【作者】 孙微微；

【导师】 赵尘；

【作者基本信息】 南京林业大学 ， 森林工程， 2005， 博士

【摘要】 碎石桩复合地基因其取材方便、施工简便、造价低廉在工程中得到了广泛应用,是一种适合我国国情的地基处理方式。但理论研究却相对滞后,尤其是沉降计算的水平还远远落后于工程实践的需要。目前有关碎石桩复合地基沉降量的计算方法主要有数值解法和解析解法两大类,数值计算法有着一定的优越性,但对测试技术及工程人员素质均要求较高,不便广大工程技术人员掌握应用,这就在客观上要求建立简便适用的解析方法以方便指导工程实践。现有的解析方法多数是基于刚性基础下桩土等应变的假定,并且不考虑桩体的径向变形,这对于路堤荷载下的碎石桩复合地基是不适用的。路堤荷载接近于柔性荷载,加固区桩间土的压缩量大于桩体的压缩量,桩将产生上下刺入现象,桩土变形不再协调;另外,碎石材料本身几乎没有粘聚力,在竖向荷载作用下,将有不可忽略的径向变形发生。本文在假设的竖向及径向位移模式下,考虑桩土相互作用,通过力学推导,得到了路堤荷载下复合地基加固区桩体正应力、桩间土正应力、桩侧摩阻力、桩及桩间土压缩量的解析表达式。并对下卧层上附加应力的取值给出合理化建议。在Terzaghi 固结理论的基础上,应用Carrillo 定理建立了路堤荷载下碎石桩复合地基的径向、竖向及整体固结微分方程,并得出其解析解。该方程具备理论合理性,且简单适用,便于工程技术人员掌握应用。经过工程实例验证,能满足工程精度要求。通过解析计算,对路堤荷载下碎石桩复合地基进行分析,包括加固区桩体、土体的应力应变在竖向及径向上的分布规律、桩侧摩阻力分布规律及沉降影响因素的分析。分析表明,桩侧摩阻力沿桩长线性变化,并且侧摩阻力随置换率的增加而减小。桩体正应力值在中性点以上随深度递增,中性点以下随深度递减,并且桩体正应力值随置换率的增加而减小。桩周土中正应力随距桩体的径向距离的增大而逐渐减小;竖直方向上,在中性点以上随深度递减,中性点以下则随深度递增。典型单元体中桩的压缩量小于土的压缩量,而且随着径向距离的增大,这种差异就越大;另外,复合地基的置换率越小,即n = b/a的值越大,这种差异也越明显,当复合地基有较高置换率时,复合地基顶面处桩、土体的沉降差异很小。随着n值的增大,桩、土体的差异沉降相应增大。加固区的沉降量随桩长的增加是线性增加的;下卧层的沉降量则随桩长的增加而线性减小。但地基的总体沉降量仍然随桩长增加而线性减小。更多还原

【Abstract】 With convenient material, simple making and low cost, the gravel pile composite foundation has been widely used in construction projects. This kind of foundation treatment is suitable for China. However, relevant theory has not been advanced. Especially the settlement computation method for this kind of foundation treatment has fallen far behind the engineering practice. At present, there are two types of settlement computation methods for the stone column composite foundation. One is the numerical analysis method and the other is the analytic method. The numerical analysis method is of some advantages. But it is not convenient to apply in engineering practice since its application requires strict test technique and high quality of staff. As a result, a convenient analytic method is needed. Existing analytic methods are mostly aimed at the composite foundation under rigid base, in which the column and the soil has the same strain. Moreover, the radial deformation of the pile has not been taken into consideration. These methods are not applicable to the gravel pile composite foundation under embankment load. Since the embankment weight is a kind of flexible load, the compressive deformation of soil is more than that of piles in the stabilized layer. The pile would stab up and down, so the deformation of piles and soil would not be compatible. Under vertical load, the radial deformation of piles should not be neglected because the crushed stone is loose. With the suggested vertical and radial displacement model, this dissertation takes the interaction of soil and column into consideration and derives some analytical-functions for the stabilized layer of the composite foundation under embankment load, including the normal stress in pile and in soil in the foundation, the frictional resistance between pile and soil, the compressive deformation of pile and soil. Furthermore, a reasonable method for estimating the extra stress in sub-layer is proposed. Based on the Terzaghi consolidation theory and the Carrillo theorem, the differential equations for vertical, radial and total consolidation of gravel pile composite foundation under embankment are derived, as well as their analytic solutions. The equations are reasonable in theory and easy for engineers to apply. Engineering cases have verified their accuracy. According to analytic computation, the stone column composite foundation under embankment is studied to find the vertical and radical distribution of stress and strain in column and in soil of the stabilized layer and the distribution of frictional resistance along column side. Analysis shows that the frictional resistance on the column side is linear along the column and decreases gradually with replacement rate. The normal stress in column increases gradually with depth above the neutral depth z m and decreases gradually with depth below the neutral depth z m, also decreases with replacement rate. The normal stress in the soil around column decreases gradually with radial distance. In the vertical direction, the normal stress in soil decreases with depth above the neutral depth z m and increases below the neutral depth z m. In a typical element, the compressive deformation of column is less than that of soil. The deformation difference increases with radial distance and decreases with replacement rate. When the replacement rate is high enough, the difference of column and soil settlements on the top of the composite foundation becomes quite small. If the replacement rate is reduced, the settlement difference will increase. Settlement of the stabilized layer increases with the length of column, and settlement of the sub-layer decreases with the length of column. Total settlement of composite foundation still decreases with the length of column.更多还原