Method and system for flexible temporary support during excavation based on stress analysis model

Abstract

The invention discloses a flexible temporary support method and system along with excavation based on a stress analysis model. The problem that in the prior art, surrounding rock deformation and damage risks of a hollow roof area in the roadway excavation process are difficult to restrain in time can be solved. The excavation-following flexible temporary supporting method is applied to a to-be-excavated area, a first empty roof area, a flexible supporting area and an excavation roadway. Establishing a first stress model, and calculating a first flexible support force required for enabling the tensile stress of the roof not to exceed the ultimate tensile strength of the roof under different empty roof distances; establishing a second stress model, and calculating a second flexible support force required for enabling the radial displacement of the roof not to exceed the maximum allowable radial displacement of the roof under different empty roof distances; and comparing the first flexible supporting force with the second flexible supporting force for the same empty roof distance, selecting the larger flexible supporting force as the target flexible temporary supporting force under the empty roof distance, selecting the corresponding target flexible temporary supporting force in the roadway tunneling process, and implementing tunneling-following flexible temporary supporting on the flexible supporting area.

Description

Technical Field

[0001] This application relates to the field of tunnel excavation and surrounding rock control technology, specifically to a flexible temporary support method and system based on a stress analysis model during tunnel excavation. Background Technology

[0002] During the excavation of underground coal mine roadways, the original triaxial stress balance of the surrounding rock is disrupted, transforming it from a triaxial compression state to an approximately biaxial compression state. Stress redistribution occurs in the roadway roof, sides, and floor, forming different stress zones such as fracture zones, plastic zones, and elastic zones. The mechanical behavior of the immediate roof and its overlying key rock strata has a decisive influence on the stability of the roadway's surrounding rock. After roadway excavation is completed, it is usually necessary to promptly install support components such as anchor bolts, anchor cables, steel strips, metal mesh, and shotcrete within the roadway cross-section to form a combined support system of "anchor bolts (cables) – shotcrete layer – surrounding rock." This system aims to inhibit further development of surrounding rock relaxation, fissure propagation, and large deformation, ensuring the overall stability of the roadway roof and sides, and providing safe space conditions for subsequent production.

[0003] In existing technologies, tunnel excavation often employs a cyclic advance method. While the working face advances, support procedures such as drilling, installing bolts and cables, wire mesh installation, and shotcreting must be completed sequentially within the excavated tunnel. This type of permanent support construction requires considerable time and space, making it difficult to achieve complete synchronization with the working face's progress. Consequently, an unsupported roof area inevitably exists between the excavation face and the final permanent support. As the distance and duration of this unsupported roof increase, the direct roof is more prone to subsidence, bending, and fracture under its own weight and the load of the overlying rock strata. The fractured and plastic zones of the surrounding rock further extend into the depths of the tunnel, significantly increasing the deformation of the sidewalls and floor. This not only significantly increases the safety risks of roof collapse and spalling during excavation but also leads to thickening of the fractured roof zone and a decrease in the overall stiffness and integrity of the surrounding rock. This makes it difficult for subsequent permanent supports such as bolts and cables to be effectively anchored within the stable rock mass, affecting the support effect and long-term stability, and hindering the formation of a reasonable load-bearing structure. Summary of the Invention

[0004] Therefore, this application provides a flexible temporary support method and system based on a stress analysis model to solve the problem that the risk of deformation and damage of the surrounding rock in the roof area during tunnel excavation is difficult to suppress in a timely manner in the prior art.

[0005] To achieve the above objectives, this application provides the following technical solution: A flexible temporary support method based on a stress analysis model is applied to tunnels including the area to be excavated in front of the working face, the first unsupported roof area behind the working face, the flexible support area, and the permanent support area that has been permanently supported. Establish the first stress model. Based on the rock layer thickness, rock layer unit weight, ultimate tensile strength of the roof and the distance between the roof and the roof in the first open roof area, simplify the roof in the first open roof area into a rock beam that is fixed at one end and supported by a spring support at the other end. Calculate the first flexible support force required to keep the tensile stress of the roof from not exceeding the ultimate tensile strength of the roof under different roof distances. A second stress model is established, which equates the tunneling roadway to a circular roadway. Under the assumptions that the original rock stress is isotropic, the surrounding rock of the roadway is a continuous homogeneous isotropic elastic body and is under plane strain conditions, the relationship between the radial displacement of the surrounding rock of the roadway section and the total support resistance is established. Based on the preset maximum allowable roof radial displacement, the second flexible support force required to keep the roof radial displacement from exceeding the maximum allowable roof radial displacement is calculated under different unsupported roof distances. For the same roof gap distance, the first flexible support force and the second flexible support force are compared, and the larger one is selected as the target flexible temporary support force for that roof gap distance. During the tunnel excavation process, the corresponding target flexible temporary support force is selected according to the actual roof gap distance of the first roof gap area, and flexible temporary support is implemented in the flexible support area during excavation.

[0006] Optionally, in the first force model: The uniformly distributed load acting on the top plate of the first open roof area is determined by the product of the unit weight of the overlying rock layer on the top plate of the first open roof area and the thickness of the overlying rock layer on the top plate of the first open roof area. The top plate of the first open roof area is treated as a rectangular rock beam with a cross-sectional height equal to the thickness of the top plate and a cross-sectional width equal to the preset dangerous width. The maximum tensile stress of the top plate at different open roof distances is determined based on the formula for calculating the bending normal stress of a rectangular cross-section. The support reaction force of the spring support is proportional to the displacement of the spring support in the direction perpendicular to the top plate. The proportionality coefficient is the elastic coefficient of the flexible temporary support device, and the support reaction force of the spring support is used as the first flexible support force.

[0007] Optionally, when using the first stress model to determine the ultimate ceiling distance of the first ceiling zone, the ultimate ceiling distance is obtained by taking the maximum tensile stress of the ceiling plate as equal to the ultimate tensile strength of the ceiling plate as the ultimate condition, and the ultimate ceiling distance is divided by the safety factor to obtain the corrected ultimate ceiling distance, where the safety factor is greater than 1.

[0008] Optionally, in the second stress model, the radius of the equivalent circular roadway is determined by the size and shape of the tunnel. Based on the elastic modulus, Poisson's ratio, and isotropic stress of the original rock, the elastic mechanical solution of the circular roadway under plane strain is adopted. The radial displacement of the surrounding rock at the roadway boundary is expressed as a function of the original rock stress, total support resistance, radius of the equivalent circular roadway, elastic modulus, and Poisson's ratio. A second flexible support force is introduced into the total support resistance. The second flexible support force is solved by ensuring that the radial displacement of the equivalent circular roadway does not exceed the maximum allowable radial displacement of the roof.

[0009] Optionally, the total support resistance includes the second flexible support force provided by the flexible temporary support device and the support resistance provided by the self-supporting capacity of the surrounding rock.

[0010] Optionally, the support pressure provided by the self-supporting capacity of the surrounding rock is equivalently represented in the form of virtual support force. The virtual support force is the equivalent radial support pressure generated by the unexcavated surrounding rock in front of the tunnel face on the tunnel section under the spatial effect. Its magnitude is determined by the stress release coefficient of isotropic compressive stress of the original rock and decreases as the tunneling distance between the tunnel face and the tunnel section increases.

[0011] Optionally, the tunneling roadway includes, along the tunneling direction, a zone to be excavated and a first roof area, a flexible support area, a second roof area, and a permanent support area located behind the tunneling face.

[0012] This application also discloses a support system applicable to the flexible temporary support method for tunneling, including a tunneling machine and a support device connected to the tunneling machine, the support device comprising: The roof support module connected to the top of the tunneling machine is used to apply flexible temporary support force to the roadway roof at the top of the tunneling machine; Side support modules connected to both sides of the tunneling machine are used to apply flexible temporary support force to the two sides of the roadway on both sides of the tunneling machine. The flexible temporary support force applied by the roof support module and / or side support module is set as the target flexible temporary support force determined according to the stress analysis model-based flexible temporary support method described above.

[0013] Optionally, the roof support module includes a roof support body for abutting against the roof of the tunnel and a first drive unit connected to the tunneling machine. The first drive unit is used to drive the roof support body to move relative to the tunneling machine in directions toward and away from the roof, so as to form an adjustable flexible temporary support for the roof during the tunneling process. The side support module includes a side support body for abutting against the side of the roadway and a second drive unit connected to the tunneling machine. The second drive unit is used to drive the side support body to move relative to the tunneling machine in directions toward and away from the corresponding side, so as to form an adjustable flexible temporary support for the side during the tunneling process. The target flexible temporary support force is distributed according to a preset ratio as flexible temporary support force applied by the top plate support module and flexible temporary support force applied by the side support module.

[0014] Optionally, the roof support and the side support are in rolling or sliding contact with the roadway roof and sidewalls through roller support components or tracked support components, so that the roof support module and the side support module can maintain continuous flexible temporary support for the roof and sidewalls within the first open roof area as the tunneling machine moves forward along the tunneling direction.

[0015] Compared with the prior art, this application has at least the following beneficial effects: By simultaneously establishing a first stress model and a second stress model under the same tunneling conditions, the first stress model simplifies the roof of the first open roof area into a rock beam with one end fixed and the other end supported by spring supports. Using the ultimate tensile strength of the roof as the control index, the relationship between the open roof distance, the self-weight of the overlying strata and the bending tensile stress of the roof is established. Then, the first flexible support force required to ensure that the roof does not crack under different open roof distances is calculated in reverse. This realizes the quantitative determination of the flexible temporary support force by the "strength criterion". The second stress model adopts an elastic theoretical model that treats the tunnel cross-section as an equivalent circular tunnel. Under the assumptions of isotropic stress in the original rock, elastic surrounding rock, and plane strain, the functional relationship between the radial displacement of the surrounding rock and the total support resistance of the tunnel cross-section is obtained through equilibrium equations, geometric equations, and constitutive equations. Using the maximum allowable radial displacement of the roof as the control index, the second flexible support force required to limit the radial displacement of the roof to not exceed the allowable value under different unsupported roof distances is calculated in reverse. This realizes the quantitative determination of the flexible temporary support force based on the "deformation criterion". By comparing the first and second flexible support forces at the same roof distance and selecting the larger one as the target flexible temporary support force, the support parameters used on site can simultaneously meet the dual requirements of roof strength safety and surrounding rock deformation control. This avoids the hidden dangers caused by designing support based solely on a single strength or displacement criterion, and ensures that the support design has a higher safety margin and adaptability.

[0016] During tunnel excavation, the corresponding target flexible temporary support force is applied based on the actual distance of the first unsupported roof area. Flexible temporary support is then implemented in the flexible support area as the tunnel face advances, allowing the flexible temporary support force to be adjusted in real time. This creates a continuous and adjustable support band between the tunnel face and the permanent support, effectively shortening the length of the dangerous unsupported roof area, reducing roof subsidence and tunnel surrounding rock deformation, improving roof stability and operational safety during excavation, and creating more favorable surrounding rock conditions for subsequent permanent support, thus improving the anchoring effect and long-term bearing capacity of the permanent support. Attached Figure Description

[0017] To more intuitively illustrate the prior art and this application, several exemplary figures are provided below. It should be understood that the specific shapes and structures shown in the figures should not generally be regarded as limiting conditions for implementing this application; for example, based on the technical concept disclosed in this application and the exemplary figures, those skilled in the art are able to easily make conventional adjustments or further optimizations to the addition / reduction / classification, specific shapes, positional relationships, connection methods, size ratios, etc. of certain units (components).

[0018] Figure 1 A schematic diagram of a tunneling roadway in which a flexible temporary support method based on a stress analysis model is applied, according to an embodiment of this application. Figure 2 A schematic diagram of the first stress model of a flexible temporary support method for tunneling based on a stress analysis model provided in one embodiment of this application; Figure 3 A schematic diagram of the rock beam cross-section of the first stress model of a flexible temporary support method based on a stress analysis model provided in one embodiment of this application; Figure 4 A schematic diagram of the equivalent circle of the second force model of a flexible temporary support method for tunneling based on a force analysis model provided in one embodiment of this application; Figure 5 A schematic diagram of the second force model of a flexible temporary support method for tunneling based on a force analysis model provided in one embodiment of this application; Figure 6 This is a schematic diagram of the structure of a support system applicable to the flexible temporary support method during excavation, provided as an embodiment of this application.

[0019] Explanation of reference numerals in the attached figures: 1. Excavation area; 11. Excavation face; 2. First unsupported roof area; 3. Flexible support area; 4. Second unsupported roof area; 5. Permanent support area; 6. Tunneling machine; 7. Roof support module; 71. Roof support body; 72. First drive unit; 8. Side support module; 81. Second drive unit; 82. Side support body. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0021] In the description of this application: unless otherwise stated, "a plurality of" means two or more. The terms "first," "second," "third," etc., in this application are intended to distinguish the objects referred to and do not have any special meaning in terms of technical connotation (e.g., they should not be construed as an emphasis on importance or order). Expressions such as "including," "comprising," and "having" also mean "not limited to" (certain units, components, materials, steps, etc.).

[0022] refer to Figure 1-5 This application discloses a flexible temporary support method based on a stress analysis model, which is applied to a tunneling roadway including a to-be-excavated area 1 in front of the tunneling face, a first open roof area 2 behind the tunneling face, a flexible support area 3, and a permanent support area 5 that has been permanently supported. Establish the first stress model. Based on the rock layer thickness, rock layer unit weight, ultimate tensile strength of the roof and the distance between the roof and the roof in the first open roof area, simplify the roof in the first open roof area into a rock beam that is fixed at one end and supported by a spring support at the other end. Calculate the first flexible support force required to keep the tensile stress of the roof from not exceeding the ultimate tensile strength of the roof under different roof distances. A second stress model is established, which equates the tunneling roadway to a circular roadway. Under the assumptions that the original rock stress is isotropic, the surrounding rock of the roadway is a continuous homogeneous isotropic elastic body and is under plane strain conditions, the relationship between the radial displacement of the surrounding rock of the roadway section and the total support resistance is established. Based on the preset maximum allowable roof radial displacement, the second flexible support force required to ensure that the roof radial displacement does not exceed the maximum allowable roof radial displacement is calculated under different unsupported roof distances. For the same roof gap distance, the first flexible support force and the second flexible support force are compared, and the larger one is selected as the target flexible temporary support force for that roof gap distance. During the tunnel excavation process, the corresponding target flexible temporary support force is selected according to the actual roof gap distance of the first roof gap area, and flexible temporary support is implemented in the flexible support area during excavation.

[0023] By simultaneously establishing a first stress model and a second stress model under the same tunneling conditions, the first stress model simplifies the roof of the first open roof area into a rock beam with one end fixed and the other end supported by spring supports. Using the ultimate tensile strength of the roof as the control index, the relationship between the open roof distance, the self-weight of the overlying strata and the bending tensile stress of the roof is established. Then, the first flexible support force required to ensure that the roof does not crack under different open roof distances is calculated in reverse. This realizes the quantitative determination of the flexible temporary support force by the "strength criterion". The second stress model adopts an elastic theoretical model that treats the tunnel cross-section as an equivalent circular tunnel. Under the assumptions of isotropic stress in the original rock, elastic surrounding rock, and plane strain, the functional relationship between the radial displacement of the surrounding rock and the total support resistance of the tunnel cross-section is obtained through equilibrium equations, geometric equations, and constitutive equations. Using the maximum allowable radial displacement of the roof as the control index, the second flexible support force required to limit the radial displacement of the roof to not exceed the allowable value under different unsupported roof distances is calculated in reverse. This realizes the quantitative determination of the flexible temporary support force based on the "deformation criterion". By comparing the first and second flexible support forces at the same roof distance and selecting the larger one as the target flexible temporary support force, the support parameters used on site can simultaneously meet the dual requirements of roof strength safety and surrounding rock deformation control. This avoids the hidden dangers caused by designing support based solely on a single strength or displacement criterion, and ensures that the support design has a higher safety margin and adaptability.

[0024] During tunnel excavation, the corresponding target flexible temporary support force is called according to the actual distance of the first unsupported roof area. Flexible temporary support can be implemented in the flexible support area through flexible temporary support devices, so that the flexible temporary support force can be adjusted in real time as the excavation face advances. This can form a continuous and adjustable support zone between the excavation face and the permanent support, effectively shortening the length of the dangerous unsupported roof area, reducing roof subsidence and tunnel surrounding rock deformation, improving roof stability and operational safety during excavation, and creating more favorable surrounding rock conditions for subsequent permanent support, improving the anchoring effect and long-term bearing capacity of the permanent support.

[0025] The flexible temporary support method for tunneling is applicable not only to rock tunnels but also to coal seam tunnels.

[0026] In the first stress model: the uniformly distributed load acting on the top plate of the first void area is determined by the product of the unit weight of the overlying rock layer on the top plate of the first void area and the thickness of the overlying rock layer on the top plate of the first void area. After the tunnel is excavated, the load on the roof beam directly above the tunnel. Calculated using the following formula: (1.1); In formula 1.1, The uniformly distributed load on the roof rock beam of the tunnel; The unit weight of the overlying rock strata on the top plate is kN / m³. The thickness of the overlying strata on the top plate is in meters. The roof of the first open roof area is treated as an equivalent rectangular rock beam with a cross-sectional height equal to the thickness of the roof and a cross-sectional width equal to the preset dangerous width. The maximum tensile stress of the roof at different open roof distances is determined based on the formula for calculating the bending normal stress of a rectangular cross-section. The expression for the normal stress on the beam can be obtained from the analysis of mechanics of materials. The formula for calculating the bending normal stress on the beam cross-section is: , (1.2); In equation 1.2, The bending normal stress at a point on the beam cross section. The bending moment on that section. This is the distance from the point to the neutral axis (z-axis). It is the second moment / moment of inertia of the cross section relative to the neutral axis (z-axis).

[0027] Generally, the maximum normal stress occurs at the section with the largest bending moment, and at the position farthest from the neutral axis. Therefore, equation 1.2 can be written as: , (1.3); Introduction (1.4), where, As the distance to the neutral axis, and for Then equation 1.3 can be written as: (1.5).

[0028] The rock beam has a cross-section of height. ,Width A rectangle, (1.6).

[0029] The support reaction force of the spring support is proportional to the displacement of the spring support in the direction perpendicular to the top plate. The proportionality coefficient is the elastic coefficient of the flexible temporary support device, and the support reaction force of the spring support is taken as the first flexible support force.

[0030] If the flexible temporary support is simplified to a spring support, the support reaction force can be calculated using the following formula 1.7: , (1.7); The support reaction force of the spring support is used to equivalently represent the first flexible support force applied to the roof by the flexible temporary support device. The spring support has an elastic modulus (stiffness) in kN / m. The displacement of the support in the direction of force (vertical) is expressed in meters (m). The flexible temporary support is considered as a "spring," and the first flexible support force equals stiffness multiplied by compression.

[0031] Under uniformly distributed load, the bending moment at any section of a beam with one end supported by a spring and the other end fixed is expressed as shown in Equation 1.8: , (1.8); in, This is the distance from the spring support to the cross-section. In actual engineering, the exposed surface of the top slab often fails first. Therefore, the maximum bending moment that causes the lower part of the beam to be under tension and the upper part to be under compression should be considered, i.e., the maximum bending moment below the beam.

[0032] Suppose that When the bending moment below the beam reaches its maximum value, then: (1.9), combining equations 1.2, 1.3, 1.5, and 1.6 above, we get: , (1.10); To prevent the roof from cracking, the deformation of the roof is kept within a certain range at different open roof distances, ensuring that the tensile stress in the roof does not exceed its ultimate tensile strength. Therefore, the stress components of the roof... ,when When the critical failure value of the rock beam is reached, the rock beam begins to fail, and the expression for the maximum length of the rock beam is obtained as follows: (1.11) In equation 1.11, The maximum length of the rock beam is equivalent to the maximum allowable ceiling distance. The support reaction force of the spring support is equivalent to the first flexible support force; This represents the tensile strength of the beam material (ultimate tensile strength of the top slab). Therefore, the first flexible support force required to prevent the top slab from cracking can be calculated by inversely using the gap between the top and bottom surfaces.

[0033] When using the first stress model to determine the ultimate ceiling distance of the first ceiling zone, the ultimate ceiling distance is obtained by taking the maximum tensile stress of the roof plate as equal to the ultimate tensile strength of the roof plate as the ultimate condition. The ultimate ceiling distance is then divided by the safety factor to obtain the corrected ultimate ceiling distance, and the safety factor is greater than 1.

[0034] When determining the ultimate roof distance in the first unsupported roof zone using the first stress model, the maximum tensile stress of the roof is taken as equal to the ultimate tensile strength of the roof as the ultimate condition for the rock beam to enter the failure state. Given the roof thickness, the unit weight of the overlying strata, and the dimensions of the critical section, the theoretical ultimate roof distance is obtained by solving the first stress model. This ultimate roof distance corresponds to the span at which the roof just reaches the critical tensile cracking point under ideal working conditions, with completely accurate parameter values ​​and no amplification of construction disturbances and time effects. However, in the actual working conditions of the tunnel excavation site, the physical properties of the overlying surrounding rock are discrete, the measured values ​​of strata thickness and unit weight have errors, the degree of development of roof joints and fissures and the distribution of weak structural surfaces are difficult to fully and accurately grasp, blasting or mechanical disturbances during the excavation process may cause additional loads and local damage, and the surrounding rock may also undergo unfavorable evolution such as creep and expansion of the loose zone over time. These factors will cause the actual bearing capacity of the roof to be lower than the theoretical limit value. Therefore, based on the maximum tensile stress of the roof equaling its ultimate tensile strength, the ultimate unsupported roof distance is calculated. This distance is then divided by a safety factor greater than 1 to obtain the corrected ultimate unsupported roof distance. Essentially, this compresses the design-allowed unsupported roof distance to a more conservative range within the theoretical limit. By using this method, which is based on the ultimate strength state and incorporates a safety factor reduction, we can fully utilize the first stress model to quantitatively reflect the roof's bearing capacity. Furthermore, we can reserve a safety margin in the support design to account for unfavorable factors such as geological uncertainties, construction disturbances, and long-term deformation. This reduces the risk of tensile cracking due to overestimation of the roof's bearing capacity and improves the reliability and engineering applicability of the flexible temporary support scheme under complex roadway surrounding rock conditions.

[0035] In the second stress model, the radius of the equivalent circular roadway is determined by the size and shape of the tunnel. Based on the elastic modulus, Poisson's ratio, and isotropic stress of the original rock, the elastic mechanical solution of the circular roadway under plane strain is adopted. The radial displacement of the surrounding rock at the roadway boundary is expressed as a function of the original rock stress, total support resistance, radius of the equivalent circular roadway, elastic modulus, and Poisson's ratio. A second flexible support force is introduced into the total support resistance. The second flexible support force is solved by ensuring that the radial displacement of the equivalent circular roadway does not exceed the maximum allowable radial displacement of the roof.

[0036] Based on existing elasticity theory, when studying the distribution of secondary stress, non-circular structures can be standardized first, and then the influence of the cross-sectional dimensions and shape of the underground chamber can be considered. This method is called the equivalent circle method (equivalent to a circular tunnel). The formula for calculating the equivalent circle is: , (2.1); In equation 2.1, a is the radius of the equivalent circle, in meters (m). The cross-sectional height is in meters (m). The span of the tunnel is in meters (m).

[0037] In the basic assumptions, the surrounding rock of the circular tunnel is a continuous, homogeneous, and isotropic elastic body, the original rock stress is in an isotropic pressure (hydrostatic pressure) state, the effect of the tunneling face on the spatial effect of the surrounding rock is equivalent to the virtual support force around the tunnel, the deformation of the surrounding rock in the area affected by the flexible temporary support is relatively small, and the surrounding rock is in an elastic state.

[0038] In the fundamental equations, the equilibrium equations are: , (2.2); In equation 2.2, Radial stress (normal stress pointing towards / away from the center of the roadway); This refers to circumferential stress (tangential stress along the circumference of the tunnel). The coordinates are the radius coordinates from the center of the tunnel.

[0039] The geometric equation is: , (2.3); In equation 2.3, For radial strain, is and for circumferential strain, is .

[0040] The constitutive equation (plane strain) is: ,(2.4; In equation 2.4, For elastic modulus, It is Poisson's ratio.

[0041] In equations 2.2, 2.3, and 2.4, The solution can be found by considering the five unknowns and the boundary conditions.

[0042] Stress boundary conditions: The surrounding rock of the chamber has inner and outer boundaries. The stress at the boundaries must satisfy certain limiting conditions, i.e., stress boundary conditions. ,(2.5; ,(2.6; In equations 2.5 and 2.6, The coordinates are the radius coordinates from the center of the tunnel. The radius of the inner wall of the tunnel (the radius of an equivalent circular tunnel); This refers to the original rock stress, which is the isotropic compressive stress of the surrounding rock at a distance before it has been disturbed. The total support resistance of the roadway is the combined support pressure acting on the roadway wall.

[0043] Solving the system of equations simultaneously using equations 2.2, 2.3, and 2.4, we obtain the general solution: ,(2.7; In equation 2.7, A and B are two integration constants, determined according to the boundary conditions.

[0044] Based on equations 2.5 and 2.6, the two integration constants A and B are determined as follows: , (2.8); Substituting the integration constants A and B into Equation 2.7, we get: , (2.9); According to the method of elasticity mechanics, the elastic strain of the axisymmetric circular chamber is calculated by equation 2.9: , (2.10); In equation 2.9, ; .

[0045] Using geometric equations, a commonly used formula for calculating radial displacement can be derived. The relationship between the total support resistance and displacement around the chamber, i.e., at r=a, is as follows: , (2.11); In equation 2.11, Radial displacement at the tunnel wall (r=a). Substituting equations 2.9 and 2.10 into equation 2.11, we obtain the radial displacement of the tunnel at the flexible temporary support location as follows: , (2.12); In equation 2.12, The support pressure provided by the flexible temporary support at the roadway wall, where y is the distance from the excavation face to the calculated section; in, The displacement variation coefficient is obtained by fitting mathematical software (through numerous numerical simulation experiments); (2.16) (2.17) This is virtual support force.

[0046] If we assume the flexible support is like a spring, according to Hooke's Law: , (2.13); Therefore, support force With displacement The relationship is: , (2.14); when Take the maximum allowable displacement At that time, the supporting force in the second force model The minimum is: , (2.15).

[0047] Total support resistance includes the second flexible support force provided by the flexible temporary support device and the support resistance provided by the self-supporting capacity of the surrounding rock.

[0048] In the aforementioned technical solution, by decomposing the total support resistance at the roadway cross-section into two parts: the second flexible support force provided by the flexible temporary support device and the support pressure provided by the self-supporting capacity of the surrounding rock, the "total support resistance" in the second force model is no longer considered an abstract quantity from a single source. Instead, it can be physically interpreted as a superposition of components based on the contributions of the support and the self-bearing capacity of the surrounding rock in actual engineering. Specifically, in the elastic mechanics model of the surrounding rock, the total support resistance directly participates in the calculation of radial displacement at the roadway wall. If the contribution of the self-supporting capacity of the surrounding rock is not distinguished when calculating the flexible temporary support force, all displacement control requirements will be incorrectly applied to the flexible temporary support device, resulting in an overly conservative flexible support design and significantly oversized equipment capacity and support strength.

[0049] By attributing a portion of the total support resistance to the support force of permanent support structures (such as anchor bolts, anchor cables, steel frames, etc.) to the self-supporting capacity of the surrounding rock, the support share provided by permanent support and the self-supporting capacity of the surrounding rock can be reasonably deducted under the premise of a given total support resistance requirement. Only the remaining part is borne by the second flexible support force, so that the design of the flexible temporary support device is more in line with the actual force division and the collaborative working mechanism of the support system during the construction stage.

[0050] The support pressure provided by the self-supporting capacity of the surrounding rock is equivalently represented in the form of virtual support force. The virtual support force is the equivalent radial support pressure generated by the unexcavated surrounding rock in front of the tunnel face on the tunnel section under the spatial effect. Its magnitude is determined by the stress release coefficient of isotropic compressive stress of the original rock and decreases as the tunneling distance between the tunnel face and the tunnel section increases.

[0051] Tunnel excavation is a three-dimensional process. In front of the tunnel face is the unexcavated rock layer, and behind it is the excavated rock layer. As the tunnel face moves forward, the stress and deformation of the surrounding rock near the tunnel face are continuously released. The deformation and stress redistribution of the surrounding rock within a certain range near the tunnel face are constrained by itself, which prevents the stress from being fully released. The stress redistribution of the surrounding rock cannot be completed in one go. Without flexible temporary support, based on a large amount of engineering experience, the influence range of the spatial effect of the tunnel face is twice the tunnel diameter in front of the tunnel face and three times the tunnel diameter behind the tunnel face. As the tunnel face advances, the stress released by the surrounding rock gradually increases, and the radial deformation of the surrounding rock increases.

[0052] The "spatial effect" of the tunnel face on the surrounding rock can be simplified as an equivalent supporting force (virtual supporting force) acting around the tunnel. This process can be explained by introducing a stress release coefficient λ. The stress release coefficient is generally related to factors such as the tunnel's cross-sectional shape, excavation method, lateral pressure coefficient, and Poisson's ratio. Due to the "spatial effect" of the tunnel face, the released load acting on the tunnel cross-section does not immediately reach the initial stress state, but rather has a time history. The process of this released load changing with space is as follows: , (3.1); In formula 3.1, For the release load affected by the "spatial effect"; To measure the distance traveled, m; Let the radius of the circular tunnel be m; This is the stress relief coefficient.

[0053] "Spatial effect" tunnel "virtual support" The expression for " is: (3.2); In equation 3.2, represents the virtual support force.

[0054] The tunneling roadway includes, in sequence along the tunneling direction, the area to be excavated, as well as the first roof area, the flexible support area, the second roof area, and the permanent support area located behind the tunneling face.

[0055] The tunneling roadway is divided into four zones along the tunneling direction: the un-excavated zone, the first unsupported roof zone, the flexible support zone, the second unsupported roof zone, and the permanent support zone. The second unsupported roof zone is located between the flexible support zone and the permanent support zone. When the tunneling face advances, the first unsupported roof zone is adjacent to the tunneling face, and the flexible temporary support devices deployed along with the tunneling face are responsible for controlling the deformation of the roof. Flexible temporary support devices have been deployed in the flexible support zone, and the roof is in a stable and controlled state. The second unsupported roof zone, which is behind the flexible support zone, is within the transition zone influenced by both permanent and flexible temporary support. As the flexible support gradually moves forward and the permanent support is successively reinforced, the two support forms can work together to constrain the roof of the second unsupported roof zone.

[0056] refer to Figure 6 This application also discloses a support system applicable to the flexible temporary support method for tunneling, including a tunneling machine 6 and a support device connected to the tunneling machine, the support device including: The roof support module 7, connected to the top of the tunneling machine, is used to apply flexible temporary support force to the roadway roof at the top of the tunneling machine. Side support modules 8, which are connected to both sides of the tunneling machine, are used to apply flexible temporary support force to the two sides of the roadway on both sides of the tunneling machine. The flexible temporary support force applied by the roof support module and / or side support module is set as the target flexible temporary support force determined according to the above-mentioned flexible temporary support method based on the stress analysis model.

[0057] By integrating the roof support module and sidewall support module onto the tunneling machine body, the flexible temporary support device is integrated with the tunneling equipment. It moves forward synchronously with the tunneling machine, providing flexible temporary support to the tunnel roof and sides within the tunneling machine's top and sides, closely following the tunneling face. Furthermore, the flexible temporary support force applied by the roof support module and / or sidewall support module is set as the target flexible temporary support force determined by the in-situ flexible temporary support method based on a stress analysis model. This ensures a structurally compatible relationship between the support system and the support method in terms of parameter control. Specifically, the method calculates the required target flexible temporary support force for different unsupported roof distances, and the support system then actually applies this target flexible temporary support force to the corresponding areas on the top and sides of the tunneling machine. This effectively transforms the stress analysis model into engineering support parameters and on-site support behavior.

[0058] In some embodiments, the roof support module includes a roof support body 71 for abutting against the roof of the tunnel and a first drive unit 72 connected to the tunneling machine. The first drive unit is used to drive the roof support body to move relative to the tunneling machine in directions toward and away from the roof, so as to form an adjustable flexible temporary support for the roof during the tunneling process. The side support module includes a side support body 82 for abutting against the side of the roadway and a second drive unit 81 connected to the tunneling machine. The second drive unit is used to drive the side support body to move relative to the tunneling machine in the direction toward and away from the corresponding side, so as to form an adjustable flexible temporary support for the side during the tunneling process. The target flexible temporary support force is distributed according to a preset ratio as flexible temporary support force applied by the roof support module and flexible temporary support force applied by the side support module.

[0059] In the aforementioned support system, by setting up a roof support module consisting of a roof support body and a first drive unit, and a side support module consisting of a side support body and a second drive unit, both the roof support body and the side support body can reciprocate relative to the tunneling machine in directions toward and away from the surrounding rock of the roadway. This allows for real-time adjustment of the contact state and contact pressure between the roof and the sidewalls during the tunneling machine's advance. As the tunneling machine advances forward and the positions of the first open roof area and the flexible support area change accordingly, the first drive unit drives the roof support body to move toward or away from the roof to maintain a roof support force at the top of the tunneling machine that matches the target flexible temporary support force; the second drive unit drives the side support body to move toward or away from the sidewalls to maintain side support forces on both sides of the tunneling machine that match the target flexible temporary support force.

[0060] The target flexible temporary support force is distributed between the roof support module and the side support module according to a preset ratio, so that the support of the roof and the two sides is reasonably divided: on the one hand, the roof is guaranteed to receive sufficient flexible support to control subsidence and bending deformation; on the other hand, the side support module controls the convergence and shear failure of the side walls, thereby achieving coordinated matching of the support forces of the roof and the two sides under different roof distances and different surrounding rock conditions.

[0061] In some embodiments, the first drive unit and the second drive unit may include a plurality of hydraulic cylinders, hydraulic pump stations and associated hydraulic pipelines and control valve groups arranged along the length or width direction of the tunneling machine. The extension and retraction stroke of the hydraulic cylinders is used to drive the roof support and side support to move toward or away from the corresponding surrounding rock. The roof support and side support may be plate-shaped structures or frame structures. The plate is provided with arc-shaped or zigzag support surfaces that cooperate with the roof or side. Wear-resistant pads or high friction coefficient materials may be laid on the support surfaces to improve the fit with the surrounding rock and the uniformity of stress.

[0062] After the target flexible temporary support force is distributed between the roof support module and the sidewall support module, it corresponds to the preload applied to the roof support body and the sidewall support body, respectively. The hydraulic system converts this preload into the working pressure and thrust of the hydraulic cylinder through a pressure regulating valve or a proportional valve. When the surrounding rock of the roadway deforms, the roof sinks, or the sidewall converges, the roof support body and the sidewall support body are displaced under the squeezing action of the surrounding rock. The hydraulic cylinder retracts or extends accordingly. The hydraulic system dynamically adjusts the position and applied force of the roof support body and the sidewall support body through pressure feedback and stroke adjustment, so that the flexible temporary support force automatically changes with the deformation of the surrounding rock within a predetermined range. Together with the self-supporting capacity of the surrounding rock, it forms a flexible support system with variable stiffness and adjustable preload. In this system, the initial deformation of the surrounding rock is absorbed by its own bearing capacity and preload. When the deformation approaches the allowable value, the hydraulic drive system inhibits further deformation by increasing the reaction force, thereby effectively limiting the maximum deformation of the roof and sidewalls, reducing the range of the surrounding rock entering the plastic failure zone, and improving the safety margin and long-term stability of the roadway support.

[0063] In some embodiments, the roof support and side support are in rolling or sliding contact with the roadway roof and sidewalls via roller support assemblies or tracked support assemblies, enabling the roof support module and side support module to maintain continuous flexible temporary support for the roof and sidewalls within a first open roof area as the tunneling machine moves forward along the tunneling direction.

[0064] In the above technical solution, by enabling the roof support and side support to achieve rolling or sliding contact with the roadway roof and sidewalls through roller support components or crawler support components, the roof support module and side support module can move synchronously with the tunneling machine while maintaining a basic fit with the roof and sidewalls and a support force level, without the need for frequent complete unloading, recycling and re-tightening of the support. Roller support assemblies or tracked support assemblies provide a movable support interface between the support body and the surrounding rock. On the one hand, this significantly reduces the frictional resistance and local shearing effect during the movement of the support body relative to the surrounding rock, reducing the risk of disturbance and scraping damage to the roof and sidewall rock surfaces, and reducing the possibility of loosening of the surrounding rock surface and spalling. On the other hand, it enables the support body to adapt to the changes in the roadway contour by rolling or sliding when the tunneling machine moves forward, and to move forward continuously and smoothly within the first unsupported roof area, thereby continuously applying flexible temporary support force to the roof and sidewalls during the tunneling process.

[0065] The technical features of the above embodiments can be combined in any way (as long as there is no contradiction in the combination of these technical features). For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described; these embodiments not explicitly written should also be considered to be within the scope of this specification.

[0066] The present application has been described in a relatively specific and detailed manner above through general descriptions and specific embodiments. It should be understood that, based on the technical concept of the present application, several conventional adjustments or further innovations can be made to these specific embodiments; however, as long as they do not depart from the technical concept of the present application, the technical solutions obtained by these conventional adjustments or further innovations also fall within the protection scope of the claims of the present application.

Claims

1. A method for flexible temporary support during excavation based on a stress analysis model, characterized in that, It is applicable to tunneling roadways including the area to be excavated in front of the working face, the first unsupported roof area behind the working face, the flexible support area, and the permanent support area that has been permanently supported; Establish the first stress model. Based on the rock layer thickness, rock layer unit weight, ultimate tensile strength of the roof and the distance between the roof and the roof in the first open roof area, simplify the roof in the first open roof area into a rock beam that is fixed at one end and supported by a spring support at the other end. Calculate the first flexible support force required to keep the tensile stress of the roof from not exceeding the ultimate tensile strength of the roof under different roof distances. A second stress model is established, which equates the tunneling roadway to a circular roadway. Under the assumptions that the original rock stress is isotropic, the surrounding rock of the roadway is a continuous homogeneous isotropic elastic body and is under plane strain conditions, the relationship between the radial displacement of the surrounding rock of the roadway section and the total support resistance is established. Based on the preset maximum allowable roof radial displacement, the second flexible support force required to keep the roof radial displacement from exceeding the maximum allowable roof radial displacement is calculated under different unsupported roof distances. For the same roof gap distance, the first flexible support force and the second flexible support force are compared, and the larger one is selected as the target flexible temporary support force for that roof gap distance. During the tunnel excavation process, the corresponding target flexible temporary support force is selected according to the actual roof gap distance of the first roof gap area, and flexible temporary support is implemented in the flexible support area during excavation.

2. The support method according to claim 1, characterized in that, In the first force model: The uniformly distributed load acting on the top plate of the first open roof area is determined by the product of the unit weight of the overlying rock layer on the top plate of the first open roof area and the thickness of the overlying rock layer on the top plate of the first open roof area. The top plate of the first open roof area is treated as a rectangular rock beam with a cross-sectional height equal to the thickness of the top plate and a cross-sectional width equal to the preset dangerous width. The maximum tensile stress of the top plate at different open roof distances is determined based on the formula for calculating the bending normal stress of a rectangular cross-section. The support reaction force of the spring support is proportional to the displacement of the spring support in the direction perpendicular to the top plate. The proportionality coefficient is the elastic coefficient of the flexible temporary support device, and the support reaction force of the spring support is used as the first flexible support force.

3. The support method according to claim 1 or 2, characterized in that, When using the first stress model to determine the ultimate ceiling distance of the first ceiling zone, the ultimate ceiling distance is obtained by taking the maximum tensile stress of the roof plate as equal to the ultimate tensile strength of the roof plate as the ultimate condition, and then dividing the ultimate ceiling distance by the safety factor to obtain the corrected ultimate ceiling distance, where the safety factor is greater than 1.

4. The support method according to claim 1, characterized in that, In the second stress model, the radius of the equivalent circular tunnel is determined by the size and shape of the tunnel. Based on the elastic modulus, Poisson's ratio, and isotropic stress of the original rock, the elastic mechanical solution of the circular tunnel under plane strain is adopted. The radial displacement of the surrounding rock at the tunnel boundary is expressed as a function of the original rock stress, total support resistance, radius of the equivalent circular tunnel, elastic modulus, and Poisson's ratio. A second flexible support force is introduced into the total support resistance. The second flexible support force is solved by ensuring that the radial displacement of the equivalent circular tunnel does not exceed the maximum allowable radial displacement of the roof.

5. The support method according to claim 4, characterized in that, The total support resistance includes the second flexible support force provided by the flexible temporary support device and the support resistance provided by the self-supporting capacity of the surrounding rock.

6. The support method according to claim 5, characterized in that, The support pressure provided by the self-supporting capacity of the surrounding rock is equivalently represented in the form of virtual support force. The virtual support force is the equivalent radial support pressure generated by the unexcavated surrounding rock in front of the tunnel face on the tunnel section under the spatial effect. Its magnitude is determined by the stress release coefficient of isotropic compressive stress of the original rock and decreases as the tunneling distance between the tunnel face and the tunnel section increases.

7. The support method according to claim 1, characterized in that, The tunneling roadway includes, in sequence along the tunneling direction, a zone to be excavated and a first roof area, a flexible support area, a second roof area, and a permanent support area located behind the tunneling working face.

8. A support system applicable to the flexible temporary support method during excavation, characterized in that, It includes a tunneling machine and a support device connected to the tunneling machine, the support device comprising: The roof support module connected to the top of the tunneling machine is used to apply flexible temporary support force to the roadway roof at the top of the tunneling machine; Side support modules connected to both sides of the tunneling machine are used to apply flexible temporary support force to the two sides of the roadway on both sides of the tunneling machine. The flexible temporary support force applied by the roof support module and / or side support module is set as the target flexible temporary support force determined by the on-site flexible temporary support method based on the force analysis model according to any one of claims 1 to 7.

9. The support system according to claim 8, characterized in that, The roof support module includes a roof support body for abutting against the roof of the tunnel and a first drive unit connected to the tunneling machine. The first drive unit is used to drive the roof support body to move relative to the tunneling machine in directions toward and away from the roof, so as to form an adjustable flexible temporary support for the roof during the tunneling process. The side support module includes a side support body for abutting against the side of the roadway and a second drive unit connected to the tunneling machine. The second drive unit is used to drive the side support body to move relative to the tunneling machine in directions toward and away from the corresponding side, so as to form an adjustable flexible temporary support for the side during the tunneling process. The target flexible temporary support force is distributed according to a preset ratio as flexible temporary support force applied by the top plate support module and flexible temporary support force applied by the side support module.

10. The support system according to claim 9, characterized in that, The roof support and the side support are in rolling or sliding contact with the roadway roof and sidewalls through roller support components or tracked support components, so that the roof support module and the side support module can maintain continuous flexible temporary support for the roof and sidewalls within the first open roof area as the tunneling machine moves forward along the tunneling direction.

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