深长大直径扩底灌注桩承载性能试验研究

Experimental study on bearing capacity behavior of deep large diameter cast-in-place belled pile

随着软土地区高层建筑及大跨桥梁等的承载力要求的提高,深长大直径扩底灌注桩因其单桩承载力高、经济效益好等优点得到较广泛的应用。但基于中短桩理论的计算标准与实测得到的深长大直径扩底桩的结果有较大差别,因而需根据现场试验结果分析软土中深长大直径扩底桩的承载性状和荷载传递机理。基于现场静载荷试验及桩身应力测试结果分析了深长大直径扩底桩的荷载传递机理和承载性状。研究表明,深厚软土地区深长大直径扩底灌注桩的侧阻先于端阻发挥,同时其荷载传递不同于等直径的灌注桩,深长大直径扩底灌注桩在荷载水平较高时会产生桩侧摩阻力软化;扩底桩的桩端扩大部分对承载能力影响较大,不仅影响到桩端阻力的发挥,还影响到桩侧阻力的发挥,深长大直径扩底灌注桩在低水平荷载作用下表现为摩擦桩性状,在高水平荷载作用下表现为端承摩擦桩性状。

With the improvement of bearing capacity requirements of high-rise buildings and long-span bridges in soft soils, the deep large diameter cast-in-place belled piles were widely used because of their advantages, such as higher bearing capacity of single pile and better economic benefits. There were greater differences between the field test results of deep large diameter cast-in-place belled piles and the calculation results based on the middle and short piles theory in the current specifications. So the bearing capacity behavior and load transfer mechanism of deep large diameter cast-in-place belled piles were studied based on the static load tests and stress measurement in deep soft soil foundation. The results show that the lateral friction resistance of deep large diameter cast-in-place belled piles takes effect firstly, and their load transfer behavior is different from that of equal-diameter cast-in-place piles. The belled part affects not only the pile end resistance but also the lateral friction resistance. Also the frictional resistance of deep large diameter cast-in-place belled piles can be degraded under higher load level. The bearing behavior of deep large diameter cast-in-place belled pile is that of friction piles under low load level and that of end-bearing friction piles under high load level.