灌注桩套管高频振动贯入砂土中的孔压性状分析

Finite element analysis of pore pressure generated by sleeve for cast-in-place piles installation into sand using high frequency vibratory hammers

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,但是关于灌注桩套管高频振动贯入机理,特别是套管贯入引起的超孔隙水压力的研究还不全面。在全面介绍了套管高频振动贯入有限元分析模型的建立过程后,对套管高频振动贯入引起的超孔隙水压力分布规律、变化趋势进行了详细研究。同时,采用正交试验与数值模拟相结合的正交有限元法评价了各因素对孔压性状的影响程度。研究结果表明:套管振动贯入过程中,超孔隙水压力随距套管端部垂直距离、水平距离的增大而减小,且超孔隙水压力幅值随时间逐渐增大,随振动频率增大而减小;套管振动贯入结束后,超孔隙水压力随时间大致呈指数型衰退,且主要沿套管内侧路径消散;影响孔压性状的主要因素为贯入深度和渗透系数。研究结果对套管高频振动贯入砂土中的孔压性状分析具有理论和实际意义。

With the development of the construction technique of cast-in-place piles with sleeves driven by using high frequency vibratory hammers,the cast-in-place piles have been widely used in construction engineering.But the researches on the penetration mechanism of sleeve for cast-in-place piles driven by using high frequency vibratory hammers,especially the excess pore pressure generated by sleeve for cast-in-place piles installation into sand,are still not complete.The paper presents the FEM model of penetration of sleeve driven by using high frequency vibratory hammers,and studies in detail the formation,distribution and variance tendence of excess pore pressure.And factors affecting behavior of pore pressure such as penetration depths,outer diameters of sleeve,displacement amplitudes and permeability coefficients are also studied by orthogonal finite element method combining the orthogonal experiment with numerical simulation.The results of finite element analysis show that excess pore pressure decreases with the increase of vertical distance and radial distance from the tip of sleeve.Excess pore pressure amplitude increases gradually with time,and decreases with the increase of vibratory frequency in sleeve penetration.Excess pore pressure assumes roughly exponential decay trend with time,and dissipates mainly along the inside of sleeve at the end of sleeve penetration.The primary factors affecting behavior of pore pressure are penetration depth and permeability coefficient.The results provide theoretical and practical reference to analysis of pore pressure generated by sleeve for cast-in-place piles installation into sand using high frequency vibratory hammers.