灌注桩套管高频振动贯入过程中挤土效应研究

Squeezing effect in the high-frequency vibratory penetration process of the cast-in-place pile sleeve

随着全套管振动取土灌注桩施工工艺的发展,灌注桩在工程中的应用越来越广泛,但关于灌注桩套管高频振动贯入机制,特别是套管贯入引起的挤土效应研究还不全面。全面介绍了套管高频振动贯入全过程的有限元-无限元耦合模型的建立过程后,对地表隆起、土体侧移及超孔隙水压力等挤土效应的变化规律进行了详细研究。研究结果表明:水平向的挤土位移随套管贯入深度的增加而增大,竖向挤土位移随着套管贯入深度的增加,浅层土表现为隆起量增大,而深层土表现为下沉量增大;最大挤土位移与套管贯入深度存在滞后效应;浅层土体的隆起为水平向应力加载引起竖向应力增加所致,且隆起分界面深度随着动力荷载幅值增大而增大,随振动频率的增大而减小;超孔隙水压力随套管贯入深度增加而增大,随径向距离增大呈指数型衰减。

With the development of the technique for constructing the cast-in-place piles with high frequency vibratory hammers, the cast-in-place piles have been widely used in construction engineering. The penetration mechanism of the pile sleeve driven by high frequency vibratory hammers remains unclear, and particularly the squeezing effect in the sleeve penetration has yet to be investigated. In this paper, a finite elements and infinite elements coupling model is developed for simulating the sleeve penetration process driven by high frequency vibratory hammers, and used to study the squeezing effects such as ground heaves, lateral soil displacement and excess pore pressure generation. The results indicate that the horizontal displacement induced by soil compaction increases with the increase of sleeve penetration depth, and for the vertical compaction displacement, the heave increases in shallow soil layers and the settlement increases in deep soil layers as the sleeve penetration depth increases. The maximum compaction displacement lags behind the sleeve penetration depth. The reason for heave in shallow soil layers is that the horizontal stress increment causes an increase in the vertical stress, and the depth of heave interface increases with the increase of dynamical load amplitude, while decreases with the increase of vibration frequency. The excess pore pressure increases with the increase of sleeve penetration depth, and exhibits an exponential attenuation trend as the radial distances increases.