Method for comprehensively judging water leakage of deep foundation pit through multi-parameter coupling

Abstract

The invention relates to a method for comprehensively judging water leakage of a deep foundation pit through multi-parameter coupling, and belongs to the technical field of foundation pit water leakage monitoring. The method comprises the following steps that in a deep foundation pit support structure, an observation well and a dewatering well are arranged on the periphery, primary and secondary monitoring sections are arranged, and the underground water level is monitored in real time; in the rainfall process, the automatic collecting device records the change of the underground water level outside the pit, and if the change of the water level does not exceed 0.5 m, it is considered that no leakage point exists; if the length exceeds 0.5 m, judging that a potential leakage point exists, calculating the horizontal flow velocity of underground water, and determining a leakage zone; and further putting a tracer into the observation well with abnormal flow velocity, measuring conductivity, temperature and water level data, analyzing the data, judging whether abnormity occurs or not, and calculating the flow velocity of the underground water, so that the leakage position of the foundation pit support structure and the flowing direction of the underground water are accurately determined. According to the invention, misjudgment caused by faults or errors of a single sensor can be reduced, and the reliability and precision of leakage point positioning are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of foundation pit leakage monitoring, and particularly relates to a method for comprehensively judging deep foundation pit leakage through multi-parameter coupling. Background Technique

[0002] Currently, with the acceleration of the urbanization process, projects such as high-rise and super-high-rise buildings, underground transportation facilities (such as subways, underground parking lots, etc.), and large commercial complexes are emerging in cities. These projects often require deep foundation pit excavation to meet the usage requirements of building foundations, basements, or underground spaces. The safety of foundation pit engineering is directly related to the success or failure of the entire project and the safety of the surrounding environment. Leakage is one of the common risks in foundation pit engineering, which may lead to serious consequences such as instability of the foundation pit slope and base heave. In order to ensure the safety of foundation pit engineering during construction and use, it is necessary to monitor the foundation pit leakage in real time so as to timely discover problems and take effective measures for treatment.

[0003] Most traditional leakage monitoring methods rely on setting several water level observation wells around and inside the foundation pit, and monitoring the underground water level by measuring the change of the water level in the wells. Use a water level measuring instrument to measure the water level regularly. If it is found that the underground water level drops abnormally, it may be that there is leakage in the foundation pit resulting in the loss of groundwater. Judging whether there is leakage only through the change of the water level has a huge error and cannot indicate the specific leakage point, which is likely to cause unnecessary waste in the later reinforcement. Therefore, the present invention proposes to use multi-parameter joint analysis, which greatly improves the accuracy of leakage monitoring and reduces the later maintenance cost to a certain extent. Summary of the Invention

[0004] In order to solve the above problems, the present invention provides a method for comprehensively judging deep foundation pit leakage through multi-parameter coupling.

[0005] To achieve the above object, the present invention is realized through the following technical solutions: The present invention provides a method for comprehensively judging deep foundation pit leakage through multi-parameter coupling, including the following steps: S1. Set several observation wells along the outside of the diaphragm wall of the deep foundation pit retaining structure, set a dewatering well inside the diaphragm wall, and arrange the main monitoring section and the secondary monitoring section; S2. Dewater the dewatering well, use an automatic acquisition device to collect the buried depth of the groundwater level outside the pit, calculate the water level change according to the buried depth of the groundwater level outside the pit. If the water level change of the observation well does not exceed 0.5 meters, there is no leakage point in the diaphragm wall; if the water level change of the observation well exceeds 0.5 meters, there is a potential leakage point in the diaphragm wall, and calculate the horizontal flow velocity of the groundwater in the area where the water level change outside the pit exceeds 0.5 meters according to Darcy's law. The place with the maximum horizontal flow velocity is the leakage zone; S3. Inject a tracer into the observation wells where the flow velocity of the monitoring section is greater than the average flow velocity, measure the conductivity value of the groundwater in each observation well, the temperature value at different depths, and the water level elevation of each observation well; based on the conductivity value, temperature value, and the rise and fall of the groundwater level, determine whether data anomalies occur. At the same time, according to the measured conductivity value, temperature value, and water level data, calculate the horizontal and vertical flow velocities of the groundwater, and finally obtain the location of the leakage point of the foundation pit enclosure structure and the direction of groundwater flow.

[0006] Further, step S1 specifically includes: S11. Arrange several observation wells outside the diaphragm wall of the deep foundation pit enclosure structure, set the main monitoring section and the secondary monitoring section. If the length of the foundation pit is less than 100m, set a main monitoring section every 20m, and no secondary monitoring section is set; because the length of the foundation pit is relatively short, a 20m spacing can ensure that representative data can be obtained at different positions, and a 20m spacing is the optimal spacing and cannot be set arbitrarily; if the length of the foundation pit is greater than 100m, set a main monitoring section every 40m, and arrange a secondary monitoring section in the middle of two main monitoring sections; if there are protruding parts in the foundation pit, the spacing can be adjusted appropriately according to the actual situation; if the protruding length is closer to 10m, set 1 secondary monitoring section; if it is close to 20m, 2 secondary monitoring sections can be set to make the monitoring section spacing about 10m. Among them, in the overall outline of the foundation pit, the protruding part of the foundation pit is the part that protrudes outward, usually appearing at the corners and edges of the foundation pit. S12. Arrange 3 observation wells on each main monitoring section, which are 2m, 7m, and 15m away from the foundation pit respectively; arrange 1 observation well on each secondary monitoring section, which is 2m away from the foundation pit; the distance between the observation well and the edge of the foundation pit is less than the excavation depth of the foundation pit; the dewatering well at the edge of the foundation pit is set in the middle position between the main monitoring section and the secondary monitoring section, and the rest of the dewatering wells are set at the positions of each main monitoring section. S13. Each observation well includes a set of monitoring systems, and the monitoring system includes a PVC pipe, a temperature sensor, a conductivity sensor, and a water level automatic acquisition device. There is generally no fixed standard for the depth of the PVC pipe in the observation well. For areas where the buried depth of the groundwater level is less than 5m, the depth of the PVC pipe in the observation well is usually 5 - 10m. For areas where the buried depth of the groundwater level is greater than 5m, the depth of the PVC pipe is often deeper and is selected within the range of 10 - 30m. The lowest depth of the temperature and conductivity sensors is determined according to the lowest designed water level of the foundation pit, 2 - 3m below the lowest designed water level of the foundation pit, and the highest depth is determined according to the highest designed water level of the foundation pit, 2 - 3m above the highest designed water level of the foundation pit. A measurement point is arranged every 2m vertically along the monitoring hole. The water level monitoring uses an automated monitoring system, and the water level data is automatically collected every 1m along the depth of the observation well. Further, the structure of the monitoring system is as follows: One end of the PVC pipe is connected to the conductivity sensor, the temperature sensor, and the water level automatic acquisition device, the other end of the PVC pipe is connected to one end of the instrument head, and the other end of the instrument head is connected to the computer.

[0007] Further, step S2 specifically includes: S21. Lower the water level in the dewatering well in the foundation pit by 2m, automatically collect the water level data in the observation well every 4h, record the monitoring section where the water level change exceeds 0.5m, and preliminarily judge it as the position where leakage may occur; S21. Calculate the horizontal groundwater flow velocity value of each monitoring section through Darcy's law, and further locate the leakage position through the position with the maximum horizontal flow velocity value. The position with the maximum horizontal flow velocity is prone to foundation pit leakage. The formula is as follows: , , , Wherein, represents the horizontal groundwater flow velocity of the monitoring section, represents the water level difference inside and outside the foundation pit, represents the coefficient of water flow permeability, represents the length of the flow path, which is the distance between the observation well and the dewatering well; represents the hydraulic gradient, represents the water level in the dewatering well before precipitation, represents the water level in the observation well after precipitation; Record the horizontal flow velocity values of each monitoring section, and then obtain the average horizontal flow velocity.

[0008] Further, in step S3, after the precipitation ends, inject sodium chloride into the observation wells where the horizontal flow velocity of the monitoring section is greater than the average horizontal flow velocity, and record the conductivity value and temperature value of each well through the monitoring system; Deduce the leakage point position by calculating the conductivity and temperature anomaly points. The calculation method of the conductivity anomaly point is as follows: , , Wherein, represents the conductivity value of the i-th measurement point; represents the average value of the conductivity values of this monitoring section, represents the number of measurement points; Set a conductivity anomaly threshold The formula is as follows: , When If so, it is determined that the conductivity of this point is abnormal; otherwise, it is normal. The calculation method of the temperature abnormal point is the same as that of the conductivity abnormal point. By plotting the conductivity-hole depth and temperature-hole depth diagrams with the collected data, the positions of mutations or inflection points are the leakage positions. Calculate the seepage direction angle based on the horizontal and vertical flow velocities of groundwater, analyze the seepage direction, and the calculation process is as follows: Calculate the vertical flow velocity of groundwater, and the formula is as follows: , where, represents the vertical flow velocity of groundwater, represents the migration distance of the tracer in the vertical direction, with the unit of m, represents the arrival time of the tracer; calculate the seepage angle based on the horizontal and vertical flow velocities, and the formula is as follows: , where, represents the seepage angle, represents the arctangent function; obtain the vertical depth position of the leakage based on the positions of the conductivity and temperature abnormal points, the water level difference inside and outside the foundation pit, the hydraulic gradient, and the seepage angle, and the formula is as follows: , where, represents the vertical depth of the leakage point, represents the depth of the abnormal points of the temperature value and conductivity value, represents the water level difference inside and outside the foundation pit, represents the hydraulic gradient.

[0009] The advantages of the present invention are as follows: Compared with other monitoring methods, the present invention avoids the installation of expensive equipment, thus significantly reducing the project cost. By reasonably arranging the main monitoring sections and secondary monitoring surfaces of the deep foundation pit, the project cost is reduced on the premise of ensuring full coverage of the foundation pit monitoring range, and at the same time, it meets the environmental protection requirements. The specific operation process is relatively simple, and the detailed calculation process does not require high-difficulty engineering processes or equipment, so it is easy to implement. The present invention fully adopts the combined analysis of temperature sensors and conductivity sensors, through multi-parameter coupling data fusion, and uses the Kalman filtering method to optimize the data. Compared with the traditional single-sensor monitoring method, using the data obtained by multiple sensors for cross-validation and fusion analysis not only improves the accuracy of the data, but also reduces the misjudgment caused by the failure or error of a single sensor, significantly improving the reliability and accuracy of leakage point positioning. The present invention provides guidance for the leakage detection of deep foundation pits. Through accurate leakage source positioning, the present invention can be widely applied to the safety monitoring, groundwater flow control, and disaster prevention in the foundation pit construction stage, etc., and has important engineering significance and application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The accompanying drawings are provided to further understand the present invention, and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention, and do not constitute a limitation to the present invention.

[0011] Figure 1 is a flowchart of the steps of the method of the present invention; Figure 2 is a schematic diagram of the monitoring section of the present invention; Figure 3 is the conductivity - hole depth and temperature - hole depth diagram of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0012] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0013] Embodiment 1 In this embodiment, as Figure 1 shown, the present invention provides a method for comprehensively judging the leakage of deep foundation pits by multi - parameter coupling. The specific steps include: S1. Along the outer periphery of the diaphragm wall of the deep foundation pit retaining structure, several observation wells are set, a dewatering well is set in the diaphragm wall, and the main monitoring section and the secondary monitoring section are arranged. Specifically, S11. Several observation wells are arranged outside the diaphragm wall of the deep foundation pit retaining structure, and the main monitoring section and the secondary monitoring section are set. If the length of the foundation pit is less than 100 m, a main monitoring section is set every 20 m, and no secondary monitoring section is set; if the length of the foundation pit is greater than 100 m, a main monitoring section is set every 40 m, and a secondary monitoring section is arranged at the middle position between two main monitoring sections; if there are protruding parts in the foundation pit, the spacing can be appropriately adjusted according to the actual situation. S12. Three observation wells are arranged on each main monitoring section, which are 2 m, 7 m, and 15 m away from the foundation pit respectively; one observation well is arranged on each secondary monitoring section, which is 2 m away from the foundation pit; the distance between the observation well and the edge of the foundation pit is less than the excavation depth of the foundation pit; the dewatering well at the edge of the foundation pit is set at the middle position between the main monitoring section and the secondary monitoring section, and the remaining dewatering wells are set at the positions of each main monitoring section. S13. Each observation well includes a set of monitoring systems, and each monitoring system includes a PVC pipe, a temperature sensor, a conductivity sensor, and a water level automatic acquisition device. Specifically, the structure of the monitoring system is as follows: One end of the PVC pipe is connected to the conductivity sensor, the temperature sensor, and the water level automatic acquisition device, and the other end of the PVC pipe is connected to one end of the instrument head, and the other end of the instrument head is connected to the computer.

[0014] S2. Lower the water level in the precipitation well, use the automatic acquisition device to collect the buried depth of the groundwater level outside the pit, calculate the water level change based on the buried depth of the groundwater level outside the pit. If the water level change of the observation well does not exceed 0.5 meters, there is no leakage point in the diaphragm wall; if the water level change of the observation well exceeds 0.5 meters, there is a potential leakage point in the diaphragm wall. Calculate the horizontal groundwater flow velocity in the area where the groundwater level change outside the pit exceeds 0.5 meters according to Darcy's law, and the location with the maximum horizontal flow velocity is the leakage zone. Specifically, S21. Lower the water level in the precipitation well in the foundation pit by 2m, automatically collect the water level data in the observation well every 4h, record the monitoring section where the water level change exceeds 0.5m, and initially judge it as the location where leakage will occur. S21. Calculate the horizontal groundwater flow velocity values of each monitoring section according to Darcy's law, and further locate the leakage location through the position with the maximum horizontal flow velocity value. The formula is as follows: , , , Among them, represents the horizontal groundwater flow velocity of the monitoring section, represents the water level difference inside and outside the foundation pit, represents the coefficient of water flow permeability, represents the length of the flow path, which is the distance between the observation well and the precipitation well; represents the hydraulic gradient, represents the water level in the precipitation well before precipitation, represents the water level in the observation well after precipitation; Record the horizontal flow velocity values of each monitoring section, and then obtain the average horizontal flow velocity.

[0015] S3. Inject a tracer into the observation well where the flow velocity of the monitoring section is greater than the average velocity, and measure the conductivity value of the groundwater, the temperature value at different depths, and the water level elevation of each observation well in the observation well; According to the conductivity value, the temperature value, and the change in the groundwater level rise and fall, judge whether data anomalies occur. At the same time, based on the measured conductivity value, temperature value, and water level data, calculate the horizontal and vertical flow velocities of the groundwater, and finally obtain the location of the leakage point of the foundation pit enclosure structure and the direction of groundwater flow.

[0016] Specifically, in S31, after the precipitation ends, sodium chloride is injected into the observation wells where the horizontal flow velocity of the monitoring section is greater than the average horizontal flow velocity, and the conductivity values and temperature values of each well are recorded through the monitoring system. In S32, the leakage point location is deduced by calculating the conductivity and temperature anomaly points. The calculation method of the conductivity anomaly point is as follows: , , Among them, represents the conductivity value of the i-th measurement point; represents the average value of the conductivity values of this monitoring section, represents the number of measurement points; a conductivity anomaly threshold is set, and the formula is as follows: , When , it is determined that the conductivity of this point is abnormal; otherwise, it is normal; the calculation method of the temperature anomaly point is the same as that of the conductivity anomaly point; the conductivity-depth and temperature-depth diagrams are drawn through the collected data, and the positions of mutations or inflection points are the leakage positions. The combination modes of each parameter are shown in Table 1 below.

[0017] Table 1 Early warning classification of each parameter combination In S33, the seepage direction angle is calculated according to the horizontal and vertical flow velocities of the groundwater, and the seepage direction is calculated and analyzed. The calculation process is as follows: Calculate the vertical flow velocity of the groundwater. The formula is as follows: , Among them, represents the vertical flow velocity of the groundwater, represents the migration distance of the tracer in the vertical direction, with the unit of m, represents the arrival time of the tracer; calculate the seepage angle according to the horizontal and vertical flow velocities. The formula is as follows: , Among them, represents the seepage angle, represents the arctangent function; obtain the vertical depth position of the leakage according to the positions of the conductivity and temperature anomaly points, the water level difference inside and outside the foundation pit, the hydraulic gradient, and the seepage angle. The formula is as follows: , Among them, represents the vertical depth of the leakage point, represents the depth of the temperature value and conductivity value anomaly points represents the water level difference inside and outside the foundation pit, represents the hydraulic gradient.

[0018] Embodiment 2 In this embodiment, the standard section of Chedai Station with a width of 43.9 m and a construction length of about 163.6 m is taken as an example for illustration; Monitoring section layout: The monitoring system is constructed as shown in Figure 2 As shown. Since the length of the foundation pit is greater than 100 m, a main monitoring section is set every 40 m, and a secondary monitoring section is arranged between two main monitoring sections. That is, the red sections 1, 2, 3, 4, 5, and 6 are the main monitoring sections, and the yellow sections A, B, C, and D are the secondary monitoring sections. Since there is no protruding part in the standard section of Chedai Station foundation pit, no monitoring adjustment is required.

[0019] Observation well and dewatering well arrangement: Three observation wells are set in each main monitoring section, with the edges being 2 m, 7 m, and 15 m away from the foundation pit respectively; one observation well is set in the secondary monitoring section, 2 m away from the foundation pit. The monitoring sections at the edge of the foundation pit correspond to the dewatering wells, which are set in the main monitoring section and the secondary monitoring section, and the other dewatering wells are set at the corresponding positions of the main monitoring section.

[0020] Composition of the monitoring system: According to the geological exploration report, the initial water level burial depth is 0 - 5.30 m (elevation -0.94 - 2.92 m), and the stable water level burial depth is 0 - 6.50 m (elevation -2.14 - 2.68 m). Since the water level burial depth is relatively deep, PVC pipes with a length of 10 m are selected. The arrangement range of temperature and conductivity sensors is determined according to the designed water level of the foundation pit. It is 3 m below 7 m of the lowest designed water level of the foundation pit and 3 m above 4 m of the highest designed water level of the foundation pit. Therefore, a measurement point is arranged every 1 m vertically along the monitoring hole from 1 m to 10 m.

[0021] Preliminary leakage judgment: Lower the water level of each dewatering well in the foundation pit to 2 m, and automatically collect the water level data in the observation wells every 4 h. Record the observation sections where the water level change exceeds 0.5 m. See the following Table of Observation Well Water Level Data Changes to preliminarily judge the possible leakage locations. Observe the water level changes in the observation wells. The data table of water level changes in the observation wells is shown in Table 2.

[0022] Table 2 Data Table of Observation Well Water Level Changes Analysis of preliminary leakage judgment: Screening of abnormal sections (Δh ≥ 0.5 m), main monitoring section 2, main monitoring section 3, main monitoring section 4, secondary monitoring section D.

[0023] Calculate the flow velocity using Darcy's law, and calculate the Darcy flow velocity of each observation well in 10 monitoring sections. Taking the secondary monitoring section D as an example: : The horizontal velocity of groundwater at this monitoring section; : The water level difference inside and outside the foundation pit; : The coefficient of water flow permeability; : The hydraulic gradient; : The length of the flow path, the distance between the observation well and the dewatering well; : The water level in the dewatering well before dewatering; : The water level in the observation well after dewatering; Leakage point inference: At the main monitoring sections 2 and 3, in the sand layer area on the west side of the foundation pit, leakage may be caused by local cracks in the diaphragm wall. At the secondary section D, at the joint of the diaphragm wall, the risk of the water-stop curtain failure is relatively high; At the same time, record the flow velocity values of each monitoring section. As shown in Table 3, the sum of the flow velocities of each monitoring section is added and divided by the total number of monitoring sections to obtain the average flow velocity. Judge whether the flow velocity in each monitoring section is greater than the average flow velocity. Calculate the average flow velocity as follows: Table 3 Judgment table of flow velocity values of each monitoring section After the dewatering is completed, inject sodium chloride into the observation wells in the monitoring sections (main monitoring section 2, main monitoring section 3, secondary monitoring section C, secondary monitoring section D) where the flow velocity is greater than the average flow velocity, and record the conductivity value and the temperature value.

[0024] Calculate the difference between the conductivity of each measurement point and the average conductivity in this monitoring section and the difference between the temperature and the average temperature in this monitoring section. Take the secondary monitoring section D as an example: Calculation of average conductivity and temperature: , , Calculation of conductivity and temperature thresholds The abnormal points of the secondary monitoring section D are shown in Table 4 below. Draw the conductivity-depth and temperature-depth change diagrams, as shown in Figure 3 After calculation, there are no abnormal points in the remaining abnormal monitoring sections, so they are not listed here.

[0025] Table 4 Abnormal Points of the Second Monitoring Section D Calculate the seepage direction angle based on the horizontal and vertical flow velocities of groundwater, and analyze the seepage direction.

[0026] Calculate the vertical flow velocity. The sodium chloride tracer at a depth of 8 m in the observation well was detected at a depth of 6 m in the precipitation well, taking 13 h.

[0027] Vertical migration distance of the tracer: ; Vertical flow velocity: ; Calculate the seepage angle based on the horizontal and vertical flow velocities: ; Finally, calculate the specific vertical depth position of the leakage according to the positions of the conductivity and temperature abnormal points, the water level difference inside and outside the foundation pit, the hydraulic gradient, and the seepage angle. The formula is as follows: .

[0028] Traditional leakage monitoring methods rely on setting several water level observation wells around and inside the foundation pit, and monitoring the groundwater level by measuring the changes in the water level in the wells. Use a water level measuring instrument to measure the water level regularly. If it is found that the groundwater level drops abnormally, it may be due to leakage in the foundation pit resulting in groundwater loss, so as to judge whether the foundation pit leaks. The traditional method can only obtain the general orientation of the leakage location; the method of the present invention can not only judge whether the foundation pit leaks, but also give the location of the leakage in the foundation pit through data analysis.

[0029] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for comprehensively judging water leakage in deep foundation pits by multi-parameter coupling, characterized in that: The following steps are involved: S1. Set up several observation wells along the outer periphery of the ground-connected wall of the deep foundation pit retaining structure, set up drainage wells inside the ground-connected wall, and arrange the main monitoring section and secondary monitoring section; S2. Dewatering the well, using an automatic data acquisition device to collect the buried depth of the groundwater level outside the pit, and calculating the water level change according to the buried depth of the groundwater level outside the pit. If the water level change in the observation well does not exceed 0.5 meters, there is no leakage point in the underground continuous wall; if the water level change in the observation well exceeds 0.5 meters, there is a potential leakage point in the underground continuous wall. According to Darcy's law, the groundwater horizontal flow velocity in the area where the groundwater level outside the pit changes by more than 0.5 meters is calculated, and the place with the maximum horizontal flow velocity is the leakage zone; S3. Place tracers into observation wells where the flow velocity of the monitoring section is greater than the average flow velocity, and measure the conductivity of groundwater in each observation well, the temperature values ​​at different depths and the water level elevation of each observation well; determine whether data anomalies occur based on the conductivity values, temperature values ​​and changes in groundwater levels; and calculate the horizontal and vertical flow velocities of groundwater based on the measured conductivity values, temperature values ​​and water level data, ultimately obtaining the location of the leakage point of the foundation pit retaining structure and the direction of groundwater flow.

2. The method for comprehensively judging deep foundation pit water leakage by multi-parameter coupling according to claim 1 is characterized in that: Step S1 specifically includes: S11. Several observation wells are arranged outside the ground-connected wall of the deep foundation pit retaining structure, and primary and secondary monitoring sections are set up. If the length of the foundation pit is less than 100m, a primary monitoring section is set up every 20m, and no secondary monitoring section is set up; if the length of the foundation pit is greater than 100m, a primary monitoring section is set up every 40m, and a secondary monitoring section is set up between the two primary monitoring sections; if there are protruding parts in the foundation pit, the spacing can be appropriately adjusted according to the actual situation; S12. Three observation wells are arranged on each main monitoring section, 2m, 7m and 15m away from the foundation pit respectively; one observation well is arranged on each secondary monitoring section, 2m away from the foundation pit; the distance between the observation well and the edge of the foundation pit is less than the excavation depth of the foundation pit; the drainage well at the edge of the foundation pit is set in the middle of the main monitoring section and the secondary monitoring section, and the remaining drainage wells are set at the positions of each main monitoring section; S13. Each observation well includes a monitoring system, which includes a PVC pipe, a temperature sensor, a conductivity sensor and an automatic water level collection device.

3. The method for comprehensively judging deep foundation pit water leakage by multi-parameter coupling according to claim 2 is characterized in that: Step S2 specifically includes: S21. Dewater the dewatering wells in the foundation pit by 2m, automatically collect water level data in the observation wells every 4 hours, and record the monitoring sections where the water level changes by more than 0.5m, and preliminarily determine the leakage location; S21. Calculate the horizontal velocity of groundwater at each monitoring section using Darcy's law, and further locate the leakage location through the location with the maximum horizontal velocity value. The formula is as follows: ， ， ， in, Indicates the horizontal flow velocity of groundwater in the monitoring section. Indicates the water level difference inside and outside the foundation pit. represents the water flow permeability coefficient, represents the flow path length, which is the distance between the observation well and the precipitation well; represents the hydraulic slope, Indicates the water level in the precipitation well before precipitation. Indicates the water level in the observation well after precipitation; records the horizontal flow velocity value of each monitoring section, and then obtains the average horizontal flow velocity.

4. The method for comprehensively judging deep foundation pit water leakage by multi-parameter coupling according to claim 3 is characterized in that: In step S3, precipitation is terminated, sodium chloride is injected into the observation wells where the horizontal flow velocity of the monitoring section is greater than the average horizontal flow velocity, and the conductivity value and temperature value of each well are recorded by the monitoring system.

5. The method for comprehensively judging deep foundation pit water leakage by multi-parameter coupling according to claim 4 is characterized in that: In step S3, the leakage point location is deduced by calculating the conductivity and temperature abnormal points. The calculation method of the conductivity abnormal point is as follows: ， ， in, represents the conductivity value of the i-th measurement point; It represents the average value of the conductivity value of the monitoring section. Indicates the number of measurement points; sets a conductivity abnormality threshold , the formula is as follows: ， when When , the conductivity of the point is determined to be abnormal; otherwise, it is normal; the calculation method of the temperature abnormal point is the same as the calculation method of the conductivity abnormal point; the conductivity-hole depth and temperature-hole depth diagrams are drawn based on the collected data, and the location of the mutation or inflection point is the leakage location.

6. The method for comprehensively judging deep foundation pit water leakage by multi-parameter coupling according to claim 5 is characterized in that: In step S3, the seepage direction angle is calculated according to the horizontal flow velocity and the vertical flow velocity of the groundwater, and the direction of the seepage is calculated and analyzed. The calculation process is as follows: The formula for calculating the vertical flow velocity of groundwater is as follows: ， in, It represents the vertical velocity of groundwater. Indicates the vertical migration distance of the tracer, in meters. represents the arrival time of the tracer; the seepage angle is calculated according to the horizontal flow velocity and the vertical flow velocity, and the formula is as follows: ， in, represents the seepage angle, represents the inverse tangent function; the vertical depth position of the leakage is obtained according to the location of the conductivity and temperature anomaly point, the water level difference inside and outside the foundation pit, the hydraulic slope and the seepage angle. The formula is as follows: ， in, Indicates the vertical depth of the leak point. Indicates the depth of abnormal temperature and conductivity values. Indicates the water level difference inside and outside the foundation pit. Indicates the hydraulic slope.

7. The method for comprehensively judging deep foundation pit water leakage by multi-parameter coupling according to claim 6 is characterized in that: The structure of the monitoring system is as follows: one end of the PVC pipe is connected to the conductivity sensor, the temperature sensor and the automatic water level acquisition device, the other end of the PVC pipe is connected to one end of the instrument header, and the other end of the instrument header is connected to the computer.

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