Analysis on Bearing Characteristics of Pile Groups with Post-Grouting at PileEnds in Loess Areas

By studying the variations of bearing capacity characteristics of two bored piles before and after being grouted, the radius of the plastic influential zone of cement pastes after being compactedly grouted at pile ends was derived by Vesic's theory. A single pile model and pile group models considering different quantities of piles, pile spacing, and grouting conditions were respectively constructed, in which the pile spacing was 2 to 6-times pile diameters for 2×2 pile groups and 3-times pile diameters for 3×3 pile groups. Then, the effect of grouting at pile ends on settlement, pile end resistance, pile side resistance, and ratios of pile end resistance and total resistance were studied. The conclusions were that the grouting bearing capacity efficiency for pile group foundations dropped with an increase in pile quantities in the same pile space. The order of the bearing capacity of 2×2 pile group foundations from large to small was the foundation with pile space of 5-, 6-, 4-, and 3-times pile diameters. When the pile spacing was 5-times pile diameters, the bonding effect of expanding heads of pile ends and pile group effect were maximized. In the same working condition, the ratio of end resistance and total resistance was significantly enhanced after being grouted, while in the same quantity of piles, the ratio of end resistance and total resistance dropped gradually with an increase in pile space. When the pile space was smaller, the end resistance of piles increased more apparently than the side friction resistance of piles. As the ferrule effect by side piles, corner piles and surrounding soil on middle piles in settlement processes of pile foundations, lateral friction resistance of corner piles and side piles worked earlier than that of middle piles. The order of lateral friction resistance from large to small was that of corner piles, side piles and middle piles.