基于系统分析的桩网复合地基荷载效应定量评价模型研究

目前对桩-网复合地基的设计主要存在两点不足,一是计算路堤底桩土荷载分担时需要假设土拱高度,二是对桩间地基土反力的定量评价偏于保守。针对这两个问题,重点分析了路堤荷载作用下土拱效应与加筋薄膜效应,根据堤底桩土相对位移得到计算的土拱高度,推导土拱效应与薄膜效应共同作用下路堤荷载在桩与土之间的分配计算公式;考虑刚性桩桩顶与桩端位置的桩土相对位移以及桩周土对桩侧作用摩阻力存在中性点,根据应力、位移连续性条件,建立桩-网-土联合作用的桩承式加筋路堤的荷载效应计算模型并给出求解方法,通过3个工程实例对该方法进行合理性验证。结果表明,具备一定刚度的桩端下卧层时,采用本模型的计算结果与实测值比较接近,可为工程应用借鉴。

Quantitative evaluation of load effects of pile-net composite foundation based on systems analysis

In the current design of geosynthetic and pile supported (GSP) composite foundation, a pre-assumed soil arch height is always utilized in load sharing calculation, and the contribution of subsoil resistance is weakened in supporting the embankment fill. To improve the above two defects, the soil arching effect and the geomembrane effect are analyzed, and then the quantitative evaluation methods are presented. In the derivation, the pile-soil differential settlements at pile top and toe are considered, and the arch height can be calculated according to the relative pile-soil displacement. Simultaneously, the neutral point is adopted in skin friction analysis, and hence a formula for the load distribution is obtained based on the mobilized shearing stress developing from bottom to top. This method can take good care of the interaction between the embankment fill, pile-reinforced area and lower underlying layer, which can consider the penetration of pile tops, interaction between piles and surrounding soil and penetration of pile ends. According to the continuity condition of stress and displacement, a load effect solution of GSP composite foundation is obtained. The present method is validated to be reasonable by comparing the analytical solutions with the FEM results and the monitoring data, and can be adopted by engineers when it comes to the situation in presence of the bearing stratum at pile tip with certain stiffness.