动荷载下桩承式路堤的承载特性及机制研究

对于桩承式路堤作用效应的研究目前主要侧重于对静荷载作用下桩土应力比和土拱效应等,较少考虑动荷载的影响,而车辆运行产生的动应力会对路堤中的土拱产生一定的影响,进而影响桩承式路堤的整体性能。为了分析静、动荷载作用下桩承式加筋路堤的性能变化,采用可视化模型试验和颗粒流数值模拟相结合的方法,对桩承式路堤在静载和动载下的应力传递和变形性状进行研究,分析动载作用下填土高度、桩帽、桩距、加筋形式、荷载频率的影响。试验结果表明,在动载下无筋路堤的桩顶的应力减小,而桩间的应力和位移增大,并且变化的幅度均比加筋路堤大,加筋材料的设置有利于减小动载的影响效应,但不同加筋形式下桩承式路堤的工作性状有所不同,受动载影响程度的大小主要与土拱效应的强弱有关。设置双层加筋时,因加筋材料与周围砂土形成半刚性平台,土拱效应减弱,故受动载影响的程度最小,单层加筋时,格栅设于桩顶上方10 cm比格栅置于桩顶受动载影响的程度明显减小,颗粒流的模拟结果验证了以上结果,并且进一步得出随荷载频率的增加、填土高度与桩净距的减小,动载的影响效应增大的结论。

Bearing behavior and mechanism of pile-supported embankment under dynamic load

At present, studies of pile-supported embankment focus mainly on the stress ratio of pile to soil and the soil arch effect under static loading, less considering effects of dynamic loading. But dynamic stress resulting from vehicle operation has a certain influence on the embankment of soil arch, which affects the overall behavior of pile-supported embankment. In order to analyze the change of bearing behavior of pile-supported embankment under static and dynamic loading, through visible laboratory test and analysis of particle flow code(PFC), the mechanism of stress transfer and deformation of pile-supported embankment under static and dynamic loading have been studied. Some factors affecting soil arching are investigated, such as filling height, pile cap size, pile spacing, reinforcing modes, loading frequency. The results show that the stress on top of piles decreases under dynamic loading, which resulted in increase of stress between piles and displacement of embankment. The effect of dynamic loading on unreinforced embankment is larger than that on reinforced embankment. And reinforcement material is helpful to reduce the impact of dynamic loading. The mechanisms of load transfer and deformation are different depending on the types and numbers of the geogrid; and the impact of dynamic loading is mainly related to the strength of the soil arch effect. In the case of piled embankment reinforced by two layer geogrids, because the mechanism of semi-rigid platform takes effect due to the interaction of reinforcement and the surrounding fill, the soil arching decreases which leads to the effect of dynamic loading minimally; and for embankment with a single geogrid, the impact by dynamic loading decreases remarkably when geogrid is set above 10 cm of top of piles compared with geogrid on the top of piles. The PFC simulation results confirm the above conclusion, and further conclud that with the increase of loading frequency and the filling soil height, the decrease of pile net spacing, the effect of dynamic loading increases.