刚性基础下筋箍碎石桩复合地基桩土应力比计算模型

桩土应力比是筋箍碎石桩复合地基沉降计算中最重要的参数,但由于其涉及到桩体、土体及筋材三者之间的复杂关系且影响因素众多,目前尚无明确的计算方法.基于此,根据刚性基础下筋箍碎石桩复合地基的受力变形特征,首先通过数值模型研究筋箍碎石桩复合地基桩土应力比与荷载、埋深、筋材刚度以及桩土弹性模量比的关系.根据数值模型揭示的桩土应力比变化规律,提出一个新的桩土应力比计算模型,并依据该模型在假设桩体、土体及筋材应变协调的基础上利用弹塑性分析方法推导刚性基础下筋箍碎石桩桩土应力比的解析公式;基于建立的模型及计算公式探讨桩土应力比与各主要影响因素之间的关系.研究结果表明:该解析公式基于弹塑性理论分析,但也能考虑现场桩土应力比实测值,能够综合反映桩体、土体、筋材、埋深及荷载之间的相互影响作用,并且形式简单,计算方便;刚性基础下筋箍碎石桩桩土应力比在相同荷载水平下随埋深、筋材刚度、面积置换率、桩土弹性模量比及桩体摩擦角的增大而增大,随着荷载水平的增加则会逐渐降低并趋于稳定值;在碎石桩复合地基沉降计算中不宜采取单一的桩土应力比参数,而是应该根据荷载水平以及计算深度分层选取合适的桩土应力比作为计算参数.

Calculation Model for Stress Concentration Ratio of Composite Foundation Reinforced by Geosynthetic-encased Stone Columns

Stress concentration ratio is the most important parameter in the settlement calculation of a composite foundation reinforced by geosynthetic-encased stone columns. However, the calculation method of stress concentration ratio has not been well established due to the extremely complicated interactions in the stone column-soil encasement system. In this work, the stress concentration ratio of a composite foundation was calculated using both numerical and analytical methods, taking into account the load-deformation behavior of a composite foundation reinforced by geosynthetic-encased stone columns. A new calculation model for the stress concentration ratio was proposed based on the strain compatibility assumption of the stone column-soil encasement system, and its analytical solution was presented. The proposed model can reflect complicated interactions between the stone column, surrounding soil, geosynthetic encasement, and load. The stress concentration ratio increases with increasing depth, encasement stiffness, replacement ratio, stiffness ratio between the stone column and soil, and friction angle of the stone column under the same load, and decreases with an increase in the load. Therefore, a constant stress concentration ratio is not recommended for use in the settlement analysis of the composite foundation reinforced by geosynthetic-encased stone columns, and a suitable stress concentration ratio should be used taking the load and depth into account.