超大吨位基桩静载对桩周土的影响范围试验
Influence Range of Soil Around Pile by Extra-tonnage Pile Foundation Static Test

针对广州某中央商务区核心区地下空间钻孔灌注桩的超大吨位静载试验，分析了静载试验加卸载过程中荷载？渤两登？线和桩周土体的位移变化。结果表明：当荷载小于试桩竖向承载力特征值时，试桩的竖向刚度几乎保持不变；荷载大于试桩竖向承载力特征值时，刚度逐渐减小但幅度很小；荷载达到试桩承载力极限值之前，随着荷载增加，桩顶沉降线性增加，每级加载桩顶沉降增量也几乎线性增加；试验加载时，越靠近大梁的土体出现卸载回弹的现象越明显，同时桩周土体由于剪切作用会发生沉降，两者同时作用造成桩周一定范围内土体隆起；加载过程对桩周土体的影响范围可定为4d(d为桩径)；卸载完成后距试桩中心1.67d~2.22d？？范围内的土体出现隆起现象；加载过程中距试桩中心2.78d 范围以外的土体处于弹性阶段。
Based on extra-tonnage pile foundation static load test of bored pile in CBD underground space in Guangzhou, the load-settlement relationship curves and the displacement variation of soil around pile were analyzed. The results show that when the load value is lower than the eigenvalue of vertical bearing capacity of test pile, the vertical rigidity of test pile almost keeps unchanged. When the load value is higher than the eigenvalue of vertical bearing capacity of test pile, the rigidity of pile reduces gradually, but the reduction is less obvious. When the load is lower than the ultimate load-bearing capacity, the settlement of pile tip increases linearly along with the increasing of load, every increment of settlement almost increases linearly too. During the loading process, the closer to the beam of soil, the more obvious phenomenon of unloading rebound, at this time, the soil around pile starts settle due to the shear action. The simultaneous occurrence of both impacts causes upheaval of soil within certain limits around pile. The influence range of soil around pile during loading process can be set to 4d(d is pile diameter). The soil within the scope of the 1.67d-2.22d away from the midpoint of pile behaves heaving after completion of unloading. The soil that beyond the range of 2.78d from the midpoint of pile is in elastic stage during loading process