软土地区扩底抗拔桩承载特性试验研究

扩底抗拔桩在软土地区的研究与工程应用较少。设计出适合于上海软土地区的扩底形状与机具,并采用现场足尺试验对等截面桩与扩底桩的抗拔承载特性进行了对比研究。试验共分两组,两组试桩的桩长与桩径皆不同。每组试桩由一根等截面桩与二根扩底桩组成。试验表明,扩底抗拔桩的荷载变形曲线相对平缓,表现得更有后劲,极限承载力比等截面桩提高50%以上,扩底效果明显。并对扩底抗拔桩的桩顶和桩端变形随荷载发展规律、桩身变形与回弹规律进行了初步探讨。足尺试验初步验证了上海地区采用小角度扩底抗拔桩的可行性,为认识此类扩底抗拔桩的承载特性并推动其在工程上的应用迈出了第一步。

Full-scale field tests on uplift behavior of piles with enlarged base

The feasibility of adopting piles with enlarged base for uplift resistance in Shanghai soft soil district has been not well known up to now. To study the uplift behavior of piles with enlarged base, the reasonable base shape and machine for base enlarging were designed. Then full-scale contrast tests on piles with normal straight-shaft and enlarged base were done. The tests were divided into two groups, and there were three piles in each group, one with straight-shaft and the other with enlarged base. The diameter and length of piles in these two groups were different. It indicated that load-settlement curves of piles with enlarged base were flat compared with the steep curves of piles with straight-shaft. With the increase of 5% in concrete material the uplift capacity of the piles with enlarged base increased 50% more than that of the piles with straight-shafted. Based on the tests, the movement of pile top and toe with increasing loading and rebound rates of pile top and toe after unloading were studied. The full-scale tests verified the effectiveness of uplift resistance of piles with small extend angle in Shanghai soft soil area. The tests were advantageous to the understanding of the bearing mechanism and to the application of such piles with enlarged base.