列车荷载作用下X形桩-网复合地基动力响应研究

Dynamic response of XCC pile-net composite foundation under train loading

基于大比例X形桩‑网复合地基模型,开展了高速铁路列车荷载下桩‑网复合地基的动力特性试验研究,分析了不同车速情况下地基土的振动速度、动应力和动位移的分布特性,探讨了循环荷载下轨道路堤地基系统的振动响应和路堤内部动应力的分布特征和衰减规律。采用PLAXIS 3D建立数值分析模型,研究了不同列车轴重及振动频率对路堤振动速度响应的影响,对比了无筋路堤与双层土工格栅加筋路堤在动荷载作用下桩顶与桩间土竖向应力的分布规律。结果表明:轨道板表面处竖向位移随时间呈“M”形周期性变化;竖向速度响应在路堤表层处最大,沿地基横向及深度方向逐渐衰减,在路堤中衰减了近90%。随着加载频率及加载幅值的增大,土体振动速度逐渐增大。动荷载对无筋路堤影响显著,土拱效应明显减弱,桩土应力比值随加载频率的提高逐渐减小。土工格栅加筋路堤张力膜效应能够减小动荷载对复合地基的影响。

Based on the large-scale model test on the XCC pile-net composite foundation subjected to dynamic loading induced by high-speed train,the distribution characteristics of vibration velocity,dynamic stress,and dynamic displacement of foundation soil are analyzed under different train speeds.The vibration response of the track-subgrade system and attenuation law of dynamic stress of foundation soil under cyclic loading are discussed.A numerical model is established in this paper using PLAXIS 3D to study the effect of axle weight and vibration frequency of train on the vibration response of the composite foundation.Moreover,the vertical stress distributions of pile top soil and soil between piles under dynamic loading are compared between non-reinforced embankment and double-layered geogrid reinforced embankment.The results show that the vertical displacement of the track slab changes periodically with the time of“M”type;the vertical velocity is the largest at the surface of the embankment,and gradually attenuates along the horizontal and depth direction of the foundation.The vertical velocity attenuates nearly 90%in the embankment.With the increase of loading frequency and loading amplitude,the vibration velocity of soil increases gradually.The dynamic loading has a significant effect on the unreinforced embankment,which weakens the soil arching effect.The vertical stress ratio of pile to soil decreases with the increase of loading frequency.Additionally,the tension membrane effect of geogrid reinforced embankment can reduce the influence of dynamic loading on composite foundation.