Study on effect of base grouting on shaft friction of overlength large diameter pile

The shaft friction can be improved greatly by base grouting, and the increment is the major part of ultimate bearing capacity increment of the overlength large diameter pile. There is a weak layer between a pile and the soil around it, so the grout always flows upward along the weak layer, squeezing the soil to a larger diameter and improving the shaft friction. According to the results of the self-balanced static load testing method, the SPT test and the CT scanning test of a project with overlength large diameter piles, the strength of soils in a large range above pile-bases was improved and the shaft friction was increased 12.39 %-52.87 %, the ratios of shaft friction in the increment of ultimate bearing capacities was 56 %-88 %.