Load-bearing characteristics and optimization design for rock-socketed bored piles in sandy silty clay in coastal areas

The Qingdao region in China is a typical coastal city characterized by “upper soil lower rock” binary composite formations, with a weak upper layer of sandy silty clay that cannot provide sufficient bearing capacity. Through conducting vertical compression static load tests, the vertical bearing characteristics of the socketed moderately weathered rock bored piles were revealed. Combined with theoretical analysis and numerical simulation methods, the applicability of different theoretical models in predicting the vertical compressive ultimate bearing capacity of single piles was evaluated. Further, the influencing factors of bearing performance were analyzed. The research results show that the load-displacement (Q-s) curves of the three test piles were of the gradual type, and the rock-socketed piles exhibit the characteristics of friction end-bearing piles to varying degrees. The accuracy of various theoretical models in predicting the vertical compressive ultimate bearing capacity of single piles was as follows, in descending order: adjusted hyperbolic model, hyperbolic model, exponential curve model, pile material strength calculation formula. Under similar engineering geological conditions, the reasonable ranges of parameters in the influencing factors of the rock-socketed piles were as follows: length-to-diameter ratio of 12≤L/d ≤ 15, rock-socketed ratio of 2≤h_r/d ≤ 3, pile-rock elastic modulus ratio of 10≤E_p/E_r ≤ 30, and friction coefficient of 0.4≤μ≤0.6.