Energy tunnel structure system based on gradient type heat conduction buffer layer

Abstract

The invention discloses an energy tunnel structure system based on a gradient type heat conduction buffer layer. Comprising surrounding rock and a lining constructed in the surrounding rock, the buffer layer is embedded between the surrounding rock and the lining of the tunnel, and the steel fiber content and porosity of the buffer layer are gradually changed; the heat exchange pipe is embedded in the lining; the distributed optical fiber sensor is pre-buried in the buffer layer and monitors thermal stress change data in real time; and the phase deformation structure is arranged between the buffer layer and the lining and is used for absorbing and sensing temperature and thermal stress so as to carry out deformation adaptation on the lining under the influence of temperature and vibration. The technical problem that an existing energy tunnel causes circumferential penetrating cracks due to the fact that tensile stress in a lining is concentrated under the temperature circulation effect is solved, thermal stress mutation at the surrounding rock-lining interface is effectively reduced, and the stability of a structural temperature field is maintained while the efficient geothermal collection efficiency is ensured; the anti-cracking performance and long-term stability of the energy tunnel structure are improved, and the service life of the structure is prolonged.

Description

TECHNICAL FIELD

[0001] The present application relates to an energy tunnel structure system based on a steel fiber reinforced foamed concrete buffer layer, belonging to the technical field of underground engineering and comprehensive utilization of geothermal energy. BACKGROUND

[0002] The energy tunnel realizes the collection and utilization of geothermal energy by embedding heat exchange pipes in the tunnel lining and connecting them into a closed pipe system. The system usually uses water as the heat transfer medium, and the fluid circulation is driven by a water pump for heat exchange. This new type of tunnel structure not only has the bearing and protection functions of traditional tunnels, but also realizes the composite functions of energy transmission, heat dissipation regulation and heat energy storage. As a key technology for the green transformation of tunnel engineering, the popularization and application of energy tunnel provides important support for building an efficient and sustainable energy system.

[0003] The practice of existing demonstration projects shows that the homogeneous concrete or double-layer structure lining widely used at present has the following technical defects: the thermal expansion performance of the lining material (thermal expansion coefficient 10-14×10 -6 / ℃) and the surrounding rock medium (thermal expansion coefficient 4-7×10 -6 / ℃) is significantly different. Under low temperature working conditions, the shrinkage deformation of the concrete lining is constrained by the surrounding rock, resulting in tensile stress concentration phenomenon inside the structure. When the tensile strain exceeds 1.0×10 -4 critical value or the tensile stress exceeds the tensile strength of C30 concrete (2.01 MPa), it is easy to cause circumferential through cracks, which seriously affects the overall stability and waterproof performance of the structure.

[0004] In view of the above technical problems, the existing solutions mainly include: 1. The fiber-rubber composite material disclosed in patent CN101842210A realizes stress redistribution through the synergistic effect of the viscoelastic energy dissipation characteristics of the rubber matrix and the fiber reinforced phase; 2. The aluminum-based sandwich buffer plate structure recorded in patent CN105398123A uses a sandwich structure combined with the multi-stage energy dissipation mechanism of composite foam aluminum to improve the impact resistance; 3. Foam concrete and EPS concrete buffer materials commonly used in engineering; 4. Large-diameter spherical SAP brittle buffer material developed by Wuhan Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, which realizes energy absorption through the volume compression mechanism of its honeycomb structure and improves the water seepage problem.

[0005] However, the existing technical solutions mainly focus on the mechanical strength, impermeability and brittleness of the material, and there are obvious deficiencies in the regulation of key thermal physical parameters such as thermal expansion coefficient and thermal conductivity. SUMMARY

[0006] The purpose of the present application is to overcome the deficiencies in the prior art, solve the deficiencies and problems in the background art, and provide an energy tunnel thermal stress buffer layer based on steel fiber reinforced foamed concrete, and an energy tunnel structure system based on a gradient heat conduction buffer layer, which solves the technical problem of circumferential through cracks caused by internal tensile stress concentration of the lining under the action of temperature cycling in the existing energy tunnel.

[0007] Based on the above technical status, the present application proposes to develop a new buffer layer material with gradient heat conduction characteristics, which significantly improves the safety and reliability of the energy tunnel structure and the service life by optimizing the thermal stress buffering performance of the material. The technical scheme focuses on solving the core problem of insufficient thermal performance regulation of existing buffer layer materials, and provides a more perfect thermal coupling solution for energy tunnel systems.

[0008] The present application adopts the optimization combination and structural design innovation of multi-layer composite materials to construct a structural system with high efficient heat conduction characteristics, and effectively suppresses the thermal stress concentration effect.

[0009] In order to achieve the purpose of the present application, the technical scheme adopted is as follows:

[0010] I. An energy tunnel structure system based on a gradient heat conduction buffer layer, comprising surrounding rock and a lining constructed in the surrounding rock:

[0011] The buffer layer is embedded between the surrounding rock and the lining of the tunnel, has pores and contains steel fibers in the interior, and the content of the steel fibers and the porosity gradually change from the side close to the surrounding rock to the side close to the lining;

[0012] The heat exchange pipe is embedded and arranged in the interior of the lining;

[0013] The distributed optical fiber sensor is pre-buried in the buffer layer and is used for monitoring the thermal stress change data of temperature and strain in real time and feeding back to the central control system;

[0014] The phase deformation structure is arranged between the buffer layer and the lining and is used for absorbing and sensing temperature and stress to adapt to the influence of temperature and vibration on the lining, dynamically adjusts the constraint state of the lining through the expansion and contraction of the phase deformation structure, converts the concentrated thermal stress into mechanical displacement dissipation, and triggers rigid locking when the ground temperature is abnormal to form over-temperature protection, thereby significantly reducing the tensile stress peak value in the interior of the lining and ensuring the integrity, waterproofness and long-term service stability of the tunnel structure.

[0015] The content of the steel fibers in the buffer layer decreases from the side close to the surrounding rock to the side close to the lining, and the porosity increases from the side close to the surrounding rock to the side close to the lining.

[0016] The phase deformation structure is arranged on the outer surface of the lining and comprises:

[0017] The ring-shaped limiting track frame is fixed to the outer side surface of the lining.

[0018] The at least one heat-conducting sliding block is slidably mounted on the limiting track frame and is positionally locked by the phase-change limiting block, so as to dynamically adapt to thermal stress and adjust the deformation distribution.

[0019] The phase-change limiting block is arranged on the heat-conducting sliding block and is used for sensing temperature to limit and lock the position of the heat-conducting sliding block on the limiting track frame.

[0020] The elastic damping gasket is arranged between the limiting track frame and the outer side surface of the lining and is used for buffering and heat insulation.

[0021] The limiting track frame is a ring-shaped frame structure. The limiting track frame serves as a track for the heat-conducting sliding block to slide. The limiting track frame is indirectly connected to the outer side surface of the lining through the elastic damping gasket at four corners. The limiting track frame does not contact the outer side surface of the lining except for the four corner portions, and a gap is maintained between the limiting track frame and the outer side surface of the lining.

[0022] The plurality of heat-conducting moving assemblies each include one heat-conducting sliding block and one phase-change limiting block arranged on each side of the heat-conducting sliding block. The heat-conducting sliding block is slidably embedded in a sliding groove provided on the limiting track frame and moves along the sliding groove. The phase-change limiting blocks on the two sides of the heat-conducting sliding block are fixed to the heat-conducting sliding block at one end and are connected to the limiting track frame at the other end.

[0023] The buffer layer is made of steel fiber reinforced foamed concrete and is mainly composed of steel fiber and reinforced foamed concrete.

[0024] The composition materials and their mass percentages of the steel fiber reinforced foamed concrete of the buffer layer are as follows: cement 30%–50%, fly ash 20%–40%, fine aggregate 10%–20%, foaming agent 0.5%–2%, and steel fiber 1%–3%.

[0025] The length of the steel fiber is 5–20 mm, and the diameter is 0.1–0.3 mm.

[0026] The foaming agent is a composite synthetic surfactant.

[0027] The buffer layer is prepared according to the following steps:

[0028] S1, dry materials such as steel fiber, cement, fine aggregate, and fly ash are put into a mixer according to mass ratio, dry mixing for 1–2 minutes to ensure that the steel fiber is preliminarily dispersed, and a cement slurry is obtained.

[0029] S2, separately prepare foaming foam in a foaming machine with a foaming agent, foaming time 1-2 minutes, foam diameter 1-3 mm, then add the foaming foam to the cement slurry, stir for 1-2 minutes to mix evenly, to make a steel fiber reinforced foamed concrete with a steel fiber content and a porosity;

[0030] S3, repeat the above steps S1-S2 to make steel fiber reinforced foamed concrete with different steel fiber contents and different porosities and lay them on the lining surface in layers, so that the lining surface finally forms a plurality of layers of steel fiber reinforced foamed concrete with increasing steel fiber content and decreasing porosity.

[0031] The total mixing time of the preparation is prolonged by 1-2 minutes (total time about 5-7 minutes) compared with ordinary foamed concrete, avoiding excessive stirring to cause foam rupture.

[0032] The lining is mainly composed of a plurality of pipe segments connected by mortise and tenon structure.

[0033] The heat exchange pipe is uniformly arranged in the lining in S shape / serpentine shape; each pipe segment of the lining is provided with a respective heat exchange pipe, the heat exchange pipes of adjacent pipe segments are connected in butt joint and expanded joint, and the elastic deformation of the pipe end with reduced diameter at one end is caused by hydraulic expansion, and the interference fit with the pipe end at the other end is formed.

[0034] The lining is provided with a plurality of distributed optical fiber sensors, and the plurality of distributed optical fiber sensors form a distributed optical fiber sensor network along the horizontal direction of the tunnel portal at a spacing of not more than 0.5 m, continuously collect temperature and strain data and transmit them to the central control system for analysis and display processing.

[0035] The present application realizes the gradient transition matching of the thermal expansion coefficient and the deformation modulus of the buffer layer material by adopting the innovative design of the steel fiber reinforced foamed concrete buffer layer, effectively reduces the thermal stress mutation at the surrounding rock-lining interface. The buffer layer material has optimized high thermal conductivity characteristics, which ensures efficient heat collection efficiency while maintaining the stability of the structural temperature field.

[0036] The present application integrates a dynamic adjustment mechanism composed of a limiting rail frame and a heat-conducting sliding block, cooperates with the synergistic effect of an elastic damping gasket, realizes the dynamic release of thermal stress and the efficient conduction of heat. At the same time, through the pre-embedded distributed optical fiber sensor network, the change characteristics of the structural temperature field and the strain field are monitored in real time, providing data support for the structural health state evaluation.

[0037] The implementation of the present application improves the crack resistance and long-term stability of the energy tunnel structure, prolongs the service life of the structure, and provides a reliable technical solution for the safe and cooperative use of geothermal energy and underground engineering.

[0038] The beneficial effects of the present application are:

[0039] 1. Coefficient of thermal expansion gradient matching: By designing a gradient heat-conducting material, the coefficient of thermal expansion gradually transitions from low to high from the surrounding rock to the lining, which can achieve coordinated matching of the thermal conductivity between the buffer layer and the surrounding rock and the lining, thereby effectively reducing the stress discontinuity at the interface and avoiding circumferential cracks caused by thermal expansion differences.

[0040] 2. Deformation modulus and thermal expansion coefficient are optimized: The gradient transition of the deformation modulus alleviates the stiffness difference between the lining and the surrounding rock, reducing the risk of cracking; by gradient regulating the mass fraction of steel fibers, the deformation modulus and thermal parameters are optimized. The gradient structure can effectively alleviate the stiffness difference between the lining and the surrounding rock, significantly reducing the risk of structural cracking.

[0041] 3. High thermal conductivity takes into account efficient geothermal collection and temperature stability: By using high-thermal-conductivity buffer materials, heat exchange efficiency can be significantly improved, peak temperature can be reduced, thermal gradient can be reduced, heat distribution can be improved, and the risk of local overheating can be reduced.

[0042] 4. Dynamic thermal stress adjustment structure: The cooperative design of the limiting rail frame and the heat-conducting sliding block realizes dynamic stress adjustment of the energy tunnel under thermal expansion differences through elastic damping gaskets and temperature-triggered locking, which not only guarantees the stability of the structure, but also improves the thermal management efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 is a decomposition view of the energy tunnel buffer layer;

[0044] Figure 2 is a side view schematic diagram of the energy tunnel buffer layer;

[0045] Figure 3 is a heat exchange pipe connection schematic diagram of the energy tunnel buffer layer;

[0046] Figure 4 is a single-ring component connection structure schematic diagram of the energy tunnel buffer layer;

[0047] Figure 5 is a mortise and tenon joint connection diagram of the energy tunnel buffer layer multi-ring component;

[0048] Figure 6 is a state process diagram of the phase change deformation structure deformed self-adaptive motion affected by the thrust generated by the lining thermal expansion difference

[0049] Figure 7 is a state process diagram of the phase change deformation structure deformed self-adaptive motion affected by the thrust generated by the lining thermal expansion difference

[0050] In the figure, 1 is the buffer layer, 2 is the heat exchange pipe, 3 is the limiting track frame, 4 is the heat-conducting slider, 5 is the phase change limiting block, 6 is the steel fiber reinforced foamed concrete, 7 is the elastic damping pad, 8 is the distributed optical fiber sensor, 9 is the lining, 10 is the surrounding rock, 11 is the steel fiber, 12 is the tenon, 13 is the mortise and tenon, and 14 is the pipe segment. Detailed Implementation

[0051] The present invention will be further described below with reference to embodiments. The description of the embodiments below is only for the purpose of helping to understand the present invention. It should be noted that those skilled in the art can make several modifications to the present invention without departing from the principle of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0052] like Figure 1 As shown, the energy tunnel specifically implemented includes surrounding rock 10 of soil and lining 9 constructed within the surrounding rock 10, and:

[0053] The buffer layer 1 is embedded between the surrounding rock 10 and the lining 9 of the tunnel. It has pores and steel fibers 11 inside, and the content of steel fibers 11 and the porosity inside it gradually change from the side closer to the surrounding rock 10 to the side closer to the lining 9. The thermal conductivity and deformation modulus are controlled, that is, the thermal conductivity and expansion coefficient are controlled.

[0054] The heat exchange tubes 2 are arranged in a ring and are embedded inside the lining 9;

[0055] Distributed fiber optic sensor 8, embedded in buffer layer 1, is used to monitor the thermal stress change data of temperature and strain in real time and feed it back to the external central control system for observation.

[0056] A phase-deformation structure is arranged between the buffer layer 1 and the lining 9, specifically on the lining 9. It works in conjunction with the thermally conductive slider 4 and the limiting connection frame 3 to absorb the sensed temperature and thermal stress, thereby adapting the lining 9 to deformation caused by temperature and vibration. The solid-liquid phase transformation of the low-melting alloy at a specific temperature drives the mechanical structure to achieve a state transition from "free sliding to rigid locking". It converts concentrated thermal stress into frictional energy dissipation, ultimately reducing the peak tensile stress inside the lining by more than 60%, significantly suppressing circumferential cracks and improving the seismic resistance and long-term stability of the structure.

[0057] The content of steel fiber 11 in the buffer layer 1 decreases from the side closer to the surrounding rock 10 to the side closer to the lining 9, and the porosity increases from the side closer to the surrounding rock 10 to the side closer to the lining 9, specifically from 15% to 30%.

[0058] This results in a higher content of steel fiber 11 near the surrounding rock 10 to improve thermal conductivity, while a high porosity of 30% is maintained near the lining 9 to enhance the ability to absorb thermal expansion strain.

[0059] As shown in Figure 2 The phase change deformation structure is arranged on the outer surface of the lining 9, including a limiting track frame 3, a heat-conducting sliding block 4, a phase change limiting block 5, and an elastic damping gasket 7:

[0060] The limiting track frame 3 is annular and is fixed to the outer surface of the lining 9 segment of the tunnel, and the inner side is provided with the elastic damping gasket 7.

[0061] The at least one heat-conducting sliding block 4 is slidably mounted on the limiting track frame 3 and is position-locked by the phase change limiting block 5, and is used to dynamically adapt to thermal stress and adjust the deformation distribution.

[0062] The phase change limiting block 5 is arranged on the heat-conducting sliding block 4, and each heat-conducting sliding block 4 is provided with a phase change limiting block 5, which is used to sense the temperature and limit and lock the position of the heat-conducting sliding block 4 on the limiting track frame 3.

[0063] The elastic damping gasket 7 is arranged between the limiting track frame 3 and the outer surface of the lining 9, and is used to buffer and insulate heat.

[0064] The limiting track frame 3 is an annular frame structure, the limiting track frame 3 serves as a track for the heat-conducting sliding block 4 to slide, the limiting track frame 3 is indirectly connected to the outer surface of the lining 9 through the elastic damping gasket 7 at four corners, and the limiting track frame 3 does not contact the outer surface of the lining 9 except for the four corner portions, and a gap is maintained between the limiting track frame 3 and the outer surface of the lining 9.

[0065] The heat-conducting mobile assembly includes a plurality of heat-conducting sliding blocks 4 and phase change limiting blocks 5, each heat-conducting mobile assembly includes one heat-conducting sliding block 4 and one phase change limiting block 5 located on each side of the heat-conducting sliding block 4, the heat-conducting sliding block 4 is slidably embedded in the sliding groove provided on the limiting track frame 3 and moves along the sliding groove, and the phase change limiting blocks 5 on both sides of the heat-conducting sliding block 4 are fixed to one end of the heat-conducting sliding block 4 and connected to the limiting track frame 3 at the other end.

[0066] The material of the elastic damping gasket 7 is rubber composite material, the elastic modulus is 0.5-1.0 MPa, the thermal conductivity is ≥0.5 W / (m·k), and the elastic damping gasket 7 has the dual functions of absorbing assembly impact and conducting heat.

[0067] The sliding resistance of the heat-conducting sliding block 4 is ≤50 N, and the sliding stroke is designed according to the segment expansion and contraction amount.

[0068] The heat-conducting sliding block 4 is made of aluminum alloy material, and the phase change limiting block 5 is made of low-melting alloy phase change material.

[0069] The trigger temperature of the phase change limiting block 5 is 60℃. When the temperature is greater than or equal to 60℃, the phase change limiting block 5 expands to lock the movement of the heat-conducting sliding block 4 on the limiting rail frame 3, and the displacement is terminated. The specific design is to fix the phase change limiting block 5 in the clamping groove opposite to the side surface of the heat-conducting sliding block 4. When the phase change material expands due to heating, the wedge-shaped push rod is horizontally inserted into the sliding block clamping groove, forming a mechanical interlocking arrangement and connection relationship, which ensures that the locking becomes tighter under external force after locking, and is not automatically released when the temperature is below 45℃, thereby reliably achieving displacement termination.

[0070] When the temperature is greater than or equal to 60℃, i.e. the temperature is greater than or equal to 60℃, the phase change limiting block 5 expands to lock the movement of the heat-conducting sliding block 4 on the limiting rail frame 3, so that the heat-conducting sliding block 4 cannot move on the limiting rail frame 3;

[0071] When the temperature is less than 60℃, i.e. the temperature is less than 60℃, the phase change limiting block 5 does not expand, and cannot lock the movement of the heat-conducting sliding block 4 on the limiting rail frame 3, so that the heat-conducting sliding block 4 can move freely on the limiting rail frame 3.

[0072] In a specific implementation, the buffer layer 1 is made of steel fiber reinforced foamed concrete 6, which is mainly composed of steel fibers 11 and reinforced foamed concrete 6. The composition of the steel fiber reinforced foamed concrete 6 of the buffer layer 1 and the mass percentage thereof are as follows: cement 30%-50%, fly ash 20%-40%, fine aggregate 10%-20%, foaming agent 0.5%-2%, and steel fiber 1%-3%.

[0073] The length of the steel fiber 11 is 5-20mm, and the diameter is 0.1-0.3mm.

[0074] The buffer layer 1 is prepared according to the following steps:

[0075] S1, the dry materials such as steel fiber, cement, fine aggregate and fly ash are put into the mixer according to the mass ratio, and dry mixing is carried out for 1-2 minutes to ensure that the steel fiber is preliminarily dispersed, and a cement slurry is obtained;

[0076] S2, the foaming agent is used to prepare foaming foam in the foaming machine, the foaming time is 1-2 minutes, the foam diameter is 1-3mm, and then the foaming foam is slowly added into the cement slurry, and stirring is carried out for 1-2 minutes to uniformly mix, so as to prepare a steel fiber reinforced foamed concrete with a steel fiber content and a porosity;

[0077] S3, the above steps S1-S2 are repeated to prepare steel fiber reinforced foamed concretes with different steel fiber contents and different porosities, and the steel fiber reinforced foamed concretes are sequentially layered and laid on the surface of the lining 9, so that a multi-layer steel fiber reinforced foamed concrete layer with gradually increasing steel fiber content and gradually decreasing porosity outward is finally formed on the surface of the lining 9.

[0078] The total stirring time of the preparation described above is prolonged by 1-2 minutes than the general foamed concrete, and the total time is about 5-7 minutes, so as to avoid excessive stirring to cause the foam to break.

[0079] The lining 9 is mainly composed of a plurality of segments 14 connected in sequence along the direction of the energy tunnel and perpendicular to the direction of the energy tunnel.

[0080] As shown in the figure, the lining 9 is divided into a plurality of segments 14 along the direction perpendicular to the energy tunnel, and the left and right adjacent segments 14 are connected by the mortise and tenon structure through the convex and concave tenon 12 and the mortise 13. Figure 4 As shown in the figure, the lining 9 is divided into a plurality of segments 14 along the direction perpendicular to the energy tunnel, and the left and right adjacent segments 14 are connected by the mortise and tenon structure through the convex and concave tenon 12 and the mortise 13.

[0081] As shown in the figure, the lining 9 is divided into a plurality of segments 14 along the direction perpendicular to the energy tunnel, and the left and right adjacent segments 14 are connected by the mortise and tenon structure through the convex and concave tenon 12 and the mortise 13. Figure 5 As shown in the figure, the lining 9 is divided into a plurality of segments 14 along the direction perpendicular to the energy tunnel, and the left and right adjacent segments 14 are connected by the mortise and tenon structure through the convex and concave tenon 12 and the mortise 13.

[0082] The heat exchange pipe 2 can adopt a plastic pipe, for example, a PE pipe.

[0083] The heat exchange pipe 2 is uniformly distributed inside the lining 9. More specifically, the heat exchange pipe 2 is arranged in an S shape / serpentine shape inside the lining 9.

[0084] As shown in the figure, the lining 9 is divided into a plurality of segments 14 along the direction perpendicular to the energy tunnel, and the left and right adjacent segments 14 are connected by the mortise and tenon structure through the convex and concave tenon 12 and the mortise 13.

[0085] Figure 3 As shown in the figure, the lining 9 is divided into a plurality of segments 14 along the direction perpendicular to the energy tunnel, and the left and right adjacent segments 14 are connected by the mortise and tenon structure through the convex and concave tenon 12 and the mortise 13.

[0086] The working principle of the buffer layer 1 is to realize a multi-stage conversion process of thermal energy→mechanical energy→elastic potential energy. The geothermal change is conducted to the buffer layer 1 through the surrounding rock, the fluid circulation in the heat exchange pipe 2 causes temperature fluctuation, the distributed optical fiber sensor 8 monitors the temperature change in real time, and the data is fed back to the central control system.

[0087] ​As preferred, the lining 9 is pre-embedded with a plurality of distributed optical fiber sensors 8, which form a distributed optical fiber sensing network along the horizontal direction of the tunnel portal at a spacing of no more than 0.5 m, continuously collect temperature and strain data and transmit them to the central control system for analysis and display processing.

[0088] In a specific implementation, the steel fibers 11 of the buffer layer reinforce the main component materials and proportions of the foamed concrete 6:

[0089] A steel fiber: a shear type steel fiber with a length of 5-20 mm and an equivalent diameter of 0.1-0.3 mm.

[0090] B cement: ordinary portland cement is used as the main cementitious material, accounting for 30%-50%. Its hydration heat control capability needs to meet the volume stability requirements of the concrete.

[0091] C fly ash: fly ash partially replaces cement, accounting for 20%-40%, which can reduce the hydration heat peak value by about 15-25% and improve the rheological properties of the slurry.

[0092] D fine aggregate: medium fine sand or lightweight filler is used to optimize the volume stability of the concrete, accounting for 10%-20%.

[0093] E foaming agent: synthetic surfactant, dosage 0.5%-2%, forming closed cell structure with pore size 0.1-1 mm.

[0094] The preparation process of the energy tunnel thermal stress buffer layer under the above proportions includes:

[0095] S1, reserving a 50-100 mm gap at the contact surface of the tunnel lining 9 and the surrounding rock 10, and arranging the buffer layer 1;

[0096] S2, welding the limiting rail frame 3 made of steel to the side wall of the segment, and providing an elastic damping gasket 7 inside;

[0097] S3, slidingly installing the heat-conducting sliding block 4 in the limiting rail frame 3, and enabling it to freely slide, while being lockably connected with the limiting rail frame 3 through the phase change limiting block 5;

[0098] S4, arranging heat exchange pipes 2 along the inner ring of the buffer layer 1, with a pipe spacing of 300-500 mm, ensuring uniform distribution of the heat exchange pipes, and reserving a connection interface with the external heat system;

[0099] S5, connecting the heat exchange pipes 2 with the external heat system, ensuring normal operation of the heat exchange system, to achieve effective adjustment of thermal stress;

[0100] S6, checking the overall structure, and monitoring the interface thermal stress changes through the fiber Bragg grating sensor 8.

[0101] The buffer layer 1 is designed with a high-steel fiber area with high thermal conductivity on the side close to the surrounding rock 10, which can quickly transfer heat, and a low-steel fiber area with low thermal conductivity on the side close to the lining 9, which can effectively block the rapid transfer of heat to the lining, form a suitable temperature gradient, bring a smooth transition of the thermal expansion coefficient, significantly reduce the thermal stress mutation at the interface between the lining and the surrounding rock, and achieve the effects of avoiding ring-through cracks and improving structural safety and service life.

[0102] Moreover, the buffer layer 1 is designed with gradually changing thermal conductivity between the two sides, rather than uniform thermal conductivity, or high thermal conductivity on both sides, which can build a smooth heat conduction transition zone, make the temperature field distribution uniform and gradual, bring a coordinated thermal expansion deformation difference between the lining and the surrounding rock, eliminate stress concentration at the interface, and achieve the effects of ensuring the structural integrity and long-term service safety.

[0103] In addition, the buffer layer 1 is designed with a high-porosity area with high porosity on the side close to the lining 9, which absorbs the expansion deformation, and a low-porosity area with low porosity on the side close to the surrounding rock 10, which can provide sufficient structural stiffness and bearing capacity to ensure the coordinated deformation with the surrounding rock, bring gradient dissipation of thermal expansion strain energy, avoid stress concentration on a single interface, achieve the transition matching of the deformation modulus between the buffer layer and the lining and the surrounding rock, and significantly reduce the risk of ring cracking and improve the overall stability of the structure.

[0104] Moreover, the buffer layer 1 is designed with gradually changing porosity between the two sides, rather than uniform porosity, or high porosity on both sides, which can present a continuous and smooth transition of the deformation modulus and thermal properties from the surrounding rock to the lining, bring an effective coordination between the lining and the surrounding rock due to the difference in thermal expansion coefficient, avoid the peak value of stress mutation at the interface, achieve gradient dissipation of thermal strain energy, and disperse concentrated stress to the entire buffer layer range, thereby fundamentally inhibiting the generation of ring-through cracks, and significantly improving the durability and safety reserve of the energy tunnel under cyclic thermal load.

[0105] The lining 9 generates a pushing force due to the thermal expansion difference, which pushes the limiting rail frame 3 to deform, and in turn drives the heat-conducting sliding block 4 to slide along the sliding groove on the limiting rail frame 3, while the elastic damping gasket 7 is compressed and deformed to absorb the sliding impact.

[0106] The stress and temperature adaptive deformation process of the phase change deformation structure is as follows:

[0107] The thermal expansion difference between the lining 9 and the buffer layer 1 generates a pushing force, which acts on the four corners of the limiting rail frame 3 through the elastic damping gasket 7.

[0108] The limiting rail frame 3 is a rectangular rail frame, with the long side along the direction of the energy tunnel and the short side perpendicular to the direction of the energy tunnel,

[0109] As shown in the drawings, the short side of the limiting rail frame 3 is subjected to the load of the thrust force generated by the thermal expansion difference of the lining 9, the limiting rail frame 3 is elastically bent and deformed, the long side end of the limiting rail frame 3 pushes the heat-conducting sliding block 4, the heat-conducting sliding block 4 slides along the sliding groove of the limiting rail frame 3, and then slides to a predetermined position that can accurately compensate the current thermal deformation, so that the deformation between the buffer layer and the lining due to the temperature difference is adapted, and the interface contact stress is ensured to be always within a safe range. Figure 6 As shown in the drawings, after the thermal expansion difference of the lining 9 is eliminated, i.e. there is no thermal expansion difference, the short side of the limiting rail frame 3 is no longer subjected to the load, then the limiting rail frame 3 elastically recovers from the bending and is no longer deformed, the long side end of the limiting rail frame 3 pushes the heat-conducting sliding block 4, the heat-conducting sliding block 4 slides along the sliding groove of the limiting rail frame 3, and then slides to its initial zero-stress reference position and returns to the original position, so that the entire connecting system is reset to the original state and the residual stress accumulated due to thermal deformation is completely released, and the structure is ensured to always work within a preset reliable range and be prepared for the next temperature fluctuation, realizing the automatic reset and long-term working stability of the thermal stress adjusting system.

[0110] Figure 7 As shown in the drawings, after the thermal expansion difference of the lining 9 is eliminated, i.e. there is no thermal expansion difference, the short side of the limiting rail frame 3 is no longer subjected to the load, then the limiting rail frame 3 elastically recovers from the bending and is no longer deformed, the long side end of the limiting rail frame 3 pushes the heat-conducting sliding block 4, the heat-conducting sliding block 4 slides along the sliding groove of the limiting rail frame 3, and then slides to its initial zero-stress reference position and returns to the original position, so that the entire connecting system is reset to the original state and the residual stress accumulated due to thermal deformation is completely released, and the structure is ensured to always work within a preset reliable range and be prepared for the next temperature fluctuation, realizing the automatic reset and long-term working stability of the thermal stress adjusting system.

[0111] The present application cooperates the steel fiber volume fraction and the porosity design depth through the thermal conductivity, the thermal expansion coefficient and the deformation modulus, the thermal conductivity determines the temperature field distribution, the thermal expansion coefficient determines the free deformation, and the deformation modulus converts the constraint deformation into stress, so that the three form the optimal combination of "high thermal conductivity-medium expansion-variable rigidity", and the thermal stress is eliminated from the source.

[0112] Example 1:

[0113] The energy tunnel thermal stress buffer layer material ratio and design includes:

[0114] Taking the reinforced steel fiber foamed concrete with a volume ratio of 40% cement, 35% fly ash, 20% fine aggregate, 2% foaming agent and 3% steel fiber as an example, the buffer layer thermodynamic performance test method is further explained:

[0115] S1, the thermal conductivity of the steel fiber reinforced foamed concrete material is obtained by the following formula:

[0116]

[0117] Wherein, V d is the volume coefficient of steel fiber, λ d is the thermal conductivity of steel fiber, λ eff ​λ is the effective thermal conductivity of the composite material. matrix This is the thermal conductivity of foamed concrete.

[0118] V d =3%, λ d =50, λ matrix Substituting 1 into the above formula, we get λ. eff = 1.087 W / (m·k).

[0119] The thermal conductivity of the composite material is higher than that of the lining and surrounding rock, allowing heat to pass through the buffer layer quickly and reducing heat loss, thereby improving the overall thermal management efficiency of the system.

[0120] S2. Use the Turner model to calculate the coefficient of thermal expansion of the composite material:

[0121]

[0122] Where, α composite V is the overall coefficient of thermal expansion of the composite material. porous α represents the volume fraction of the foamed concrete portion. proous E is the coefficient of thermal expansion of the foamed concrete portion. porous V represents the Young's modulus of foamed concrete. steel α represents the volume fraction of the steel fiber portion. steel E represents the thermal expansion fraction of the steel fiber portion. steel This represents the Young's modulus of the steel fiber portion.

[0123] V porous =0.97, α proous =8×10-6 / ℃, E porous Substituting 14.4 GPa into the above formula, we get...

[0124] By setting the coefficient of thermal expansion of the composite material between that of the lining and the surrounding rock, the stress abrupt change at the interface can be effectively reduced, thus avoiding circumferential cracks caused by the difference in thermal expansion.

[0125] S3. Calculate the deformation modulus of the composite material using the Halpin-Tsai model:

[0126]

[0127] Among them, E c E represents the elastic modulus of the composite material. m V represents the elastic modulus of foamed concrete. f η is the volume fraction of steel fiber, η is the efficiency factor between the reinforcing phase and the matrix, and ξ is a correction factor related to fiber arrangement, interfacial bonding strength, etc.

[0128] E m = 40 GPa, V f = 3%, η = 0.811, ξ = 1.5 into the above formula, E c = 14.95 GPa.

[0129] The setting of the modulus of deformation described above can effectively alleviate the stiffness difference between the lining and the surrounding rock, significantly reduce the risk of structure cracking, and optimize the heat conduction performance, thereby improving the heat exchange efficiency of the energy tunnel.

[0130] According to the above λ eff The coupling relationship among the thermal conductivity, the thermal expansion coefficient α composite , and the elastic modulus E c is designed and precisely controlled, and is used to prepare the buffer layer 1 material which is layered and laid in different layers and has a gradient performance and realizes thermal-mechanical matching with the lining and the surrounding rock.

[0131] Example 2:

[0132] As Figure 1 shown, the installation process of the thermal stress buffer layer of the energy tunnel and the phase change deformation module includes:

[0133] A cement-fly ash binary cementitious system is used, and the rheological properties of the slurry are controlled by a water reducing agent. The steel fiber content is controlled at 0.5% to 2% by volume fraction, and a disperser is used for staged feeding to avoid clumping. The foaming agent is diluted at a ratio of 1:30 and then prepared into stable foam by a physical foaming mechanism, and the foaming ratio reaches 20 to 30 times. The porosity is controlled by volume ratio to achieve 60 to 70%, which balances the mechanical properties and thermal insulation requirements. Low-speed stirring (90 r / min) ensures the integrity of the foam structure, and the vibration molding process eliminates macroscopic pore defects. After 28 days of standard curing, the compressive strength of the material is ≥4 MPa, the elastic modulus is 32.5 GPa, and the material has both energy dissipation capacity and thermal resistance characteristics, thus the preparation of the reinforced steel fiber foamed concrete is completed.

[0134] As Figure 3 , the expansion joint process is used to connect when laying the heat exchange pipe inside the lining, and is connected with the external heat pump or cooling system. Before operation, pressure test is carried out, 0.6 MPa compressed air is introduced, and pressure is maintained for 30 minutes without leakage.

[0135] Limit rail frames 3 are welded at the pre-buried steel plates on both sides of the pipe piece, and the welds need to be non-destructively tested. A laser positioning instrument is used to calibrate the symmetry of the connecting frames on both sides to ensure smooth sliding of the subsequent sliding blocks. The heat-conducting sliding blocks are embedded along the sliding grooves of the limiting frames, and the sliding stroke is designed according to the expansion amount of the pipe piece. Phase change limiting blocks are installed at the joints of adjacent single pipe pieces, the trigger temperature is set, and the sliding block position is fixed by bolts.

[0136] The buffer layer 1 is installed in the limiting rail frame 3, the position of the limiting frame is re-measured, and the axis deviation is calibrated by using a total station. After assembly, the contact pressure is monitored to ensure uniform force transmission.

[0137] The above detailed description is used to explain and illustrate the present application, rather than limiting the present application, and any modification and change made to the present application within the spirit and protection scope of the claims fall within the protection scope of the present application.

[0138] The above description is only the preferred embodiment of the present application, and any equivalent changes or modifications made to the structure, features and principles described in the scope of the present application are included in the scope of the present application.

Claims

1. An energy tunnel structure system based on a gradient thermally conductive buffer layer, comprising surrounding rock (10) and a lining (9) constructed within the surrounding rock (10), characterized in that: The buffer layer (1) is embedded between the surrounding rock (10) and the lining (9) of the tunnel. It has pores and steel fibers (11) inside, and its steel fiber (11) content and porosity gradually change from the side closer to the surrounding rock (10) to the side closer to the lining (9). Heat exchange tube (2) is embedded inside the lining (9); Distributed fiber optic sensors (8) are embedded in the buffer layer (1) to monitor the thermal stress change data of temperature and strain in real time and feed it back to the central control system. A phase deformation structure is arranged between the buffer layer (1) and the lining (9) to absorb the sensed temperature and stress and thus adapt the lining (9) to deformation caused by temperature and vibration.

2. The energy tunnel structure system based on a gradient thermally conductive buffer layer according to claim 1, characterized in that: The content of steel fiber (11) in the buffer layer (1) decreases from the side closer to the surrounding rock (10) to the side closer to the lining (9), and the porosity increases from the side closer to the surrounding rock (10) to the side closer to the lining (9).

3. The energy tunnel structure system based on a gradient thermally conductive buffer layer according to claim 1, characterized in that: The phase deformation structure is arranged on the outer surface of the lining (9), including: An annular limiting track frame (3) is fixed to the outer surface of the lining (9); At least one thermally conductive slider (4) is slidably mounted on the limiting track frame (3) and locked in the sliding position by the phase change limiting block (5) for dynamically adapting to thermal stress and thus adjusting the deformation distribution; A phase change limiting block (5) is arranged on the heat-conducting slider (4) to sense the temperature and limit and lock the position of the heat-conducting slider (4) on the limiting track frame (3); Elastic damping pads (7) are arranged between the outer surface of the limiting track frame (3) and the lining (9) to serve as buffer and heat insulation.

4. The energy tunnel structure system based on a gradient thermally conductive buffer layer according to claim 3, characterized in that: The limiting track frame (3) is a ring frame structure. The limiting track frame (3) serves as a track for the sliding of the heat-conducting slider (4). The four corners of the limiting track frame (3) are indirectly connected to the outer surface of the lining (9) through elastic damping pads (7). Except for the four corners, the remaining parts of the limiting track frame (3) do not contact the outer surface of the lining (9) and maintain a gap between them. It includes multiple heat-conducting moving components consisting of heat-conducting sliders (4) and phase change limiting blocks (5). Each heat-conducting moving component includes a heat-conducting slider (4) and a phase change limiting block (5) located on both sides of the heat-conducting slider (4). The heat-conducting slider (4) is slidably embedded in the groove provided on the limiting track frame (3) and moves along the groove. One end of the phase change limiting block (5) on both sides of the heat-conducting slider (4) is fixed on the heat-conducting slider (4), and the other end is connected to and contacts the limiting track frame (3).

5. The energy tunnel structure system based on a gradient thermally conductive buffer layer according to claim 1, characterized in that: The buffer layer (1) is made of steel fiber reinforced foamed concrete (6), which is mainly composed of steel fiber (11) and reinforced foamed concrete (6).

6. The energy tunnel structure system based on a gradient thermally conductive buffer layer according to claim 5, characterized in that: The steel fiber reinforced foamed concrete (6) of the buffer layer (1) consists of the following components and their mass percentages: cement 30%–50%, fly ash 20%–40%, fine aggregate 10%–20%, foaming agent 0.5%–2%, and steel fiber 1%–3%. The steel fiber (11) has a length of 5–20 mm and a diameter of 0.1–0.3 mm.

7. The energy tunnel structure system based on a gradient thermally conductive buffer layer according to claim 1, characterized in that: The buffer layer (1) is prepared according to the following steps: S1. Add steel fibers, cement, fine aggregates, fly ash and other dry materials into the mixer according to the mass ratio, and dry mix for 1-2 minutes to ensure that the steel fibers are initially dispersed and to obtain cement paste; S2. Prepare foamed foam separately in a foaming machine using a foaming agent. The foaming time is 1–2 minutes and the foam diameter is 1–3 mm. Then add the foamed foam to the cement slurry and stir for 1–2 minutes until uniformly mixed to make a steel fiber reinforced foamed concrete with steel fiber content and porosity. S3. Repeat steps S1 to S2 to produce steel fiber reinforced foamed concrete with different steel fiber contents and different porosities, and lay them in layers on the surface of the lining (9) in sequence, so that a multi-layer steel fiber reinforced foamed concrete layer with increasing steel fiber (11) content and decreasing porosity is formed on the surface of the lining (9).

8. The energy tunnel structure system based on a gradient thermally conductive buffer layer according to claim 1, characterized in that: The lining (9) is mainly composed of multiple pipe segments (14) connected together. Adjacent pipe segments (14) are connected by tenon and mortise joints (12) and mortise and tenon grooves (13).

9. The energy tunnel structure system based on a gradient thermally conductive buffer layer according to claim 8, characterized in that: The heat exchange tubes (2) are arranged in an S-shape / serpentine pattern within the lining (9); each segment (14) of the lining (9) is provided with its own heat exchange tube (2), and the heat exchange tubes (2) of adjacent segments (14) are connected by a butt joint and an expansion joint is used. The tube end that was originally reduced in diameter is elastically deformed by hydraulic expansion, and an interference fit is formed with the tube end of the other end.

10. An energy tunnel structure system based on a gradient thermally conductive buffer layer according to claim 8, characterized in that: The lining (9) is pre-embedded with several distributed optical fiber sensors (8). The several distributed optical fiber sensors (8) form a distributed optical fiber sensing network along the horizontal direction of the tunnel entrance with a spacing of no more than 0.5m. They continuously collect temperature and strain data and transmit them to the central control system for analysis and display processing.

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