How to deal with hole collapse of punching pile driver during drilling?
1. Quality problems and phenomena of punching pile driver
The borehole wall collapses during or after drilling.
2. Cause analysis of punching pile driver
1) Due to the low consistency of mud and poor wall protection effect, water leakage occurs; Or the pile casing is buried shallowly, or the surrounding sealing is not dense, resulting in water leakage; Or the thickness of the clay layer at the bottom of the pile casing is insufficient, and the bottom of the pile casing leaks, resulting in insufficient height of the mud head and reduced pressure on the hole wall.
2) The relative density of mud is too small, resulting in low pressure of water head on hole wall.
3) When drilling in soft sand layer, the footage is too fast, the formation of slurry wall protection is slow, and water seepage occurs in the wall.
4) During drilling, there was no continuous operation, the drilling was stopped for a long time, and the water head in the hole failed to maintain 2m above the water level outside the hole or the groundwater level, reducing the pressure of the water head on the hole wall.
5) Improper operation, colliding with the hole wall when lifting the drill bit or lifting the reinforcement cage.
6) There are large equipment operations near the borehole, or temporary access roads, which produce vibration when vehicles pass.
7) The concrete is not poured in time after hole cleaning, and the placing time is too long.
3. Preventive measures
1) Temporary access roads shall not be set near the borehole, and large equipment operation is prohibited.
2) When the pile casing is buried on land, 50cm thick clay shall be tamped at the bottom and around the pile casing, and attention shall be paid to tamping. The pile casing shall be backfilled evenly to ensure the stability of the pile casing and prevent the infiltration of surface water.
3) When vibrating in water and sinking into the pile casing, the pile casing shall be sunk through the mud and impermeable layer according to the geological data, and the joints between the pile casings shall be sealed to prevent water leakage.
4) According to the geological exploration data provided by the design department and different geological conditions, appropriate mud specific gravity, mud viscosity and different drilling speeds shall be selected. For example, when drilling in the sand layer, the mud consistency shall be increased, better slurry making materials shall be selected, the viscosity of the mud shall be increased to strengthen the wall protection, and the footage speed shall be appropriately reduced.
5) When the water level changes greatly in flood season or tidal area, measures such as raising the pile casing, increasing the water head or using siphons shall be taken.
