地震波作用下非饱和土中PHC管桩水平振动机理研究

In view of the imperfection of calculation theory for the seismic response of PHC pipe piles presently, the project aims to establish a mechanical model to analyze the horizontal dynamic response of PHC pipe piles in unsaturated soil subject to two chief types of incident seismic waves - shear wave and Rayleigh wave. The hydraulic tortuosity factor is introduced to describe the seepage path with full of twists and turns, and the governing dynamic equation of unsaturated porous media is modified to take into account the resulting inertia coupling mechanism between the pore fluids and the solid movements. By virtue of the Helmholtz decomposition to decouple the motion equation, the displacement and stress distributions of unsaturated free field caused by pile-soil interaction are first obtained. Then, using the Novak’s thin layer method, and considering the radial inhomogeneity of squeezing soil and partially filling effect of soil plug, closed-form solutions in the frequency domain for transverse seismic performance of single pile excited by incident shear waves are derived. And the response of single pile is further extended to PHC pipe pile groups under shear wave and Rayleigh wave, respectively, by employing the superstition of pile-pile interaction. Furthermore, a small shaking table model test of the earthquake performance of PHC pipe pile under seismic excitations considering soil-pile-structure interaction effect is presented. The influences of compacted zone radius and soil moisture content on the horizontal dynamic behaviour and failure forms are investigated. This research will promote the development of seismic analysis theory of PHC pipe pile, and provide scientific references to its validity for seismic resistance.

本项目针对PHC管桩地震响应计算理论和方法尚不完善的现状，旨在建立土体非饱和条件下，PHC管桩在剪切波和Rayleigh波两类主要地震波作用下水平振动的解析力学模型。项目首先引入水力迂曲度因子描述孔隙通道弯曲所引起的固、液间惯性耦合效应，改进现有非饱和土波动方程，通过方程解耦，求得剪切波作用下考虑桩土相互影响的非饱和自由场的位移和应力分布，再基于Novak薄层法原理，建立考虑土体径向非均质和桩芯土部分填充影响下PHC管桩的水平振动理论模型，并借助桩-土-桩相互作用的叠加，进一步推导剪切波和Rayleigh波作用下PHC管桩群桩基础横向振动问题的频域解答；同时开展考虑土-桩-结构相互作用的小型振动台试验，研究不同地震动条件下，挤密区半径和土体含水量对PHC管桩水平动力特性和破坏模式的影响，并验证理论模型的可靠性。研究成果将推动PHC管桩地震响应分析理论的发展，并为其抗震适用性提供科学依据。

本课题基于修正的三相多孔介质波动方程和结构动力学理论，考虑桩土相互作用，对剪切波和Rayleigh波作用下非饱和土中管桩水平动力响应特性开展研究，完成了预期研究目标，取得了预期的研究成果。主要研究成果如下：.(1) 基于Young-Laplace方程，建立了两椭球颗粒与液桥相互作用的微观水力计算模型，为研究低饱和土毛细作用机理及土-水特征曲线提供了思路。.(2) 通过将孔隙迂曲效应引入孔隙流体的渗流连续性方程，对非饱和土波动方程进行修正，建立了双层(带表面层)非饱和地基中Rayleigh波的弥散特征方程；并基于有限元-解析法，对带覆盖层饱和地基中R波的频散特性进行了研究。.(3) 基于三相多孔介质波动方程，推导了SH波作用下非饱和土中土塞部分填充管桩水平地震响应解析解，并分别采用Novak三维连续介质模型和虚拟桩模型，求得了非饱和土中单桩水平动力阻抗的频域形式解答。.(4) 在考虑地基土成层性、径向非均质性、土塞部分填充及桩顶柔性约束等因素的基础上，建立了饱和土中管桩水平及扭转振动理论，讨论了管桩桩身设计参数、土体参数等对管桩振动特性的影响。.(5) 通过开展管桩水平地震响应的小型振动台实验及数值模拟研究，探讨了地层分布、土体挤密扰动、土塞填充和桩头连接形式等对管桩水平地震响应的影响规律。.(6) 在课题执行期内发表学术论文12篇，其中SCI/EI收录论文5篇，申请发明专利16项，授权4项；另有两篇论文正在外审。