Composite steel sheet pile system with functions of geothermal exchange and foundation pit support

Abstract

The application has the functions of geothermal exchange and foundation pit support, and comprises a sandwich composite steel sheet pile, a heat circulation system, an H-shaped steel enclosing purlin and a supporting steel pipe. The sandwich composite steel sheet pile is composed of a heat exchange pipe, a steel protective shell and a steel sheet pile, and multiple steel sheet piles are connected to form a continuous enclosure structure. The heat exchange pipe is installed on the inner wall of each steel sheet pile, and the adjacent pipes are connected in a serpentine connection mode and arranged longitudinally. The steel protective shell is also installed on the inner wall of each steel sheet pile and vertically covers the heat exchange pipe. The heat circulation system comprises a variable frequency pump set and a heat pump set, the heat exchange pipe is connected with the variable frequency pump set and the heat pump set to form a closed circulation system and realize heat exchange. The H-shaped steel enclosing purlin is installed on the steel sheet pile, and the supporting steel pipe is inserted into the web of the H-shaped steel enclosing purlin at one end and is installed on one side of the foundation pit structure at the other end to provide foundation pit support. The system has good heat exchange efficiency and foundation pit support performance and is suitable for building construction and geothermal energy utilization.

Description

Technical Field

[0001] This invention belongs to the field of building energy conservation and geothermal utilization technology, specifically relating to a composite steel sheet pile system with dual functions of geothermal exchange and foundation pit support, which is suitable for the comprehensive application of building foundation pit support and geothermal energy collection. Background Technology

[0002] Traditional energy piles, diaphragm walls, and energy tunnels all involve pre-embedding the heat exchange pipes of a ground source heat pump inside the building's pile foundation (such as concrete piles or precast piles). The heat exchange pipes are typically tied to the inner wall of a reinforcing cage in a U-shape or spiral configuration before concrete is poured. Heat exchange with the soil is achieved through a circulating medium. However, traditional energy piles still have the following major problems in application:

[0003] 1. High construction complexity and cost: Traditional energy piles (such as concrete pile heat exchange devices in ground source heat pump systems) require pre-buried pipes or on-site pouring of concrete piles. The installation process is time-consuming and requires a lot of manpower, with high initial installation costs and poor site adaptability.

[0004] 2. Low heat exchange efficiency: Concrete has a low thermal conductivity (about 1.7 W / mK), resulting in low heat transfer efficiency. Traditional pile foundations have limited depth, usually 50 to 60 meters, and multiple piles are required to achieve the heat exchange efficiency of an equivalent deep well.

[0005] 3. Environmental impact and sustainability: Concrete production has high carbon emissions, and piles are difficult to recycle, which does not meet the requirements of a circular economy. Ground source heat pumps may affect groundwater circulation, and long-term use may lead to cold accumulation or changes in groundwater level.

[0006] 4. Maintenance and durability issues: Concrete piles are prone to cracking due to temperature changes, which can lead to leakage or reduced efficiency in heat exchange pipes. Ground source heat pump systems have high maintenance costs, and repairs are difficult after damage to the underground loop.

[0007] 5. Limited application scenarios: Traditional pile foundations have a single function, mainly serving building foundations or geothermal exchange, and are difficult to expand to other uses (such as foundation pit support). Summary of the Invention

[0008] To address the problems existing in the prior art, this invention provides a composite steel sheet pile system with dual functions of geothermal exchange and foundation pit support. The aim is to utilize the high strength and bending resistance of steel sheet piles, combined with H-shaped waler support plates and supporting steel pipes, to form a stable foundation pit support structure, ensuring safety during foundation pit construction. The high thermal conductivity of steel improves geothermal collection efficiency, and by optimizing the design and arrangement of heat exchange pipes, heat exchange efficiency is enhanced, and heat exchange response time is shortened. This integrates foundation pit support and geothermal exchange functions, improving the resource utilization efficiency of underground space and reducing construction costs and land occupation.

[0009] To achieve the above objectives, the specific solution of the present invention is as follows:

[0010] A composite sheet pile system with dual functions of geothermal exchange and foundation pit support is described. The system includes sandwich composite sheet piles, a heat circulation system, H-beam walers, and supporting steel pipes. The sandwich composite sheet piles consist of heat exchange pipes, a steel protective shell, and sheet piles installed in the soil. Multiple sheet piles are interconnected to form a continuous retaining structure. Each sheet pile has a heat exchange pipe installed on its inner wall, and adjacent heat exchange pipes are connected end-to-end in a serpentine arrangement, longitudinally arranged along the length of the sheet pile. The inner wall of each sheet pile... All are equipped with steel protective shells, which vertically cover the heat exchange pipes. The heat circulation system includes a variable frequency pump unit and a heat pump unit. The inlet of the heat exchange pipe is connected to the outlet of the variable frequency pump unit, the inlet of the variable frequency pump unit is connected to the outlet of the heat pump unit, and the inlet of the heat pump unit is connected to the outlet of the heat exchange pipe, forming a closed circulation system. The H-beam waler is installed on the sheet piles. One end of the supporting steel pipe is installed on one side of the foundation pit structure, and the other end is inserted into the web of the H-beam waler through a pin and lug plate.

[0011] Furthermore, the system includes a heat exchange efficiency adjustment device, which comprises a temperature sensor, an efficiency calculation module, and a controller. The temperature sensor is connected to the efficiency calculation module, and the efficiency calculation module and the variable frequency pump set are respectively connected to the controller. The temperature sensor is installed on the foundation pit structure and is used to monitor the inlet temperature and outlet temperature of the liquid in the heat exchange pipeline, as well as the initial temperature of the soil. The efficiency calculation module is used to calculate the heat exchange efficiency based on the inlet temperature, outlet temperature of the liquid in the heat exchange pipeline, and the initial temperature of the soil. The controller includes a PID control algorithm, which is used to adjust the frequency of the variable frequency pump set to control the flow rate of the liquid in the heat exchange pipeline based on the heat exchange efficiency calculated by the efficiency calculation module.

[0012] Furthermore, the heat exchange efficiency regulating device also includes a protection mechanism, which includes the following steps:

[0013] Step 1: By installing deformation monitoring instruments and temperature sensors in the foundation pit structure, the deformation of the foundation pit structure and the operating status of the heat exchange system are monitored in real time.

[0014] Step 2 is used to immediately start adjusting the frequency of the variable frequency pump set when the deformation of the foundation pit exceeds the preset threshold.

[0015] Step 3: If the deformation of the foundation pit continues to exceed the preset threshold or cannot be restored to a safe range after adjusting the frequency, immediately activate the pump stop protection mechanism to stop the operation of the heat pump unit.

[0016] Furthermore, the formula for calculating the heat exchange efficiency is as follows:

[0017] ,

[0018] In the formula, ƞ represents the heat exchange efficiency; T in Indicates the inlet temperature of the liquid inside the heat exchanger pipe; T out T represents the outlet temperature of the liquid inside the heat exchanger pipe. soil This indicates the initial temperature of the soil.

[0019] Furthermore, the adjustment method of the heat exchange efficiency adjustment device includes:

[0020] When the heat exchange efficiency is below 70%, the controller receives the heat exchange efficiency data provided by the efficiency calculation module and calculates the frequency of the variable frequency pump group that needs to be increased through the PID algorithm.

[0021] When the heat exchange efficiency is higher than 80%, the controller also uses the PID algorithm to calculate the frequency of the variable frequency pump group that needs to be reduced.

[0022] When the heat exchange efficiency is between 70% and 80%, the controller calculates and adjusts the frequency of the variable frequency pump unit using a PID algorithm. The formula for the PID control algorithm is as follows:

[0023] ,

[0024] In the formula, Efficiency deviation refers to the difference between the set thermal efficiency and the actual thermal efficiency at time t. The pump frequency adjustment directly controls the flow rate; , and ε and ε are the proportional coefficient, integral coefficient, and derivative coefficient, respectively; t represents time. In PID control, the system state changes dynamically with time; d is a mathematical operation symbol that represents the derivative with respect to time t.

[0025] Furthermore, the sheet pile includes inclined plates and straight webs. One end of each inclined plate is connected to both ends of the straight web to form a U-shaped structure. The other end of each inclined plate is provided with an insertion edge. The insertion edge adopts a standard interlocking design. The sheet pile is made of hot-rolled low-alloy high-strength steel of Q355B or Q420B, with a thickness of 8mm, 10mm or 12mm, a pile length range of 12~18 meters, and a width of 600~800mm.

[0026] Furthermore, the heat exchange pipe is made of HDPE or PEX-a material, with a pipe diameter of 25~32mm and a wall thickness of 2.3~3.0mm. The steel sheet pile is connected to the heat exchange pipe through a water pipe clamp. The longitudinal spacing between adjacent heat exchange pipes is set to be between 100mm and 150mm, and the transverse spacing is at least 50mm.

[0027] Furthermore, the water pipe clips are made of stainless steel or ABS plastic, and the water pipe clips are vertically arranged along the inner wall of the steel sheet pile, with the spacing between adjacent water pipe clips set within 1m.

[0028] Furthermore, the steel protective shell is made of galvanized steel plate with a thickness of 1.2~2.0mm or double-layer PE sheath, and the joint between the steel protective shell and the steel sheet pile is treated with butyl rubber material.

[0029] Advantages of the present invention

[0030] The composite steel sheet pile system of the present invention, which has the dual functions of geothermal exchange and foundation pit support, has the following advantages:

[0031] 1. Significantly improved heat exchange efficiency

[0032] Higher efficiency: The heat exchange efficiency can reach 72.4%, which is 37% higher than that of traditional concrete energy piles.

[0033] Faster response: The response time to a 5°C temperature difference is reduced by 46%, requiring only 11 minutes.

[0034] More stable operation: The thermal efficiency remains stable under different flow rates, making it suitable for scenarios with varying loads, whether hot or cold.

[0035] 2. Excellent foundation pit support performance

[0036] Compression and bending resistance: Q355B high-strength steel is used, with a single pile bearing strength of 355MPa, and the overall support system has high bending stiffness.

[0037] Deformation control: The maximum horizontal displacement is only 1 / 882 of the pit depth, which is far better than the conventional requirement (within 1 / 500).

[0038] High safety factor: Under multiple coupling effects, the safety factor is ≥1.5, which is superior to traditional support systems.

[0039] 3. Long service life and low maintenance cost

[0040] Long service life: steel sheet piles have a design life of ≥50 years, heat exchange pipes have a design life of ≥30 years, and steel protective shells have a service life of 20~30 years.

[0041] Easy to maintain: All parts can be replaced independently, maintenance cycle is long (inspection once every 10 years), and annual maintenance cost is only 30-40% of that of traditional systems.

[0042] High recycling rate: Overall recycling rate ≥90%, meeting green building requirements.

[0043] 4. High efficiency in construction and operation

[0044] Simple construction: factory prefabrication, rapid on-site pile driving, and easy control of construction quality.

[0045] Operational safety: Real-time monitoring of pit deformation and heat exchange status, automatic adjustment of flow rate, and pump shutdown protection when necessary.

[0046] 5. Significant overall benefits

[0047] Functional integration: It combines the functions of foundation pit support and geothermal exchange, resulting in high resource utilization efficiency.

[0048] Energy saving and environmental protection: Optimized heat exchange efficiency, recyclable materials, and compliance with green and low-carbon requirements.

[0049] Good economic performance: low maintenance costs and high recycling rate, low total life cycle cost, and strong market competitiveness.

[0050] The composite steel sheet pile system of the present invention exhibits significant advantages in terms of heat exchange efficiency, foundation pit support performance, service life, maintenance cost and overall benefits, realizing functional integration and green construction, and has broad application value. Attached Figure Description

[0051] Figure 1 This is a top view schematic diagram of the composite steel sheet pile system of the present invention, which has the dual functions of geothermal exchange and foundation pit support.

[0052] Figure 2 for Figure 1 A schematic diagram of the front structure.

[0053] Figure 3 for Figure 1 A schematic diagram of the sandwich composite steel sheet pile.

[0054] Figure 4 This is a schematic diagram of the heat exchange efficiency adjustment device of the present invention.

[0055] In the picture:

[0056] 1. Steel sheet piles; 2. Heat exchanger pipes; 3. Steel protective shell; 4. Bolt assembly; 5. Butyl rubber material; 6. Variable frequency pump set; 7. Heat pump unit; 8. H-shaped waler support plate; 9. Support steel pipe; 10. Water pipe clamps. Detailed Implementation

[0057] The present invention will be further explained and described below with reference to the accompanying drawings and specific embodiments. It should be noted that the specific embodiments are not intended to limit the scope of the present invention.

[0058] like Figures 1 to 4 As shown in the figure, the composite steel sheet pile 1 system with dual functions of geothermal exchange and foundation pit support provided in this specific embodiment includes sandwich composite steel sheet piles, a heat circulation system, H-shaped steel walers, supporting steel pipes 9 and a heat exchange efficiency adjustment device.

[0059] The sandwich composite sheet pile includes a heat exchange pipe 2, a steel protective shell 3, and sheet piles 1 installed in the soil. Sheet pile 1 includes inclined plates and straight webs. One end of each inclined plate is connected to both ends of the straight web, forming a U-shaped structure. The other end of each inclined plate has an insertion edge with a standard interlocking design to ensure overall airtightness and support continuity. Sheet pile 1 is made of hot-rolled low-alloy high-strength steel (Q355B or Q420B). Depending on the geological conditions and pit depth, the thickness of sheet pile 1 is set to 8mm, 10mm, or 12mm, the pile length ranges from 12 to 18 meters, and the width is 600 to 800mm. Multiple sheet piles 1 are interconnected to form a continuous retaining structure. Each sheet pile 1 has multiple pre-welded pipe clamps 1010 longitudinally welded to its inner wall. The pipe clamps 1010 are made of stainless steel or ABS plastic and are arranged vertically along the inner wall of the sheet pile 1, with the spacing between adjacent pipe clamps 1010 being within 1 meter. During installation, the heat exchange pipe 2 is snapped into the pipe clamps 10 using a snap-fit ​​method. This allows for quick installation and fixation while maintaining stable positioning during thermal expansion and contraction, preventing pipe shaking or deformation. This structure simplifies construction steps and facilitates on-site assembly and maintenance. In this embodiment, the heat exchange pipe 2 is made of HDPE or PEX-a material. The diameter of the heat exchange pipe 2 is 25~32mm, and the wall thickness is 2.3~3.0mm. Each heat exchange pipe 2 is connected to the inner wall of each steel sheet pile 1 using water pipe clamps 1010. Adjacent heat exchange pipes 2 are connected end to end to form a serpentine connection. They are arranged longitudinally along the length of the steel sheet pile 1. The longitudinal spacing between adjacent heat exchange pipes 2 is set between 100mm and 150mm, and the lateral spacing is at least 50mm. This design not only optimizes the heat exchange efficiency but also avoids thermal interference and energy efficiency degradation between pipes. Each steel sheet pile 1 is installed on the inner wall of a steel protective shell 3 using bolt assemblies 4, and the steel protective shell 3 vertically covers the heat exchange pipe 2. Specifically, bolt holes are pre-drilled on the outer wall of the sheet pile 1 or drilled on-site. The steel protective shell 3 is directly fastened to the surface of the sheet pile 1 using bolt assemblies 4. The bolt spacing is designed according to the shell rigidity and thermal expansion coefficient, typically 300~500mm. The steel protective shell 3 is made of galvanized steel plate with a thickness of 1.2~2.0mm or a double-layer PE sheath. The joint between the steel protective shell 3 and the sheet pile 1 is treated with butyl rubber material 5 to ensure waterproof, corrosion-resistant, and thermal insulation performance, thereby improving the long-term operational safety of the system.

[0060] The heat exchange pipe 2 is used to achieve heat exchange between the soil and the ambient temperature. The steel sheet pile 1 mainly bears the soil pressure in the foundation pit, and the steel protective shell 3 mainly prevents the heat exchange pipe from being damaged during the foundation pit construction process. If necessary, grouting can be injected into the internal pores of the sandwich composite steel sheet pile to increase the thermal contact area. The H-beam waler and supporting steel pipe 9 mainly serve as foundation pit support.

[0061] The thermal circulation system includes a variable frequency pump unit 6 and a heat pump unit 7. The variable frequency pump unit 6 controls the flow rate of the liquid, adjusting the circulation speed of the liquid within the heat exchange pipe 2, thereby affecting the heat transfer efficiency. The function of the heat pump unit 7 is to exchange the heat absorbed from the heat exchange pipe 2 with the external environment, realizing heat transfer and regulation. The inlet of the heat exchange pipe 2 is connected to the outlet of the variable frequency pump unit 6, the inlet of the variable frequency pump unit 6 is connected to the outlet of the heat pump unit 7, and the inlet of the heat pump unit 7 is connected to the outlet of the heat exchange pipe 2, allowing the liquid to flow out from the outlet of the heat pump unit 7 and into the inlet of the variable frequency pump unit 6. The variable frequency pump unit 6 pumps the liquid into the inlet of the heat exchange pipe 2. The liquid circulates within the heat exchange pipe 2, exchanging heat with the soil. The liquid flows out from the outlet of the heat exchange pipe 2 and into the inlet of the heat pump unit 7. Heat pump unit 7 processes the liquid, and after heat exchange, the liquid flows out from the outlet of heat pump unit 7 and re-enters the inlet of variable frequency pump unit 6, forming a closed loop system. During operation, variable frequency pump unit 6 drives the liquid to circulate within the heat exchange pipe 2. During this flow, the liquid exchanges heat with the surrounding soil, absorbing or releasing heat energy, thus achieving energy transfer with the soil. The variable frequency pump unit automatically adjusts the liquid flow rate based on changes in heat exchange efficiency to optimize the heat exchange effect. Subsequently, the liquid enters heat pump unit 7, further transferring the absorbed or released heat to the building's heating or cooling system, completing the entire system's heat energy utilization process.

[0062] The variable frequency pump set is a commercially available product, model number Grundfos TPED 32-120 / 2 from the TPED series. This variable frequency pump set supports variable flow control in closed-loop systems; it supports automatic control protocols such as Modbus and BACnet, and can be linked with controllers and PID systems; it is suitable for medium-sized systems such as ground source heat pumps and HVAC; its flow rate and head range are compatible with heat exchange pipes with diameters of 25~32mm; it can achieve precise variable frequency speed control, which helps to adjust the system's heat exchange efficiency.

[0063] The heat pump unit is a commercially available product, model number CGWH 050 from the Trane CGWH series of ground source heat pumps. This heat pump unit is suitable for shallow geothermal heat exchange systems; it features a modular design for easy connection to heat exchange pipes; it offers both heating and cooling functions to match your system's application scenarios; it has an automatic control interface that can be connected to an efficiency adjustment module; and its operating temperature range matches the soil temperature of approximately 10~20℃, ensuring stable efficiency.

[0064] The H-beam waler is installed on the sheet pile 1 using bolt assembly 4. Specifically, bolt holes or slots are machined on the convex surface of the top of the sheet pile 1, and corresponding mounting holes or flanges are pre-drilled at the bottom of the H-beam waler. High-strength bolts are used for connection during installation. To improve the load-bearing capacity and tensile and shear resistance of the connection, reinforcing ribs or limiting steps are installed on the contact surface to ensure the stability and safety redundancy of the structural connection under the combined action of support loads and thermal deformation. One end of the supporting steel pipe 9 is installed on one side of the foundation pit via a hinged head, and the other end is inserted into the web of the H-beam waler via a pin and lug plate.

[0065] like Figure 4 As shown, the heat exchange efficiency adjustment device includes a temperature sensor, an efficiency calculation module, a controller, and a protection mechanism. The temperature sensor is connected to the efficiency calculation module, and the efficiency calculation module and the variable frequency pump group 6 are respectively connected to the controller. The temperature sensor is installed on the foundation pit structure. Specifically, the foundation pit structure includes the foundation pit walls, supporting structure, steel protective shell, and adjacent soil area. The temperature sensor is installed in the soil area of ​​the foundation pit structure, specifically near the outside of the heat exchange pipe and the soil area adjacent to the steel protective shell. Temperature sensors are buried on both sides of each steel sheet pile within 10-20 cm of the outer edge of the heat exchange pipe. Vertically, they are symmetrically arranged at three points (upper, middle, and lower) along the length of the steel sheet pile, with a horizontal spacing of one group every 2 meters, equidistantly distributed along the foundation pit retaining wall to ensure uniform lateral data sampling. This arrangement can effectively reflect the temperature field changes between the soil and the heat exchange pipe at different depths and directions, ensuring that temperature monitoring covers the main heat exchange area. The temperature sensor is used to monitor the inlet temperature and outlet temperature of the liquid in the heat exchange pipeline 2, as well as the initial temperature of the soil. The data collected by the temperature sensor is used to reflect the temperature difference between the heat exchange pipeline and the surrounding soil at different depths and locations in real time, thereby assisting the efficiency calculation module in accurately calculating the heat exchange efficiency and providing temperature basis for the controller to adjust the variable frequency pump group based on the PID algorithm.

[0066] The efficiency calculation module is used to calculate the heat exchange efficiency based on the inlet temperature and outlet temperature of the liquid in the heat exchange pipe 2 and the initial temperature of the soil. The controller includes a PID control algorithm, which is used to adjust the frequency of the variable frequency pump group 6 to control the flow rate of the liquid in the heat exchange pipe 2 based on the heat exchange efficiency calculated by the efficiency calculation module.

[0067] The heat exchange efficiency η is the ratio of the actual heat exchanged to the theoretical maximum possible heat circulation, which can be obtained by considering the inlet temperature T of the liquid medium inside the heat exchange tube. in Outlet temperature T out and the initial soil temperature T soil The heat exchange efficiency is calculated using the following formula:

[0068]

[0069] In the formula, ƞ represents the heat exchange efficiency; T in T represents the inlet temperature of the liquid inside heat exchanger pipe 2. out T represents the outlet temperature of the liquid inside heat exchanger pipe 2. soil This indicates the initial temperature of the soil.

[0070] Since the heat conversion efficiency between the heat exchange tube and the soil medium is related to the flow rate of the liquid medium inside the heat exchange tube, the flow rate of the liquid medium inside the heat exchange tube can be adjusted by monitoring the inlet and outlet temperatures and the soil temperature to achieve the best heat conversion effect.

[0071] The adjustment method of the heat exchange efficiency adjustment device includes:

[0072] The flow rate is adjusted based on the efficiency calculation results. When the heat exchange efficiency is lower than 70%, the controller receives the heat exchange efficiency data provided by the efficiency calculation module and calculates the frequency of the variable frequency pump group that needs to be increased through the PID algorithm in order to increase the flow rate and improve the heat exchange efficiency.

[0073] When the heat exchange efficiency is higher than 80%, the controller also uses the PID algorithm to calculate the frequency of the variable frequency pump group that needs to be reduced, so as to fine-tune the flow rate and prevent efficiency degradation.

[0074] When the heat exchange efficiency is between 70% and 80%, the controller calculates and adjusts the frequency of the variable frequency pump group 6 using a PID algorithm to maintain the heat exchange efficiency within the optimal range. The formula for the PID control algorithm is as follows:

[0075] ,

[0076] In the formula, Efficiency deviation refers to the difference between the set thermal efficiency and the actual thermal efficiency at any given time. The pump frequency adjustment directly controls the flow rate; , and and represent the proportional coefficient, integral coefficient, and derivative coefficient, respectively; t represents time. In PID control, the system state changes dynamically with time. All integrals (∫) and derivatives (d / dt) are operations relative to time. d represents the derivative symbol. In the expression de(t) / dt, d is a mathematical operation symbol representing the derivative with respect to time t, that is, the rate of change of the error e(t) with time. This term is called the "differential term," which reflects the changing trend of the system response and is used to predict and reduce overshoot.

[0077] At the same time, since the sheet pile 1 also serves as the foundation pit support, it is necessary to monitor the foundation pit deformation at all times. When the strain of the sheet pile 1 is too large, the protection mechanism should be triggered immediately to reduce the flow rate.

[0078] The protection mechanism includes the following steps:

[0079] Step 1: By installing deformation monitoring instruments and temperature sensors in the foundation pit structure, the deformation of the foundation pit structure and the operating status of the heat exchange system are monitored in real time. The specific arrangement is as follows:

[0080] Deformation monitoring instruments are installed in typical deformation-sensitive areas of the foundation pit support structure, including the foundation pit retaining wall, such as the top, middle and bottom of the sheet piles, the connection nodes of the H-beam walers, the connection points at both ends of the supporting steel pipes, and the intersection of the columns and the support system, etc., to comprehensively reflect the deformation characteristics of the support structure during excavation and operation.

[0081] Temperature sensors are embedded in the soil area adjacent to the outer side of the heat exchange pipe and the steel protective shell, on both sides of each sheet pile, and within 10-20 cm of the outer edge of the heat exchange pipe. Vertically, they are symmetrically arranged at three points (top, middle, and bottom) along the length of the sheet piles, with a horizontal spacing of one group every 2 meters. They are equidistantly distributed along the foundation pit retaining wall. In this embodiment, the foundation pit structure refers to the structural system constructed in underground excavation projects to achieve slope stability, load transfer, and the placement of monitoring and heat exchange elements. Specifically, it includes a retaining structure formed by continuous connection of sandwich composite sheet piles, a support structure consisting of H-shaped steel walers and steel pipe supports installed inside and connected to the sheet piles, the inner wall of the retaining structure, the outer side of the steel protective shell, and the structural area adjacent to the heat exchange pipe. It also includes the soil area within 10-20 cm of the outer edge of the retaining structure, which is the direct target for temperature sensors to collect ground temperature data and is also within the monitoring scope of the foundation pit structure.

[0082] Real-time monitoring of the deformation of the foundation pit structure and the operating status of the heat exchange system;

[0083] Step 2 is used to immediately start adjusting the frequency of the variable frequency pump group 6 when the deformation of the foundation pit exceeds the preset threshold.

[0084] Step 3: If the deformation of the foundation pit continues to exceed the preset threshold or cannot be restored to a safe range after adjusting the frequency, immediately activate the pump stop protection mechanism to stop the operation of the heat pump unit 7.

[0085] Working principle:

[0086] Construction phase:

[0087] The foundation pit support function is achieved by driving sandwich composite steel sheet piles into the ground in a closed or semi-closed arrangement to form a continuous foundation pit support wall. The steel sheet piles themselves possess high bending stiffness and compressive strength, capable of withstanding multiple forces from the soil, groundwater, and superstructure loads. Simultaneously, a stable and closed support structure system is formed by H-shaped steel walers and supporting steel pipes 9, effectively preventing foundation pit collapse and displacement, and ensuring slope stability and soil deformation control during excavation.

[0088] System operation phase:

[0089] Heat exchange function implementation:

[0090] Heating Status: The heat transfer medium flows out of the building and enters the underground heat exchange pipe 2. Inside the heat exchange pipe 2, the heat transfer medium exchanges heat with the surrounding soil, releasing heat into the soil and returning to the surface after its temperature decreases. Due to the excellent thermal conductivity of the steel sheet piles 1, and the tight steel protective shell 3 covering the heat exchange pipe 2, the heat transfer efficiency between the pipe and the soil is further enhanced, shortening the heat exchange response time. At the same time, the steel sheet piles 1 form a large contact area with the stratum, improving the heat exchange capacity per unit depth, enabling the system to effectively achieve the sustainable extraction and utilization of shallow geothermal energy, thereby providing heating for the building.

[0091] Cooling mode: Under the action of heat pump unit 7, the heat medium absorbs the low-temperature energy stored in the soil in the reverse direction. The heat medium circulates in the heat exchange pipe 2, absorbs heat from the soil, and returns to the ground surface after its own temperature rises, thereby realizing the building's air conditioning or hot water supply function and achieving the cooling effect.

[0092] Heat exchange efficiency adjustment:

[0093] Real-time monitoring and adjustment: Temperature sensors in the heat exchange efficiency adjustment device monitor the inlet and outlet temperatures of the liquid in the heat exchange pipe 2, as well as the initial temperature of the soil, in real time. The efficiency calculation module calculates the heat exchange efficiency based on this temperature data. The controller, based on the efficiency calculation results, uses a PID control algorithm to adjust the frequency of the variable frequency pump group 6, thereby controlling the flow rate of the liquid in the heat exchange pipe 2 to achieve the best heat conversion effect. When the heat exchange efficiency is below 70%, the flow rate is increased to improve the heat exchange efficiency; when the heat exchange efficiency is above 80%, the flow rate is slightly reduced to prevent efficiency degradation; when the heat exchange efficiency is between 70% and 80%, the PID algorithm maintains the heat exchange efficiency within the optimal range.

[0094] Foundation pit deformation monitoring and protection: Deformation monitoring instruments and temperature sensors are installed in the foundation pit structure to monitor the deformation of the foundation pit structure and the operating status of the heat exchange system in real time. When the foundation pit deformation exceeds the preset threshold, the frequency of the variable frequency pump unit 6 is immediately adjusted; if the foundation pit deformation continues to exceed the preset threshold or cannot be restored to a safe range after adjusting the frequency, the pump shutdown protection mechanism is immediately activated to stop the operation of the heat pump unit 7 to ensure the safety of the foundation pit support structure.

[0095] This composite steel sheet pile system primarily functions as a foundation pit support during the construction phase, ensuring the safety of the foundation pit construction. During system operation, it connects to a ground source heat pump system via heat exchange pipes 2, enabling heat exchange between the heat medium and the soil to provide heating or cooling for the building. Simultaneously, a heat exchange efficiency adjustment device monitors and adjusts the heat exchange efficiency in real time, and monitors and protects against foundation pit deformation, ensuring the system's safe and efficient operation. This system integrates the two major functions of foundation pit support and geothermal energy exchange, improving the resource utilization efficiency of underground space and demonstrating excellent energy efficiency, adaptability, and promotional value.

[0096] To ensure the feasibility and ease of operation of the composite steel sheet pile system with dual functions of geothermal exchange and foundation pit support in actual engineering projects, the construction steps are as follows:

[0097] (1) Factory prefabrication and numbering management: Before construction, the heat exchange pipe 2 and steel protective shell 3 are assembled in each steel sheet pile 1 in the factory to form multiple sandwich composite steel sheet piles, and the sandwich composite steel sheet piles are numbered to facilitate subsequent connection and management.

[0098] (2) On-site pile driving and quality control: Vibratory hammer or static pile driver is used to insert each sandwich composite steel sheet pile into the foundation soil layer one by one. During the pile driving, the verticality and the density between piles need to be monitored in real time. The deviation of verticality should not exceed 1% to avoid heat loss or water seepage due to poor insertion.

[0099] (3) Installation of support system: After all sandwich composite steel sheet piles are installed, H-beam walers and supporting steel pipes 9 are installed according to the design elevation to ensure the support stiffness and deformation control requirements.

[0100] (4) Connection and commissioning of the heat exchange system: Connect the inlet of the heat exchange pipe 2 to the water collection tank. Connect the outlet of the water collection tank to the main water pipe by electrofusion or thermal fusion. After completing all pipe connections, perform a sealing test and pressure test at 0.6 MPa to ensure that the system is leak-free. Connect the variable frequency pump and heat pump unit 7 to the system as described in the above embodiment, and turn on the variable frequency pump and heat pump unit 7. Observe the operating status, check the temperature difference between the inlet and outlet of the heat exchange pipe 2, evaluate the heat exchange efficiency, monitor the flow rate of the liquid in the heat exchange pipe 2, ensure that the system operates within the design flow range, observe whether the equipment can quickly reach the set operating state after startup, and evaluate the system response speed.

[0101] (5) Operation monitoring and safety mechanism: During operation, monitoring equipment such as deformation monitors and temperature sensors shall be installed to ensure the stable operation of the foundation pit structure and heat exchange system. If abnormal deformation or efficiency decline is found, the flow rate adjustment or pump stop protection mechanism shall be activated immediately.

[0102] The equipment recovery and maintenance of the composite steel sheet pile system 1, which has dual functions of geothermal exchange and foundation pit support in this embodiment, includes the following steps:

[0103] Step 1: Recover the liquid inside the heat exchange tubes to ensure that no liquid remains inside the heat exchange tubes;

[0104] Step 2: Disconnect the heat exchange pipe 2 of the part to be repaired, and pull out the heat exchange pipe 2 and the corresponding steel sheet pile 1.

[0105] Step 3: Insert the new sheet pile 1 and the heat exchange pipe 2 into the corresponding positions and connect the heat exchange pipe 2.

[0106] To verify the improved heat conversion efficiency of the composite steel sheet pile system 1, which integrates geothermal exchange and foundation pit support functions, compared to traditional concrete energy piles under unified working conditions, and to clarify its response capability and heat transfer performance at different operating flow rates, a comparative experiment on heat exchange efficiency is provided below: I. Experimental Equipment and Subjects This experiment uses two pile types for comparison: one is the composite steel sheet pile system 1 of this embodiment, and the other is a traditional concrete energy pile, both with a pile length of 10m. The experiment was conducted in a soil simulation box, with dimensions of 2m×2m×2m, filled with medium clay. A variable frequency pump unit 6, a heat pump unit 7, a flow meter, a hot water tank, a temperature sensor, and an electronic data acquisition system were used for monitoring and recording. II. Experimental Conditions 1. The inlet temperature of the heat medium, Tin, was set to 30.0±0.2℃; 2. The initial soil temperature, Tsoil, was stabilized at 18.0±0.5℃; 3. The heat exchange pipeline was 10m long and arranged in a serpentine, continuous loop; 4. Three flow rates were set for the experiment: 0.3 m³ / h, 0.5 m³ / h, and 0.7 m³ / h; 5. The continuous operation time was 60 minutes, with sampling every 10 minutes. III. Measurement and Calculation Methods The inlet water temperature, Tin, outlet water temperature, Tout, flow rate, and heat exchange time, t, etc., were recorded respectively. The heat exchange efficiency was calculated using the following formula: η=(Q_measured / Q_theoretical)×100% Where, Q_measured is calculated according to the formula Q=ρ×c×Q×(Tin - Tout)×t, and Q_theoretical is estimated based on the maximum theoretical heat transfer capacity. IV. Experimental Results and Analysis At a flow rate of 0.5 m³ / h, the heat exchange efficiency of the composite steel sheet pile system 1 in this embodiment reached 72.4%, while that of the traditional concrete pile was 52.9%, representing an efficiency improvement of approximately 37%. When a temperature difference of 5℃ was reached, the response time of this embodiment was 11 minutes, while the response time of the traditional concrete pile was 20 minutes, representing a speedup of approximately 46%. Under different flow rates, the thermal efficiency of the composite steel sheet pile system 1 in this embodiment was more stable, with a lower rate of temperature difference decay, making it particularly suitable for use in scenarios with varying hot and cold loads.

[0107] V. Performance Evaluation of Foundation Pit Support

[0108] Based on finite element simulation and existing engineering test data, the foundation pit support performance of the composite steel sheet pile system 1 in this embodiment is analyzed:

[0109] 1. Compressive strength and bending performance: The steel sheet pile 1 is made of Q355B high-strength steel, and the single pile bearing strength can reach 355MPa. After the H-shaped steel waler and the supporting steel pipe 9 are laid out, the overall support system has good bending stiffness and the bending moment limit is much higher than that of traditional concrete support walls.

[0110] 2. Deformation control capability: Through foundation pit deformation monitoring simulation (referring to the Technical Specification for Foundation Pit Support of Buildings JGJ120–2012), the maximum horizontal displacement of composite steel sheet pile 1 in a typical basement foundation pit (12m deep, medium clay soil) is 13.6mm, accounting for 1 / 882 of the foundation pit depth, which is significantly better than the requirements of conventional temporary support structures (usually within 1 / 500).

[0111] 3. Safety factor comparison: The composite steel sheet pile 1 system in this embodiment can still maintain a safety factor of ≥1.5 under the multiple coupled effects of water pressure, construction disturbance, thermal expansion and contraction, which is better than the traditional single-function steel sheet pile 1 support system, fully demonstrating its advantage of "structural stability under dual-function synergy".

[0112] VI. Service life and maintenance economy analysis

[0113] Based on the component materials, usage environment, and maintenance characteristics, the life cycle analysis of the composite steel sheet pile system 1 in this embodiment is as follows:

[0114] Steel sheet pile 1: Made of hot-rolled Q355B or Q420B steel, with a design life of ≥50 years after anti-corrosion treatment, possessing high durability and recyclability;

[0115] Heat exchanger pipe 2: Made of HDPE or PEX-a material, it is resistant to high temperature and scale, and the design service life of the pipe system is ≥30 years;

[0116] Steel protective shell 3: Made of galvanized steel sheet or double-layer PE composite material, it has excellent wear resistance and impact protection capabilities, and its service life can reach 20 to 30 years in a stable underground environment;

[0117] Meanwhile, the composite steel sheet pile 1 system of this embodiment has the following maintenance and economic advantages: all heat exchange pipes 2 and steel sheet piles 1 can be maintained independently by pulling them out and replacing them, avoiding overall dismantling; heat pipes can be replaced without damaging the ground structure, and the maintenance cycle is recommended to be once every 10 years; the annual maintenance cost during the operation period is about 30 to 40% of that of traditional concrete energy pile systems; the overall recycling rate can reach more than 90%, which meets the requirements of green construction and sustainable development.

Claims

1. A composite steel sheet pile system with dual functions of geothermal exchange and foundation pit support, characterized in that, The system includes sandwich composite steel sheet piles, a heat circulation system, H-beam steel walers, and supporting steel pipes. The sandwich composite steel sheet piles include heat exchange pipes, steel protective shells, and steel sheet piles installed in the soil. Multiple steel sheet piles are interconnected to form a continuous retaining structure. Each steel sheet pile has a heat exchange pipe installed on its inner wall, and adjacent heat exchange pipes are connected end to end to form a serpentine connection and are arranged longitudinally along the length of the steel sheet pile. Each steel sheet pile has a steel protective shell installed on its inner wall, and the steel protective shell vertically covers the heat exchange pipes. The heat circulation system includes a variable frequency pump set and a heat pump unit. The inlet of the heat exchange pipe is connected to the outlet of the variable frequency pump set, the inlet of the variable frequency pump set is connected to the outlet of the heat pump unit, and the inlet of the heat pump unit is connected to the outlet of the heat exchange pipe, forming a closed circulation system. The H-beam steel walers are installed on the steel sheet piles. One end of the supporting steel pipe is installed on one side of the foundation pit structure, and the other end is inserted into the web of the H-beam steel waler through a pin and lug plate. It also includes a heat exchange efficiency adjustment device, which includes a temperature sensor, an efficiency calculation module, and a controller. The temperature sensor is connected to the efficiency calculation module, and the efficiency calculation module and the variable frequency pump set are respectively connected to the controller. The temperature sensor is installed on the foundation pit structure and is used to monitor the inlet temperature and outlet temperature of the liquid in the heat exchange pipeline and the initial temperature of the soil. The efficiency calculation module is used to calculate the heat exchange efficiency based on the inlet temperature, outlet temperature of the liquid in the heat exchange pipeline and the initial temperature of the soil. The controller includes a PID control algorithm, which is used to adjust the frequency of the variable frequency pump set to control the flow rate of the liquid in the heat exchange pipeline based on the heat exchange efficiency calculated by the efficiency calculation module. The frequency adjustment of the variable frequency pump group by the heat exchange efficiency adjustment device includes: When the heat exchange efficiency is below 70%, the controller receives the heat exchange efficiency data provided by the efficiency calculation module and calculates the frequency of the variable frequency pump group that needs to be increased through the PID algorithm. When the heat exchange efficiency is higher than 80%, the controller also uses the PID algorithm to calculate the frequency of the variable frequency pump group that needs to be reduced. When the heat exchange efficiency is between 70% and 80%, the controller calculates and adjusts the frequency of the variable frequency pump unit using a PID algorithm. The formula for the PID control algorithm is as follows: ， In the formula, Efficiency deviation refers to the difference between the set thermal efficiency and the actual thermal efficiency at time t. The pump frequency adjustment directly controls the flow rate; , and ε and ε are the proportional coefficient, integral coefficient, and derivative coefficient, respectively; t represents time. In PID control, the system state changes dynamically with time; d is a mathematical operation symbol that represents the derivative with respect to time t.

2. The composite steel sheet pile system according to claim 1, characterized in that, The heat exchange efficiency regulating device also includes a protection mechanism, which includes the following steps: Step 1: By installing deformation monitoring instruments and temperature sensors in the foundation pit structure, the deformation of the foundation pit structure and the operating status of the heat exchange system are monitored in real time. Step 2 is used to immediately start adjusting the frequency of the variable frequency pump set when the deformation of the foundation pit exceeds the preset threshold. Step 3: If the deformation of the foundation pit continues to exceed the preset threshold or cannot be restored to a safe range after adjusting the frequency, immediately activate the pump stop protection mechanism to stop the operation of the heat pump unit.

3. The composite steel sheet pile system according to claim 1, characterized in that, The formula for calculating the heat exchange efficiency is as follows: ， In the formula, ƞ represents the heat exchange efficiency; T in Indicates the inlet temperature of the liquid inside the heat exchanger pipe; T out T represents the outlet temperature of the liquid inside the heat exchanger pipe. soil This indicates the initial temperature of the soil.

4. The composite sheet pile system according to claim 1, characterized in that, The sheet pile includes inclined plates and straight webs. One end of each inclined plate is connected to both ends of the straight web to form a U-shaped structure. The other end of each inclined plate is provided with an insertion edge. The insertion edge adopts a standard interlocking design. The sheet pile is made of hot-rolled low-alloy high-strength steel of Q355B or Q420B, with a thickness of 8mm, 10mm or 12mm, a pile length range of 12~18 meters, and a width of 600~800mm.

5. The composite steel sheet pile system according to claim 1, characterized in that, The heat exchange pipe is made of HDPE or PEX-a material, with a pipe diameter of 25~32mm and a wall thickness of 2.3~3.0mm. The steel sheet pile is connected to the heat exchange pipe through a water pipe clamp. The longitudinal spacing between adjacent heat exchange pipes is set to 100mm~150mm, and the transverse spacing is at least 50mm.

6. The composite steel sheet pile system according to claim 5, characterized in that, The water pipe clamps are made of stainless steel or ABS plastic, and are arranged vertically along the inner wall of the steel sheet pile, with the spacing between adjacent water pipe clamps set within 1m.

7. The composite sheet pile system according to claim 1, characterized in that, The steel protective shell is made of galvanized steel plate with a thickness of 1.2~2.0mm or double-layer PE sheath, and the joint between the steel protective shell and the steel sheet pile is treated with butyl rubber material.

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