Integrated emission reduction and foundation pit excavation construction method

Abstract

The application discloses a kind of integrated foundation pit excavation construction methods of reducing and discharging, belong to geotechnical engineering and underground space engineering technical field, this method includes pre-construction preparation, surface excavation clear discharge, middle layer joint precipitation, deep layer cascade depressurization, and six steps of dynamic control and discharge water separation quality recycling throughout whole process of differential pressure.Differential pressure dynamic control step is calculated by pore water pressure gauge and pit outside liquid level gauge real time each partition differential pressure value, with excavation depth and weather warning level as double input parameter dynamic update control threshold, according to differential pressure exceeding amplitude trigger three-stage pumping rate response and linkage recharge volume adjustment.Discharge water is filtered after three-stage series sedimentation by programmable logic controller according to turbidity threshold value, automatically shunted to concrete curing, equipment cooling or road dust pipe network, realize on-site resource recycling.The application solves the problems of high engineering safety risk in the prior art, weak response ability in extreme working conditions and serious waste of water resources in the process of foundation pit construction.

Description

Technical Field

[0001] This invention relates to the fields of geotechnical engineering and underground space engineering technology, specifically to an integrated method for excavating and constructing foundation pits that combines drainage and excavation. Background Technology

[0002] A foundation pit is a large space excavated below ground level in order to meet the needs of underground space use during engineering construction. Dewatering of foundation pits is a fundamental construction procedure in underground engineering.

[0003] In existing technologies, a fixed dewatering scheme and target water level need to be determined using empirical formulas based on a geological survey report before construction, and these are generally not adjusted during the entire construction process. During surface excavation, drainage ditches are dug around the bottom of the pit and a sump is constructed. Small water pumps are used to pump the accumulated water to a sedimentation tank outside the pit. The drainage system and the subsequent well dewatering system are independent of each other in terms of physical pipe network and operating teams. During the medium-deep excavation stage, the pre-constructed dewatering wells are started, and submersible pumps are run at a fixed speed to continuously pump water. During construction, adjustments are made based on empirical observations of water level during manual inspections, usually once or twice a day. When approaching the design excavation elevation, depressurization wells are started to depressurize the confined water, also using a fixed-frequency pumping mode. Finally, the groundwater pumped out at each stage is discharged into a temporary sedimentation tank outside the pit through drainage pipes. After simple sedimentation, all of it is discharged into the municipal pipe network or natural water bodies.

[0004] However, the above-mentioned scheme has the following drawbacks during construction: First, static control leads to high engineering safety risks. The current static dewatering mode of "preliminary design, fixed parameters, and manual inspection" does not automatically adjust the dewatering rate according to changes in real-time differential pressure inside and outside the pit and meteorological conditions. When extreme rainfall or excavation disturbance causes sudden changes in the seepage field, the water level inside the pit rises sharply and the pumping system cannot respond in time. This can cause water accumulation at the bottom of the pit, affecting construction, or even trigger catastrophic geological disasters such as quicksand, piping, or confined water surge. Conversely, when the precipitation exceeds the actual demand, the water level outside the pit drops excessively, causing significant ground subsidence in the surrounding area and endangering the safety of existing buildings and underground pipelines. Second, the isolated systems result in poor linkage and weak ability to cope with extreme working conditions. The three systems of open ditch drainage, wellpoint dewatering, and deep depressurization are managed by different teams, lacking a unified scheduling protocol and physical pipeline interface. Switching between systems relies on manual judgment and experience, and there are no quantitative standards for the timing and procedures of the switch. During the critical time window of transitioning from surface drainage to mid-level well dewatering, a "dewatering vacuum period" can easily occur due to a lag in the transition, causing groundwater in the water-rich sand layer to form seepage channels on the pit wall, triggering collapse. Third, direct discharge leads to a serious waste of water resources. Current technologies do not incorporate any online water quality assessment and diversion mechanisms for dewatering at the construction process level, discharging all pumped water indiscriminately to the outside. The daily pumping volume for large-scale hydraulic foundation pit construction often ranges from several thousand to tens of thousands of cubic meters, a large portion of which is shallowly filtered groundwater of good quality, fully meeting the water quality requirements for concrete curing, equipment cooling, and road dust suppression at the construction site. Direct discharge results in a huge waste of high-quality water resources. Summary of the Invention

[0005] The purpose of this invention is to provide an integrated excavation and construction method for foundation pits that combines drainage and drainage, in order to solve the problems of high engineering safety risks, weak ability to cope with extreme working conditions, and serious waste of water resources in the construction of foundation pits in the prior art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: an integrated dewatering and drainage foundation pit excavation construction method, including a pre-construction preparation step, a surface excavation and open drainage step, a middle layer combined dewatering step, a deep layer cascade depressure step, and a differential pressure dynamic control step and a dewatering and drainage separation and reuse step that run through all the above steps.

[0007] As a preferred technical solution of the present invention: the pre-construction preparation steps include: dividing the foundation pit plane into several rectangular control zones, and vertically dividing it into three vertical layers according to the distribution of aquifers: surface unconfined water zone, middle water-rich sand layer zone, and deep confined water zone, and constructing a three-dimensional grid control system; burying pore water pressure gauges at the center of each control zone, and deploying high-precision level gauges in observation wells at corresponding positions outside the pit, and connecting the sensor data to the construction information management platform; completing the pre-construction of dewatering wells, light well points, depressurization wells and pipelines, and entering the benchmark differential pressure threshold table corresponding to each excavation depth.

[0008] As a preferred technical solution of the present invention: the differential pressure dynamic control step includes: collecting pore water pressure in each zone pit and groundwater level outside the pit according to a fixed control cycle, calculating the real-time differential pressure value of each vertical layer in each zone, and taking the global maximum differential pressure value as the current control characteristic quantity; obtaining the benchmark upper limit threshold and benchmark lower limit threshold by querying the benchmark threshold table according to the current excavation depth, and then applying a correction coefficient to the benchmark upper limit threshold according to the current meteorological warning level to obtain the dynamic upper limit threshold; comparing the global maximum differential pressure value with the dynamic upper limit threshold and lower limit threshold, and triggering the corresponding level of variable frequency precipitation pumping rate adjustment command and linking the adjustment of the external recharge volume according to the excess amplitude.

[0009] As a preferred technical solution of the present invention: the surface excavation and drainage step includes: starting the pit bottom open ditch drainage system and simultaneously running the differential pressure dynamic control step; when the distance between the excavation face and the top plate of the aquifer is no more than 2 meters and it is planned to continue excavation within 48 hours, the light well point and pipe well combined dewatering system is started 24 to 48 hours in advance, and the physical connection between the open drainage system and the pipe well system is completed through the diversion channel. After confirming that the water level in the pit has dropped to at least 0.5 meters below the top plate of the aquifer, the middle layer combined dewatering step is entered.

[0010] As a preferred technical solution of the present invention: the intermediate layer combined dewatering step includes: using well combined dewatering as the main method, switching the open drainage system to an auxiliary mode, and the differential pressure dynamic control step being involved throughout the process; when the distance between the excavation face and the top plate of the confined aquifer is no more than 3 meters, the anti-surge stability safety factor is no less than 1.1, and the depressurization well is commissioned, the depressurization well is started to lower the confined water head to a safe water level below the bottom of the pit, the open drainage network is transformed into an emergency backup external drainage channel, and the deep layer stepped depressurization step is entered.

[0011] As a preferred technical solution of the present invention: the deep cascade depressurization step includes: continuous operation of the depressurization well, real-time monitoring by the differential pressure control system, bottom sealing construction after excavation to the design elevation, and gradually stopping the operation of the depressurization well according to the bottom anti-buoyancy calculation results after the bottom sealing is completed.

[0012] As a preferred technical solution of the present invention: the step of separating and reusing the dewatering water includes: the groundwater pumped out in each step is collected into the main pipe, and then subjected to progressive physical filtration through a three-stage series sedimentation transfer tank, with the pore sizes of each stage being 5 mm, 1 mm, and 0.2 mm respectively; the turbidity value of the water is collected in real time by an online turbidity sensor at the outlet of the final sedimentation tank; the programmable logic controller automatically drives an electric three-way diversion valve according to the comparison result of the turbidity value and the preset turbidity classification threshold: water with turbidity not greater than 10 NTU is introduced into the low turbidity water pipeline network for concrete curing spraying and equipment cooling circulation system; water with turbidity greater than 10 NTU but not greater than 50 NTU is introduced into the medium turbidity water pipeline network for on-site road dust suppression spraying and mechanical cleaning; water with turbidity greater than 50 NTU is introduced into the excess water pipeline network and discharged into a temporary sedimentation tank outside the pit, and discharged after the water quality is retested and meets the discharge standards.

[0013] As a preferred technical solution of the present invention: In the differential pressure dynamic control step, when the dynamic upper limit threshold is exceeded, a three-level response is triggered based on the magnitude of the exceedance: When the global maximum differential pressure value exceeds the dynamic upper limit threshold by no more than 10%, a first-level response is triggered, the frequency converter dewatering well group speeds up to 70% of the rated speed, and the external reinjection volume is simultaneously reduced to 10% of the rated reinjection volume; When the global maximum differential pressure value exceeds the dynamic upper limit threshold by more than 10% but no more than 30%, a second-level response is triggered, the frequency converter dewatering well group speeds up to 100% of the rated speed, external reinjection is stopped, and a warning notification is issued to project management personnel; When the global maximum differential pressure value exceeds the dynamic upper limit threshold by more than 30%, a third-level response is triggered: the standby pump group is started to run at full speed, the emergency drainage channel is activated, an on-site audible and visual alarm is issued, and personnel are notified to evacuate to a safe area; When the global maximum differential pressure value is lower than the lower limit threshold, the frequency converter dewatering well group speeds up to 40% of the rated speed, and the external reinjection volume is increased to 80% of the rated reinjection volume.

[0014] As a preferred technical solution of the present invention: in the surface excavation and open drainage step, the diversion channel is set on the side wall of the cofferdam or underground continuous wall, and the diversion channel interface is reserved at an appropriate position above the manhole. The diversion channel is a precast concrete channel or a welded steel plate channel, sloping towards the manhole with a slope of not less than 1%, and a filter screen is set at the interface of the diversion channel.

[0015] As a preferred technical solution of the present invention: the benchmark differential pressure threshold table is pre-formulated by geotechnical engineers based on geological survey reports, soil permeability parameters, and anti-surge stability calculation results. It includes the benchmark upper limit threshold and benchmark lower limit threshold corresponding to each excavation depth, and is fixed as construction parameters in the construction information management platform; the control cycle is 30 seconds; in the step of separating and reusing dewatering water, a closed-loop water quality re-inspection is set up in the excess water pipeline: after sedimentation treatment in the temporary sedimentation tank outside the pit, the turbidity of the water body is detected again. If the turbidity meets the discharge standard, it is discharged into the municipal pipeline or natural water system. If the turbidity still exceeds the standard, it is returned to the filter box for re-treatment; all recycled water volume is included in the water recycling metering ledger, a daily water recycling report is generated and uploaded to the construction information management platform.

[0016] By adopting the above technical solution, the beneficial effects of the present invention are: 1. By introducing meteorological early warning signals and real-time differential pressure monitoring to drive the variable frequency dewatering well group to automatically adjust the pumping rate in stages, and linking it with the external recharge system, active safety control with millisecond-level response is achieved, keeping the risks of ground settlement outside the pit and pit bottom heave within the design allowable range, and significantly improving the safety factor of foundation pit construction.

[0017] 2. By formulating a three-stage seamless connection standard for drainage procedures, which uses "starting dewatering 24 to 48 hours in advance" as a time constraint, "physical connection of diversion channels to achieve pipeline reuse" as a structural constraint, and "anti-surge safety factor of not less than 1.1" as a conversion judgment criterion, the system island phenomenon is eliminated, and the reliability of foundation pit drainage under extreme working conditions is significantly enhanced.

[0018] 3. By embedding an on-site online water quality identification and classification utilization process, the dewatering wastewater is diverted to construction water networks for concrete curing, equipment cooling, and road dust suppression according to the turbidity threshold, realizing the on-site resource recycling of dewatering wastewater, significantly reducing the cost of tap water procurement and reducing the amount of external drainage. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the main technical framework of the integrated drainage and excavation method for foundation pit excavation of the present invention; Figure 2 This is a flowchart of the differential pressure dynamic reduction and discharge linkage control in this invention; Figure 3 This is a flowchart illustrating the seamless connection of the three-stage emission reduction process in this invention. Figure 4 This is a flowchart of the wastewater separation and reuse system of the present invention. Detailed Implementation

[0020] The embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention. In the description of the present invention, it should be understood that the terms "upper," "lower," "front," "upper surface," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the present invention. In the present invention, unless otherwise expressly specified and limited, the terms "installed," "connected," "joined," "fixed," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or mutual communication; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the present invention can be understood according to the specific circumstances.

[0021] Please see Figure 1 The present invention provides an integrated dewatering and drainage excavation method for foundation pits, comprising three functional layers: a perception layer responsible for real-time collection of multi-source data from pore water pressure gauges, external level gauges, pipeline turbidity sensors, and external meteorological stations in various sections of the foundation pit; a decision-making layer calculating real-time differential pressure values ​​based on the collected data, dynamically updating control thresholds, and triggering tiered early warning signals; and an execution layer receiving early warning commands and synchronously driving four types of actuators—variable frequency dewatering well groups, external reinjection systems, dewatering and drainage conversion systems, and differentiated reuse systems—to coordinate their actions. These three layers interact and issue commands through a unified construction information management platform, forming a closed-loop control system of "perception—decision—execution—feedback."

[0022] Pre-construction preparation: Before construction, a construction plan is prepared based on the survey data and hydrogeological parameters. The foundation pit is divided into several rectangular control zones in plan view, and vertically divided into three levels according to the distribution of aquifers: surface unconfined water zone, intermediate water-rich sand layer zone, and deep confined aquifer zone, constructing a three-dimensional grid control system. Pore water pressure gauges are installed at the center of each control zone, and high-precision level gauges are installed in observation wells at corresponding locations outside the pit. Sensor data is connected to the construction information management platform. Pre-construction of dewatering wells, lightweight well points, pressure reduction wells, and pipelines is completed, and the benchmark differential pressure threshold table corresponding to each excavation depth is entered. The benchmark threshold table is then fixed in the control system, and the meteorological information interface is debugged, and the separate reuse valve group is commissioned.

[0023] Differential pressure dynamic control: such as Figure 2As shown, the differential pressure dynamic control steps are executed cyclically according to a fixed control cycle (30 seconds is recommended) throughout the entire foundation pit excavation process.

[0024] Real-time differential pressure calculation: For the i-th planar section and the j-th vertical control layer within the foundation pit, the pore water pressure at that location is read by a pore water pressure gauge. (Unit: kPa), convert to the equivalent water head value in the pit using the following formula. (Unit: m):

[0025] in, Absolute elevation of the pore water pressure gauge installation location (unit: m); The specific weight of water is taken as 9.81 kN / m³. 3 .

[0026] The groundwater level outside the pit is read from the level gauge of the corresponding observation well outside the pit. (Unit: m), calculate the real-time differential pressure value of the j-th layer in the i-th partition. (Unit: m):

[0027] when When the water head outside the pit is higher than inside, and the seepage direction is from outside to inside, there is a risk of seepage pressure. This indicates that the water head inside the pit is higher than outside, indicating excessive precipitation, which may cause an excessive drop in the water level outside the pit. The maximum value among the real-time differential pressure values ​​of each zone and level is taken. As the global control differential pressure characteristic at the current moment, it is input to the dynamic threshold judgment module.

[0028] Dynamic threshold update: The system reads the current excavation depth every control cycle. (Unit: m) and current weather warning level Weather warning level The definition is as follows: No warning issued (clear weather); A blue alert has been issued (rainfall exceeding 50mm is expected within 6 hours). A yellow alert has been issued (rainfall exceeding 50 mm is expected within 3 hours). An orange alert or higher is issued (rainfall is expected to exceed 50 mm within one hour).

[0029] According to the excavation depth Query the benchmark threshold table to obtain the benchmark upper limit threshold. and the lower limit threshold According to the weather warning level Corresponding correction factor Dynamic tightening control upper limit:

[0030] in, The rules for determining the value are as follows: hour ; hour ; hour ; hour The higher the weather warning level, the greater the tightening of the dynamic upper threshold, and the earlier the system enters high-speed pumping mode, achieving proactive defense based on prior meteorological data. Lower threshold. Take directly It will not be revised according to the weather warning level.

[0031] Tiered and coordinated response: Will and and Comparison: when and At this time, maintain the current operating state and keep the normal control parameters unchanged.

[0032] when When the frequency conversion dewatering well group is reduced to 40% of its rated speed, the amount of water recharge outside the pit is simultaneously increased to 80% of the rated amount to prevent excessive water level drop outside the pit from causing ground subsidence.

[0033] when When the exceedance is not greater than 10%, a three-level response is triggered: When this occurs, a Level 1 response is triggered, increasing the speed of the variable frequency dewatering well group to 70% of its rated speed, while simultaneously reducing the external recharge volume to 10% of the rated recharge volume; if the excess exceeds 10% but not more than 30% (i.e., ... When this occurs, a Level 2 response is triggered, the variable frequency dewatering well group accelerates to 100% of its rated speed, stops external recharge, and sends a warning SMS to project management personnel; if the deviation exceeds 30% (i.e., When the emergency response is activated, a Level 3 response is triggered, the backup pump unit starts running at full speed, the emergency drainage channel is activated, an on-site audible and visual alarm is issued, and personnel are notified to evacuate to a safe area.

[0034] After each control action is executed, the latest monitoring data is written back to the historical database for subsequent trend analysis.

[0035] like Figure 3As shown, the entire process of foundation pit excavation is divided into three main stages, and the stages are judged and switched through clear quantitative conditions.

[0036] Surface Excavation and Drainage: The excavation face is located within 2 meters above the top of the aquifer. Drainage ditches are constructed around the perimeter of the pit, with sump pits at the four corners. The pit bottom drainage system is activated, and small pumps pump the accumulated water from the ditches to the drainage collection pipe. Differential pressure dynamic control is implemented simultaneously. Checking the transition conditions from Stage 1 to Stage 2: If the current excavation face is no more than 2 meters from the top of the aquifer and excavation is planned to continue within 48 hours, the transition conditions are met, and the transition procedure begins; otherwise, excavation continues, drainage is maintained, and differential pressure anomalies are monitored.

[0037] Start the light wellpoint and well combined dewatering system 24 to 48 hours in advance, connect the open ditch diversion channel to the redundant water collection space of the well, the diversion channel is a precast concrete channel or a welded steel plate channel, sloping towards the wellhead of the well with a slope of not less than 1%, and install a filter screen at the interface of the diversion channel to prevent large-diameter debris from entering the well and clogging the pump unit; after confirming that the water level in the pit has dropped to at least 0.5 meters below the top plate of the aquifer, excavation can continue.

[0038] Mid-level combined dewatering: This primarily utilizes combined well dewatering, with the open drainage system becoming an auxiliary mode. Open water flows through diversion channels into the redundant collection space of the wells, and differential pressure dynamic control is implemented throughout the process. The transition conditions from Stage Two to Stage Three are checked as follows: If the distance between the excavation face and the top of the confined aquifer is no more than 3 meters, the anti-surge stability safety factor is no less than 1.1, and the depressurization wells are fully commissioned, then the transition conditions are met; otherwise, the excavation plan is suspended, additional depressurization wells are added, or support is strengthened, and the formation parameters are recalculated.

[0039] The pressure-reducing well is activated to lower the pressurized water head to a safe level below the bottom of the pit; the open drainage network is transformed into an emergency backup drainage channel and connected to an emergency drainage pump to achieve the reuse of network resources.

[0040] Deep cascade depressurization: Depressurization wells operate continuously, monitored in real time by a differential pressure control system. After excavation to the design elevation, the bottom slab is sealed. After sealing, the depressurization wells are stopped based on the bottom slab's anti-buoyancy calculations: if the bottom slab structure has anti-buoyancy capabilities, the operation of each depressurization well is gradually stopped; otherwise, the depressurization wells are maintained until the superstructure has anti-buoyancy capabilities. After construction is completed, all dewatering systems are shut down in an orderly manner, temporary facilities are dismantled, and water resource utilization records and construction monitoring reports are compiled.

[0041] like Figure 4 As shown, the wastewater separation and reuse steps are carried out in parallel throughout the three excavation stages mentioned above.

[0042] After the groundwater pumped out at each stage flows into the main drainage pipe, it first enters a three-stage series sedimentation transfer tank for progressive physical filtration: the first-stage tank is equipped with a self-cleaning filter screen with a pore size of 5 mm to remove large suspended particles; the second-stage tank is equipped with a self-cleaning filter screen with a pore size of 1 mm to further remove fine particles; and the final-stage tank is equipped with a self-cleaning filter screen with a pore size of 0.2 mm to complete fine filtration.

[0043] An online turbidity sensor is installed at the outlet of the final sedimentation tank to collect the turbidity value (unit: NTU) of the treated water in real time, with a sampling frequency of no less than once per minute. An electric three-way diversion valve is installed approximately 0.5 meters downstream of the turbidity sensor. A programmable logic controller (PLC) automatically switches the diversion direction based on the turbidity sensor signal. The grading thresholds are set as follows: the low turbidity threshold (NTU not greater than 10) is based on the water quality requirements for non-potable water used for concrete curing in the "Standard for Water Used in Concrete" (JGJ 63); the medium turbidity threshold (NTU greater than 10 and not greater than 50) is based on engineering practice experience values ​​for road washing and construction machinery cleaning water; water exceeding 50 NTU enters a temporary sedimentation tank to ensure that the final effluent meets the "Integrated Wastewater Discharge Standard" (GB 8978) and the discharge requirements of the local environmental protection authority.

[0044] For water with a turbidity of no more than 10 NTU, the electric three-way valve switches to the low-turbidity water supply network and directs it into the concrete curing spray system and construction equipment cooling circulation system. For water with a turbidity greater than 10 NTU but no more than 50 NTU, the electric three-way valve switches to the medium-turbidity water supply network and directs it into the on-site road dust suppression spray system and tracked mechanical cleaning tank. For water with a turbidity greater than 50 NTU, the electric three-way valve switches to the excess wastewater network and discharges it into a temporary sedimentation tank outside the pit. Only after the water quality is retested and meets the discharge standards can it be discharged into the municipal pipe network or natural water system. Water that does not meet the standards will continue to undergo sedimentation treatment or be returned to the filter box for retreatment. All recycled water volume is included in the water recycling metering ledger, generating daily water recycling reports and uploading them to the construction information management platform to achieve full traceability of water resource utilization.

[0045] In practical engineering applications, compared with existing static dewatering schemes, this invention can effectively eliminate the risks of water accumulation at the bottom of the pit and excessive ground settlement caused by the lag in the rate of precipitation. The seamless switching of the three drainage systems eliminates the "dewatering vacuum period". The separate reuse of dewatering and drainage can significantly reduce the daily water consumption at the construction site and greatly reduce the amount of external drainage. It comprehensively achieves a triple improvement in safety, coordination and resource utilization in foundation pit dewatering and drainage construction.

[0046] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A method for integrated excavation and drainage of foundation pits, characterized in that, It includes pre-construction preparation steps, surface excavation and drainage steps, intermediate layer combined dewatering steps, deep layer cascade depressurization steps, differential pressure dynamic control steps and dewatering and drainage separation and reuse steps that run through all the above steps.

2. The integrated excavation and construction method for foundation pits with drainage and lowering as described in claim 1, characterized in that, The pre-construction preparation steps include: dividing the foundation pit into several rectangular control zones in plan, and vertically dividing it into three levels according to the distribution of aquifers: surface unconfined water zone, middle water-rich sand layer zone, and deep confined water zone, thus constructing a three-dimensional grid control system; burying pore water pressure gauges at the center of each control zone, and deploying high-precision level gauges in observation wells at corresponding locations outside the pit, with sensor data connected to the construction information management platform; completing the pre-construction of dewatering wells, lightweight well points, pressure-reducing wells, and pipelines, and entering the benchmark differential pressure threshold table corresponding to each excavation depth.

3. The integrated excavation and construction method for foundation pits with drainage and lowering as described in claim 1, characterized in that, The differential pressure dynamic control steps include: collecting pore water pressure inside the pit and groundwater level outside the pit according to a fixed control cycle; calculating the real-time differential pressure value of each vertical level in each zone; taking the global maximum differential pressure value as the current control characteristic quantity; obtaining the benchmark upper limit threshold and benchmark lower limit threshold by querying the benchmark threshold table according to the current excavation depth; then applying a correction coefficient to the benchmark upper limit threshold according to the current meteorological warning level to obtain the dynamic upper limit threshold; comparing the global maximum differential pressure value with the dynamic upper limit threshold and lower limit threshold; and triggering the corresponding level of variable frequency precipitation pumping rate adjustment command and linking the external recharge volume adjustment according to the excess amplitude.

4. The integrated excavation and construction method for foundation pits with drainage and lowering as described in claim 1, characterized in that, The surface excavation and drainage steps include: starting the open ditch drainage system at the bottom of the pit and simultaneously operating the differential pressure dynamic control steps; when the distance between the excavation face and the top plate of the aquifer is no more than 2 meters and it is planned to continue excavation within 48 hours, starting the light well point and pipe well combined dewatering system 24 to 48 hours in advance, completing the physical connection between the open drainage system and the pipe well system through the diversion channel, and after confirming that the water level in the pit has dropped to at least 0.5 meters below the top plate of the aquifer, proceeding to the middle layer combined dewatering steps.

5. The integrated excavation and construction method for foundation pits with drainage and lowering as described in claim 1, characterized in that, The intermediate-level combined dewatering steps include: using well-based combined dewatering as the main method, switching the open drainage system to an auxiliary mode, and the differential pressure dynamic control step being involved throughout the process; when the distance between the excavation face and the top plate of the confined aquifer is no more than 3 meters, the safety factor for anti-surge stability is no less than 1.1, and the depressurization well is commissioned, the depressurization well is activated to lower the confined water head to a safe water level below the bottom of the pit, the open drainage network is transformed into an emergency backup external drainage channel, and the deep-level stepped depressurization step is entered.

6. The integrated excavation and construction method for foundation pits with drainage and lowering functions according to claim 1, characterized in that, The deep-level step-by-step depressurization process includes: continuous operation of the depressurization well, real-time monitoring by the differential pressure control system, bottom sealing construction after excavation to the design elevation, and gradual cessation of depressurization well operation based on the bottom plate anti-buoyancy calculation results after the bottom sealing is completed.

7. The integrated excavation and construction method for foundation pits with drainage and lowering as described in claim 1, characterized in that, The groundwater recycling process includes: collecting the groundwater pumped from each step into a main pipe, and then subjecting it to progressive physical filtration through a three-stage series sedimentation transfer tank, with filter apertures of 5 mm, 1 mm, and 0.2 mm respectively; real-time turbidity values ​​of the water body are collected by an online turbidity sensor at the outlet of the final sedimentation tank; and automatically driving an electric three-way diversion valve based on the comparison between the turbidity value and a preset turbidity classification threshold: water with turbidity not exceeding 10 NTU is diverted to a low-turbidity water network for concrete curing spraying and equipment cooling circulation systems; water with turbidity greater than 10 NTU but not exceeding 50 NTU is diverted to a medium-turbidity water network for on-site road dust suppression spraying and mechanical cleaning; and water with turbidity greater than 50 NTU is diverted to an excess water network and discharged into a temporary sedimentation tank outside the pit, where it is discharged after a water quality retest to meet discharge standards.

8. The integrated excavation and construction method for foundation pit with drainage and lowering as described in claim 3, characterized in that, In the differential pressure dynamic control step, when the dynamic upper limit threshold is exceeded, a three-level response is triggered based on the magnitude of the exceedance: when the global maximum differential pressure value exceeds the dynamic upper limit threshold by no more than 10%, a first-level response is triggered, the frequency converter dewatering well group is accelerated to 70% of the rated speed, and the external reinjection volume is simultaneously reduced to 10% of the rated reinjection volume; when the global maximum differential pressure value exceeds the dynamic upper limit threshold by more than 10% but no more than 30%, a second-level response is triggered, the frequency converter dewatering well group is accelerated to 100% of the rated speed, external reinjection is stopped, and an early warning notification is issued to the project management personnel. When the global maximum differential pressure exceeds the dynamic upper limit threshold by more than 30%, a level 3 response is triggered: the backup pump unit is started to run at full speed, the emergency drainage channel is activated, an on-site audible and visual alarm is issued, and personnel are notified to evacuate to a safe area. When the global maximum differential pressure value is lower than the lower limit threshold, the variable frequency dewatering well group reduces its speed to 40% of the rated speed, and the amount of external recharge increases to 80% of the rated recharge.

9. The integrated excavation and construction method for foundation pits with drainage and lowering functions according to claim 4, characterized in that, In the surface excavation and open-drainage step, the diversion channel is set on the side wall of the cofferdam or underground continuous wall, and the diversion channel interface is reserved at an appropriate position above the manhole. The diversion channel is a precast concrete channel or a welded steel plate channel, sloping towards the manhole with a slope of not less than 1%. A filter screen is set at the interface of the diversion channel.

10. The integrated excavation and construction method for foundation pits with drainage and lowering as described in claim 1, characterized in that, The benchmark differential pressure threshold table is pre-formulated by geotechnical engineers based on geological survey reports, soil permeability parameters, and anti-surge stability calculation results. It includes benchmark upper and lower threshold values ​​corresponding to each excavation depth and is fixed as construction parameters in the construction information management platform. The control cycle is 30 seconds. In the step of separating and reusing dewatering water, a closed-loop water quality re-inspection is set up in the excess water pipeline: after sedimentation treatment in the temporary sedimentation tank outside the pit, the turbidity of the water is tested again. If the turbidity meets the discharge standard, it is discharged into the municipal pipeline or natural water system. If the turbidity still exceeds the standard, it is returned to the filter box for re-treatment. All recycled water volume is included in the water recycling metering ledger, and a daily water recycling report is generated and uploaded to the construction information management platform.

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