Precipitation excavation and deformation control construction method for coastal facies soft soil stratum subway station

Abstract

The invention discloses a coastal facies soft soil stratum subway station precipitation excavation and deformation control construction method which comprises the following steps: carrying out three-shaft stirring pile reinforcement construction on two sides of a diaphragm wall construction position, and then constructing a diaphragm wall; a plurality of drainage deep wells are constructed in a soil layer of a foundation pit construction area, each drainage deep well is provided with a water pumping device and an air supply device, when dewatering construction is conducted on the tops of the drainage deep wells, the water pumping devices and the air supply devices work synchronously, the air supply devices supply air into drainage pipes, and the water pumping devices suck water in the drainage deep wells; the foundation pit excavation construction is carried out, a plurality of concrete supporting structures and a plurality of steel supporting structures are arranged on the inner wall of the foundation pit from top to bottom, and a servo system is arranged between the steel supporting structures and the inner wall of the diaphragm wall and used for monitoring the deformation condition of the inner wall of the foundation pit in real time and compensating and adjusting the axial force of the steel supporting structures in time according to the deformation condition. And deformation of the foundation pit is controlled. The rainfall effect and the foundation pit deformation control effect can be improved.

Description

Technical Field

[0001] The present application relates to the field of subway station construction, and in particular to a method for dewatering, excavating and controlling deformation of a subway station in soft soil strata in coastal facies. Background Art

[0002] The soft soil layer in the coastal phase has the characteristics of high water content, poor permeability, strong compressibility and low bearing capacity. These characteristics lead to many difficulties in the construction of subway stations. In order to ensure the stability and safety of the foundation pit and prevent groundwater from pouring into the foundation pit and causing collapse or other safety accidents, precipitation excavation technology and foundation pit deformation control are indispensable measures.

[0003] When constructing in poor geological conditions such as silty fine sand, silty soil, and silty medium-coarse sand, it is pressure-bearing and a thick continuous sand layer is developed in the site, which may be connected to the surface water. Because the permeability coefficient in the shallow soil layer is small and drainage is difficult, there is a pressure-bearing aquifer within the excavation range and a certain depth at the bottom of the foundation pit. It has strong permeability and rich water content. Under the action of head difference, it is easy to produce unfavorable geological phenomena such as quicksand, which is extremely unfavorable for foundation pit excavation. In related technologies, dewatering excavation construction usually involves constructing a dewatering well first, and then using a water pump to pump water for dewatering, but the conventional dewatering method has poor dewatering effect. In addition, the foundation pit deformation control method usually uses a concrete structure for support. When the foundation pit wall is partially deformed, it is difficult to adjust and control it in a targeted manner, and the control effect is not good, so there is still room for improvement. Summary of the invention

[0004] In order to improve the dewatering effect and the foundation pit deformation control effect, the present application provides a dewatering excavation and deformation control construction method for a subway station in a soft soil stratum in a coastal phase.

[0005] The present application provides a method for dewatering excavation and deformation control of a subway station in a coastal soft soil layer, which adopts the following technical solutions: A construction method for dewatering excavation and deformation control of a subway station in a coastal soft soil layer, comprising the following steps: S1: Three-axis mixing pile reinforcement construction: measure and lay out the lines in the foundation pit construction area, delineate the underground continuous wall construction location, then carry out three-axis mixing pile reinforcement construction on both sides of the ground-connected wall construction location, and then excavate a trench in the ground-connected wall construction area; S2: Underground continuous wall construction: hoist the underground continuous wall steel cage into the groove one by one, and cast it to form the main structure of the underground continuous wall; S3: Dewatering construction: multiple drainage deep wells are constructed in the soil layer of the foundation pit construction area. Each drainage deep well is equipped with a set of pumping devices and air supply devices. The drainage pipe of the pumping device and the air supply pipe of the air supply device are both extended into the drainage deep well. The air supply pipe of the air supply device is connected to the lower part of the drainage pipe of the pumping device. The top opening of the drainage deep well is closed by a cover plate. When dewatering construction is carried out, the pumping device and the air supply device work synchronously. The air supply device supplies air into the drainage pipe, and the pumping device sucks the water in the drainage deep well. S4: Foundation pit excavation and support construction: The foundation pit excavation construction is carried out in the manner of longitudinal segmentation, vertical stratification, top-down, support first and then excavation, and layered excavation. Multiple concrete support structures and multiple steel support structures are arranged from top to bottom on the inner wall of the foundation pit. A servo system is set between the steel support structure and the inner wall of the ground-connected wall. The servo system is used to monitor the deformation of the inner wall of the foundation pit in real time, and compensate and adjust the axial force of the steel support structure in time according to the deformation situation to control the deformation of the foundation pit.

[0006] By adopting the above technical scheme, during the dewatering construction, the pumping device and the air supply device through hole work synchronously, the air supply device provides compressed air, and under the action of the liquid surface pressure in the well, the water in the well enters the drainage pipe and mixes with the gas, and rises in the drainage pipe to achieve "pressure". At the same time, the pumping device sucks the water vapor mixture through the drainage pipe to accelerate the rising speed and achieve "suction", thereby reducing the groundwater level in the soil layer by combining pressure suction and pumping, strengthening the dewatering effect, and can effectively target complex formations that are difficult to handle in conventional dewatering forms such as silt, silty soil, and clay soil; in addition, multiple concrete support structures and steel support structures are arranged on the inner wall of the foundation pit, and the combination of the two can reduce the probability of collapse of the inner wall of the foundation pit. In addition, a servo system is arranged between the steel support structure and the inner wall of the foundation pit, and the deformation of the inner wall of the foundation pit is monitored in real time, and the axial force of the steel support structure is compensated and adjusted in time according to the deformation, so as to achieve the purpose of accurately controlling the deformation of the foundation pit, which is conducive to improving the control effect of the deformation of the foundation pit.

[0007] Preferably, in the deep well dewatering construction step of S3, a reverse circulation drilling rig is used to perform hole construction in the soil layer in the foundation pit construction area to form a wellbore, and then the well pipe of the deep well dewatering is lowered to the hole center of the wellbore, and then filter material is backfilled into the wellbore to form a filter layer on the outer periphery of the lower position of the well pipe.

[0008] By adopting the above technical solution, the filter material forms a filter layer on the outer periphery of the lower part of the well pipe, which can block or reduce the entry of mud and sand into the drainage pipe, which is beneficial to improving the clogging problem of the pores around the drainage pipe.

[0009] Preferably, before the precipitation construction step of S3, a well washing operation is performed first. By starting the air supply device and passing compressed air to the lower part of the drain pipe through the air supply pipe, a pressure difference is generated inside and outside the drain pipe. The mud and water mixture outside the drain pipe flows into the drain pipe under the action of the pressure difference and is continuously carried out of the drainage deep well. The soil component in the filter material becomes less and less until it is cleaned.

[0010] Preferably, before the foundation pit excavation step S4 is performed, dewatering construction is first performed to lower the water level to below the foundation pit excavation area. When the foundation pit is excavated, the pumping device maintains a continuous pumping action to drain the soil in the foundation pit excavation area.

[0011] By adopting the above technical solution, the deep well dewatering should be carried out about 15 days or earlier before the foundation pit excavation to ensure the effective reduction of the water content in the excavated soil and ensure the smooth progress of the foundation pit excavation construction. During the excavation process, continuous pumping is maintained to further drain the upper soil.

[0012] By adopting the above technical scheme, before the formal pumping step is carried out, compressed air is first passed to the lower part of the drain pipe through the air supply pipe by the air supply device. The density of the air-water mixture in the drain pipe is lower than the density of the mud-water mixture outside the drain pipe, and a pressure difference is generated inside and outside the drain pipe. The mud-water mixture outside the drain pipe flows into the drain pipe under the action of the pressure difference, and the well pipe becomes a three-phase mixture of air, water and soil. The density of the three-phase mixture decreases with the increase of the air mixing amount, and the three-phase mixture is continuously taken out of the drainage deep well. The soil component in the filter material becomes less and less until it is cleaned, so as to reduce the damage caused by the main structure of the pumping device being blocked by soil.

[0013] Preferably, during dewatering construction, after all the groundwater in the well pipe has been pumped out, the air supply device stops supplying air and the water pumping device continues to operate, so that a vacuum is quickly formed in the well pipe and the rate of groundwater convergence is accelerated; when the groundwater in the well pipe has accumulated to a certain amount, the air supply device is started again and the water pumping device continues to perform the pumping operation, and the cycle is repeated to achieve the purpose of draining the soil.

[0014] By adopting the above technical scheme, since the pressure-suction combined pumping speed is higher than the gathering speed of water inside the soil, after all the groundwater in the well pipe is pumped out, the air supply device stops supplying air and the pumping device continues to operate, so that a vacuum is quickly formed in the well pipe and the groundwater gathering rate is accelerated. When the groundwater in the well pipe gathers to a certain amount, the air supply device is started again and the pumping operation is continued in cooperation with the pumping device, which is beneficial to improving the efficiency of soil drainage.

[0015] Preferably, when performing the foundation pit excavation step S4, the soil outside the well pipe is manually excavated, and the excess portion of the well pipe top protruding from the soil is gradually cut off as the foundation pit excavation depth increases.

[0016] By adopting the above technical solution, the soil excavation step at the outside of the well pipe is carried out by manual soil insertion, which is beneficial to reducing the probability of the well pipe being accidentally cracked by the excavation equipment. As the excavation depth of the foundation pit increases, the excess part of the top of the well pipe protruding out of the soil is gradually cut off, so that the dewatering construction can continue during the foundation pit excavation step. When the water in the soil gathers again, the soil can be drained in time.

[0017] Preferably, before constructing the concrete support structure, a steel support structure and a servo system are temporarily added above the construction position of the concrete support structure. The servo system compensates and adjusts the axial force of the steel support structure based on real-time monitoring of the deformation of the inner wall of the foundation pit to control the deformation of the foundation pit.

[0018] By adopting the above technical solution, when the horizontal displacement of the continuous wall exceeds 70 mm at the concrete support construction position, a steel support structure and a servo system can be temporarily added to support the deformed position of the continuous wall in time, and then the concrete support structure can be constructed, which is beneficial to improving the safety of foundation pit construction.

[0019] Preferably, when installing the steel support structure and the servo system, a steel purlin is first arranged on the inner wall of the foundation pit, and the steel support structure and the servo system are placed up to the steel purlin.

[0020] By adopting the above technical solution, the steel purlin plays a role in strengthening the structural strength of the inner wall of the foundation pit, which is conducive to the safe force application operation of the steel support structure servo system at the inner wall of the foundation pit.

[0021] In summary, the present application includes at least one of the following beneficial technical effects: 1. In the dewatering construction step, the pumping device and the air supply device through-hole work synchronously. The air supply device provides compressed air. Under the action of the liquid surface pressure in the well, the water in the well enters the drainage pipe and mixes with the gas, and rises in the drainage pipe to achieve "pressure". At the same time, the pumping device sucks the water vapor mixture through the drainage pipe to accelerate the rising speed and achieve "suction", thereby lowering the groundwater level in the soil layer by combining pressure suction and pumping, strengthening the dewatering effect, and can effectively target complex formations such as silt, silty soil, and clay soil that are difficult to handle with conventional dewatering methods; 2. Arrange multiple concrete support structures and steel support structures on the inner wall of the foundation pit. The combination of the two can reduce the probability of collapse of the inner wall of the foundation pit. In addition, arrange a servo system between the steel support structure and the inner wall of the foundation pit to monitor the deformation of the inner wall of the foundation pit in real time and compensate and adjust the axial force of the steel support structure in time according to the deformation, so as to achieve the purpose of accurately controlling the deformation of the foundation pit, which is conducive to improving the control effect of the deformation of the foundation pit; 3. Since the pressure-suction combined pumping speed is higher than the gathering speed of water inside the soil, after all the groundwater in the well pipe is pumped out, the air supply device stops supplying air and the pumping device continues to operate, so that a vacuum is quickly formed in the well pipe and the groundwater gathering rate is accelerated. When the groundwater in the well pipe gathers to a certain amount, the air supply device is started again and the pumping operation is continued in cooperation with the pumping device, which is beneficial to improve the efficiency of soil drainage. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a structural schematic diagram of a deep well dewatering in a construction method for dewatering excavation and deformation control of a subway station in soft soil strata in coastal facies according to an embodiment of the present application.

[0023] Figure 2 It is a schematic diagram of a concrete support structure and a steel support structure in a dewatering excavation and deformation control construction method for a subway station in soft soil strata in coastal facies according to an embodiment of the present application.

[0024] Explanation of the reference numerals: 1. Well pipe; 2. Pumping device; 21. Drain pipe; 22. Branch pipe; 3. Air supply device; 31. Air supply pipe; 4. Water-steam mixer; 5. Cover plate; 6. Steel support structure; 61. Servo system; 62. Steel purlin; 7. Concrete support structure. DETAILED DESCRIPTION

[0025] The following is combined with Figure 1-2 This application is described in further detail.

[0026] The present application embodiment discloses a method for dewatering excavation and deformation control of a subway station in a soft soil layer in a coastal facies, referring to Figure 1 and Figure 2 , including the following steps: S1: Three-axis mixing pile reinforcement construction. According to the construction design drawing, the foundation pit construction area is measured and laid out, and the underground continuous wall construction position is delineated. Then, the three-axis mixing pile reinforcement construction is carried out on both sides of the ground-connected wall construction position. The three-axis mixing pile body adopts the two-mixing and two-spraying construction process, and the cement slurry and the original foundation soil are fully mixed while mixing and spraying. Then, a trench is excavated in the ground-connected wall construction area. The trenching construction adopts a trenching machine + double-wheel milling + rotary drilling to form a trench.

[0027] S2: Construction of underground continuous wall. Guide walls are constructed on both sides of the trench, and then the ground-connected wall steel cage is hoisted into the trench in turn. Due to the reinforcement of the three-axis mixing pile, the strength of the inner and outer sides of the trench wall is different, and the verticality deviation is large, which easily causes problems such as obstruction of the lowering of the steel cage. Therefore, before lowering the steel cage, the trench wall needs to be brushed. When brushing the wall, a customized joint scraper and steel brush are used to clean the mud on the wall brush in time, and the wall is brushed more than 10 times to make the trench wall smooth. The steel cage is made in one go and hoisted as a whole to smoothly hoist the steel cage into the trench.

[0028] Finally, the main structure of the ground-connected wall is formed by pouring concrete. Two conduits with an inner diameter of 250 mm are used when pouring concrete, and the watertight method is used to detect the sealing. In this embodiment, the foundation pit support system uses a 1.2m thick underground continuous wall as the enclosure. There are 358 underground continuous walls in total, using C35 P8 underwater concrete, I-shaped steel sealing joints, and glass fiber I-shaped steel sealing joints at the fiberglass reinforcement position. Before the excavation of the foundation pit, the closed joints of the underground continuous wall are reinforced by grouting, and steel plate sealing measures are taken for the joints of the ground-connected wall in the sand layer section to reduce the risk of leakage during the excavation of the foundation pit.

[0029] S3: Dewatering construction. A plurality of deep drainage wells are constructed in the soil layer of the foundation pit construction area, each of which is equipped with a set of pumping devices 2 and air supply devices 3. The drainage pipe 21 of the pumping device 2 and the air supply pipe 31 of the air supply device 3 are both extended into the deep drainage well. The air supply pipe 31 of the air supply device 3 is connected to the lower part of the drainage pipe 21 of the pumping device 2. The top opening of the well pipe 1 of the deep drainage well is closed by a cover plate 5.

[0030] In this embodiment, the drilling equipment used in the deep well dewatering construction is a reverse circulation drilling rig, and the drill bit is a three-wing drill bit with a diameter ring. The diameter of the deep well dewatering pipe 1 is 0.3m and the thickness is 4mm; the bottom of the well pipe 1 is closed with a 6mm thick steel plate. A plurality of filter holes are arranged on the outer periphery of the well pipe 1, and the well pipe 1 is covered with three layers of 60-mesh filter screens and tied with 14# lead wire at intervals of 0.8m.

[0031] During construction, a reverse circulation drilling rig is used to drill holes in the soil layer in the foundation pit construction area to form a wellbore. During the drilling process, the mud level must always be kept at least 1.0m above the groundwater level or level with the natural ground to ensure that hole collapse accidents are unlikely to occur during the drilling process.

[0032] After drilling to the designed depth, stop drilling, lift the drill bit 10-20cm away from the bottom of the hole, keep the mud circulating normally, and rotate the drill head while rotating the drill bit to grind the residual mud at the bottom of the hole into mud and discharge it. The hole cleaning requirements must meet the following standards: the sediment at the bottom of the hole is basically completely removed, the hole depth can be accurately measured, and there is no mud suspended in the mud in the hole.

[0033] Then, the well pipe 1 for draining the deep well is lowered to the center of the wellbore to prevent the well pipe 1 from sticking to the wall and affecting the water output. After it is placed to the designed elevation, it is immediately fixed.

[0034] Then fill the filter material back into the wellbore to 1-2 meters below the designed height. The filter material forms a filter layer around the lower part of the well pipe 1 to form a filter layer. The air supply device 3 specifically adopts an air compressor, and the air inlet pipe is connected to the air compressor. The air compressor can control the air supply pressure, air supply time and air supply volume. The water pumping device 2 adopts a vacuum pump. The vacuum pump is connected to the drainage pipe 21. A water vapor mixer 4 is installed at the connection between the air supply pipe 31 and the drainage pipe 21. The water vapor mixer 4 is sunk into the water in the well pipe 1. The vacuum device, the air supply device 3, and the water vapor mixer 4 constitute a super pressure suction combined water pumping system, and are controlled by a control system.

[0035] Before the dewatering construction is carried out, the well washing operation is carried out first, and the vacuum pump is connected to the drainage pipe 21. By starting the air supply device 3 and passing the compressed air to the lower part of the drainage pipe 21 through the air supply pipe 31, a pressure difference is generated inside and outside the drainage pipe 21. The mud and water mixture outside the drainage pipe 21 flows into the drainage pipe 21 under the action of the pressure difference and is continuously taken out of the drainage deep well. The mud content in the filter material becomes less and less until it is cleaned.

[0036] When performing precipitation construction, connect the vacuum pump and the drainage pipe 21, the pumping device 2 and the air supply device 3 work synchronously, the air supply device 3 supplies air into the drainage pipe 21, and the pumping device 2 sucks the water in the drained deep well. Through the control system parameter setting, the air supply device 3 provides compressed air, which enters the water vapor mixer 4 through the air supply pipe 31. Under the action of the liquid surface pressure in the well pipe 1, the water in the well pipe 1 enters the mixer, forms a water vapor mixture with the gas, and rises in the drainage pipe 21, realizing the "pressure" function. At the same time, the pumping device 2 sucks the water vapor mixture through the drainage pipe 21, accelerates the rising speed, and realizes the "suction" function.

[0037] In this embodiment, one side of the drainage pipe 21 of the pumping device 2 is connected to a branch pipe 22, the pipe mouth of the branch pipe 22 penetrates the cover plate 5 and extends to the top position of the well pipe 1, and the branch pipe 22 and the drainage pipe 21 are respectively controlled to open and close by independent valves. When all the groundwater in the well pipe 1 is pumped out, the air supply device 3 stops supplying air, the pumping device 2 continues to operate, and the valves of the drainage pipe 21 and the branch pipe 22 are opened to quickly form a vacuum in the well pipe 1, thereby accelerating the groundwater gathering rate. When the groundwater in the well pipe 1 gathers to a certain amount, the valve of the branch pipe 22 is closed, the air supply device 3 is started again, and the pumping device 2 is cooperated to continue the pumping operation, and the cycle is repeated to achieve the purpose of soil drainage.

[0038] S4: Foundation pit excavation and support construction. Before foundation pit excavation, dewatering construction is carried out first. The dewatering construction step is carried out 15 days before foundation pit excavation to ensure that the water content in the excavated soil is effectively reduced, so as to lower the water level to below the foundation pit excavation area and ensure the smooth progress of foundation pit excavation construction.

[0039] When excavating the foundation pit, the pumping device 2 maintains continuous pumping action to drain the soil in the foundation pit excavation area. When performing the foundation pit excavation step S4, the soil outside the well pipe 1 is manually inserted into the soil, and the excess part of the top of the well pipe 1 protruding from the soil is gradually cut off as the depth of the foundation pit excavation deepens. Implementing the soil excavation step outside the well pipe 1 by manually inserting the soil is beneficial to reducing the probability of the well pipe 1 being accidentally cracked by the excavation equipment, and gradually cutting the excess part of the top of the well pipe 1 protruding from the soil as the depth of the foundation pit excavation deepens, so that the precipitation construction can be continued during the foundation pit excavation step, and when the water in the soil is gathered again, the soil can be drained in time.

[0040] The excavation of the foundation pit is carried out in a longitudinal segmented, vertically layered, top-down, support-first-then-excavation, and layered excavation manner. Multiple concrete support structures 7 and multiple steel support structures 6 are arranged from top to bottom on the inner wall of the foundation pit. A servo system 61 is set between the steel support structure 6 and the inner wall of the ground-connected wall. The servo system 61 is used to monitor the deformation of the inner wall of the foundation pit in real time, and timely compensate and adjust the axial force of the steel support structure 6 according to the deformation to control the deformation of the foundation pit.

[0041] Specifically, the servo system 61 includes a hydraulic system module and an automatic control system module. The hydraulic system module is mainly composed of a mechanical one-way self-locking hydraulic jack, a hydraulic pump, a proportional pressure reducing and amplifying distribution cabinet, hydraulic oil pipes and cables, and a pressure sensor. The hydraulic jack is installed at the end of the steel support structure 6, and these components work together to achieve precise control and adjustment of the steel support axial force. Automatic control system module: It is composed of hardware equipment such as industrial control computers, signal communication converters, PLC modules, control cabinets, UPS battery cabinets, and computer control software. This module is responsible for real-time monitoring of parameters such as steel support axial force, enclosure structure deformation and temperature, and automatic compensation and adjustment according to preset values.

[0042] The deformation detection method is to arrange monitoring points around the foundation pit, use precision measuring instruments (such as total stations, levels, inclinometers, etc.) to monitor the deformation of the foundation pit in real time, install jack displacement sensors and laser displacement convergence meters and other equipment inside the steel support, monitor the displacement of the jack inside the steel support and the displacement convergence value of the foundation pit, and thus feedback the deformation conditions such as the inclinometer of the underground continuous wall.

[0043] The deformation control method is to compensate and adjust the steel support axial force in time according to the monitoring data to control the deformation of the foundation pit. By presetting the axial force value and warning value, it will automatically compensate when the axial force is insufficient, and give a timely warning when the axial force is too large, and adjust the steel support axial force at any time according to the displacement of the surrounding structure.

[0044] During the foundation pit excavation process, after the earthwork is excavated to the design elevation of the first concrete support structure 7, the first concrete support structure 7 is constructed, and the remaining multiple concrete support structures 7 are installed in this construction sequence.

[0045] Before the construction of the concrete support structure 7, a steel support structure 6 and a servo system 61 are temporarily added above the construction position of the concrete support structure 7. The servo system 61 compensates and adjusts the axial force of the steel support structure 6 according to the real-time monitoring of the deformation of the inner wall of the foundation pit to control the deformation of the foundation pit.

[0046] In order to improve the structural strength of the inner wall of the foundation pit, when installing the steel support structure 6 and the servo system 61 , a steel purlin 62 is first set around the inner wall of the foundation pit, and the steel support structure 6 and the servo system 61 are placed up to the steel purlin 62 .

[0047] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A construction method for dewatering excavation and deformation control of a subway station in a coastal soft soil layer, characterized in that: The following steps are involved: S1: Three-axis mixing pile reinforcement construction: measure and lay out the lines in the foundation pit construction area, delineate the underground continuous wall construction location, then carry out three-axis mixing pile reinforcement construction on both sides of the ground-connected wall construction location, and then excavate a trench in the ground-connected wall construction area; S2: Underground continuous wall construction: hoist the underground continuous wall steel cage into the groove one by one, and cast it to form the main structure of the underground continuous wall; S3: Dewatering construction: construct multiple drainage deep wells in the soil layer of the foundation pit construction area, each drainage deep well is equipped with a set of pumping devices (2) and air supply devices (3), the drainage pipe (21) of the pumping device (2) and the air supply pipe (31) of the air supply device (3) are both extended into the drainage deep well, the air supply pipe (31) of the air supply device (3) is connected to the lower part of the drainage pipe (21) of the pumping device (2), and the top opening of the drainage deep well is closed by a cover plate (5). When dewatering construction is carried out, the pumping device (2) and the air supply device (3) work synchronously, the air supply device (3) supplies air into the drainage pipe (21), and the pumping device (2) sucks water in the drainage deep well; S4: Foundation pit excavation and support construction: The foundation pit excavation construction is carried out in a longitudinal segmentation, vertical layering, top-down, support-first-then-excavation, and layered excavation manner, and multiple concrete support structures (7) and multiple steel support structures (6) are arranged from top to bottom on the inner wall of the foundation pit. A servo system (61) is set between the steel support structure (6) and the inner wall of the ground-connected wall. The servo system (61) is used to monitor the deformation of the inner wall of the foundation pit in real time, and timely compensate and adjust the axial force of the steel support structure (6) according to the deformation condition to control the deformation of the foundation pit.

2. The method for dewatering, excavating and controlling deformation of a subway station in soft soil layer in coastal facies according to claim 1 is characterized by: In the deep well drainage construction step S3, a reverse circulation drilling rig is used to perform drilling construction in the soil layer of the foundation pit construction area to form a well hole, and then the well pipe (1) of the deep well drainage is lowered to the hole center of the well hole, and then filter material is backfilled into the well hole, and the filter material forms a filter layer on the outer periphery of the lower position of the well pipe (1).

3. The method for dewatering, excavating and controlling deformation of a subway station in soft soil layer in coastal facies according to claim 1 is characterized by: Before the foundation pit excavation step S4 is performed, dewatering construction is first performed to lower the water level to below the foundation pit excavation area. When the foundation pit is excavated, the pumping device (2) maintains a continuous pumping action to drain the soil in the foundation pit excavation area.

4. The method for dewatering, excavating and controlling deformation of a subway station in soft soil layer in coastal facies according to claim 1 is characterized by: Before the formal pumping step is carried out, compressed air is first passed through the air supply pipe (31) to the lower part of the drainage pipe (21) by the air supply device (3). The density of the air-water mixture in the drainage pipe (21) is less than the density of the mud-water mixture outside the drainage pipe (21). A pressure difference is generated inside and outside the drainage pipe (21). The mud-water mixture outside the drainage pipe (21) flows into the drainage pipe (21) under the action of the pressure difference. The well pipe (1) becomes a three-phase mixture of air, water and soil. The density of the three-phase mixture decreases with the increase of the air mixing amount. The three-phase mixture is continuously taken out of the drainage deep well, and the soil component in the filter material becomes less and less until it is cleaned, so as to reduce the situation where the main structure of the pumping device (2) is blocked by soil and damaged.

5. The method for dewatering, excavating and controlling deformation of a subway station in soft soil layer in coastal facies according to claim 1 is characterized by: During dewatering construction, after all the groundwater in the well pipe (1) has been pumped out, the air supply device (3) stops supplying air, and the pumping device (2) continues to operate, so that a vacuum is quickly formed in the well pipe (1) and the groundwater gathering rate is accelerated; when the groundwater in the well pipe (1) gathers to a certain amount, the air supply device (3) is started again, and the pumping operation is continued in cooperation with the pumping device (2), and the cycle is repeated to achieve the purpose of draining the soil.

6. The method for dewatering, excavating and controlling deformation of a subway station in soft soil layer in coastal facies according to claim 1, characterized in that: When the foundation pit excavation step S4 is performed, the soil outside the well pipe (1) is manually excavated, and the excess portion of the top of the well pipe (1) protruding outside the soil is gradually cut off as the foundation pit excavation depth increases.

7. The method for dewatering, excavating and controlling deformation of a subway station in soft soil layer in coastal facies according to claim 1, characterized in that: Before the construction of the concrete support structure (7), a steel support structure (6) and a servo system (61) are temporarily added above the construction position of the concrete support structure (7). The servo system (61) compensates and adjusts the axial force of the steel support structure (6) according to the deformation of the inner wall of the foundation pit by real-time monitoring, so as to control the deformation of the foundation pit.

8. The method for dewatering, excavating and controlling deformation of a subway station in soft soil layer in coastal facies according to claim 1 is characterized by: When installing the steel support structure (6) and the servo system (61), a steel purlin (62) is first arranged on the inner wall of the foundation pit, and the steel support structure (6) and the servo system (61) are placed up to the steel purlin (62).

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