primary support structure; during the re-spraying process, the protruding part of the embedded grid steel frame is reserved to ensure its connection with the secondary lining; Step 4, application of waterproof layer by spraying: After the primary support is closed, a waterproof layer by spraying is applied on the surface of the primary support; the waterproof layer by spraying is made of high adhesion performance material with a spraying thickness of 1-2mm and is uniformly constructed by automatic spraying equipment; Step 5, secondary lining construction: Before the secondary lining construction, a single-layer steel mesh is laid, the longitudinal steel of which penetrates through the protruding outer edge of the embedded grid steel frame and is firmly connected therewith to form an integrated force system; the longitudinal steel is fixed to the grid steel frame by binding or mechanical connection; cast-in-place concrete is poured to form the secondary lining structure; Step 6, control of the arrangement spacing of embedded grid steel frame: The arrangement spacing of the embedded grid steel frame is determined by calculation and needs to meet the shear resistance requirement; the installation position and protruding length of the embedded grid steel frame are accurately controlled to ensure its effective connection with the secondary lining.

3. The construction method of a tunnel single lining embedded grid steel frame structure according to claim 2, characterized in that: The calculation process of the arrangement spacing of the embedded grid steel frame is as follows: Step 6.1, calculation of interface shear flow q: The calculation formula of the interface shear flow q is: In the formula, V is the maximum shear value of the required tunnel section; S* is the area moment of the combined section at the interface; I is the moment of inertia of the combined section; Step 6.2, calculation of shear flow q2 borne by the concrete at the interface: The calculation formula of the shear flow q2 borne by the concrete at the interface is: q2 = a cv • f td,min • bh0; In the formula, α cv is the contribution coefficient of concrete, and is taken as 0.7; f td,min is the design value of the tensile strength of the initial supporting concrete at the interface; b is the calculation single width, and is taken as 1 m; h0 is the interface height, that is, the effective height of the interface between the initial support and the secondary lining. Step 6.3, calculation of shear bearing capacity R of single grid steel frame: The calculation formula of the shear bearing capacity R of single grid steel frame is: R = n • f yd • A S • sin θ; In the formula, n is the number of lattice steel frame web members and stirrups; f yd is the design value of tensile strength of the lattice steel frame web members and stirrups; A S is the interface area of a single web member and stirrup; and θ is the angle between the lattice steel frame web member and the main reinforcement. Step 6.4, calculation of grid steel frame arrangement spacing s: The calculation formula of the grid steel frame arrangement spacing s is: In the formula, R is the shear capacity of the single lattice steel frame; q1 is the shear flow required to be borne by the lattice steel frame at the interface; and q2 is the shear flow required to be borne by the concrete at the interface.

4. The construction method of a tunnel single lining embedded grid steel frame structure according to claim 3, characterized in that: In step 6.1, the calculation process of the moment of inertia I of the combined section is as follows: The basic parameters of the composite beam are determined, including: the thickness of the initial support h2 and the thickness of the secondary lining h1; the total height of the composite beam h is represented as: h=h1+h2; the elastic modulus E2 of the initial support and the elastic modulus E1 of the secondary lining are determined; According to the deformation compatibility principle, the axial forces of the neutral axis on both sides of the composite beam are equal: where ε is the strain, usually assumed to be linearly distributed across the composite beam; y a is the position of the neutral axis, i.e. the position where the strain of the composite cross section is zero when bending. The expression for the neutral axis y a is given by According to the parallel shift axis theorem, the moment of inertia of the composite beam is calculated: where y1 is the distance from the centroid of the primary support to the bottom of the composite section, y2 is the distance from the centroid of the secondary lining to the bottom of the composite section 5. The construction method of a tunnel single lining embedded grid steel frame structure according to claim 4, characterized in that: In step 6.1, the calculation formula of the area moment S* of the combined section at the interface is as follows: S* = bh1|y1-y a |

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