Difference in Dynamic Response of Large Diameter and Variable Cross Section Single and Group Piles in Liquefied Sites

With the purpose of researching the distinctions between the anti liquefaction capability of large-diameter variable cross-section group piles foundation and single pile foundation under earthquake condition, relying on the Second East Passage Project, the dynamic response difference of large-diameter variable cross-section single pile and group piles foundation was studied by vibration table model testing, and the difference of pore pressure ratio, pile shaft acceleration, pile top horizontal displacement and pile shaft bending moment between large-diameter variable cross-section single pile and group of piles in saturated sandy soil under earthquake load was analyzed. The research results show that under the seismic load of 0.30 g, the foundation of large diameter and variable cross-section single pile and pile group are liquefied, and the complete liquefaction time of large diameter and variable cross-section group piles foundation is 1.58~1.61 s later than that of single pile foundation; The maximum acceleration of large diameter variable cross-section group piles is reduced compared to single piles, and the occurrence time is more delayed than single piles; The maximum horizontal displacement of the top of a large diameter variable cross-section pile group is reduced by 0.68 mm compared to a single pile, with a time lag of 1.44 seconds; The maximum bending moment of large diameter variable cross-section group piles foundation is 11.99% less than that of single pile foundation, and the maximum bending moment of great diameter variable cross-section group piles foundation lags 1.88 s behind that of single pile foundation; It reveals that the anti liquefaction features of large diameter and variable cross-section group piles foundation are significantly higher than that of single pile foundation, and the dynamic response is more delayed. In the design of pile foundation in earthquake area, the anti liquefaction features of large diameter and variable cross-section group piles foundation can be increased by using the form of large diameter and varying cross-section group piles foundation.