Field investigations on bearing characteristics of composite post-grouting piles in clastic rock layers

As a novel technology for improving the bearing capacity of pile foundations, composite post grouting at pile bottom has not been applied in clastic rock layers. In this study, on-site static load tests are conducted on two composite post-grouted piles to investigate their performance, enhancement mechanism, and vertical bearing characteristics in clastic rock layers. The load-settlement behavior, pile axial force, pile end-resistance, pile side frictional resistance, and relative displacement between a pile and soil are analyzed and discussed. The results show that applying composite post grouting at the pile bottom increases the ultimate bearing capacity of bored piles by more than 50% in clastic rock layers. The ultimate bearing capacity test value of the composite grouting of debris rock layers can reach 1.1-1.5 times the existing calculated ultimate bearing capacity after grouting. Moreover, the side-resistance enhancement coefficient is between 1.7 and 2.0, which is 1.3–1.5 times higher than the current standard values. The current research results have limited sample size, but provide important reference data for the improvement and application of composite post grouting pile foundations, as well as the rapid development of bridge foundations in high-altitude areas.