Roadway and cave structure for compressed air energy storage and transformation method

Abstract

The invention discloses a roadway and cave structure for compressed air energy storage and a transformation method. The roadway and cave structure comprises a surrounding rock body which is supported and reinforced; the phase change concrete lining layer is attached to the inner wall of the surrounding rock body, and the sealing layer is laid on the inner surface of the phase change concrete lining layer. The transformation method comprises the following steps: determining a loosening circle range of surrounding rock of a to-be-transformed tunnel; the outer boundary of the loose circle serves as the outline, and the roadway and the cave to be transformed are excavated in an expanding mode and trimmed into a preset shape; the roadway and cave surrounding rock after expanding excavation is supported and reinforced; constructing a phase change concrete lining layer on the surface of the supported surrounding rock; and the sealing layer is laid on the surface of the phase change concrete lining layer. The mechanical stability and air tightness of the roadway and the cave are improved, and it is ensured that the roadway and cave can be used for a compressed air energy storage system.

Description

Technical Field

[0001] This invention relates to the field of energy storage and underground space reuse technology, and in particular to a tunnel structure and modification method for compressed air energy storage. Background Technology

[0002] Compressed air energy storage, as a highly efficient and scalable large-scale energy storage technology, is a key means to solve the intermittency problem of renewable energy sources such as wind and solar power. Due to its stable geological structure, large spatial capacity, and relatively low development cost, underground tunnel spaces are considered highly promising candidate sites for compressed air energy storage.

[0003] The compressed air energy storage system for tunnels faces two major challenges: thermal fatigue caused by hot and cold cycles and low system energy conversion efficiency.

[0004] (1) Collapse of tunnels caused by hot and cold cycles. The essence of compressed air energy storage is the conversion between electrical energy and molecular potential energy and thermal energy. The daily storage or release of electrical energy will cause the temperature of the stored gas to rise sharply to 140°C or drop sharply to -40°C, which will put the tunnel in a hot and cold cycle environment of different degrees and cause thermal fatigue damage. The thermal fatigue life of the surrounding rock closer to the tunnel is shorter. The design service life of the compressed air energy storage system in tunnels is mostly 30 to 50 years, but the thermal fatigue life of rock materials is generally less than 1 year.

[0005] (2) Low system energy conversion rate. The essence of compressed air energy storage is the conversion between electrical energy and molecular potential energy and thermal energy. Therefore, when releasing electrical energy, it is necessary to supplement the surface turbine for power generation. The volume and surface area of ​​the tunnel space are relatively large, and the heat exchange loss at the interface during the energy storage process is more obvious. A large amount of natural gas needs to be burned on the surface to supplement the turbine for heat generation. As a result, the total life cycle cost of tunnel compressed air energy storage is 15% to 45% higher than that of the same type of salt cavern compressed air energy storage system. Enterprises "cannot calculate the economic benefits".

[0006] Therefore, how to modify the tunnels to prevent them from being damaged by thermal fatigue and improve the energy conversion efficiency of the system when constructing a tunnel compressed air energy storage system has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0007] To address the technical problems existing in the prior art, this invention proposes a tunnel structure and modification method for compressed air energy storage, in order to improve the mechanical stability and airtightness of the tunnel.

[0008] On the one hand, to achieve the above objectives, the present invention provides a tunnel structure for compressed air energy storage, the tunnel structure comprising, from the outside to the inside:

[0009] Supported and reinforced surrounding rock mass;

[0010] A phase change concrete lining layer attached to the inner wall of the surrounding rock mass, and a sealing layer laid on the inner surface of the phase change concrete lining layer.

[0011] The phase change concrete lining layer stores and releases heat through the phase change process, maintaining the temperature stability of the surrounding rock mass and providing heat replenishment for the gas during the release phase.

[0012] Preferably, the cross-section of the tunnel structure is circular, and the radius of the circle is not less than the radius of the maximum loosening zone of the surrounding rock mass.

[0013] Preferably, the performance parameters and conditions to be satisfied by the phase change concrete lining layer include:

[0014] Compressive strength of phase change concrete: ;

[0015] In the formula, σ c σ0 is the compressive strength of phase change concrete, σ0 is the original rock stress, σ0 is the compressive strength of phase change concrete. g_max This is the maximum gas pressure when compressed air is used for energy storage.

[0016] Phase transition temperature of phase change concrete: ;

[0017] In the formula, T1 is the original rock temperature. Phase transition temperature;

[0018] The heat storage capacity of phase change concrete is greater than the heat release during the single compressed air energy storage and filling stage. The phase change enthalpy and construction thickness of phase change concrete are as follows:

[0019] ;

[0020] In the formula, ρL is the phase change enthalpy of the phase change concrete, L is the unit length, A is the inner surface area of ​​the laid phase change concrete, d is the thickness of the phase change concrete, n1 is the total amount of air under standard atmospheric pressure, n2 is the total amount of air under maximum gas pressure, P1 is the standard atmospheric pressure, P2 is the maximum gas pressure, V is the area of ​​the tunnel cross section after the phase change concrete is laid, and R is the ideal gas constant.

[0021] On the other hand, to achieve the above objectives, the present invention also provides a method for modifying tunnel structures, comprising:

[0022] Determine the extent of the loosened zone of the surrounding rock in the tunnel to be modified;

[0023] Using the outer boundary of the loosened ring as the outline, the tunnel to be modified is widened and shaped into a predetermined form;

[0024] The surrounding rock of the enlarged tunnel is supported and reinforced;

[0025] A phase change concrete lining layer is constructed on the surface of the surrounding rock after support.

[0026] The sealing layer is laid on the surface of the phase change concrete lining layer.

[0027] Preferably, the range of the loosened zone of the surrounding rock of the tunnel to be modified is determined as follows:

[0028] ;

[0029] In the formula, R p R is the radius of the loosened zone, r0 is the radius of the tunnel, σ0 is the original rock stress, and P i S represents the support resistance provided by the existing support to the roadway wall, S is the cohesion of the surrounding rock, and φ is the internal friction angle of the surrounding rock.

[0030] Preferably, the tunnel to be modified is widened and shaped into a predetermined form, including:

[0031] The tunnel is enlarged into a structure with a circular cross-section by using tunneling machines, blasting, or other mechanical methods.

[0032] Preferably, a phase change concrete lining layer is constructed on the surface of the supported surrounding rock, including:

[0033] Based on the predetermined operating conditions of the tunnel structure and the performance parameters of the phase change concrete lining layer, the appropriate phase change concrete material is selected or prepared for pouring.

[0034] Preferably, the sealing layer is a steel plate layer or a polymer composite material layer, and the permeability of the sealing layer material is less than 1×10⁻⁶. -20 m 2 .

[0035] Compared with the prior art, the present invention has the following advantages and technical effects:

[0036] (1) This invention reduces the risk of tunnel instability caused by loose surrounding rock during energy storage by identifying and removing loose surrounding rock in the tunnel; it reduces the risk of tunnel instability caused by tensile stress, shear stress and stress concentration by expanding the tunnel into a circular shape; and it temporarily stores the heat released during the charging stage of the compressed air energy storage system by pouring phase change concrete, which is then used for gas reheating during the venting stage. The temporary storage of heat not only keeps the temperature of the surrounding rock in the tunnel stable, avoiding the tunnel from being in a hot-cold cycle environment, but also increases the gas temperature during the venting stage by using the temporarily stored heat, indirectly reducing the amount of natural gas used for reheating combustion of the surface turbine and improving the system's energy conversion rate.

[0037] (2) By laying sealing materials, the present invention ensures that there is no air leakage during energy storage and that the system can operate normally. This process not only improves the mechanical stability and air tightness of the tunnel, ensuring that it can be used for compressed air energy storage systems, but also solves the problem of thermal fatigue during system operation from the root by pouring phase change concrete; and at the same time, it greatly improves the energy conversion efficiency of the system. Attached Figure Description

[0038] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0039] Figure 1 This is a schematic diagram of the cross-sectional structure of the tunnel before modification, according to an embodiment of the present invention.

[0040] Figure 2 This is a schematic diagram showing the relative construction positions of the tunnel cross-section after the modifications in steps one and two, according to an embodiment of the present invention.

[0041] Figure 3 This is a schematic diagram of the cross-sectional structure of the tunnel after step three modifications according to an embodiment of the present invention.

[0042] Figure 4 This is a schematic diagram of the cross-sectional structure of the tunnel after step four modifications according to an embodiment of the present invention.

[0043] Figure 5 This is a schematic diagram of the cross-sectional structure of the tunnel after step five of the present invention.

[0044] Figure 6 This is a schematic diagram illustrating the structure and operating principle of the modification process according to an embodiment of the present invention;

[0045] Among them, 1. gas storage space, 2. the expanded tunnel outline, 3. the supporting and reinforced surrounding rock, 4. phase change concrete, and 5. steel plate. Detailed Implementation

[0046] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0047] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0048] In this embodiment, the tunnel space refers to the underground tunnel or chamber space formed by underground artificial operations in coal mines, metal mines, non-metal mines, artificial tunnels, etc., which is either usable or abandoned. This technical solution aims to transform the tunnel space so that it will not experience thermal fatigue when used for compressed air energy storage, and that the energy conversion efficiency will be higher.

[0049] This embodiment proposes a tunnel structure for compressed air energy storage, the tunnel structure comprising, from the outside to the inside:

[0050] Supported and reinforced surrounding rock mass;

[0051] A phase change concrete lining layer attached to the inner wall of the surrounding rock mass, and a sealing layer laid on the inner surface of the phase change concrete lining layer.

[0052] The phase change concrete lining layer stores and releases heat through the phase change process, maintaining the temperature stability of the surrounding rock mass and providing heat replenishment for the gas during the release phase.

[0053] Specifically, common rock support methods such as anchor bolts, anchor cables, shotcrete, and U-shaped steel are used to reinforce the surrounding rock.

[0054] Furthermore, the cross-section of the tunnel structure is circular, and the radius of the circle is not less than the radius of the maximum loosening zone of the surrounding rock mass.

[0055] Furthermore, the performance parameters and conditions that the phase change concrete lining layer must meet include:

[0056] Compressive strength of phase change concrete: ;

[0057] In the formula, σ c σ0 is the compressive strength of phase change concrete, σ0 is the original rock stress, σ0 is the compressive strength of phase change concrete. g_max This is the maximum gas pressure when compressed air is used for energy storage.

[0058] Phase transition temperature of phase change concrete: ;

[0059] In the formula, T1 is the original rock temperature. Phase transition temperature;

[0060] The heat storage capacity of phase change concrete is greater than the heat release during the single compressed air energy storage and filling stage. The phase change enthalpy and construction thickness of phase change concrete are as follows:

[0061] ;

[0062] In the formula, ρL is the phase change enthalpy of the phase change concrete, L is the unit length, A is the inner surface area of ​​the laid phase change concrete, d is the thickness of the phase change concrete, n1 is the total amount of air under standard atmospheric pressure, n2 is the total amount of air under maximum gas pressure, P1 is the standard atmospheric pressure, P2 is the maximum gas pressure, V is the area of ​​the tunnel cross section after the phase change concrete is laid, and R is the ideal gas constant.

[0063] like Figure 6 The structural and operational principle diagrams for the modified process.

[0064] This embodiment also provides a method for modifying tunnel structures, including:

[0065] Step 1: Determine the extent of the loosened zone of the surrounding rock in the tunnel to be modified;

[0066] Step 2: Using the outer boundary of the loosened ring as the outline, widen and trim the tunnel to be modified into the predetermined shape;

[0067] Step 3: Reinforce and support the surrounding rock of the enlarged tunnel;

[0068] Step 4: Construct a phase change concrete lining layer on the surface of the supported surrounding rock.

[0069] Step 5: Lay the sealing layer on the surface of the phase change concrete lining layer.

[0070] Furthermore, in step one, the range of the loosened zone of the surrounding rock of the tunnel to be modified is determined as follows:

[0071] ;

[0072] In the formula, R p R is the radius of the loosened zone, r0 is the radius of the tunnel, σ0 is the original rock stress, and P i S represents the support resistance provided by the existing support to the roadway wall, S is the cohesion of the surrounding rock, and φ is the internal friction angle of the surrounding rock.

[0073] Then, one or more of the following methods—seismic wave method, acoustic wave method, resistivity method, electromagnetic method, and core drilling—are used to verify the calculation results.

[0074] The purpose of step one is to determine the extent of the plastic zone in the original tunnel to prevent rock instability during subsequent compressed air energy storage operations. In this embodiment, the tunnel used for compressed air energy storage has long served mining operations and pedestrian traffic, resulting in a large area of ​​developed plastic zones in the surrounding rock. These plastic zones exhibit poor mechanical and thermal properties; if not identified and removed, the loosened surrounding rock will directly disrupt the stability of the compressed air system.

[0075] Furthermore, in step two, the tunnel to be modified is widened and shaped into a predetermined form, including:

[0076] The tunnel is enlarged into a structure with a circular cross-section by using tunneling machines, blasting, or other mechanical methods.

[0077] Specifically, the purpose of step two is to ensure that the tunnel is subjected to uniform stress during compressed air energy storage, thereby reducing the risk of surrounding rock instability. Common tunnel spaces are often arched or rectangular; directly using them for compressed air energy storage will generate varying degrees of shear and tensile stress, leading to stress concentration and threatening tunnel stability. Expanding the tunnel into a circular shape ensures that the surrounding rock is subjected to only the same magnitude of circumferential compressive stress, thus minimizing the risk of tunnel instability.

[0078] Furthermore, the purpose of step three is to reinforce the expanded tunnel to ensure that the surrounding rock of the tunnel remains stable and does not collapse during the construction of steps four and five.

[0079] The specific operation method for step three is as follows: reinforce the surrounding rock using common support methods for surrounding rock such as anchor bolts, anchor cables, shotcrete, and U-shaped steel.

[0080] Furthermore, a phase change concrete lining layer is constructed on the surface of the supported surrounding rock, including:

[0081] Based on the predetermined operating conditions of the tunnel structure and the performance parameters of the phase change concrete lining layer, the appropriate phase change concrete material is selected or prepared for pouring.

[0082] Specifically, the purpose of step four is to pour a phase change concrete layer to store heat, preventing thermal fatigue in the tunnel and improving the system's energy conversion rate. The heat released during the compressed air energy storage system's charging phase is temporarily stored and used for gas reheating during the venting phase. This temporary heat storage not only keeps the temperature of the surrounding rock in the tunnel stable, preventing the tunnel from being in a hot-cold cycle environment, but also, by using the temporarily stored heat to increase the gas temperature during the venting phase, indirectly reduces the amount of natural gas used for reheating combustion in the surface turbine, thus improving the system's energy conversion rate.

[0083] The specific operation method for step four is as follows: install steel bars in the tunnel wall and pour phase change concrete with specified compressive strength, phase change temperature, phase change enthalpy, and thickness.

[0084] To ensure that the phase change concrete does not suffer mechanical damage during the operation of the compressed air energy storage system in the tunnel, the compressive strength of the phase change concrete must meet the following formula:

[0085] ;

[0086] In the formula, σ c σ0 is the compressive strength of phase change concrete, σ0 is the original rock stress, σ0 is the compressive strength of phase change concrete. g_max This is the maximum gas pressure when compressed air is used for energy storage.

[0087] To ensure that the phase change concrete can store heat during the operation of the compressed air energy storage system in the tunnel, the phase change temperature of the phase change concrete in step four must satisfy the following formula:

[0088]

[0089] In the formula, T1 is the original rock temperature. Phase transition temperature;

[0090] To ensure that the phase change concrete can store all the heat released during the air filling stage of the compressed air energy storage system in the tunnel, the phase change enthalpy and construction thickness of the phase change concrete in step four must meet the following formula:

[0091]

[0092] In the formula, ρL is the phase change enthalpy of the phase change concrete, L is the unit length, A is the inner surface area of ​​the laid phase change concrete, d is the thickness of the phase change concrete, n1 is the total amount of air under standard atmospheric pressure, n2 is the total amount of air under maximum gas pressure, P1 is the standard atmospheric pressure, P2 is the maximum gas pressure, V is the area of ​​the tunnel cross section after the phase change concrete is laid, and R is the ideal gas constant.

[0093] Furthermore, the purpose of step five is to ensure that the tunnel does not leak air during compressed air energy storage.

[0094] The specific operation method for step five is as follows: A sealing layer is laid on the outside of the phase change concrete. The sealing layer is a steel plate layer or a polymer composite material layer, and the permeability of the sealing layer material is less than 1×10⁻⁶. -20 m 2 .

[0095] To more clearly illustrate the technical solution of the present invention, specific embodiments are provided below for description:

[0096] A certain tunnel is a development roadway for closing a coal mine. The roadway has a rectangular cross-section with a length of 5200mm and a height of 3500mm. Figure 1 As shown. The tunnel is 300m deep, with an original rock temperature of 15℃ and an original rock stress of 7.5MPa. The surrounding rock is sandstone with an internal friction angle of 40° and a cohesion of 1.788MPa. The existing support resistance of the tunnel wall is taken as 0.445MPa. The maximum gas pressure of the compressed air energy storage system in the tunnel is 10MPa.

[0097] The appropriate modification process for the aforementioned tunnels used in compressed air energy storage, enabling them to be used in compressed air energy storage systems without tunnel thermal fatigue and with higher energy conversion efficiency, includes the following steps:

[0098] Step 1: Substitute the working conditions of the tunnel into the following formula to calculate the range of the loosened zone of the surrounding rock, where r0 is the radius of the circumscribed circle of the rectangular tunnel cross section.

[0099] ;

[0100] R p The calculated radius of the loosening zone is 3.5m.

[0101] Core samples were drilled from both sides of the tunnel and from the upper part. The core samples were found to be continuous and stable with no obvious cracks after depths of 3.3m, 3.4m, and 3.3m, respectively. This proves that the calculation of the loosened zone radius was correct.

[0102] This step aims to identify the extent of the surrounding rock in the tunnels that has poor mechanical and thermal properties due to long-term operation.

[0103] Step 2: Using the centroid of the rectangular tunnel section as the center, a tunneling machine is used to expand the rectangular section, which is 5200mm long and 3500mm high, into a circle with a radius of 3.5m. The modified tunnel is as follows: Figure 2 As shown, it includes a gas storage space 1 and an expanded tunnel outline 2.

[0104] This step aims to remove the surrounding rock of the tunnel with poor mechanical and thermal properties, and ensure that the surrounding rock is subjected to only the same circumferential compressive stress, thereby minimizing the risk of mechanical instability of the tunnel during energy storage.

[0105] Step 3: Reinforce the roadway using a combination of anchor bolts, anchor cables, metal mesh, and shotcrete. The anchor bolts are 3.5m MG500 type, spaced 2000mm apart, with a row spacing of 1000mm; the anchor cables are 12m MS15-1 / 1860 type, spaced 2000mm apart, with a row spacing of 2000mm; the metal mesh is 50×50mm DM50 type. The modified roadway is as follows: Figure 3 As shown, this includes the surrounding rock 3, which is supported and reinforced.

[0106] This step aims to stabilize the expanded tunnel and ensure that it does not collapse during the construction of steps four and five.

[0107] Step 4: To ensure that the phase change concrete does not suffer mechanical damage during the operation of the compressed air energy storage system in the tunnel, the compressive strength threshold of the phase change concrete is calculated using the following formula. It can be seen that the compressive strength of the phase change concrete needs to be greater than 17.5 MPa.

[0108] ;

[0109] To ensure that the phase change concrete can store heat during the operation of the compressed air energy storage system in the tunnel, the phase change temperature of the phase change concrete is calculated using the following formula, which shows that the phase change temperature of the phase change concrete needs to be greater than 15℃.

[0110] ;

[0111] To ensure that the phase change concrete can store all the heat released during the air filling stage of the compressed air energy storage system in the tunnel, the phase change enthalpy and construction thickness of the phase change concrete are calculated using the following formula. It can be seen that when the construction thickness of the phase change concrete is 0.5m, the volumetric phase change enthalpy needs to be greater than 136.4 MJ / m³. 3 .

[0112] ;

[0113] Based on the above requirements for compressive strength, phase transition temperature, phase transition enthalpy, and construction thickness of phase change concrete, C30 cement was selected as the cementitious material, expanded graphite as the porous aggregate, and paraffin wax as the phase change material. An appropriate amount of aggregate was added to prepare a concrete with a compressive strength of 30 MPa, a phase transition temperature of 25℃, and a volumetric phase transition enthalpy of 200 MJ / m³. 3 The phase change concrete is first reinforced with steel bars in the tunnel wall, and then a 0.5m thick layer of the aforementioned phase change concrete material is poured inside the steel bars. The modified tunnel is as follows: Figure 4 As shown, this includes phase change concrete 4.

[0114] This step aims to store heat through phase change concrete to prevent thermal fatigue in the tunnel and improve the system's energy conversion efficiency. The heat released during the charging phase of the compressed air energy storage system is temporarily stored and used for gas reheating during the venting phase. This temporary heat storage not only keeps the temperature of the surrounding rock in the tunnel stable, preventing the tunnel from being in a hot-cold cycle environment, but also indirectly reduces the amount of natural gas needed for reheating combustion in the surface turbine, thus improving the system's energy conversion efficiency.

[0115] Step 5: Lay a 3mm thick steel plate over the solidified phase change concrete. The modified tunnel will look like this. Figure 5 As shown, this includes steel plate 5.

[0116] This technical solution can temporarily store the heat released during the charging phase of a compressed air energy storage system and use it for gas reheating during the venting phase. This temporary heat storage not only keeps the temperature of the surrounding rock in the tunnel stable, preventing thermal fatigue damage, but also increases the gas temperature during the venting phase, indirectly reducing the amount of natural gas needed for reheating the surface turbine and improving the system's energy conversion rate.

[0117] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A tunnel structure for compressed air energy storage, characterized in that, The tunnel structure, from the outside to the inside, includes: Supported and reinforced surrounding rock mass; A phase change concrete lining layer attached to the inner wall of the surrounding rock mass, and a sealing layer laid on the inner surface of the phase change concrete lining layer. The phase change concrete lining layer stores and releases heat through the phase change process, maintaining the temperature stability of the surrounding rock mass and providing heat replenishment for the gas during the release phase.

2. The tunnel structure for compressed air energy storage according to claim 1, characterized in that, The cross-section of the tunnel structure is circular, and the radius of the circle is not less than the radius of the maximum loosening zone of the surrounding rock mass.

3. The tunnel structure for compressed air energy storage according to claim 1, characterized in that, The performance parameters and conditions that the phase change concrete lining layer must meet include: Compressive strength of phase change concrete: ; In the formula, σ c σ0 is the compressive strength of phase change concrete, σ0 is the original rock stress, σ0 is the compressive strength of phase change concrete. g_max This is the maximum gas pressure when compressed air is used for energy storage. Phase transition temperature of phase change concrete: ; In the formula, T1 is the original rock temperature. Phase transition temperature; The heat storage capacity of phase change concrete is greater than the heat release during the single compressed air energy storage and filling stage. The phase change enthalpy and construction thickness of phase change concrete are as follows: ； In the formula, ρL is the phase change enthalpy of the phase change concrete, L is the unit length, A is the inner surface area of ​​the laid phase change concrete, d is the thickness of the phase change concrete, n1 is the total amount of air under standard atmospheric pressure, n2 is the total amount of air under maximum gas pressure, P1 is the standard atmospheric pressure, P2 is the maximum gas pressure, V is the area of ​​the tunnel cross section after the phase change concrete is laid, and R is the ideal gas constant.

4. A method for modifying the tunnel structure described in any one of claims 1-3, characterized in that, include: Determine the extent of the loosened zone of the surrounding rock in the tunnel to be modified; Using the outer boundary of the loosened ring as the outline, the tunnel to be modified is widened and shaped into a predetermined form; The surrounding rock of the enlarged tunnel is supported and reinforced; A phase change concrete lining layer is constructed on the surface of the surrounding rock after support. The sealing layer is laid on the surface of the phase change concrete lining layer.

5. The modification method according to claim 4, characterized in that, The range of the loosened zone of the surrounding rock in the tunnel to be modified is determined as follows: ； In the formula, R p R is the radius of the loosened zone, r0 is the radius of the tunnel, σ0 is the original rock stress, and P i S represents the support resistance provided by the existing support to the roadway wall, S is the cohesion of the surrounding rock, and φ is the internal friction angle of the surrounding rock.

6. The modification method according to claim 4, characterized in that, The tunnel to be modified will be widened and reshaped to the predetermined form, including: The tunnel is enlarged into a structure with a circular cross-section by using tunneling machines, blasting, or other mechanical methods.

7. The modification method according to claim 4, characterized in that, A phase change concrete lining layer is constructed on the surface of the supported surrounding rock, including: Based on the predetermined operating conditions of the tunnel structure and the performance parameters of the phase change concrete lining layer, the appropriate phase change concrete material is selected or prepared for pouring.

8. The modification method according to claim 4, characterized in that, The sealing layer is a steel plate layer or a polymer composite material layer, and the permeability of the sealing layer material is less than 1×10⁻⁶. -20 m 2 .

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