“柔性基础”刚性桩复合地基试验分析与变形计算

为了建立路堤下刚性桩复合地基变形计算模型,通过对14组刚性4桩复合地基的现场试验结果的分析,研究柔性基础条件下刚性桩复合地基的工作性状。试验研究表明采用一定强度或刚度的加筋垫层配合合适的桩帽设置,可改善柔性基础条件下刚性桩复合地基的工作性状,有效减小复合地基变形。复合地基承载力相同时,"柔性基础"沉降量为刚性基础的1.1~1.5倍。在一定荷载或承载力条件下,垫层中不设加筋材料时"柔性基础"短桩复合地基变形接近加筋垫层天然地基。垫层加筋有帽桩复合地基变形明显小于其他情况。对"柔性基础"短桩复合地基,设桩帽、垫层加筋,桩土应力比与不加筋相比增加了1~3倍;对刚性基础长短桩复合地基,碎石垫层中加筋与不加筋相比,桩土应力比范围得到延伸,其中长桩桩土压力比增大明显。提出了"柔性基础"条件下刚性桩复合地基承载力确定,以及考虑桩"上刺入"的刚性桩复合地基变形计算方法。该方法采用力平衡方程计算桩身中性点位置,将复合土层变形计算分为中性点平面

Working mechanism analysis and deformation calculation on rigid pile reinforced soil with flexible foundation

In order to setup the deformation calculation algorithm for Rigid Pile Reinforced Soil with Flexible Foundation(RPRSFF),14 groups of rigid pile reinforced composite foundation tests are carried out on site,and each composite foundation consists of four piles.The working mechanism and deformation calculation model for RPRSFF are investigated.It is manifested that with the suitable cushion caps on the top of piles,when suitable strength or rigid fibre reinforced cushion is employed,the working mechanism of RPRSFF will be improved,and the final settlement decreases.With the equal load bearing capacity,the settlement in flexible foundation is about 1.1-1.5 times that of the rigid foundation.When the cushion is not reinforced with fibre,the settlement of flexible foundation with short-pile is almost equivalent to that of natural foundation with the fibre reinforced cushions.After RPRSFF is strengthened by fibre reinforced cushion and cushion cap,the final settlement is reduced significantly.In the circumstance of short pile RPRSFF which is strengthened by reinforced cushion and cushion cap,the stress ratio of pile-soil is 1-3 times that of the one without reinforcement.Then,the calculation model of load bearing capacity of RPRSFF is set up.Furthermore,taking into consideration of the effect of upward puncture,the deformation calculation algorithm of RPRSFF is proposed.The total settlement of composite foundation is divided into three parts: the compression over the axial-force-zero point,the contraction of pile beneath the axial-force-zero point,and the bottom puncture deformation.In the process of determining the compression of bed soil under RPRSFF,the stress diffusing model is employed.Field application shows that the suggested algorithm is more suitable for practical design.