水泥土加固桩水平循环承载性能足尺试验研究

Full-scale tests on horizontal cyclic bearing capacity of cement-soil-improved piles

选取宿迁典型饱和粉土场地,采用水泥土搅拌桩加固钻孔灌注桩桩周土,开展灌注桩水平循环加载足尺试验。探究水泥土加固试验桩(TPI)和未加固试验桩(TPU)在循环水平荷载作用下的滞回特性、弯矩、刚度退化、位移延性、水平承载力与残余变形能力。试验结果表明:TPI比TPU桩的弯矩减小47%,屈服位移减小41%,水平承载力提升150%,有效刚度提升240%,等效黏滞阻尼比提升233%,桩的开裂荷载提升150%,屈服荷载阶段桩体的残余变形能力减小17%。水泥土搅拌法不仅可以限制桩侧粉土液化,增加桩基础的耗能及位移延性,而且可以显著的降低桩头水平位移和弯矩的发展。从抗震性能的角度分析,水泥土搅拌桩加固既有桩基,有效抑制了加固范围内地基土刚度衰减,增强了桩-土结构的总耗能、等效黏滞阻尼系数与变形恢复能力,提高桩基础在大变形阶段的抗震性能。

The cement-soil mixing columns are used to improve the surrounding soils of drilled cast-in-place piles in a typical saturated silt site in Suqian City.The full-scale horizontal cyclic loading tests on the cast-in-place piles on site are conducted.The hysteresis characteristics,bending moment,stiffness degradation,displacement ductility,horizontal bearing capacity and residual deformation capacity of test piles in improved soil(TPI)and those in unimproved soil(TPU)under horizontal cyclic loading are explored.The test results show that the bending moment of TPI piles decreases by 47%and the yield displacement decreases by 41%compared to those of TPU piles.The horizontal bearing capacity of TPI piles increases by 150%,the effective stiffness increases by 240%,and the equivalent viscous damping ratio increases by 233%.The cracking load of the piles increases by 150%,and the residual deformation capacity of the piles during the yield load stage decreases by 17%.The cement-soil mixing method can limit the liquefaction of silt at pile side,increase the energy consumption and displacement ductility of pile foundation,and significantly reduce the development of horizontal displacement and bending moment of pile head.From the perspective of seismic performance,strengthening the existing pile foundations with cement-soil mixing piles can effectively suppress the stiffness attenuation of the foundation soils within the reinforcement range.The cement-soil-reinforced piles enhance the total energy consumption,equivalent viscous damping coefficient and deformation recovery capability of the pile-soil structure.Therefore,the seismic performance of pile foundations during large deformation is improved.