Treatment of Cast-in-place Pile Foundation Bottom Sediment Accident in Muddy Silt-stone Region

This paper introduced the method for the treatment of a cast-in-place pile foundation accident in muddy silt-stone region. Pile cap foundation was adopted in this project, and the pile tip embedded into the intermediary weathered muddy silt-stone for the length of 1~3m. Core drilling tests of several piles were conducted to inspect the pile integrity quality and the bottom sediment, and the sediment at pile bottom was found to be up to 150 cm, through the pile body integrity quality was rather good. Five expansion tests reached the same conclusion. Since the pile bottom sediment was close to mud, the allowable axial bearing capacity of these piles might not fulfill the design requirements. Hence, these piles were treated as accident piles. After several technical proposals comparison, coring and grouting method was finally adopted. Unlike common post-grouting method, an improved method was utilized in this project. Clean water was first injected to the intake to wash the pile bottom sediment until the water from the delivery port turned to be clean, and then cement slurry was grout. Load test results indicated that this method has achieved good results. After the treatment, the ultimate pile bearing capacity could meet the design requirements, which indicates that coring and grouting method is effective for the treatment of soft bottom sediment in muddy silt-stone region.