A method, system and equipment for foundation pit dewatering and recharging in a sensitive area of a spring field

Abstract

This invention discloses a method, system, and equipment for recharge of groundwater from foundation pits in sensitive spring areas, belonging to the field of foundation pit dewatering and recharge technology. The method includes: rechargeing extracted groundwater into multiple recharge wells after sedimentation and filtration; real-time acquisition of wellhead pressure and injection flow rate of each recharge well; constructing a dual-medium response model that distinguishes between water-conducting channels and fissures, and calculating model parameters; using a recursive filtering algorithm to invert model parameters online; identifying the recharge water flow pattern based on the inversion results, and adopting an adaptive recharge method to dynamically adjust the flow distribution of each recharge well to maintain constant wellhead pressure; when the injection flow rate of a recharge well decreases beyond a preset threshold and the wellhead pressure fluctuation is within a preset range, a blockage trend is determined and an alarm is triggered. This invention, through variable frequency constant pressure control and adaptive decision-making based on a dual-medium model, adopts a differentiated recharge strategy for both water-conducting channels and fissures, effectively protecting groundwater resources while ensuring the safety of foundation pit construction.

Description

Technical Field

[0001] This invention relates to the field of foundation pit dewatering and recharge technology, specifically to a method, system, and equipment for foundation pit dewatering and recharge in spring-sensitive areas. Background Technology

[0002] When constructing deep foundation pits in karst areas, groundwater is often extracted through dewatering wells to lower the water level to ensure operational safety. To prevent waste of groundwater resources and ground subsidence, recharge technology is introduced in practice, where a portion of the extracted groundwater is reinjected into the aquifer to achieve a balance between extraction and recharge. However, the commonly used foundation pit dewatering and recharge methods have significant shortcomings in practical applications: It lacks the ability to independently monitor and warn of each reinjection well, and cannot identify abnormal conditions such as blockage and backflow in a timely manner. It often relies on manual periodic backflow and dredging, which results in high operation and maintenance costs and slow response. Especially in sensitive areas of springs, karst aquifers exhibit dual media characteristics of water-conducting channels and fissures. Existing unified reinjection strategies are difficult to adapt to this heterogeneity, often resulting in excessive pressure in the channel area and insufficient reinjection in the fissure area, which wastes water resources and fails to effectively raise the regional water level. Summary of the Invention

[0003] To address the problems existing in the prior art, this invention provides a method, system, and equipment for recharge of groundwater in foundation pits in sensitive spring areas. Through variable frequency constant pressure control and adaptive decision-making based on a dual-medium model, it can adopt differentiated recharge strategies for dual-medium zones of karst water-conducting channels and fissures, thereby effectively protecting groundwater resources while ensuring the safety of foundation pit construction.

[0004] The technical solution of the present invention is as follows: In a first aspect of the present invention, a method for recharge of foundation pit dewatering in spring-sensitive areas is provided, comprising: The extracted groundwater was filtered and then reinjected into multiple injection wells. During the reinjection process, the wellhead pressure and injection flow rate of each reinjection well, as well as the water level data of the monitoring well, are collected in real time. A dual-medium response model for karst aquifers was constructed, which distinguishes between water-conducting channels and fractures, and the model parameters were calculated. A recursive filtering algorithm was used to process the wellhead pressure, injection flow rate, and water level data, and the model parameters were inverted online to obtain the inversion results. Based on the inversion results, the flow regime of the current reinjection water is identified, and an adaptive reinjection method is adopted to dynamically adjust the flow distribution of each reinjection well and maintain a constant wellhead pressure of the reinjection well. If the injection flow rate of a certain reinjection well drops below a preset threshold, and the wellhead pressure fluctuates within a preset range for a set time, it is determined that the reinjection well has a blockage trend and an alarm signal is issued.

[0005] In some embodiments of the present invention, the model parameters include the permeability coefficient of the water-conducting channel, the permeability coefficient of the fracture, and the hydraulic exchange coefficient between the two; The recursive filtering algorithm employs the extended Kalman filter algorithm. The identification results include the dominant flow regime in the water guiding channel and the dominant flow regime in the fracture. The reinjection methods include pulsed reinjection and continuous constant flow injection reinjection.

[0006] In some embodiments of the present invention, when the identification result indicates that the water guiding channel is in the dominant flow state, pulsed recharge is used. The duty cycle and pulse frequency of the pulsed recharge are dynamically set according to the ratio of the equivalent permeability coefficient of the water guiding channel to the fracture permeability coefficient. When the identification result indicates that the flow state is dominated by the fracture, continuous constant flow injection recharge is adopted. The target flow rate value of the continuous constant flow injection recharge is determined according to the hydraulic gradient requirements of the fracture.

[0007] In some embodiments of the present invention, after a blockage warning is issued, the reinjection well is automatically switched to backflushing mode to flush the well wall and aquifer pores with reverse flow. After the backflushing is completed, the reinjection is automatically restored.

[0008] In a second aspect of the invention, a foundation pit dewatering and recharge system for sensitive spring areas is provided, comprising a dewatering well, a recharge well, and a monitoring well. The dewatering well is used to store extracted groundwater, the recharge well is used to store recharge water injected into a target karst aquifer, and the monitoring well is used to monitor the dynamic changes in groundwater level around the foundation pit in real time. The monitoring well is equipped with a water level gauge and also includes: a water collection and sedimentation module, a pressurized filtration module, a distribution module, and an alarm module. The inlet of the water collection and sedimentation module is connected to the rainwater well. The water collection and sedimentation module is equipped with an overflow port and multiple liquid level sensors. The overflow port is used to discharge excess water when the liquid level in the water collection and sedimentation unit exceeds a set threshold. The multiple liquid level sensors are used to detect the liquid level height in the water collection and sedimentation unit. The pressurized filtration module includes a negative pressure unit, a recharge drive unit, a filtration unit, and a pressure unit. The inlet of the negative pressure unit is connected to the outlet of the water collection and sedimentation module, the outlet of the negative pressure unit is connected to the inlet of the recharge drive unit, the outlet of the recharge drive unit is connected to the inlet of the filtration unit, and the outlet of the filtration unit is connected to the inlet of the pressure unit. The filtration unit is equipped with multiple pressure sensors and water quality sensors. The distribution module includes a main pipe, which is connected to the outlet of the pressure unit. The main pipe is divided into several branch pipes by a distributor. Each branch pipe is connected to its own reinjection well. Each branch pipe before the reinjection well is equipped with a flow control unit. The alarm module is connected to the controller. When the injection flow rate of a certain reinjection well continues to decrease and the decrease exceeds a preset threshold, and the wellhead pressure fluctuates within a preset range, the controller determines that the reinjection well has a blockage trend and controls the alarm module to issue an alarm signal. The controller is configured to execute the aforementioned method for dewatering and recharge of foundation pits in spring-sensitive areas.

[0009] In some embodiments of the present invention, the lower part of the recharge well is provided with a mesh filter layer, which is located within the depth range of the target karst aquifer.

[0010] In some embodiments of the present invention, the filtration accuracy of the filtration unit is 50–100 µm.

[0011] In some embodiments of the present invention, the flow control unit includes an electromagnetic flow meter, a pressure transmitter, and an electric regulating valve, and the controller adjusts the opening of the electric regulating valve according to the feedback signals from the electromagnetic flow meter and the pressure transmitter.

[0012] In some embodiments of the present invention, the controller is used to receive data from multiple level sensors, flow control units, water level gauges, multiple pressure sensors and water quality sensors, and dynamically adjust the operating power of the reinjection drive unit according to a preset control algorithm, thereby adjusting the flow distribution of each reinjection well and maintaining a constant wellhead pressure of the reinjection well.

[0013] In a third aspect of the invention, a pit dewatering recharge device for spring-sensitive areas is provided, the device comprising a memory and a processor; the memory is used to store a computer program; the processor is used to execute the computer program to implement the aforementioned pit dewatering recharge method for spring-sensitive areas.

[0014] One or more technical solutions of the present invention have the following beneficial effects: To address the challenge of adapting a uniform recharge strategy to the coexistence of both channel and fissure media in sensitive karst aquifer areas, this invention constructs a dual-media response model within the controller. A recursive filtering algorithm is used to online invert the permeability coefficients of the channel and fissure, as well as the hydraulic exchange coefficient, automatically identifying the current flow regime and employing adaptive recharge methods. When the channel is identified as the dominant flow regime, pulsed recharge is used to prevent rapid water loss along the channel; when the fissure is identified as the dominant flow regime, continuous constant-flow injection is used to stably raise the regional water level. This differentiated adaptive strategy effectively resolves the contradiction between excessive pressure in the channel area and insufficient recharge in the fissure area, achieving efficient water resource utilization and stable maintenance of the regional groundwater level. This ensures the safety of foundation pit construction while effectively protecting the ecological environment of the spring area.

[0015] To address the problem of cavitation and water extraction interruption in existing reinjection systems under low water level conditions, this invention incorporates a negative pressure unit at the front end of the reinjection drive unit. This negative pressure unit actively creates a negative pressure environment, ensuring the water is smoothly drawn into the reinjection drive unit. Even with drastic fluctuations in the water level of the dewatering well and low liquid levels in the water collection and sedimentation module, the reinjection drive unit can operate continuously and stably, preventing water extraction interruptions and unstable reinjection pressure caused by cavitation.

[0016] To address the problem of existing systems' simple purification methods and low filtration accuracy leading to easy clogging of reinjection wells and karst fissures, this invention installs a filtration unit before the reinjection water enters the reinjection well, controlling the filtration accuracy within a reasonable range to effectively remove suspended particles from the water. Simultaneously, a mesh-like filter layer at the bottom of the reinjection well further blocks residual impurities. This dual filtration mechanism significantly extends the clogging cycle of the reinjection well, reduces the frequency of manual backflushing, and ensures the long-term unobstructed flow of the reinjection channel.

[0017] To address the problems of existing systems' coarse pressure control and the inability of valve throttling to dynamically adapt to aquifer conditions, this invention employs a controller combined with a PID control algorithm to dynamically adjust the operating frequency of the reinjection drive unit, maintaining a constant reinjection wellhead pressure in real time. This closed-loop constant pressure control mechanism ensures that the injection pressure remains within a safe threshold, preventing both overpressure damage to the karst aquifer structure and underpressure leading to ineffective reinjection.

[0018] To address the shortcomings of existing systems that lack independent monitoring and intelligent early warning capabilities for each reinjection well and rely on periodic manual backflow and dredging, this invention equips each branch pipe before the reinjection well with an independent flow control unit, including an electromagnetic flowmeter, a pressure transmitter, and an electric regulating valve. The controller collects the injection flow and wellhead pressure of each well in real time. When the flow rate continuously decreases while the pressure remains constant, it automatically determines the blockage trend and issues an alarm, achieving an upgrade from passive maintenance to predictive maintenance and significantly reducing operation and maintenance costs. Attached Figure Description

[0019] Figure 1 This is a framework diagram of a foundation pit dewatering and recharge system for spring-sensitive areas provided in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the composition of a foundation pit dewatering and recharge system for spring-sensitive areas provided in Embodiment 1 of the present invention. Figure 1 ; Figure 3 This is a schematic diagram of the composition of a foundation pit dewatering and recharge system for spring-sensitive areas provided in Embodiment 1 of the present invention. Figure 2 ; Figure 4 This is a flowchart of a method for recharge of foundation pit dewatering in a spring-sensitive area, as provided in Embodiment 1 of the present invention.

[0020] In the diagram: 1. Water collection and sedimentation module; 2. Inlet; 3. Overflow outlet; 4. Liquid level sensor; 5. Negative pressure unit; 6. Recharge drive unit; 7. Filtration unit; 8. Water quality sensor; 9. Pressure unit; 10. Water distributor; 11. Electromagnetic flow meter; 12. Recharge well; 13. Water level gauge; 14. Alarm module; 15. Dewatering well; 16. Flow control unit; 17. Mesh filter layer; 18. Pressure sensor. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] It should be noted that manual backfilling refers to the process where, during continuous groundwater recharge, suspended particles and air bubbles in the water gradually clog the filter pipes of the recharge well and the pores of the surrounding aquifer, leading to a decrease in recharge capacity. "Backfilling" involves stopping water injection into the well and instead pumping water outwards. This reverse flow of water draws out impurities and air bubbles clogging the filter pipes and nearby strata, thus restoring the recharge well's permeability. This method relies entirely on human judgment and operation. Traditional systems lack the ability to automatically monitor and detect blockages. On-site personnel must rely on experience or wait until a significant decrease in recharge volume is observed before manually starting the backfill pump and opening the corresponding valves to perform the pumping and unblocking operation. This process is intermittent, non-real-time, and labor-intensive.

[0023] Sensitive spring areas refer to karst regions where the groundwater system and surface springs are highly interconnected. In such areas, changes in the groundwater level directly affect the spring's flow pattern. Furthermore, karst aquifers often exhibit dual characteristics of both water-conducting channels and fissures, making them extremely sensitive to rainfall recharge disturbances. Therefore, strict control of groundwater level fluctuations is necessary to protect spring resources.

[0024] Example 1 In a typical embodiment of the present invention, this embodiment provides a method for recharge of foundation pit dewatering in spring-sensitive areas, comprising: The extracted groundwater was filtered and then reinjected into multiple injection wells. During the reinjection process, the wellhead pressure and injection flow rate of each reinjection well are collected in real time; A dual-medium response model for karst aquifers was constructed, which distinguishes between water-conducting channels and fractures, and the model parameters were calculated. A recursive filtering algorithm is used to process the wellhead pressure and injection flow rate, and the model parameters are inverted online to obtain the inversion results; Based on the inversion results, the flow regime of the current reinjection water is identified, and an adaptive reinjection method is adopted to dynamically adjust the flow distribution of each reinjection well and maintain a constant wellhead pressure of the reinjection well. If the injection flow rate of a certain reinjection well drops below a preset threshold, and the wellhead pressure fluctuates within a preset range for a set time, it is determined that the reinjection well has a blockage trend and an alarm signal is issued.

[0025] The model parameters include the permeability coefficient of the water-conducting channel, the permeability coefficient of the fracture, and the hydraulic exchange coefficient between the two. The recursive filtering algorithm employs the extended Kalman filter algorithm. The identification results include the dominant flow regime in the water guiding channel and the dominant flow regime in the fracture. The reinjection methods include pulsed reinjection and continuous constant flow injection reinjection.

[0026] When the identification result indicates that the water guiding channel is the dominant flow state, pulsed recharge is adopted. The duty cycle and pulse frequency of the pulsed recharge are dynamically set according to the ratio of the equivalent permeability coefficient of the water guiding channel to the fracture permeability coefficient. When the identification result indicates that the flow state is dominated by the fracture, continuous constant flow injection recharge is adopted. The target flow rate value of the continuous constant flow injection recharge is determined according to the hydraulic gradient requirements of the fracture.

[0027] After a blockage warning is issued, the system automatically switches the reinjection well to backflushing mode to flush the well wall and aquifer pores with reverse flow. Reinjection is automatically restored after backflushing is completed.

[0028] Specifically: A dual-medium response model for karst aquifers is constructed. The model divides the aquifer into a network of water-conducting channels and a fracture system, and includes the equivalent permeability coefficients of the water-conducting channels, the equivalent permeability coefficients of the fractures, and the hydraulic exchange coefficient between the two. Extended Kalman filtering is used to perform online inversion on the real-time collected wellhead pressure, injection flow rate and monitoring well water level data to obtain real-time estimated values ​​of the model parameters; Based on the inversion results, determine whether the current flow regime is dominated by water-conducting channels or by fractures, and assess the tendency of fracture blockage and geological safety risks. Based on the partition identification results, a multi-objective optimization scheduling model is constructed to generate opening instructions for the regulating valves of each reinjection well branch. When the dominant flow state is identified as the water guiding channel, pulsed reinjection is adopted and the duty cycle and pulse frequency are dynamically set; when the dominant flow state is identified as the fissure, continuous constant flow injection is adopted and the target flow rate is dynamically set; when blockage is detected, the system automatically switches to backwash mode. Meanwhile, geological safety feedback is embedded on the basis of PID algorithm control to build a safety-constrained model predictive control framework. Based on geological safety indicators and pump inlet pressure status, the normal mode, safety priority mode or negative pressure auxiliary mode are switched to achieve millisecond-level closed-loop control.

[0029] The response model for karst dual-medium media is constructed as follows: To address the dual structural characteristics of karst aquifers—combining water-conducting channels and karst fractures—a heterogeneous dual-medium response model with coupled flow-exchange processes is established. This model divides the aquifer into a network of water-conducting channels and a low-permeability matrix fracture system, with the following governing equations: Flow equations in the water guide channel region:

[0030] Flow equation in fractured domain:

[0031] h c , h f —Water head (m) in the water-conducting channel region and the fissure region; S c , S f —Water storage coefficient; K c , K f —Equivalent permeability coefficient; α —Hydraulic exchange coefficient (1 / s), which characterizes the intensity of water exchange between media; Q c , Q f ——Yuanhui Item.

[0032] The model obtains the initial spatial distribution field through distributed fiber optic DTS or conductivity tracer inversion, and performs parameter calibration by combining historical pumping test data.

[0033] Secondly, the real-time inversion and intelligent state recognition are as follows: An extended Kalman filter (EKF) is used to achieve online dynamic inversion of model parameters. The state vector is defined. Observation vector (Wellhead pressure, injection flow rate, and monitoring well water level) Construct a nonlinear observation equation .

[0034] The EKF recursive formula is as follows: Prediction Step:

[0035]

[0036] Update steps:

[0037]

[0038]

[0039] in , Let be the Jacobian matrix, and Q and R be the process and observation noise covariances.

[0040] Based on the inversion results, define the intelligent criterion: 1) Criterion for dominant flow in the water guiding channel: If (Pick This was determined to be the dominant flow pattern in the water guiding channel. 2) Criterion for crack blockage: If (Pick ), triggering a congestion warning; Understandably, in the actual inversion process, if the dominant flow criterion of the water guiding channel is not met and the fracture blockage criterion is not triggered at the same time, that is, the fracture permeability coefficient does not decrease significantly, it can be automatically identified as the dominant flow state of the fracture, and then continuous constant flow injection recharge can be adopted. 3) Geological safety early warning: When micro-strain or turbidity Activate the security protocol.

[0041] Furthermore, the differentiated reinjection strategy and dynamic pressure adaptive adjustment are implemented as follows; Based on the partition identification results, a multi-objective optimization scheduling model is constructed:

[0042] in These are collections of recharge wells, one for the water-conducting channel zone and the other for the fracture zone. For reference traffic.

[0043] After solving, the opening commands of the regulating valves in each branch are generated, realizing: 1) Water diversion channel area: MPa, using pulsed recharge (duty cycle) ); 2) Fractured zone: MPa, continuous constant current injection; 3) Clogged well: Automatically switch to backwash mode (reverse flow) (Continue for 5 minutes).

[0044] Simultaneously, the central controller's intelligent decision-making algorithm designs a safety-constrained model predictive control framework. Geological safety feedback is embedded into the traditional PID controller to construct a multivariate cost function.

[0045] Control strategy security constraints control conditions:

[0046] in For safety margin coefficient, This is an indicator function.

[0047] Control logic: 1) Normal mode: MPa, PID parameters ; 2) Safety Priority Mode: When or Reset (like MPa), and limit the maximum flow rate. ; 3) Negative pressure auxiliary trigger: When the pump inlet pressure MPa, activate the vacuum auxiliary system and maintain MPa, to prevent cavitation.

[0048] All algorithm modules are integrated into the central controller, with a sampling period of... s, achieving millisecond-level closed-loop control.

[0049] Example 2 like Figure 1 , Figure 2 , Figure 3 As shown, this embodiment provides a foundation pit dewatering and recharge system for sensitive spring areas. The system includes a dewatering well 15, a recharge well 12, and a monitoring well. The dewatering well 15 is used to store extracted groundwater, the recharge well 12 is used to store recharge water injected into the target karst aquifer, and the monitoring well is used to monitor the dynamic changes in groundwater level around the foundation pit in real time. A water level gauge 13 is installed in the monitoring well.

[0050] The system also includes a water collection and sedimentation module 1, a pressurized filtration module, a distribution module, and an alarm module 14.

[0051] The inlet 2 of the water collection and sedimentation module 1 is connected to the dewatering well 15. The water collection and sedimentation module 1 is equipped with an overflow port 3 and multiple liquid level sensors 4. The overflow port 3 is used to discharge excess water when the liquid level in the water collection and sedimentation module 1 exceeds the set threshold to prevent system overload. The multiple liquid level sensors 4 are used to detect the liquid level height in the water collection and sedimentation module 1 and provide water volume control signals.

[0052] The pressurized filtration module includes a negative pressure unit 5, a recharge drive unit 6, a filtration unit 7, and a pressure unit 9. The inlet of the negative pressure unit 5 is connected to the outlet of the water collection and sedimentation module 1, the outlet of the negative pressure unit 5 is connected to the inlet of the recharge drive unit 6, the outlet of the recharge drive unit 6 is connected to the inlet of the filtration unit 7, and the outlet of the filtration unit 7 is connected to the inlet of the pressure unit 9. The filtration unit 7 is equipped with multiple pressure sensors 18 and water quality sensors 8. The filtration accuracy of the filtration unit 7 is 50 to 100 microns, which can effectively remove suspended particles in the water.

[0053] The distribution module includes a main pipe, which is connected to the outlet of the pressure unit 9. The main pipe is divided into several branch pipes by the distributor 10. Each branch pipe is connected to its own reinjection well 12. Each branch pipe before the reinjection well 12 is equipped with a flow control unit 16. The flow control unit 16 includes an electromagnetic flow meter 11, a pressure transmitter and an electric regulating valve. The controller adjusts the opening of the electric regulating valve according to the feedback signals from the electromagnetic flow meter 11 and the pressure transmitter to achieve precise control of the flow of a single well.

[0054] The lower part of the reinjection well 12 is provided with a mesh filter layer 17. The mesh filter layer 17 is located within the depth range of the target karst aquifer. It can perform the final filtration before the reinjection water enters the aquifer, while uniformly dispersing the water flow to prevent local blockage or formation damage.

[0055] The alarm module 14 includes a controller and an alarm module. The controller is communicatively connected to the alarm module. The controller receives data from multiple level sensors 4, a flow control unit 16, a water level gauge 13, multiple pressure sensors 18, and a water quality sensor 8. Based on a preset control algorithm, the controller dynamically adjusts the operating power of the reinjection drive unit 6, thereby adjusting the flow distribution of each reinjection well 12 and maintaining a constant wellhead pressure. When the injection flow of a certain reinjection well 12 continuously decreases and the decrease exceeds a preset threshold, while the wellhead pressure fluctuation is within a preset range, the controller determines that the reinjection well 12 has a blockage trend and controls the alarm module to issue an alarm signal.

[0056] The working process of the foundation pit dewatering and recharge system for spring-sensitive areas provided in this embodiment is as follows: First, the extracted groundwater is filtered and then reinjected into multiple reinjection wells 12. Specifically, the dewatering well 15 extracts groundwater from the area surrounding the foundation pit. The groundwater enters the water collection and sedimentation module 1 through the inlet 2. In the water collection and sedimentation module 1, coarse particles of silt in the water settle due to gravity. Multiple level sensors 4 monitor the liquid level in the module in real time. When the liquid level exceeds a set threshold, excess water is discharged from the overflow outlet 3 to prevent system overload.

[0057] After settling, the supernatant enters the negative pressure unit 5 from the outlet of the water collection and sedimentation module 1. Before the reinjection drive unit 6 is started, the negative pressure unit 5 creates a negative pressure environment at the outlet of the water collection and sedimentation module 1, so that the water is steadily drawn into the reinjection drive unit 6. The negative pressure environment can effectively prevent cavitation in the reinjection drive unit 6 under low liquid level conditions, ensuring the stability of the water lifting process.

[0058] The reinjection drive unit 6 pressurizes the water and sends it into the filtration unit 7. Before entering the reinjection well 12, the reinjection water passes through the filtration unit 7 to remove suspended particles. The filtration unit 7 is equipped with a filter element with an accuracy of 50 to 100 microns, multiple pressure sensors 18, and a water quality sensor 8. Suspended particles in the water are filtered out, and the effluent water quality meets the reinjection requirements. The water quality sensor 8 monitors the effluent water quality in real time, and the pressure sensor 18 detects the pressure difference before and after filtration. When the pressure difference is too large, it indicates that the filter element is clogged.

[0059] The filtered clean water enters the pressure unit 9, which buffers water flow pulsation and stabilizes system pressure, reducing the frequent start-stop of the reinjection drive unit 6.

[0060] The water from pressure unit 9 enters the main pipe and is distributed to each branch pipe via distributor 10. Each branch pipe is equipped with a flow control unit 16. Electromagnetic flow meter 11 detects the injection flow of the current branch pipe, and pressure transmitter detects the wellhead pressure of reinjection well 12. The controller adjusts the operating frequency of reinjection drive unit 6 and the opening degree of each electric regulating valve through PID control algorithm according to the preset target pressure value and the actual feedback value, so as to achieve constant pressure reinjection and single well flow distribution.

[0061] The treated reinjection water is evenly injected into the target karst aquifer through the mesh filter layer 17 of the reinjection well 12. The mesh filter layer 17 can block residual fine particles, prevent karst fissures from being blocked, and ensure smooth water flow.

[0062] During the reinjection process, the controller collects the wellhead pressure and injection flow rate of each reinjection well 12 in real time. The controller constructs a dual-medium response model for the karst aquifer, which distinguishes between two media: water-conducting channels and fractures. The model parameters are calculated, including the permeability coefficient of the water-conducting channels, the permeability coefficient of the fractures, and the hydraulic exchange coefficient between the two.

[0063] The controller employs a recursive filtering algorithm to process the wellhead pressure and injection flow rate, obtaining the inversion results by online inversion of model parameters. In this embodiment, the recursive filtering algorithm uses the extended Kalman filter algorithm. The extended Kalman filter can handle the state estimation of nonlinear dynamic systems and is suitable for nonlinear processes such as karst water flow, enabling stable and rapid online inversion of medium parameters.

[0064] Based on the inversion results, the controller identifies the current flow regime of the reinjection water. The identification results include the dominant flow regime in the water guiding channel and the dominant flow regime in the fracture. Based on the identification results, the controller adopts an adaptive reinjection method to dynamically adjust the flow distribution of each reinjection well 12 and maintain a constant wellhead pressure of the reinjection well 12.

[0065] Specifically, when the identification result indicates that the water guiding channel is in the dominant flow state, the controller adopts pulsed recharge. The duty cycle and pulse frequency of the pulsed recharge are dynamically set according to the ratio of the equivalent permeability coefficient of the water guiding channel to the fissure permeability coefficient. This recharge method can prevent water from flowing out rapidly along the main channel, allowing the water to diffuse into the surrounding fissures, while preventing erosion damage to the channel wall due to continuous high pressure.

[0066] When the identification result indicates that the flow pattern is dominated by fractures, the controller employs continuous constant-flow injection recharge. The target flow rate for continuous constant-flow injection recharge is determined based on the hydraulic gradient requirements of the fractures. This recharge method can stably raise the water level in the fracture zone, ensuring recharge efficiency.

[0067] When the injection flow rate of a certain reinjection well 12 drops beyond a preset threshold, and the wellhead pressure fluctuation exceeds a preset range for a set time, the controller determines that the reinjection well 12 has a blockage trend and issues an alarm signal. The alarm module issues an audible and visual alarm and simultaneously uploads the alarm information and real-time data remotely to the monitoring platform. After issuing a blockage warning, the system automatically switches the reinjection well 12 to backflushing mode. In backflushing mode, the controller adjusts the electric regulating valve of the flow control unit 16 to reverse the water flow, or starts the backflushing pump at the bottom of the reinjection well 12 to flush the well wall, the mesh filter layer 17, and the aquifer pores with reverse flow. The backflushing automatically ends after a preset time, the system resumes reinjection mode, and re-monitors flow and pressure changes to verify the unblocking effect.

[0068] To address the issue of cavitation that easily occurs during the water pumping process in existing systems, this embodiment incorporates a negative pressure unit 5 before the reinjection drive unit 6. The negative pressure unit 5 actively creates a negative pressure environment, ensuring that even when the water level in the dewatering well 15 fluctuates significantly and the liquid level in the water collection and sedimentation module 1 is low, the reinjection drive unit 6 can still stably draw water, preventing water pumping interruptions and unstable reinjection pressure due to air intake.

[0069] To address the issues of low filtration accuracy and easy clogging of reinjection wells and karst fissures in existing systems, this embodiment incorporates a filtration unit 7 with a filtration accuracy of 50 to 100 micrometers before the reinjection water enters the reinjection well 12, effectively removing suspended particles. Simultaneously, a mesh-type filter layer 17 is installed at the bottom of the reinjection well 12 to further block residual fine particles. The combined effect of these two elements significantly extends the clogging cycle of the reinjection well 12, reduces the frequency of backflushing, and improves reinjection efficiency. When a clogging trend occurs, the system automatically issues an alarm and switches to backflushing mode, flushing the well wall and aquifer pores with reverse flow. After backflushing, reinjection is automatically restored, achieving an automated closed-loop system for early warning and treatment.

[0070] To address the issues of existing systems' coarse pressure control and inability to dynamically adapt to aquifer conditions, this embodiment employs a controller combined with a PID algorithm to dynamically adjust the operating frequency of the reinjection drive unit 6, maintaining constant pressure in the 12 reinjection wells. The controller collects pressure and flow data from each branch pipe in real time, forming a closed-loop control system that keeps the injection pressure within a safe threshold, preventing overpressure from damaging the karst structure and underpressure from causing ineffective reinjection.

[0071] To address the lack of independent monitoring and intelligent early warning capabilities for each reinjection well in existing systems, this embodiment equips each branch pipe upstream of each reinjection well 12 with an independent flow control unit 16, including an electromagnetic flowmeter 11, a pressure transmitter, and an electric regulating valve. The controller can acquire the injection flow rate and wellhead pressure of each reinjection well 12 in real time, and based on a judgment logic that determines when the flow rate drops beyond a preset threshold while the wellhead pressure fluctuation remains within a preset range, it automatically identifies blockage trends and issues an alarm.

[0072] To address the challenge of adapting a uniform recharge strategy to the coexistence of both conduits and fissures in karst aquifers, this embodiment constructs a dual-medium response model within the controller. Model parameters include the permeability coefficients of the conduits, the fissures, and the hydraulic exchange coefficient between them. An extended Kalman filter algorithm is used to invert these parameters online. Based on the inversion results, the system automatically identifies whether the current flow pattern is dominated by conduits or fissures, and then employs either pulsed recharge or continuous constant-flow injection accordingly. This differentiated adaptive recharge strategy allows for more effective distribution of recharge water to different media regions, avoiding excessive pressure in the conduit area and insufficient recharge in the fissure area, thus improving water resource utilization efficiency and better maintaining the stability of the regional groundwater level.

[0073] The system described in this embodiment has been applied and verified in a deep foundation pit project for a subway station in a spring-sensitive area. The total water inflow of the project is approximately 800 cubic meters per day. It is equipped with a 30-cubic-meter water collection and sedimentation module, a one-operation-one-standby reinjection drive unit, an 80-micron precision filtration unit, a 2-cubic-meter pressure unit, and an operating pressure of 0.1 MPa. Six reinjection wells (12 in total) are installed at a depth of 50 meters, and the controller is set to a reinjection pressure of 0.08 MPa. After three months of continuous operation, the groundwater level fluctuation was controlled within ±0.3 meters, with no ground subsidence or equipment failure, and the reinjection efficiency reached 92%. The results show that the technical solution of this embodiment can safely, efficiently, and intelligently achieve foundation pit dewatering reinjection in spring-sensitive areas, and has good engineering applicability.

[0074] Example 3 This embodiment provides a foundation pit dewatering recharge device for sensitive spring areas. The device includes a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the following foundation pit dewatering recharge method for sensitive spring areas.

[0075] The extracted groundwater is filtered and then reinjected into multiple reinjection wells. Sedimentation removes large particles of silt, and filtration removes suspended solids, ensuring the reinjection water quality meets requirements and laying the foundation for long-term stable reinjection.

[0076] During the reinjection process, the wellhead pressure and injection flow rate of each reinjection well are collected in real time. By configuring independent pressure and flow rate acquisition for each reinjection well, data support is provided for single-well status analysis and differentiated control.

[0077] A dual-medium response model for karst aquifers was constructed. This model distinguishes between two media: water-conducting channels and fractures, and calculates the model parameters. These parameters include the permeability coefficients of the water-conducting channels, fractures, and the hydraulic exchange coefficient between the two.

[0078] A recursive filtering algorithm is used to process the wellhead pressure and injection flow rate, and the model parameters are inverted online to obtain the inversion results. The recursive filtering algorithm employs the extended Kalman filter (EPF). The EPF can fuse real-time observation data with model predictions, dynamically update model parameters, and ensure that the model always reflects the actual state of the aquifer.

[0079] The flow regime of the current reinjection water is identified based on the inversion results. The identification results include the dominant flow regime in the water-conducting channel and the dominant flow regime in the fractures. An adaptive reinjection method is adopted based on the identification results, dynamically adjusting the flow distribution of each reinjection well to maintain a constant wellhead pressure. When the identification result indicates that the water-conducting channel is dominant, pulsed reinjection is used. The duty cycle and pulse frequency of pulsed reinjection are dynamically set based on the ratio of the equivalent permeability coefficient of the water-conducting channel to the permeability coefficient of the fracture. When the identification result indicates that the fracture is dominant, continuous constant-flow injection reinjection is used. The target flow rate value for continuous constant-flow injection reinjection is determined based on the hydraulic gradient requirements of the fractures.

[0080] When the injection flow rate of a reinjection well drops below a preset threshold, and the wellhead pressure fluctuates within a preset range for a set time, the well is determined to have a blockage trend and an alarm signal is issued. After the blockage warning is issued, the reinjection well is automatically switched to backflushing mode to flush the well wall and aquifer pores with reverse flow. Reinjection is automatically restored after backflushing is completed.

[0081] When the above method is executed by a controller or special equipment, it can realize fully automatic intelligent control of dewatering and recharge of foundation pits in sensitive areas of the spring.

[0082] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for recharge of foundation pit dewatering in spring-sensitive areas, characterized in that, include: The extracted groundwater was filtered and then reinjected into multiple injection wells. During the reinjection process, the wellhead pressure and injection flow rate of each reinjection well, as well as the water level data of the monitoring well, are collected in real time. A dual-medium response model for karst aquifers was constructed, which distinguishes between water-conducting channels and fractures, and the model parameters were calculated. A recursive filtering algorithm was used to process the wellhead pressure, injection flow rate, and water level data, and the model parameters were inverted online to obtain the inversion results. Based on the inversion results, the flow regime of the current reinjection water is identified, and an adaptive reinjection method is adopted to dynamically adjust the flow distribution of each reinjection well and maintain a constant wellhead pressure of the reinjection well. If the injection flow rate of a certain reinjection well drops below a preset threshold, and the wellhead pressure fluctuates within a preset range for a set time, it is determined that the reinjection well has a blockage trend and an alarm signal is issued.

2. The method for recharge of foundation pit dewatering in a spring-sensitive area as described in claim 1, characterized in that, The model parameters include the permeability coefficient of the water-conducting channel, the permeability coefficient of the fracture, and the hydraulic exchange coefficient between the two. The recursive filtering algorithm employs the extended Kalman filter algorithm. The identification results include the dominant flow regime in the water guiding channel and the dominant flow regime in the fracture. The reinjection methods include pulsed reinjection and continuous constant flow injection reinjection.

3. The method for recharge of foundation pit dewatering in a spring-sensitive area as described in claim 2, characterized in that, When the identification result indicates that the water guiding channel is the dominant flow state, pulsed recharge is adopted. The duty cycle and pulse frequency of the pulsed recharge are dynamically set according to the ratio of the equivalent permeability coefficient of the water guiding channel to the fracture permeability coefficient. When the identification result indicates that the flow state is dominated by the fracture, continuous constant flow injection recharge is adopted. The target flow rate value of the continuous constant flow injection recharge is determined according to the hydraulic gradient requirements of the fracture.

4. The method for recharge of foundation pit dewatering in spring-sensitive areas as described in claim 1, characterized in that, After a blockage warning is issued, the system automatically switches the reinjection well to backflushing mode to flush the well wall and aquifer pores with reverse flow. Reinjection is automatically restored after backflushing is completed.

5. A foundation pit dewatering and recharge system for sensitive spring areas, comprising a dewatering well, a recharge well, and a monitoring well, wherein the dewatering well is used to store extracted groundwater, the recharge well is used to store recharge water injected into a target karst aquifer, and the monitoring well is used to monitor the dynamic changes in groundwater level around the foundation pit in real time, and the monitoring well is equipped with a water level gauge, characterized in that... Also includes: Water collection and sedimentation module, pressurized filtration module, distribution module, alarm module and controller; The inlet of the water collection and sedimentation module is connected to the rainwater well. The water collection and sedimentation module is equipped with an overflow port and multiple liquid level sensors. The overflow port is used to discharge excess water when the liquid level in the water collection and sedimentation unit exceeds a set threshold. The multiple liquid level sensors are used to detect the liquid level height in the water collection and sedimentation unit. The pressurized filtration module includes a negative pressure unit, a recharge drive unit, a filtration unit, and a pressure unit. The inlet of the negative pressure unit is connected to the outlet of the water collection and sedimentation module, the outlet of the negative pressure unit is connected to the inlet of the recharge drive unit, the outlet of the recharge drive unit is connected to the inlet of the filtration unit, and the outlet of the filtration unit is connected to the inlet of the pressure unit. The filtration unit is equipped with multiple pressure sensors and water quality sensors. The distribution module includes a main pipe, which is connected to the outlet of the pressure unit. The main pipe is divided into several branch pipes by a distributor. Each branch pipe is connected to its own reinjection well. Each branch pipe before the reinjection well is equipped with a flow control unit. The alarm module is connected to the controller. When the injection flow rate of a certain reinjection well continues to decrease and the decrease exceeds a preset threshold, and the wellhead pressure fluctuates within a preset range, the controller determines that the reinjection well has a blockage trend and controls the alarm module to issue an alarm signal. The controller is configured to perform a method for recharge of foundation pit dewatering in a spring-sensitive area as described in any one of claims 1-4.

6. A foundation pit dewatering and recharge system for spring-sensitive areas as described in claim 5, characterized in that, The lower part of the recharge well is provided with a mesh filter layer, which is located within the depth range of the target karst aquifer.

7. A foundation pit dewatering and recharge system for spring-sensitive areas as described in claim 5, characterized in that, The filtration accuracy of the filter unit is 50–100 µm.

8. A foundation pit dewatering and recharge system for spring-sensitive areas as described in claim 5, characterized in that, The flow control unit includes an electromagnetic flow meter, a pressure transmitter, and an electric regulating valve. The controller adjusts the opening of the electric regulating valve based on feedback signals from the electromagnetic flow meter and the pressure transmitter.

9. A foundation pit dewatering and recharge system for sensitive spring areas as described in claim 5, characterized in that, The controller is used to receive data from multiple level sensors, flow control units, water level gauges, multiple pressure sensors and water quality sensors, and dynamically adjust the operating power of the reinjection drive unit according to a preset control algorithm, thereby adjusting the flow distribution of each reinjection well and maintaining a constant wellhead pressure of the reinjection well.

10. A foundation pit dewatering and recharge device for sensitive spring areas, characterized in that, The device includes a memory and a processor; the memory is used to store a computer program; the processor is used to implement, when executing the computer program, a method for recharge of foundation pit dewatering in a spring-sensitive area as described in any one of claims 1 to 4.

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