基于厚壁圆筒模型的筋箍碎石桩沉降计算

Settlement Calculation of Geogrid-encased Stone Columns Based on Thick-walled Cylinder Model

为解决现有方法难以考虑加筋材料实际受力状态而低估筋箍碎石桩复合地基沉降的问题,假设桩土等应变且均为线弹性材料,选取单桩有效加固单元整体作为分析对象,其中碎石桩同时受到加筋材料和土环的约束作用,而土环则可以考虑为同时受到单桩有效加固范围外土体的静止土压力和内部碎石桩鼓胀压力共同作用的厚壁圆筒,再结合广义胡克定律得到应力应变关系,进而导出了筋箍碎石桩复合地基沉降计算的新方法.采用工程实例验证并与已有方法进行比较,同时分析了外荷载水平、置换率对复合地基总沉降和桩土应力比的影响.与已有方法相比,该方法可以使上部荷载和筋箍碎石桩侧向受力变形联动进而调整加筋材料内力,从而更符合筋箍碎石桩实际受力变形情况,计算值与实测值相对误差为+5.70%,与现有保守计算方法相比误差最小.参数分析表明:置换率对于控制复合地基总沉降具有重要作用,外荷载一定时复合地基总沉降与桩土应力比均随着置换率提高而减小.

The existing method is difficult to consider the actual state of geogrid ribs under loading,which could underestimate the settlement of the geogrid-encased stone column (GESC) composite foundation.In order to solve this problem,in this paper,the unit cell concept was employed as the objects in the analysis,while it was assumed that GESC together with soil was elastic materials and evenly deformed.Stone column was constrained by geogrid and earth ring at the same time,while the earth ring can be considered as a ring with earth pressure at rest provided by soil outside and bulging pressure caused by the stone column installed inside.Hook's law was then introduced to gain the stress-strain formula of the unit cell.Then,a different method of settlement calculation of GESC composite foundation was established.The rationality of the results of this method was verified by an engineering example and also compared with the existing method.The result demonstrates that the method agrees well with the engineering example.Through the comparison with the existing method,it is found that the relative error between the calculated value and measured value is +5.70%,which demonstrates the method presented in this paper is safer and more accurate as a result of the combined top loading and lateral deformation of GESC.The parametric study shows that the replacement ratio has a significant influence on the controlling settlement of composite foundation,and the increase of the replacement ratio can effectively reduce the pile - soil ratio and settlement of composite foundation when a certain level load is applied.