What should you pay attention to when excavation of foundation pit?

1. Five boards and one map are set up at the entrance and exit of the gate. On-site personnel are familiar with the project overview, safety, quality, fire protection and other systems and control points.

2. Safety signs, posters, slogans, emergency rescue procedures, etc. will be installed on the office area fence and foundation pit perimeter of this project, and signs and warning signs will be installed on key safety locations in the production area.

3. For openings less than 1500mm, use steel grilles for protection, and the grilles are covered with wooden springboards or bamboo plywood. A safety net is installed at the opening of no less than 1500mm, and steel pipe railings are used for protection around it.

4. Temporary safety lighting should be installed in the main places and safe evacuation passages on site. Fire personnel must hold a certificate to work. Before starting a fire, they must go to the project department to activate the fire certificate, processing area, steel processing shed, warehouse, Fire extinguishers are installed in the office area and other places, and fire-fighting racks are installed near the entrances and exits of the production area. Temporary fire hydrants, fire extinguishers, hoses, fire-extinguishing buckets, fire-extinguishing shovels, fire-extinguishing axes and other tools are installed in the fire-fighting racks.

5. Conduct real-time foundation pit monitoring on site according to the foundation pit monitoring point layout plan, monitor the horizontal displacement and settlement of the foundation pit edge, anchor tension stress values, horizontal inclination measurement of the foundation pit, and groundwater level conditions , monitor the settlement of surrounding pipelines, focus on strengthening safety management in areas where the monitoring value exceeds the warning value, and take necessary reinforcement technical measures to prevent collapse events in foundation pits.

6. Set up safety railings around the foundation pit and at the opening for safety protection. The height is 1.2m. Water retaining sills are set up around the foundation pit. The surface is plastered and calendered to prevent rainwater from entering the foundation pit. Find a slope of 2% from the edge of the pit to the roadside drainage ditch. Horse paths and safety passages are provided at the upper and lower foundation pits. It is prohibited to stack materials within 2m of the periphery of the foundation pit. The height of materials stacked beyond 2m shall not be higher than 1.5m

7. Temporary drainage ditches are set up around the periphery of the foundation pit, and the drainage ditch is away from the foundation. The pit length is 300mm, and the distance from the edge of the structure is not less than 400mm. The drainage ditch is 300mm lower than the earth excavation surface. A temporary water collection pit is set up at the corner of the foundation pit and every 30m. The bottom of the water collection pit is 500mm lower than the bottom of the drainage ditch. Water collection The side walls and bottom of the pit and drainage ditch are smoothed with cement mortar, and the water in the sump is pumped to the road sedimentation tank.

8. The lighting supply voltage of the on-site lighting system in humid and electric shock-prone places must not be greater than 24V. A temporary fire pump room is set up on site. When a fire occurs, the water source is obtained from the fire pump room as soon as possible.

9. The Administrative Security Department of the project department should set up full-time personnel to carry out medical and health work, set up temporary medical stations on site, equipped with sufficient facilities, medicines, and prepare first aid stretchers and other tools on site.

Extended information:

Steps of foundation pit excavation:

The general procedures of foundation pit excavation include: measurement and setting → tangent layered excavation → Drain precipitation → repair slope → leveling → leave enough reserved soil layer, etc. When excavation of adjacent foundation pits, the construction procedure of first deep and then shallower or simultaneously should be followed. The excavation should be carried out in horizontal sections from top to bottom. The width and slope of the pit bottom should be checked while digging, and the slope should be repaired every 3m or so. , and then carry out a unified slope repair and bottom cleaning when the design elevation is reached.

Basic requirements for foundation pit excavation:

Before excavation of deep foundation pits, a special earthwork plan must be formulated and passed expert demonstration; the supporting structure, groundwater level and Carry out necessary monitoring and protection of the surrounding environment.

(1) The excavation plans for deep foundation pit projects mainly include slope excavation, center island type (also called pier type) excavation, basin excavation and reverse excavation. The former has no supporting structure, while the latter three types all have supporting structures.

(2) The sequence and method of earthwork excavation must be consistent with the design working conditions, and follow the principle of "trough support, support first and then dig, excavation in layers, and over-excavation is strictly prohibited".

(3) Prevent the excessive rebound deformation of the soil after excavation of the deep foundation pit:

An effective measure to reduce the rebound deformation of the foundation pit during construction is to try to reduce the soil rebound deformation. Changes in effective stress, reduce exposure time, and prevent foundation soil from flooding. Therefore, during and after the excavation of the foundation pit, normal dewatering at the well point should be ensured, and the cushion and floor should be poured as soon as possible after the excavation reaches the design elevation. If necessary, the soil below the foundation structure can be reinforced.

(4) Prevent slope instability.

(5) Prevent pile displacement and tilt:

After piling is completed and the foundation pit is excavated, a reasonable construction sequence and technical measures should be formulated to prevent pile displacement and tilt.

If the foundation pit is excavated immediately after piling, the soil is prone to a certain horizontal displacement due to the stress release during excavation and the lateral thrust of unloading on one side caused by the height difference of the excavation. , making the piles driven first prone to horizontal displacement. During construction in soft soil areas, such accidents have occurred frequently and deserve attention. For this reason, after the pile group foundation piles are driven, it is advisable to stay for a certain period of time and use dewatering equipment to pre-pump groundwater until the stress accumulated in the soil due to pile driving is released, the pore water pressure is reduced, and the disturbed soil is re-solidified. After the completion, the foundation pit will be excavated. Moreover, the excavation of earthwork should be uniform and layered to minimize the difference in earth pressure during excavation to ensure correct pile position and stable slope.

(6) Cooperate with the construction of deep foundation pit supporting structures:

The excavation method affects the load of the supporting structure. It is necessary to make the supporting structure evenly stressed and reduce deformation as much as possible. To this end, we must insist on using a layered, segmented, balanced and symmetrical approach to excavation.