Design and construction method of high-ground-temperature and high-ground-stress tunnel anchoring supporting structure

Abstract

The invention belongs to the technical field of engineering construction, and relates to a design and construction method of a high-ground-temperature and high-ground-stress tunnel anchoring support structure, which comprises the following steps of: establishing a high-temperature and high-ground-stress tunnel coupling model; determining a surrounding rock damage distribution rule and a crack propagation distribution rule; the surrounding rock damage condition is partitioned; and the composite anchoring support structure is formed. According to the method, a temperature field, a seepage field, a stress field and a damage field are coupled to establish a high-temperature and high-ground-stress tunnel coupling model, and a surrounding rock damage distribution rule and a crack propagation distribution rule are obtained through the high-temperature and high-ground-stress tunnel coupling model; and finally, corresponding anchoring supporting structures are selected according to the surrounding rock damage conditions and the crack extension conditions in the different subareas, the anchoring supporting structures in the different subareas jointly form a composite anchoring supporting structure, the influence of the high-gradient temperature field effect and the heat-water-force coupling effect on supporting is fully considered, and the surrounding rock damage area is prevented from being enlarged.

Description

Technical Field

[0001] The invention belongs to the technical field of engineering construction and relates to a design and construction method of a high-geotemperature and high-geostress tunnel anchoring support structure. Background Art

[0002] High geothermal and high geostress tunnels are a special and complex type of tunnel engineering. The occurrence of high geothermal phenomena (generally referring to geothermal temperatures exceeding 30°C) will, on the one hand, deteriorate the working environment and reduce construction efficiency. On the other hand, it will greatly deteriorate the working conditions of deep-buried hydraulic pressure tunnels and cause potential engineering safety problems. The operating load conditions of hydraulic high-pressure tunnels (generally referring to those with a pressure head greater than 100m) in high geothermal areas are far more complex than those of general tunnels. Under the action of high geothermal 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 and operated, the high temperature difference of "cold inside and hot outside" will form a high-gradient temperature field. The additional temperature tensile stress generated thereby causes a drastic change in the tunnel stress field, which will produce a tensile stress damage effect in the surrounding rock, not only causing severe cracking due to shrinkage deformation of the lining, but also causing the surrounding rock to enter a high stress state, thereby causing a sharp increase in the damaged area of ​​the surrounding rock. Furthermore, under the action of high internal water seepage pressure, it induces disaster phenomena such as hydraulic fracturing, collapse and instability of the surrounding rock, and even overall destruction, posing a serious threat to the safe operation of the tunnel project.

[0003] The surrounding rock is the main body that bears the water pressure of hydraulic high-pressure tunnels. At present, the high-gradient temperature field and the thermal-hydraulic-mechanical coupling effect are often ignored when supporting the surrounding rock, which can easily cause the surrounding rock damage area to increase, resulting in a decrease in the overall stability of the tunnel, and burying safety hazards for the tunnel. Summary of the invention

[0004] The purpose of the present invention is to provide a design and construction method for a high-temperature and high-stress tunnel anchor support structure, which can fully consider the influence of high-gradient temperature field and thermal-hydraulic-mechanical coupling effect on support, avoid the increase of surrounding rock damage area, and improve the overall stability of the tunnel.

[0005] To achieve the above-mentioned purpose, the specific technical scheme of the design and construction method of a high ground temperature and high ground stress tunnel anchor support structure provided by the present invention is as follows:

[0006] A design and construction method for a high ground temperature and high ground stress tunnel anchor support structure comprises the following steps:

[0007] Establish a high temperature and high geostress tunnel coupling model;

[0008] Determine the surrounding rock damage distribution law and crack extension distribution law based on the high temperature and high ground stress tunnel coupling model;

[0009] The surrounding rock damage is divided into different zones according to the surrounding rock damage distribution law and crack extension distribution law;

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

[0011] The present invention is also characterized in that:

[0012] The high temperature and high ground stress tunnel coupling model is established as follows:

[0013] Establish the stress-strain control equation considering surrounding rock damage:

[0014]

[0015] Among them, σ ij is the total stress; p is the pore water pressure of the surrounding rock caused by high pressure water; δ ij is the surrounding rock damage coefficient caused by temperature change; G(D) is the rock mass shear modulus; D is the surrounding rock damage variable; ε ij is the total strain: is the plastic strain; is the temperature strain; λ(D) is the Lame coefficient; ε kk is the total volume strain; is the plastic volume strain; is the volume strain caused by temperature change; T is the high temperature of the surrounding rock at a certain depth; σ ij，j is the stress in different directions; ρ is the density of the rock mass; f i is the volume force component of the rock medium; C T is the equivalent specific heat capacity; C w is the specific heat capacity of the fluid, calculated according to the specific heat capacity of water; q(D) T heat flux; T is the surrounding rock temperature; t is time; ρ0 is the density of the fluid; q w is the seepage volume of the surrounding rock damage cracks; is the volume heat source strength of the surrounding rock; M is the Biot modulus; q(D) i，i is the seepage volume corresponding to surrounding rock damage; q v is the fluid source term; β s is the thermal volume expansion coefficient of the undrained surrounding rock; n is the rock porosity; S is the rock saturation; α is the influence coefficient of temperature change on the permeability coefficient; ε p is the equivalent plastic strain corresponding to the residual value of elastic modulus, cohesion, internal friction angle and tensile strength; E0 is the initial elastic modulus of surrounding rock; E is the damage elastic modulus of surrounding rock under a certain high temperature; E d is the elastic modulus corresponding to the residual strength of the surrounding rock; is 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 is the influence coefficient of surrounding rock damage on permeability, ranging from 7 to 9; is the thermal conductivity of surrounding rock; is the initial thermal conductivity of the rock mass; α λ It is the influence coefficient of surrounding rock damage on thermal conductivity, and its value ranges from 4 to 4.8.

[0016] When determining the surrounding rock damage distribution law and crack extension distribution law according to the high temperature and high ground stress tunnel coupling model, a numerical simulation calculation method is used, which includes the following steps:

[0017] A high-temperature and high-in-situ stress tunnel coupling model was created in FLAC3D software, and model material parameters, stress boundary conditions, and velocity boundary conditions were set. After the initial in-situ stress was loaded to a balanced state, simulated excavation was performed.

[0018] Open the seepage field calculation mode, close the temperature field and stress field calculation mode, set the seepage boundary conditions, calculate the seepage field separately for a certain time step, solve the pore water pressure of the unit node, and determine the value of the pore water pressure;

[0019] Open the temperature field calculation mode, close the seepage field and stress field calculation modes, set the temperature boundary conditions, calculate the temperature field separately for a certain time step, and solve the unit node temperature and unit temperature strain;

[0020] Turn on the stress field calculation mode and turn off the seepage field and temperature field calculation modes. In this calculation mode, substitute the pore water pressure and unit temperature strain into formula (2) to solve the unit node stress;

[0021] Calculate the surrounding rock damage value and its damage range. Calculate the damage variable value of each unit according to formula (5). Use formula (6) and formula (7) to change the permeability and thermal conductivity of the damaged unit.

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

[0023] When zoning the surrounding rock damage according to the surrounding rock damage distribution law and crack extension distribution law, the surrounding rock is divided into residual zone, plastic softening zone, plastic hardening zone and elastic zone from the outside to the inside.

[0024] The following steps are included when selecting the corresponding anchor support structure according to the surrounding rock damage and crack expansion in different zones:

[0025] Before excavation, use advance small pipe grouting in the top arch in advance, and cooperate with advance pipe shed to reinforce the plastic softening area and residual area;

[0026] After excavation, polypropylene coarse fiber concrete is sprayed around the tunnel, steel mesh is hung on the top arch, anchor rods and grouting are used to support and reinforce the cracked surrounding rock in the residual area, anchor cables and long anchor rod structures are used to reinforce the damaged surrounding rock in the plastic softening area and plastic hardening area, steel arch frames are used in the initial support section, and then the second phase primary lining structure is constructed;

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

[0028] When using advanced small tube grouting, the grouting time is 2h~3h, the grouting pressure is 1.5MPa~2MPa, the slurry diffusion radius is 0.5m, and the grouting speed is 50L / min~100L / min.

[0029] The thickness of the primary lining structure is 0.7m to 1.0m.

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

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

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

[0033] Second, by using numerical simulation to analyze the high-temperature and high-ground stress tunnel coupling model, the surrounding rock damage distribution law and crack extension distribution law can be obtained quickly and efficiently, thereby improving the support efficiency of the high-temperature and high-ground stress tunnel. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0035] Figure 2It is the surrounding rock damage and crack expansion evolution process under the excavation working condition of the present invention;

[0036] Figure 3 This is the evolution process of surrounding rock damage and crack expansion under the first water filling condition of the present invention;

[0037] Figure 4 The curve of surrounding rock damage volume changing with temperature difference of the present invention;

[0038] Figure 5 The damage zone distribution law and crack expansion law of the high geotemperature and high geostress tunnel of the present invention;

[0039] Figure 6a Damage to tunnel lining structure caused by high ground temperature and high ground stress;

[0040] Figure 6b The crack expansion and evolution of tunnels with high geotemperature and high geostress;

[0041] Figure 7 This is the high geotemperature and high geostress tunnel surrounding rock reinforcement mechanism of the present invention. DETAILED DESCRIPTION

[0042] The technical solution in the present application will be described clearly and in detail below in conjunction with the accompanying drawings. Among them, in the description of the embodiments of the present application, unless otherwise specified, " / " means or, for example, A / B can mean A or B: "and / or" in the text is only a description of the association relationship of associated objects, indicating that there can be three relationships, such as A and / or B, which can mean: A exists alone, A and B exist at the same time, and B exists alone. In addition, in the description of the embodiments of the present application, "multiple" refers to two or more than two. The following terms "first" and "second" are used for descriptive purposes only and cannot be understood as implying or suggesting relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features.

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

[0044] Establish a high temperature and high geostress tunnel coupling model;

[0045] Determine the surrounding rock damage distribution law and crack extension distribution law based on the high temperature and high ground stress tunnel coupling model;

[0046] The surrounding rock damage is divided into different zones according to the surrounding rock damage distribution law and crack extension distribution law;

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

[0048] Among them, a high-temperature and high-geo-stress tunnel coupling model is established according to the coupling process of the mutual influence among the temperature field, seepage field, stress field and damage field formed under the operating conditions of the high-geo-temperature and high-geo-stress tunnel.

[0049] In summary, the present invention establishes a high-temperature and high-ground stress tunnel coupling model by coupling the temperature field, seepage field, stress field, and damage field. The surrounding rock damage distribution law and the crack extension distribution law are obtained through the high-temperature and high-ground stress tunnel coupling model. The surrounding rock damage conditions are then zoned according to the surrounding rock damage distribution law and the crack extension distribution law. Finally, the corresponding anchoring support structure is selected according to the surrounding rock damage conditions and crack extension conditions in different zones. The anchoring support structures in different zones together constitute a composite anchoring support structure, which fully considers the effects of high-gradient temperature fields and the thermal-hydraulic-mechanical coupling effects on support, avoids the increase of surrounding rock damage areas, and improves the overall stability of the tunnel.

[0050] Furthermore, the high temperature and high ground stress tunnel coupling model is established as follows:

[0051]

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

[0053] At the same time, in formulas (1) to (7), σ ij is the total stress; p is the pore water pressure of the surrounding rock caused by high pressure water; δ ij is the surrounding rock damage coefficient caused by temperature change, and the specific calculation method is: 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 is the total strain; is the plastic strain; is the temperature strain; λ(D) is the Lame coefficient; ε kk is the total volume strain; is the plastic volume strain; is the volume strain caused by temperature change; T is the high temperature of the surrounding rock at a certain depth; σij，j is the stress in different directions; ρ is the density of the rock mass; f i is the volume force component of the rock medium; C T is the equivalent specific heat capacity; C w is the specific heat capacity of the fluid, calculated according to the specific heat capacity of water; q(D) T heat flux; T is the surrounding rock temperature; t is time; ρ0 is the density of the fluid; q w is the seepage volume of the surrounding rock damage cracks; is the volume heat source strength of the surrounding rock; M is the Biot modulus, which is a parameter that describes the pore compression performance of a material when subjected to external pressure. It reflects the deformation of tiny pores or voids in the material when subjected to pressure. The larger the Biot modulus, the smaller the pore compression capacity of the material and the stronger the deformation capacity; q(D) i，i is the seepage volume corresponding to surrounding rock damage; q v is the fluid source term; β s is the thermal volume expansion coefficient of the undrained surrounding rock; n is the rock porosity; S is the rock saturation; α is the influence coefficient of temperature change on the permeability coefficient; ε p is the equivalent plastic strain corresponding to the residual value of elastic modulus, cohesion, internal friction angle and tensile strength; E0 is the initial elastic modulus of surrounding rock; E is the damage elastic modulus of surrounding rock under a certain high temperature; E d is the elastic modulus corresponding to the residual strength of the surrounding rock; is 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 is the influence coefficient of surrounding rock damage on permeability, ranging from 7 to 9; is the thermal conductivity of surrounding rock; is the initial thermal conductivity of the rock mass; α λ is the influence coefficient of surrounding rock damage on thermal conductivity, with a value of 4 to 4.8; Indicates the change of temperature over time; is the change of surrounding rock volume over time.

[0054] In summary, through the high-temperature and high-ground stress tunnel coupling model, the surrounding rock damage distribution law can be calculated and determined, and the crack extension 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 deeply buried high-geotemperature and high-pressure tunnel through analytical solutions. Therefore, the present invention will determine the surrounding rock damage distribution law and the crack extension distribution law through numerical simulation calculation and analysis.

[0055] Furthermore, when determining the surrounding rock damage distribution law and crack extension distribution law according to the high temperature and high ground stress tunnel coupling model, a numerical simulation calculation method is adopted, which includes the following steps:

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

[0057] Step 2, open the seepage field calculation mode, close the temperature field and stress field calculation mode, set the seepage boundary conditions, calculate formula (4) separately for a certain time step, solve the unit node pore water pressure, and determine the value 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, calculate formula (3) separately for a certain time step, and solve the unit node temperature and unit temperature strain;

[0059] Step 4, turn on the stress field calculation mode, turn off the seepage field and temperature field calculation modes. In this calculation mode, substitute the pore water pressure and unit temperature strain into formula (2) to solve the unit node stress;

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

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

[0062] In summary, steps 1 to 6 are all performed in FLAC3D software. FLAC3D is a three-dimensional fast Lagrangian analysis program. That is, in step 1, the model load command in FLAC3D is used to call the custom high-temperature and high-in-situ stress tunnel coupling model, set the model material parameters, stress boundary conditions and velocity boundary conditions, load the initial in-situ stress to the equilibrium state, and then apply the model null statement in FLAC3D to simulate excavation; in step 2, the set fluid onthermal off mech off command in FLAC3D is used to turn on the seepage field calculation mode, turn off the temperature field and stress field calculation modes, set the seepage boundary conditions, calculate the seepage field separately for a certain time step, solve the unit node pore water pressure, and determine the value of the pore water pressure; in step 3, the set fluid off thermal on mech off command in FLAC3D is used to turn on the temperature field calculation mode, turn off the seepage field and stress field calculation modes, set the temperature boundary conditions, calculate the temperature field separately for a certain time step, and solve the unit node temperature and unit temperature strain; in step 4, the set fluid offthermal on mech off command in FLAC3D is used to turn on the temperature field calculation mode, turn off the seepage field and stress field calculation modes, set the temperature boundary conditions, calculate the temperature field separately for a certain time step, and solve the unit node temperature and unit temperature strain. The off command turns on the stress field calculation mode and turns off the seepage field and temperature field calculation modes. In this calculation mode, the pore water pressure and unit temperature strain are substituted into formula (2) to solve the unit node stress.

[0063] like Figure 2 As shown in the figure, when the excavation disturbance just started, the surrounding rock damage circle depth was 0.69m, the deepest crack was 1.46m, and the surrounding rock damage volume was 3.42m 3 The damage value of the damage circle is mostly less than 0.6, while cracks have expanded locally in the surrounding rock. The damage at the cracks is relatively large, and the damage value is mostly greater than 0.8. Due to the large damage at the cracks, the permeability coefficient of the surrounding rock suddenly increases by about 1000 times, while the permeability coefficient of the part of the surrounding rock where no crack expansion occurs increases by about 20 times.

[0064] Under the condition of the first water flow, the specific values ​​of the damage range of the tunnel surrounding rock and the crack extension depth are as follows: Figure 4 As shown in the figure, the surrounding rock damage circle depth is 0.86m, which is larger than that of the excavation condition. At this time, the cracks in the surrounding rock continue to expand, with a maximum depth of 3.24m. The surrounding rock damage volume also increases accordingly, and the surrounding rock damage volume is 4.35m 3 .

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

[0066] like Figure 4 As shown in the figure, with the increase of temperature difference, the temperature gradient effect becomes more obvious, the depth of the tunnel surrounding rock damage zone, cracking depth, number of cracks and damage volume increase with the increase of temperature difference, and the bearing capacity of the tunnel tends to weaken.

[0067] like Figure 6a , Figure 6b As shown in the figure, due to the multi-physical field coupling of the deep buried tunnel, after the tunnel is filled with low-temperature and 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 on the surrounding rock. Under the action of double tensile stress, the surrounding rock is constantly damaged and destroyed, and finally cracks under tension, and several macro cracks are generated along the tunnel diameter. Low-temperature and high-pressure water enters the cracks, and the low-temperature and high-pressure water in the cracks and its seepage exchange heat with the high-temperature surrounding rock, which promotes the low-temperature boundary conditions to advance deep into the surrounding rock, resulting in the redistribution of the temperature field around the cracked surrounding rock, and then generating new temperature tensile stress, which, in combination with the high-pressure seepage in the cracks, causes the damaged area of ​​the surrounding rock to further develop deep into the surrounding rock, and eventually causes several macro cracks to continue to expand deep into the surrounding rock.

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

[0069] In order to reveal the anchoring support mechanism of surrounding rock under multi-field coupling of deep buried tunnels, and further explore the common bearing mechanism of anchoring support structure and surrounding rock, the bearing structure around the surrounding rock is divided into external bearing structure and internal bearing structure, such as Figure 5 As shown in the figure, the external bearing structure refers to the bearing structure composed of the rock mass in the elastic zone, plastic hardening zone and part of the plastic softening zone near the peak stress line of the tunnel surrounding rock. In the process of tunnel surrounding rock stabilization, the external bearing structure bears most of the rock pressure and protects the internal bearing structure, which plays a key role in the stability of the tunnel surrounding rock. The internal bearing structure refers to the tunnel supporting bearing structure such as anchor bodies, grouting bodies and brackets. 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 supporting force to the external bearing structure. It plays an important role in promoting the stability of the external bearing structure. Timely and effective internal bearing structure 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 in the figure, when selecting the corresponding anchor support structure according to the surrounding rock damage and crack expansion in different zones, the following steps are included:

[0071] Before excavation, use advance small pipe grouting in the top arch in advance, and cooperate with advance pipe shed to reinforce the plastic softening area and residual area;

[0072] After excavation, polypropylene coarse fiber concrete is sprayed around the tunnel, steel mesh is hung on the top arch, anchor rods and grouting are used to support and reinforce the cracked surrounding rock in the residual area, anchor cables and long anchor rod structures are used to reinforce the damaged surrounding rock in the plastic softening area and plastic hardening area, steel arch frames are used in the initial support section, and then the second phase primary lining structure is constructed;

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

[0074] Among them, when using advanced small-duct grouting, 50% advanced small-duct grouting is used, combined with 50% advanced pipe racks, the grouting time is 2h~3h, the grouting pressure is 1.5MPa~2MPa, the slurry 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 I22 type, 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 of 6m hollow grouting anchor rod, the thickness of acrylic coarse fiber concrete is 20cm, and the concrete model is C20.

[0075] Example 1

[0076] A water diversion tunnel is 42.35km long, with a maximum burial depth of 2187m, a designed flow rate of 75m3 / s, and a tunnel diameter of 5.3m. It is excavated by drilling and blasting method, with two steps of excavation. The excavation footage of each cycle does not exceed 25m. The maximum temperature of the surrounding rock during excavation is 114℃. During the excavation process, the surrounding rock will experience the coupling of multiple physical fields. Due to the high ground temperature, high ground stress and high water pressure, the tunnel will produce large deformation of the surrounding rock and damage to the support structure during the excavation process.

[0077] According to the coupling analysis method proposed in the present invention, the main reasons for the large deformation of the surrounding rock in the tunnel are the plastic deformation caused by tunnel excavation and the softening effect of groundwater on the surrounding rock. The damage of the supporting structure in the tunnel is jointly dominated by the extrusion deformation and the high-temperature expansion deformation. After the tunnel excavation, the seepage path of the groundwater is changed. The gravel layer with good water permeability in the middle of the tunnel becomes the migration channel of the groundwater, which significantly increases the water content or permeability of the surrounding rock in the middle and lower parts of the tunnel. At the same time, the tunnel excavation causes the surrounding rock to relax due to unloading, and the cracks in the surrounding rock are initiated, expanded and connected, which further increases the permeability coefficient of the rock mass, causing a significant change in the water content state of the tunnel surrounding rock. The surrounding rock softens under the action of high temperature, and the strength is significantly reduced and it shows a certain degree of expansion, which causes the surrounding rock to produce large plastic deformation. The difference in the mechanical properties of the surrounding rock above and below the gravel layer leads to non-uniform deformation between different rock layers, making the initial support force very uneven (manifested by the deformation of the lower part of the side wall being significantly greater than that of the upper part), which also causes the local buckling of the steel arch frame in the gravel layer.

[0078] The deep buried tunnel composite structure system with high ground temperature, high ground stress and high permeability water pressure proposed in the present invention is used to carry out the following composite support structure. The specific construction steps are as follows:

[0079] 1) Advanced support

[0080] Advanced pipe grouting support is used to prevent the expansion of cracks in the surrounding rock caused by excavation disturbance. A 160-degree Φ63mm self-propelled advanced pipe rack for pre-grouting is set on 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 section uses HW150 steel arch frames with a spacing of 0.5m. The steel arch frames are connected longitudinally with steel bars with a diameter of 20mm. A pair of 3m Φ28mm external eight-shaped locking anchors are set on both sides of the waist. Hollow grouting anchors are used to reinforce the cracked surrounding rock with a spacing of 1.25m×1.25m and a length of 3.5m. Then, spraying construction is carried out, using 20cm thick nano-silicon powder coarse fiber concrete. The initial support structure is used to reinforce the residual area and plastic softening area generated by coupling.

[0083] 3) Secondary support

[0084] A concrete lining structure is adopted with a thickness of 0.6m to 0.8m. In order to reduce the temperature tensile stress caused by the high temperature gradient caused by the high ground temperature, insulation material can be added between the primary lining and the secondary lining. The insulation material is polystyrene foam board. The polystyrene foam board can be prefabricated outside the cave according to the size of the cavern. The size of the laying is generally 1m×1m or 1m×1.5m. In addition, when laying, it is necessary to pay attention to selecting polystyrene foam boards with better flexibility, and the boards are bonded with polystyrene adhesive materials.

[0085] Example 2

[0086] The 4# construction branch tunnel of a water diversion tunnel is buried more than 480 meters deep. The surrounding rock is red mudstone of the second section (T1q2) of the Qingtianbao Formation of the Lower Triassic System with a small amount of light gray sandstone. The rock strata are gently inclined and slightly weathered. The rock is generally soft, with developed cracks and is generally broken. The cave is moist and drips locally. It is a Class V surrounding rock. The stability of the cave surrounding rock is extremely poor. There are mainly problems with the stability of the top arch controlled by the gently inclined rock strata and the deformation of the soft rock. The deformation of some sections is large, the upper left arch frame is severely squeezed and deformed, and the arch frame is broken.

[0087] Tunnel excavation and initial lining support are carried out in time, and the surrounding areas of the tunnel are deformed towards the tunnel. The excavation deformation is 50mm~125mm. The larger displacement occurs in the bottom plate, which rebounds 50mm~125mm. The other parts around the tunnel are deformed by 20mm~60mm. A stress relaxation zone with a thickness of 1m~3m is formed in the rock around the tunnel. The compressive stress of the sprayed layer in the top arch and the lower part of the arch wall is relatively large, reaching 8.0MPa~11.1MPa in some places, and the stress in other parts is basically 2MPa~6MPa. The stress of anchor rods is mostly 80~150MPa, and the stress of some anchor rods in the lower part of the arch wall is greater than 300MPa. The steel arch frame is closed into a ring as a whole, and the arch frame is mainly under pressure. The stress below the waist of the steel arch frame is 40MPa~160MPa, and the stress above the waist is 200MPa~400MPa. The local stress of the steel frame exceeds the allowable strength of the steel section and does not meet the safety requirements of the structural design.

[0088] Through the multi-physical field coupling analysis method proposed in the present invention, the damage area of ​​the tunnel surrounding rock is determined, the crack extension area and position are clarified, and a composite support lining structure is proposed. The specific construction steps are as follows:

[0089] 1) Advanced support

[0090] Use 50%Φ108 advanced pipe shed with a spacing of 0.4m×9m, a length of 12m, and a top arch range of 120°; and 50%Φ42 small pipe shed with a spacing of 0.3m×3m, a length of 4.5m, and a top arch range of 120° for grouting support.

[0091] 2) Initial support

[0092] Hang steel mesh Φ108, spacing is 0.15m×0.15m, spray C20 polypropylene coarse fiber concrete with a thickness of 0.22m, full section 122a steel arch frame, spacing is 0.6m, longitudinal connecting reinforcement Φ22, spacing is 1m, and the waist and bottom of each steel arch frame use 2Φ25 mortar lock foot anchor rods with a length of 6m. Use Φ25 hollow grouting anchor rods to reinforce the cracked surrounding rock, with a length of 6m, a hole spacing of 1.25m, and a plum blossom shape arrangement to support and reinforce the cracked surrounding rock in the residual area, and also do backfill grouting holes into the rock 0.1m, Φ56 drainage holes, plum blossom shape arrangement.

[0093] 3) Secondary support

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

[0095] It is to be understood that the present invention is described by some embodiments, and it is known to those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the scope of protection of the present invention.

Claims

1. A design and construction method for a high ground temperature and high ground stress tunnel anchor support structure, characterized in that: The following steps are involved: Establish a high temperature and high geostress tunnel coupling model; Determine the surrounding rock damage distribution law and crack extension distribution law based on the high temperature and high ground stress tunnel coupling model; The surrounding rock damage is divided into different zones according to the surrounding rock damage distribution law and crack extension distribution law; The corresponding anchoring support structure is selected according to the surrounding rock damage and crack expansion conditions in different zones. The anchoring support structures in different zones together constitute a composite anchoring support structure.

2. The design and construction method of the high ground temperature and high ground stress tunnel anchor support structure according to claim 1 is characterized in that: The high temperature and high geostress tunnel coupling model is established as follows: Among them, σ ij is the total stress; p is the pore water pressure of the surrounding rock caused by high pressure water; δ ij is the surrounding rock damage coefficient caused by temperature change; G(D) is the rock mass shear modulus; D is the surrounding rock damage variable; ε ij is the total strain; is the plastic strain; is the temperature strain; λ(D) is the Lame coefficient; ε kk is the total volume strain; is the plastic volume strain; is the volume strain caused by temperature change; T is the high temperature of the surrounding rock at a certain depth; σ ij，j is the stress in different directions; ρ is the density of the rock mass; f i is the volume force component of the rock medium; C T is the equivalent specific heat capacity; C w is the specific heat capacity of the fluid, calculated according to the specific heat capacity of water; q(D) T heat flux; T is the surrounding rock temperature; t is time; ρ0 is the density of the fluid; q w is the seepage volume of the surrounding rock damage cracks; is the volume heat source strength of the surrounding rock; M is the Biot modulus; q(D) i，i is the seepage volume corresponding to surrounding rock damage; q v is the fluid source term; β s is the thermal volume expansion coefficient of the undrained surrounding rock; n is the rock porosity; S is the rock saturation; α is the influence coefficient of temperature change on the permeability coefficient; ε p is the equivalent plastic strain corresponding to the residual value of elastic modulus, cohesion, internal friction angle and tensile strength; E0 is the initial elastic modulus of surrounding rock; E is the damage elastic modulus of surrounding rock under a certain high temperature; E d is the elastic modulus corresponding to the residual strength of the surrounding rock; is 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 is the influence coefficient of surrounding rock damage on permeability, ranging from 7 to 9; is the thermal conductivity of surrounding rock; is the initial thermal conductivity of the rock mass; α λ It is the influence coefficient of surrounding rock damage on thermal conductivity, and its value ranges from 4 to 4.

8.

3. The design and construction method of the high ground temperature and high ground stress tunnel anchor support structure according to claim 2 is characterized in that: When determining the surrounding rock damage distribution law and crack extension distribution law based on the high temperature and high ground stress tunnel coupling model, the numerical simulation calculation method is adopted, which includes the following steps: A high-temperature and high-in-situ stress tunnel coupling model was created in FLAC3D software, and model material parameters, stress boundary conditions, and velocity boundary conditions were set. After the initial in-situ stress was loaded to a balanced state, simulated excavation was performed. Open the seepage field calculation mode, close the temperature field and stress field calculation mode, set the seepage boundary conditions, calculate formula (4) separately for a certain time step, solve the unit node pore water pressure, and determine the value 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, calculate formula (3) separately for a certain time step, and solve the unit node temperature and unit temperature strain; Turn on the stress field calculation mode and turn off the seepage field and temperature field calculation modes. In this calculation mode, substitute the pore water pressure and unit temperature strain into formula (2) to solve the unit node stress; Calculate the surrounding rock damage value and its damage range. Calculate the damage variable value of each unit according to formula (5). Use formula (6) and formula (7) to change the permeability and thermal conductivity of the damaged unit. When the physical fields have not reached a state of equilibrium, the calculation mode of the seepage field is returned to and the calculation is recalculated. When the physical fields reach a state of equilibrium, the calculation ends and the distribution law of surrounding rock damage due to high geothermal and high geostress during the gradual excavation process is obtained.

4. The design and construction method of the high ground temperature and high ground stress tunnel anchor support structure according to claim 3 is characterized in that: When zoning the surrounding rock damage according to the surrounding rock damage distribution law and crack extension distribution law, the surrounding rock is divided into residual zone, plastic softening zone, plastic hardening zone and elastic zone from the outside to the inside.

5. The design and construction method of the high ground temperature and high ground stress tunnel anchor support structure according to claim 4 is characterized in that: When selecting the corresponding anchor support structure according to the surrounding rock damage and crack expansion in different zones, the following steps are included: Before excavation, use advance small pipe grouting in the top arch in advance, and cooperate with advance pipe shed to reinforce the plastic softening area and residual area; After excavation, polypropylene coarse fiber concrete is sprayed around the tunnel, steel mesh is hung on the top arch, anchor rods and grouting are used to support and reinforce the cracked surrounding rock in the residual area, anchor cables and long anchor rod structures are used to reinforce the damaged surrounding rock in the plastic softening area and plastic hardening area, steel arch frames are used in the initial support section, and then the second phase primary lining structure is constructed; On the basis of the steel arch frame, after reinforcing the residual area of ​​the surrounding rock, the secondary lining structure is constructed. The secondary lining structure adopts a concrete structure, and an insulating lining structure is added between the primary lining structure and the secondary lining structure.

6. The design and construction method of the high ground temperature and high ground stress tunnel anchor support structure according to claim 5 is characterized in that: When using advanced small tube grouting, the grouting time is 2h~3h, the grouting pressure is 1.5MPa~2MPa, the slurry diffusion radius is 0.5m~0.8m, and the grouting speed is 50L / min~100L / min.

7. The design and construction method of the high ground temperature and high ground stress tunnel anchor support structure according to claim 5 is characterized in that: The thickness of the primary lining structure is 0.7m to 1.0m.

8. The design and construction method of the high ground temperature and high ground stress tunnel anchor support structure according to claim 5 is characterized in that: The secondary lining thickness is 70cm to 100cm.

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