桩承式加筋路堤的现场试验及数值分析

Field test study and numerical analysis of a geogrid-reinforced and pile-supported embankment

对一桩体面积置换率为8.7%的低置换率桩承式加筋路堤进行了现场试验及三维有限元分析。现场主要进行了桩、土荷载分担,孔压、沉降及侧向水平变形等内容的观测。将观测数据与常规设计方法及三维有限元分析结果进行了对比研究,在此基础上对设计方法的适用性进行了分析。研究结果表明,路堤填土的土拱效应造成荷载向桩体转移,这种荷载转移大幅度减小了在软土层中产生的超孔隙水压力。当填土高度大于2.5m时,土拱效应的应力折减系数可用Russell和Pierpoint或Hewlett和Randolph提出的土拱效应分析方法进行计算,其结果与三维有限元分析也较相符,但在路堤高度较小时,只有Russell和Pierpoint方法与实测结果相接近。路堤施工过程中,实测的水平变形与沉降之比仅为0.2左右,这表明采用桩承式加筋路堤不仅可减小沉降,而且可减小水平向的变形,提高路堤的稳定性。

This paper describes a case history of a geogrid-reinforced and pile-supported （GRPS） highway embankment with a low area improvement ratio of 8.7 %. Field monitored data from contact pressures acting on the pile and soil surfaces, pore-water pressures, settlements and lateral displacements are reported and discussed. The case history is back-analysed by carrying out three-dimensional fully coupled finite element analysis. The measured and computed results are compared and discussed. Based on the field observations of contact stresses and pore-water pressures and the numerical simulations of the embankment construction, it is clear that there was a significant load transfer from the soil to the piles due to soil aching. This transfer greatly reduced excess positive pore water pressures induced in the soft silty clay. For embankment higher than 2.5 m, predictions of stress reduction ratio based on the design methods proposed by Russell and Pierpoint and Hewlett and Randolph are consistent with the measured values and the three-dimensional numerical simulations. For lower embankment, on the other hand, only the method proposed by Russell and Pierpoint gives consistent predictions with the field measurements. During the construction of the piled embankment, the measured lateral displacement-settlement ratio was only about 0.2. This suggests that the use of GRPS system can reduce lateral displacements and enhance the stability of an embankment significantly.