Safety control measures for the hottest Foundation

Safety control measures for foundation pit engineering

foundation pit engineering is a systematic engineering composed of earth excavation, earth retaining, waterproof, water stop and other links. At present, the clamping force of foundation pit engineering increases, and there are still many imperfections from theory to practice, which cause engineering accidents. Combined with many years of practical experience, the author summarizes and analyzes the safety accidents often found in foundation pit engineering at present, and on this basis, puts forward the corresponding safety control measures

1 cause analysis of common accidents in foundation pit engineering

1.1 earthwork collapse

the excavation of foundation pit is deep, the slope is not enough, or when passing through different soil layers, it is not laid into different slopes according to the characteristics of soil, resulting in slope instability and collapse; When excavating the foundation pit (groove) in the soil layer with the action of surface water and groundwater, effective water lowering and drainage measures are not taken, and the soil layer is affected by surface water and groundwater, and loses stability under the action of water, causing landslides; The surcharge on the top of the slope is too large or affected by external force vibration, which increases the shear stress in the slope body, and the soil loses stability and collapses; Soil excavation is too fast and support is not timely, resulting in landslides

1.2 failure of retaining structure

insufficient investigation of the surrounding environment before the construction of foundation pit engineering, such as insufficient investigation of the foundation conditions, underground facilities and underground structures of adjacent buildings, incomplete geological exploration, insufficient geological data, etc; In the design stage, the physical and mechanical properties of the selected soil are wrong, the selected design method is wrong, and the load estimation is insufficient; In the construction stage, the construction load on the ground around the foundation pit is increased, the foundation pit is over excavated, the backfill is not dense, the pressure behind the wall is too large, and the section of the support structure is insufficient

1.3 bolt system failure

accidents caused by non-standard support construction account for a large part. For example, the hole cleaning is not complete when the hole is formed, resulting in the reduction of the pullout resistance of the anchor rod; The drill pipe is not straight or vibrates too much during hole forming, and the soil on the hole wall is disturbed, resulting in the reduction of the pull-out force of the anchor rod and does not coincide with the main needle; Excessive hole cleaning or connection with groundwater leads to soil loss. Cause foundation settlement at the back of retaining structure; Insufficient grouting pressure and slurry loss make the strength of the consolidated body insufficient and reduce the pullout resistance of the bolt. The pressure bearing surface of anchor bolt anchor plate is too small, causing wall damage and foundation pit collapse; The foundation pit collapses due to the insufficient strength of the anchor plate, the weak connection between the waist beam and the support, and the small section of the waist beam; In winter, no antifreeze measures were taken, and the land was frost heaved, causing damage to the supporting surface structure

1.4 failure of the support system

the back of the purlin of the support system is not fully filled, causing the deformation of the retaining structure; The connection between the support end and the surrounding purlin is not filled, causing the surrounding purlin to be crushed, distorted or partially unstable at the edge; Violate the construction regulations during construction, increase the construction load on the support, or the mechanical operation collides with the support; The reinforced concrete supporting structure is crushed due to poor quality or insufficient strength of concrete

1.5 improper treatment of groundwater

the basic feature of this accident is sudden, accompanied by the deformation of the support structure, which is more harmful

(1) water stop curtain failure

water and soil flow into the foundation pit because the retaining structure is not equipped with water stop curtain or the water stop curtain is defective; The retaining structure or water stop curtain below the bottom of the foundation pit is defective, resulting in piping or quicksand at the bottom of the foundation pit; The retaining structure produces large horizontal displacement under the action of water pressure

(2) piping and flowing soil

insufficient insertion depth of retaining structure or insufficient drawdown of groundwater level. It will cause piping at the bottom of the foundation pit; When the groundwater level difference inside and outside the foundation pit is large or there is confined water under the bottom of the foundation pit, resulting in soil flow; Due to the characteristics of high strength, low toughness and high temperature resistance, the pit is set on the soil layer with high water permeability, resulting in quicksand phenomenon

(3) settlement or inclination of buildings

the precipitation of deep foundation pit often brings out fine granular soil, and can cause consolidation settlement of soft soil layer, causing settlement, horizontal displacement or inclination of buildings and underground facilities within a certain range around the foundation pit