Design and construction methods for anchorage support structures in high-temperature and high-stress tunnels

Abstract

This invention belongs to the field of engineering construction technology and relates to a design and construction method for an anchorage support structure for high-temperature and high-stress tunnels. The method includes the following steps: establishing a coupled model of the high-temperature and high-stress tunnel; determining the distribution law of surrounding rock damage and the distribution law of crack propagation; dividing the surrounding rock damage into zones; and constructing a composite anchorage support structure. This invention establishes a coupled model of the high-temperature and high-stress tunnel by coupling the temperature field, seepage field, stress field, and damage field. The distribution law of surrounding rock damage and the distribution law of crack propagation are obtained through this model. The surrounding rock damage is then divided into zones. Finally, the corresponding anchorage support structure is selected based on the surrounding rock damage and crack propagation in different zones. The anchorage support structures in different zones together constitute a composite anchorage support structure, fully considering the effects of the high-gradient temperature field and the thermal-water-mechanical coupling effect on the support, thus avoiding the increase of the surrounding rock damage zone.

Description

Technical Field

[0001] This invention belongs to the field of engineering construction technology and relates to a design and construction method for an anchorage support structure for high-temperature and high-stress tunnels. Background Technology

[0002] High-temperature and high-stress tunnels are a special and complex type of tunnel engineering. The occurrence of high ground temperature (generally referring to ground temperature exceeding 30℃) will, on the one hand, deteriorate the working environment and reduce construction efficiency, and on the other hand, greatly worsen the working conditions of deeply buried hydraulic pressure tunnels, triggering potential engineering safety problems. The operating load conditions of high-pressure hydraulic tunnels (generally referring to those with a pressure head greater than 100m) in high-temperature areas are far more complex than those of ordinary tunnels. Under the action of high temperature and high water pressure loads, the coupling effect between the three physical fields of temperature, seepage and stress is very significant. Once the tunnel is filled with water, the high temperature difference between the "cold inside and hot outside" will form a high-gradient temperature field. The additional temperature tensile stress generated by this will cause drastic changes in the tunnel stress field, which will produce tensile stress failure effect in the surrounding rock. This will not only lead to severe shrinkage deformation and cracking of the lining, but also cause the surrounding rock to enter a high-stress state, resulting in a sharp increase in the damaged area of ​​the surrounding rock. Subsequently, under the action of high internal water seepage pressure, it will induce disasters such as hydraulic splitting, collapse and instability of the surrounding rock, and even overall failure, posing a serious threat to the safe operation of the tunnel project.

[0003] Surrounding rock is the main component of hydraulic high-pressure tunnels that bear water pressure. Currently, when supporting surrounding rock, the effects of high gradient temperature fields and thermal-hydraulic-mechanical coupling effects are often overlooked, which can easily lead to an increase in the damaged area of ​​the surrounding rock, resulting in a decrease in the overall stability of the tunnel and creating potential safety hazards. Summary of the Invention

[0004] The purpose of this invention is to provide a design and construction method for anchorage support structures in high-temperature and high-stress tunnels, which can fully consider the effects of high-gradient temperature fields and thermal-hydraulic-mechanical coupling on the support, avoid increasing the surrounding rock damage zone, and improve the overall stability of the tunnel.

[0005] To achieve the above objectives, the present invention provides a specific technical solution for the design and construction method of an anchorage support structure for high-temperature and high-stress tunnels, as follows:

[0006] A design and construction method for an anchorage support structure for high-temperature and high-stress tunnels includes the following steps:

[0007] Establish a coupled model for high-temperature, high-ground-stress tunnels;

[0008] The distribution patterns of surrounding rock damage and crack propagation were determined based on a coupled model of high-temperature and high-stress tunnels.

[0009] The surrounding rock damage is divided into zones based on the distribution patterns of surrounding rock damage and crack propagation.

[0010] The corresponding anchoring support structure is selected according to the surrounding rock damage and crack propagation in different zones. The anchoring support structures in different zones together constitute a composite anchoring support structure.

[0011] The invention is further characterized by:

[0012] The high-temperature, high-stress tunnel coupling model is established as follows:

[0013] Establish the stress-strain governing equations considering surrounding rock damage:

[0014]

[0015] Where, σ ij δ is the total stress; p is the pore water pressure in the surrounding rock caused by high-pressure water; ij G(D) represents the surrounding rock damage coefficient caused by temperature change; D represents the surrounding rock damage variable; ε ij For total strain: Plastic strain; ε is the temperature strain; λ(D) is the Lamé coefficient; ε kk For total volumetric strain; For plastic volumetric strain; σ represents the volumetric strain caused by temperature change; T represents the high temperature at a certain depth in the surrounding rock; σ ij，j For stresses in different directions; ρ is the density of the rock mass; f i C represents the volume force components of the rock mass medium. T C is the equivalent specific heat capacity. w The specific heat capacity of the fluid is calculated based on the specific heat capacity of water; q(D) T Heat flux; T is the surrounding rock temperature; t is time; ρ0 is the fluid density; q w This represents the seepage flow rate through the damaged cracks in the surrounding rock. q(D) represents the volumetric heat source intensity of the surrounding rock; M represents the Biot modulus; i，i q represents the seepage flow rate corresponding to the damage to the surrounding rock; v For fluid source terms; β s ε is the thermal volume expansion coefficient of the undrained surrounding rock; n is the porosity of the rock mass; S is the rock mass saturation; α is the influence coefficient of temperature change on the permeability coefficient; ε p E represents the equivalent plastic strain corresponding to the residual values ​​of elastic modulus, cohesion, internal friction angle, and tensile strength; E0 represents the initial elastic modulus of the surrounding rock; E represents the damaged elastic modulus of the surrounding rock at a certain high temperature; E d This represents the elastic modulus corresponding to the residual strength of the surrounding rock. The equivalent plastic strain corresponding to the residual strength; k is the permeability coefficient; k0 is the initial permeability coefficient of the surrounding rock; α k The coefficient representing the influence of surrounding rock damage on the permeability coefficient is 7 to 9. The thermal conductivity coefficient of the surrounding rock; α is the initial thermal conductivity coefficient of the rock mass; λ The value is the influence coefficient of surrounding rock damage on the thermal conductivity coefficient, and its value is 4 to 4.8.

[0016] When determining the distribution patterns of surrounding rock damage and crack propagation based on a coupled model of a high-temperature, high-stress tunnel, numerical simulation is employed, including the following steps:

[0017] A high-temperature, high-stress tunnel coupled model was created in FLAC3D software. The model material parameters, stress boundary conditions and velocity boundary conditions were set. After the initial ground stress was loaded to the equilibrium state, the excavation was simulated.

[0018] Turn on the seepage field calculation mode, turn off the temperature field and stress field calculation modes, set the seepage boundary conditions, perform a certain time step calculation on the seepage field separately, solve the pore water pressure at the unit node, and determine the magnitude of the pore water pressure.

[0019] Turn on the temperature field calculation mode, turn off the seepage field and stress field calculation modes, set the temperature boundary conditions, perform a certain time step calculation on the temperature field alone, and solve for the element nodal temperature and element temperature strain.

[0020] Open the stress field calculation mode and close the seepage field and temperature field calculation modes. In this calculation mode, substitute the pore water pressure and element temperature strain into formula (2) to solve the element nodal stress.

[0021] The damage value and damage range of the surrounding rock are calculated. The damage variable value of each unit is calculated according to formula (5). The permeability coefficient and thermal conductivity coefficient of the damaged unit are changed by formula (6) and formula (7).

[0022] When the physical fields have not reached equilibrium, the calculation mode is returned to the seepage field and recalculated. When the physical fields reach equilibrium, the calculation ends, and the distribution law of surrounding rock damage during the gradual excavation process under high geothermal and high geostress is obtained.

[0023] When dividing the surrounding rock damage into zones based on the distribution patterns of surrounding rock damage and crack propagation, the surrounding rock is divided into residual zone, plastic softening zone, plastic hardening zone, and elastic zone from the outside in.

[0024] When selecting the appropriate anchoring support structure based on the surrounding rock damage and crack propagation in different zones, the following steps are included:

[0025] Before excavation, grouting was carried out in advance using advanced small pipes in the top arch, in conjunction with advanced pipe roof, to reinforce the plastic softening zone and residual zone;

[0026] After excavation, polypropylene coarse fiber concrete was sprayed around the tunnel, steel mesh was hung on the top arch, and the fractured surrounding rock in the residual area was reinforced by anchor bolts and grouting support. The damaged surrounding rock in the plastic softening zone and plastic hardening zone was reinforced by anchor cables and their long anchor bolt structures. Steel arch frames were used in the initial support section, and then the second-stage primary lining structure was constructed.

[0027] On the foundation of the steel arch frame, after reinforcing the residual area of ​​the surrounding rock, a secondary lining structure is constructed. The secondary lining structure is made of concrete, and an insulating lining structure is added between the primary lining structure and the secondary lining structure.

[0028] When using advanced small-diameter pipes for grouting, the grouting time is 2-3 hours, the grouting pressure is 1.5 MPa-2 MPa, the grout diffusion radius is 0.5 m, and the grouting speed is 50 L / min-100 L / min.

[0029] The thickness of one of the lining structures is 0.7m to 1.0m.

[0030] The secondary lining thickness is 70cm to 100cm.

[0031] The design and construction method of the high-temperature and high-stress tunnel anchorage support structure of the present invention has the following advantages:

[0032] First, a coupled model of a high-temperature, high-stress tunnel is established by coupling the temperature field, seepage field, stress field, and damage field. The distribution law of surrounding rock damage and crack propagation is obtained through the coupled model. Then, the surrounding rock damage is divided into zones based on the distribution law of surrounding rock damage and crack propagation. Finally, the corresponding anchoring support structure is selected according to the surrounding rock damage and crack propagation in different zones. The anchoring support structures in different zones together constitute a composite anchoring support structure, which fully considers the effects of the high gradient temperature field and the thermal-hydraulic-mechanical coupling effect on the support, avoids the increase of the surrounding rock damage zone, and improves the overall stability of the tunnel.

[0033] Secondly, by using numerical simulation to analyze the coupled model of high-temperature and high-stress tunnels, the distribution law of surrounding rock damage and crack propagation can be obtained quickly and efficiently, thereby improving the support efficiency of high-temperature and high-stress tunnels. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the overall process of the present invention;

[0035] Figure 2This invention describes the process of surrounding rock damage and crack propagation evolution under excavation conditions.

[0036] Figure 3 This is the first water-filled working condition of the present invention, showing the evolution of surrounding rock damage and crack propagation.

[0037] Figure 4 This is the curve showing the change in surrounding rock damage volume with temperature difference according to the present invention;

[0038] Figure 5 The present invention relates to the distribution pattern of damage zones and crack propagation patterns in high-temperature and high-stress tunnels.

[0039] Figure 6a Damage to the lining structure of tunnels subjected to high ground temperature and high ground stress;

[0040] Figure 6b This is the evolution and propagation of cracks in high-temperature, high-stress tunnels.

[0041] Figure 7 This invention relates to a mechanism for reinforcing the surrounding rock of high-temperature and high-stress tunnels. Detailed Implementation

[0042] The technical solutions of this application will now be described clearly and in detail with reference to the accompanying drawings. In the description of the embodiments of this application, unless otherwise stated, " / " indicates "or," for example, A / B can mean A or B. "And / or" in the text is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, and B alone. Furthermore, in the description of the embodiments of this application, "multiple" refers to two or more. The terms "first" and "second" are used for descriptive purposes only and should not be construed as implying or suggesting relative importance or implicitly indicating the number of indicated technical features. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature.

[0043] like Figure 1 As shown, the present invention provides a design and construction method for an anchorage support structure for tunnels with high ground temperature and high ground stress, comprising the following steps:

[0044] Establish a coupled model for high-temperature, high-ground-stress tunnels;

[0045] The distribution patterns of surrounding rock damage and crack propagation were determined based on a coupled model of high-temperature and high-stress tunnels.

[0046] The surrounding rock damage is divided into zones based on the distribution patterns of surrounding rock damage and crack propagation.

[0047] The corresponding anchoring support structure is selected according to the surrounding rock damage and crack propagation in different zones. The anchoring support structures in different zones together constitute a composite anchoring support structure.

[0048] Among them, a coupled model of high temperature and high ground stress tunnels was established, which was based on the coupling process of mutual influence between the temperature field, seepage field, stress field and damage field formed under the operating conditions of high temperature and high ground stress tunnels.

[0049] In summary, this invention establishes a coupled model for high-temperature, high-stress tunnels by coupling temperature, seepage, stress, and damage fields. This model yields the distribution patterns of surrounding rock damage and crack propagation. The surrounding rock damage is then zoned based on these patterns. Finally, corresponding anchoring support structures are selected according to the damage and crack propagation conditions within each zone. These anchoring support structures collectively constitute a composite anchoring support structure, fully considering the effects of high-gradient temperature fields and thermo-hydraulic-mechanical coupling on the support, thus preventing the expansion of the surrounding rock damage zone and improving the overall stability of the tunnel.

[0050] Furthermore, a coupled model for high-temperature, high-ground-stress tunnels is established as follows:

[0051]

[0052] Among them, formula (1) is the stress-strain control equation considering the damage of the surrounding rock, formula (2) is the equilibrium equation considering the damage of the surrounding rock, formula (3) is the temperature control equation considering the influence of the damage of the surrounding rock, formula (4) is the seepage field evolution equation considering the damage of the surrounding rock, formula (5) is the deterioration evolution equation, formula (6) is the influence function relationship of the permeability coefficient, and formula (7) is the equation of the thermal conductivity coefficient of the surrounding rock evolving with damage.

[0053] Meanwhile, in formulas (1) to (7), σ ij δ is the total stress; p is the pore water pressure in the surrounding rock caused by high-pressure water; ij The damage coefficient of the surrounding rock caused by temperature changes is calculated as follows: β is the thermal expansion coefficient, T is the current temperature, T0 is the initial temperature; G(D) is the rock mass shear modulus; D is the surrounding rock damage variable; ε ij For total strain; Plastic strain; ε is the temperature strain; λ(D) is the Lamé coefficient; ε kk For total volumetric strain; For plastic volumetric strain; σ represents the volumetric strain caused by temperature change; T represents the high temperature at a certain depth in the surrounding rock; σij，j For stresses in different directions; ρ is the density of the rock mass; f i C represents the volume force components of the rock mass medium. T C is the equivalent specific heat capacity. w The specific heat capacity of the fluid is calculated based on the specific heat capacity of water; q(D) T Heat flux; T is the surrounding rock temperature; t is time; ρ0 is the fluid density; q w This represents the seepage flow rate through the damaged cracks in the surrounding rock. q(D) represents the volumetric heat source intensity of the surrounding rock; M represents the Biot modulus, which is a parameter describing the pore compressibility of a material under external pressure. It reflects the deformation of the tiny pores or voids in the material under pressure. The larger the Biot modulus, the smaller the pore compressibility and the stronger the deformation capacity of the material; i，i q represents the seepage flow rate corresponding to the damage to the surrounding rock; v For fluid source terms; β s ε is the thermal volume expansion coefficient of the undrained surrounding rock; n is the porosity of the rock mass; S is the rock mass saturation; α is the influence coefficient of temperature change on the permeability coefficient; ε p E represents the equivalent plastic strain corresponding to the residual values ​​of elastic modulus, cohesion, internal friction angle, and tensile strength; E0 represents the initial elastic modulus of the surrounding rock; E represents the damaged elastic modulus of the surrounding rock at a certain high temperature; E d This represents the elastic modulus corresponding to the residual strength of the surrounding rock. The equivalent plastic strain corresponding to the residual strength; k is the permeability coefficient; k0 is the initial permeability coefficient of the surrounding rock; α k The coefficient representing the influence of surrounding rock damage on the permeability coefficient is 7 to 9. The thermal conductivity coefficient of the surrounding rock; α is the initial thermal conductivity coefficient of the rock mass; λ The coefficient representing the influence of surrounding rock damage on the thermal conductivity is 4 to 4.8. This indicates the change in temperature over time. This represents the change in the volume of the surrounding rock over time.

[0054] In summary, the damage distribution law of the surrounding rock can be calculated and determined by the high temperature and high ground stress tunnel coupling model, and the crack propagation distribution law can be further analyzed and determined. However, since the established high temperature and high ground stress tunnel coupling model is relatively complex, it is difficult to determine the damage range of the surrounding rock of the deep-buried high temperature and high pressure tunnel through analytical solution. Therefore, this invention will determine the damage distribution law of the surrounding rock and the crack propagation distribution law through numerical simulation calculation and analysis.

[0055] Furthermore, when determining the distribution patterns of surrounding rock damage and crack propagation based on the high-temperature, high-stress tunnel coupling model, numerical simulation is employed, including the following steps:

[0056] Step 1: Create a high-temperature, high-ground-stress tunnel coupled model in FLAC3D software, set the model material parameters, stress boundary conditions and velocity boundary conditions, load the initial ground stress to the equilibrium state and then simulate excavation.

[0057] Step 2: Open the seepage field calculation mode, close the temperature field and stress field calculation modes, set the seepage boundary conditions, perform a certain time step calculation on formula (4) separately, solve the pore water pressure of the unit node, and determine the magnitude of the pore water pressure.

[0058] Step 3: Open the temperature field calculation mode, close the seepage field and stress field calculation modes, set the temperature boundary conditions, and perform a certain time step calculation on formula (3) to solve the element node temperature and element temperature strain.

[0059] Step 4: Open the stress field calculation mode and close the seepage field and temperature field calculation modes. In this calculation mode, substitute the pore water pressure and element temperature strain into formula (2) to solve the element nodal stress.

[0060] Step 5: Calculate the damage value and damage range of the surrounding rock. Calculate the damage variable value of each unit according to formula (5), and change the permeability coefficient and thermal conductivity coefficient of the damaged unit using formula (6) and formula (7).

[0061] Step 6: When the physical fields have not reached equilibrium, return to the seepage field calculation mode, that is, return to step 2 and recalculate. When the physical fields reach equilibrium, the calculation ends and the distribution law of surrounding rock damage during the gradual excavation process under high geothermal and high geostress conditions is obtained.

[0062] In summary, steps 1 through 6 are all performed in FLAC3D software, a three-dimensional fast Lagrangian analysis program. Specifically, in step 1, the `model load` command in FLAC3D is used to call a custom high-temperature, high-stress tunnel coupling model, setting model material parameters, stress boundary conditions, and velocity boundary conditions. After loading the initial ground stress to equilibrium, the `model null` statement in FLAC3D is used to simulate excavation. In step 2, the `set fluid onthermal off mech off` command in FLAC3D is used to enable the seepage field calculation mode and disable the temperature and stress field calculation modes. Seepage boundary conditions are set, and the seepage field is calculated separately at a certain time step to solve for the pore water pressure at the element nodes and determine the magnitude of the pore water pressure. In step 3, the `set fluid off thermal on mech off` command in FLAC3D is used to enable the temperature field calculation mode and disable the seepage and stress field calculation modes. Temperature boundary conditions are set, and the temperature field is calculated separately at a certain time step to solve for the element node temperature and element temperature strain. In step 4, the `set fluid offthermal on mech` command in FLAC3D is used to... The OFF command opens the stress field calculation mode and closes the seepage field and temperature field calculation modes. In this calculation mode, the pore water pressure and element temperature strain are substituted into formula (2) to solve the element nodal stress.

[0063] like Figure 2 As shown, at the beginning of excavation and disturbance, the depth of the surrounding rock damage zone was 0.69m, the deepest crack was 1.46m, and the volume of surrounding rock damage was 3.42m³. 3 The damage value of the damage zone is mostly less than 0.6, while cracks have spread locally in the surrounding rock. The damage at the cracks is greater, with damage values ​​mostly greater than 0.8. Due to the greater damage at the cracks, the permeability coefficient of the surrounding rock increases by about 1000 times. In the parts of the surrounding rock where no cracks have spread, the permeability coefficient increases by about 20 times.

[0064] Under the initial water supply condition, the specific values ​​of the damage range of the tunnel surrounding rock and the depth of crack propagation, such as... Figure 4 As shown, the depth of the surrounding rock damage zone is 0.86m, which is larger than that under the excavation condition. At this point, the cracks in the surrounding rock continue to expand, reaching a maximum depth of 3.24m, and the volume of the damaged surrounding rock also increases accordingly, reaching 4.35m³. 3 .

[0065] like Figure 3 As shown, with the continued action of the coupled thermal-hydraulic-mechanical-damage effect on the tunnel surrounding rock, the depth of the damage zone increased to 0.94m, the cracks in the surrounding rock also continued to expand, the crack depth increased to 3.87m, and the volume of damage to the surrounding rock increased to 4.83m³. 3The damage value of the surrounding rock continued to increase, with greater damage at the cracks, and the maximum damage value reached 0.86.

[0066] like Figure 4 As shown, with the increase of temperature difference, the temperature gradient effect becomes more obvious. The depth of the damage zone, crack depth, number of cracks and damage volume of the tunnel surrounding rock increase with the increase of temperature difference, and the bearing capacity of the tunnel shows a weakening trend.

[0067] like Figure 6a , Figure 6b As shown, due to the multi-physics coupling effect of deeply buried tunnels, after the tunnel is filled with low-temperature, high-pressure water, a high-gradient temperature field is formed inside the surrounding rock, generating high-temperature tensile stress. At the same time, the high internal water pressure also generates high tensile stress in the surrounding rock. Under the action of dual tensile stress, the surrounding rock is continuously damaged and eventually cracks under tension, generating several macroscopic cracks along the tunnel diameter. Low-temperature, high-pressure water enters the cracks, and the low-temperature, high-pressure water and its seepage within the cracks exchange heat with the high-temperature surrounding rock, causing the low-temperature boundary conditions to advance deeper into the surrounding rock. This leads to a redistribution of the temperature field around the cracked surrounding rock, thereby generating new temperature tensile stress. This stress, combined with the high-pressure seepage within the cracks, causes the damaged area of ​​the surrounding rock to further develop into the deeper parts of the surrounding rock, ultimately leading to the continuous expansion of several macroscopic cracks into the deeper parts of the surrounding rock.

[0068] like Figure 5 As shown, when the surrounding rock damage is divided into zones according to the distribution law of surrounding rock damage and the distribution law of crack propagation, the surrounding rock is divided into the residual zone, the plastic softening zone, the plastic hardening zone and the elastic zone from the outside to the inside. The stress concentration zone of the surrounding rock of high temperature and high stress tunnels starts in the softening zone. The stress of the surrounding rock reaches its peak in the plastic zone (non-softening zone), which will cause further damage to the surrounding rock and reduce its bearing capacity.

[0069] To reveal the anchoring support mechanism of surrounding rock under multi-field coupling in deeply buried tunnels, and to further explore the shared bearing mechanism of the anchoring support structure and the surrounding rock, the bearing structure around the surrounding rock is divided into an external bearing structure and an internal bearing structure, such as... Figure 5 As shown, the external bearing structure refers to the bearing structure near the peak stress line of the surrounding rock in the tunnel. This part is composed of rock mass in the elastic zone, plastic hardening zone, and partially plastic softening zone. During the stabilization process of the tunnel surrounding rock, the external bearing structure bears most of the rock pressure and protects the internal bearing structure, playing a key role in the stability of the tunnel surrounding rock. The internal bearing structure refers to the roadway support bearing structure such as anchor bodies, grouting bodies, and supports. The internal bearing structure can only bear a small part of the rock pressure. It mainly stabilizes the external bearing structure by increasing the radial support force of the external bearing structure. It plays an important role in promoting the stability of the external bearing structure. Timely and effective internal bearing structures can improve the stress state of the surrounding rock, reduce the softening of the surrounding rock, and ensure the stability of the tunnel surrounding rock.

[0070] like Figure 7 As shown, when selecting the appropriate anchoring support structure based on the surrounding rock damage and crack propagation in different zones, the following steps are included:

[0071] Before excavation, grouting was carried out in advance using advanced small pipes in the top arch, in conjunction with advanced pipe roof, to reinforce the plastic softening zone and residual zone;

[0072] After excavation, polypropylene coarse fiber concrete was sprayed around the tunnel, steel mesh was hung on the top arch, and the fractured surrounding rock in the residual area was reinforced by anchor bolts and grouting support. The damaged surrounding rock in the plastic softening zone and plastic hardening zone was reinforced by anchor cables and their long anchor bolt structures. Steel arch frames were used in the initial support section, and then the second-stage primary lining structure was constructed.

[0073] On the foundation of the steel arch frame, after reinforcing the residual area of ​​the surrounding rock, a secondary lining structure is constructed. The secondary lining structure is made of concrete, and an insulating lining structure is added between the primary lining structure and the secondary lining structure.

[0074] When using advanced small-diameter pipe grouting, 50% advanced small-diameter pipe grouting is used in conjunction with 50% advanced pipe roof grouting. The grouting time is 2-3 hours, the grouting pressure is 1.5MPa-2MPa, the grout diffusion radius is 0.5m-0.8m, the grouting speed is 50L / min-100L / min, the thickness of the primary lining structure is 0.7m-1.0m, the thickness of the secondary lining is 70cm-100cm, the steel arch frame is type I22, the interval between two adjacent steel arch frames is 0.6m, the steel mesh is Φ8.0@0.15mx0.15m, the anchor rod is Φ25@1.25mx1.25m, the length is 6m, the thickness of the acrylic coarse fiber concrete is 20cm, and the concrete type is C20.

[0075] Example 1

[0076] A water conveyance tunnel is 42.35 km long, with a maximum burial depth of 2187 m, a design flow rate of 75 m³ / s, and a diameter of 5.3 m. It was excavated using the drill-and-blast method, with two-stage excavation. The excavation advance in each cycle did not exceed 25 m. The highest temperature of the surrounding rock during excavation was 114 °C. During the excavation process, the surrounding rock was subjected to the coupling effect of multiple physical fields. Due to the high ground temperature, high ground stress, and high water pressure, the tunnel experienced large deformation of the surrounding rock and damage to the support structure during the excavation process.

[0077] Using the coupled analysis method proposed in this invention, the main reasons for the large deformation of the surrounding rock in tunnels are the plastic deformation caused by tunnel excavation and the softening effect of groundwater on the surrounding rock. The failure of the tunnel support structure is dominated by compression deformation and high-temperature expansion deformation. After tunnel excavation, the seepage path of groundwater is changed. The well-permeable sandstone and conglomerate layer in the middle of the tunnel becomes a channel for groundwater transport, which significantly increases the water content or permeability of the surrounding rock in the lower part of the tunnel. At the same time, tunnel excavation causes unloading and relaxation of the surrounding rock, and the initiation, expansion and connection of cracks in the surrounding rock further increases the permeability coefficient of the rock mass, resulting in a significant change in the water content of the tunnel surrounding rock. High temperature softens the surrounding rock, significantly reduces its strength and exhibits a certain degree of expansibility, resulting in large plastic deformation of the surrounding rock. The difference in mechanical properties between the upper and lower layers of the sandstone and conglomerate layer leads to non-uniform deformation between different rock layers, resulting in very uneven stress on the initial support (manifested as the deformation at the lower part of the sidewall is significantly greater than that at the upper part), which also causes local buckling of the steel arch frame in the sandstone and conglomerate layer.

[0078] The composite support structure for deep-buried tunnels, characterized by high ground temperature, high ground stress, and high permeability water pressure, proposed in this invention, is implemented using the following steps:

[0079] 1) Advanced support

[0080] Advanced grouting support with pre-grouted guide pipes is used to prevent the expansion of cracks in the surrounding rock caused by excavation disturbance. Φ63mm self-advancing pre-grouted pipe roofs with a 160-degree angle are installed at the top arch, with a spacing of 0.3m, a row spacing of 3.5-4.0m, and a length of 6m.

[0081] 2) Initial support

[0082] The entire cross-section uses HW150 steel arch frames with a spacing of 0.5m. The steel arch frames are connected longitudinally with steel bars of 20mm diameter. A pair of 3m Φ28mm outward-facing anchor bolts are installed on both sides of the waist. Hollow grouting anchor bolts are used to reinforce the fractured surrounding rock with a spacing of 1.25m × 1.25m and a length of 3.5m. Then, a 20cm thick layer of nano-silica powder coarse fiber concrete is applied. The initial support structure is used to reinforce the residual zone and plastic softening zone generated under the coupling effect.

[0083] 3) Secondary support

[0084] The structure uses a concrete lining with a thickness of 0.6m to 0.8m. To reduce the temperature tensile stress caused by the high temperature gradient due to high ground temperature, thermal insulation material can be added between the primary and secondary linings. The thermal insulation material is polystyrene foam board. The size of the prefabricated polystyrene foam board can be laid outside the tunnel according to the size of the tunnel, generally 1m×1m or 1m×1.5m. In addition, when laying, attention should be paid to selecting polystyrene foam boards with good flexibility, and the boards should be bonded together with polystyrene adhesive.

[0085] Example 2

[0086] The No. 4 construction adit of a certain water conveyance tunnel is buried at a depth of more than 480 meters. The surrounding rock is red mudstone interbedded with a small amount of light gray sandstone from the second section (T1q2) of the Lower Triassic Qingtianbao Formation. The rock strata are gently dipping, slightly weathered, generally soft, with well-developed fissures, and generally quite broken. The tunnel is damp, with localized dripping water. It is classified as Class V surrounding rock. The stability of the surrounding rock of the tunnel is extremely poor. The main problems are the stability of the arch controlled by the gently dipping rock strata and the deformation of the soft rock. Some sections have large deformations, and the upper left arch frame is severely compressed and deformed, resulting in the arch frame fracture.

[0087] The tunnel was initially lining and supported in time during excavation. The tunnel perimeter deformed inwards, with excavation deformation ranging from 50mm to 125mm. The largest displacement occurred in the bottom slab, which rebounded by 50mm to 125mm. Other parts of the tunnel perimeter deformed by 20mm to 60mm. A stress relaxation zone of 1m to 3m thick was formed in the surrounding rock. The pressure stress of the shotcrete layer in the top arch and lower part of the arch wall was relatively high, reaching 8.0MPa to 11.1MPa in some areas. The stress in other parts was basically 2MPa to 6MPa. The stress of the anchor bolts was mostly 80 to 150MPa, with some anchor bolts in the lower part of the arch wall having stresses exceeding 300MPa. The steel arch frame was a closed ring, and the arch frame mainly bore the pressure. The stress below the waist of the steel arch frame was 40MPa to 160MPa, and the stress above the waist was 200MPa to 400MPa. The local stress of the steel frame exceeded the allowable strength of the steel section, which did not meet the structural design safety requirements.

[0088] Using the multiphysics coupling analysis method proposed in this invention, the extent of the damage zone in the tunnel surrounding rock was determined, the crack propagation area and location were clarified, and a composite support lining structure was proposed. The specific construction steps are as follows:

[0089] 1) Advanced support

[0090] 50% of the pipes used are Φ108 advanced pipes with a spacing of 0.4m×9m and a length of 12m, covering a 120° range of the top arch. 50% of the pipes used are Φ42 small pipes with a spacing of 0.3m×3m and a length of 4.5m, covering a 120° range of the top arch for grouting support.

[0091] 2) Initial support

[0092] A Φ108 steel mesh is installed with a spacing of 0.15m x 0.15m. C20 polypropylene coarse fiber reinforced concrete with a thickness of 0.22m is sprayed. A full-section 122a steel arch frame is used with a spacing of 0.6m. Longitudinal connecting bars are Φ22 with a spacing of 1m. Each steel arch frame has two Φ25 mortar anchor bolts at the waist and bottom, each 6m long. Φ25 hollow grouting anchor bolts, 6m long, are used to reinforce the fractured surrounding rock with a hole spacing of 1.25m in a quincunx pattern. These anchor bolts support and reinforce the fractured surrounding rock in the residual area and also serve as backfill grouting holes with a depth of 0.1m into the rock. Φ56 drainage holes are also included, arranged in a quincunx pattern.

[0093] 3) Secondary support

[0094] On the foundation of the steel arch frame, after reinforcing the residual area of ​​the surrounding rock, a secondary lining structure is constructed. The secondary lining structure adopts a C30 concrete lining structure with a thickness of 0.7m and a C20 concrete base plate with a thickness of 25cm.

[0095] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. A design and construction method for an anchorage support structure for high-temperature and high-stress tunnels, characterized in that, Includes the following steps: Establish a coupled model for high-temperature, high-ground-stress tunnels; The distribution patterns of surrounding rock damage and crack propagation were determined based on a coupled model of high-temperature and high-stress tunnels. The surrounding rock damage is divided into zones based on the distribution patterns of surrounding rock damage and crack propagation. The corresponding anchoring support structure is selected according to the surrounding rock damage and crack propagation in different zones. The anchoring support structures in different zones together constitute a composite anchoring support structure. The high-temperature, high-stress tunnel coupling model is established as follows: in, The total stress; This refers to the pore water pressure in the surrounding rock caused by the action of high-pressure water. The damage coefficient of the surrounding rock caused by temperature changes; This refers to the rock mass shear modulus. For surrounding rock damage variables; For total strain; Plastic strain; For temperature strain; Lamé coefficient; For total volumetric strain; For plastic volumetric strain; This refers to the volumetric strain caused by temperature changes; The high temperature at a certain depth in the current surrounding rock; For stresses in different directions; The density of the rock mass; For the volume force components of the rock mass medium; This is the equivalent specific heat capacity; The specific heat capacity of the fluid is calculated based on the specific heat capacity of water. Heat flux; The temperature of the surrounding rock; For time; The density of the fluid; This represents the seepage flow rate through the damaged cracks in the surrounding rock. The intensity of the heat source in the surrounding rock volume; Biot modulus; This represents the seepage flow rate corresponding to the damage to the surrounding rock. For fluid source terms; The coefficient of thermal volume expansion of undrained surrounding rock; The porosity of the rock mass; Rock mass saturation; This is the coefficient representing the effect of temperature change on the permeability coefficient. This represents the equivalent plastic strain corresponding to the residual values ​​of elastic modulus, cohesion, internal friction angle, and tensile strength. This represents the initial elastic modulus of the surrounding rock. Let be the damage elastic modulus of the surrounding rock at a certain high temperature; This represents the elastic modulus corresponding to the residual strength of the surrounding rock. The equivalent plastic strain required to achieve residual strength; Permeability coefficient; The initial permeability coefficient of the surrounding rock; The coefficient representing the influence of surrounding rock damage on the permeability coefficient is 7 to 9. The thermal conductivity coefficient of the surrounding rock; The initial thermal conductivity coefficient of the rock mass; The value is the influence coefficient of surrounding rock damage on the thermal conductivity coefficient, and its value is 4 to 4.

8.

2. The design and construction method for the anchorage support structure of a high-temperature, high-stress tunnel according to claim 1, characterized in that, When determining the distribution patterns of surrounding rock damage and crack propagation based on a coupled model of a high-temperature, high-stress tunnel, numerical simulation is employed, including the following steps: A high-temperature, high-stress tunnel coupled model was created in FLAC3D software. The model material parameters, stress boundary conditions and velocity boundary conditions were set. After the initial ground stress was loaded to the equilibrium state, the excavation was simulated. Open the seepage field calculation mode, close the temperature field and stress field calculation modes, set the seepage boundary conditions, perform a certain time step calculation on formula (4) separately, solve the pore water pressure of the unit node, and determine the magnitude of the pore water pressure. Open the temperature field calculation mode, close the seepage field and stress field calculation modes, set the temperature boundary conditions, perform a certain time step calculation on formula (3) separately, and solve the element node temperature and element temperature strain. Open the stress field calculation mode and close the seepage field and temperature field calculation modes. In this calculation mode, substitute the pore water pressure and element temperature strain into formula (2) to solve the element nodal stress. The damage value and damage range of the surrounding rock are calculated. The damage variable value of each unit is calculated according to formula (5). The permeability coefficient and thermal conductivity coefficient of the damaged unit are changed by formula (6) and formula (7). When the physical fields have not reached equilibrium, the calculation mode is returned to the seepage field and recalculated. When the physical fields reach equilibrium, the calculation ends, and the distribution law of surrounding rock damage during the gradual excavation process under high geothermal and high geostress is obtained.

3. The design and construction method for the anchorage support structure of high-temperature and high-stress tunnels according to claim 2, characterized in that, When dividing the surrounding rock damage into zones based on the distribution patterns of surrounding rock damage and crack propagation, the surrounding rock is divided into the residual zone, the plastic softening zone, the plastic hardening zone, and the elastic zone from the outside in.

4. The design and construction method for the anchorage support structure of a high-temperature, high-stress tunnel according to claim 3, characterized in that, When selecting the appropriate anchoring support structure based on the surrounding rock damage and crack propagation in different zones, the following steps are included: Before excavation, grouting was carried out in advance using advanced small pipes in the top arch, in conjunction with advanced pipe roof, to reinforce the plastic softening zone and residual zone; After excavation, polypropylene coarse fiber concrete was sprayed around the tunnel, steel mesh was hung on the top arch, and the fractured surrounding rock in the residual area was reinforced by anchor bolts and grouting support. The damaged surrounding rock in the plastic softening zone and plastic hardening zone was reinforced by anchor cables and their long anchor bolt structures. Steel arch frames were used in the initial support section, and then the second-stage primary lining structure was constructed. On the foundation of the steel arch frame, after reinforcing the residual area of ​​the surrounding rock, a secondary lining structure is constructed. The secondary lining structure is made of concrete, and an insulating lining structure is added between the primary lining structure and the secondary lining structure.

5. The design and construction method for the anchorage support structure of a high-temperature, high-stress tunnel according to claim 4, characterized in that, When using advanced small-diameter pipes for grouting, the grouting time is 2-3 hours, the grouting pressure is 1.5MPa-2MPa, the grout diffusion radius is 0.5m-0.8m, and the grouting speed is 50L / min-100L / min.

6. The design and construction method for the anchorage support structure of a high-temperature, high-stress tunnel according to claim 4, characterized in that, The thickness of the primary lining structure is 0.7m to 1.0m.

7. The design and construction method for the anchorage support structure of high-temperature and high-stress tunnels according to claim 4, characterized in that, The secondary lining thickness is 70cm to 100cm.

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