Second, focus on the construction control of the retaining structure. For the surveying and setting out of the retaining works, the key is to control the spacing between the retaining structure and the basement exterior wall; the performance and safe operation of the equipment and machinery for foundation pit retaining construction; the qualification of raw materials for the retaining works through inspection; construction control according to the retaining design requirements to ensure that all control indicators meet the design requirements; at the same time, the preparation of construction emergency plans and the formulation of rescue measures.

Third, earthwork excavation shall be carried out after the strength of the retaining structure and water-stop curtain reaches the design requirements and when the conditions for earthwork excavation are met; strictly control the excavation depth, reserved soil slope ratio, construction sequence, location and route of soil removal and transport openings, the status of engineering piles and horizontal supports, the deformation of the retaining system, and ensure a reasonable progress of earthwork excavation; over-excavation is strictly prohibited; 20cm of original soil can be reserved at the pit bottom and excavated manually to reduce disturbance; in case of abnormal situations such as water and sand gushing or encountering obstacles, immediately notify the owner and participating units, and suspend excavation or take predetermined emergency rescue plans; for foundation pits with multiple supports, when removing supports, consider installing temporary replacement supports first, and remove the existing supports after they reach strength; the method of support removal shall be selected as manual or blasting according to the requirements of the surrounding environment and protection of completed works, and safety must be ensured.

Fourth, foundation pit dewatering control. In soft soil areas, the groundwater level is often high, involving different hydrological conditions such as phreatic water, micro-confined water, and confined water. According to the permeability characteristics of the strata where the foundation pit is located, attention should be paid to the coordination of dewatering and excavation procedures. Groundwater affects the strength of the soil layer; if there is groundwater seepage, it will increase the risk of the foundation pit; when confined water layers are involved, it may cause sudden inrush of water into the foundation pit, and even cause instability and failure of the foundation pit; therefore, effective control of foundation pit dewatering is very important. Dewatering construction should reasonably set the number, depth, and diameter of wellpoint dewatering wells; when phreatic water dewatering is involved, dewatering should be carried out before excavation, and the water level should be controlled at least 0.5m below the excavation surface; when confined water layer dewatering is involved, pressure reduction and pumping should start after excavation to a certain depth according to design calculations, and excavation can continue only after the water pressure drops to a safe water level; water level changes should be monitored through water level observation wells, and when sudden changes occur, causes should be analyzed, and dewatering measures should be adjusted in a timely manner according to the monitoring of the surrounding environment; when dewatering of confined water outside the pit is involved, recharge measures outside the pit should be provided; ensure that dewatering measures continue until the design-allowed removal time or until the basement emerges above ground; during construction excavation, avoid excavation machinery colliding with dewatering wells, which may cause dewatering wells to fail; construction must have backup power and pumping equipment.