锤击荷载作用下大直径钢管群桩的动力特性分析

Dynamic response analysis of a large-diameter steel tube pile group subjected to hammering loads

上海某机械厂有一大直径钢管桩,用于所生产柴油打桩锤出厂前的试用。目前试桩已不满足新生产大吨位柴油打桩锤的试打要求,因此拟增加8根短桩与试桩组成群桩。由于锤击荷载作用下长短组合群桩中荷载的分配及沉降的研究较少,为得到合理的群桩加固型式,采用有限元方法研究锤击荷载作用下群桩的动力承载特性。首先建立单桩有限元模型,分析竖向静荷载作用下钢管桩的沉降,并将模拟结果与现场静荷载试验结果进行对比,验证有限元模型的准确性,再分析锤击荷载作用下单桩的动力响应;其次建立锤击荷载作用下的长短组合群桩有限元模型,分析承台质量、承台埋深、辅桩桩长对群桩桩顶荷载分布及沉降的影响。结果表明锤击荷载作用过程中,角桩、边桩桩顶最大压应力较大,主桩桩顶最大压应力较小;承台埋深越浅,群桩桩顶应力越大,沉降反而越小;承台质量、辅桩桩长对群桩动力特性影响不大。

A large-diameter steel tube pile is used in a machinery factory in Shanghai to test the new produced diesel pile hammer. However, with the increase of the diesel hammer weight, it fails to meet the test requirements and a pile group is recommended to bear the hammering loads with the help of 8 added short piles. But so far, few people have investigated the displacement and load distribution of combined pile groups subjected to hammering loads. To reasonably design the reinforcement type of the pile group, the finite element method is used to study its dynamic responses. Firstly, a three-dimensional single pile model is established and verified through static load tests. The dynamic responses of the pile group are then simulated to evaluate the effects oftbe mass and depth of pile cap, the length of short piles on its settlement and load distribution. The results show that the maximum compressive stress of comer piles and edge piles are larger than that at the top of the main pile during the impact of hammering loads. For a shallower pile cap, the stress of the main pile head tends to be larger while the settlement of the main pile is smaller. Additionally, the mass of pile cap and the length of short piles have little effects on the dynamic properties of the pile group.