【作者】 江涛；

【导师】 胡亚元；

【作者基本信息】 浙江大学 ， 土木工程， 2011， 硕士

【摘要】 当高速公路或铁路修建在软土地基时,堆载预压法因其经济有效在软基处理中被广泛应用,但一些已建高速公路表明,经堆载预压处理后的软基在运行期间往往会出现比理论预测大得多的工后沉降,说明单纯采用主固结理论预测软基工后沉降,并以此提出预压持续时间会导致使用后的工后沉降超出预期,带来危害。当工程对路基的沉降要求较高时就会限制堆载预压法在软基处理中的应用。在以往堆载预压的研究中,另一个没有得到足够重视的问题就是土的预固结现象,大部分天然软土都属于准超固结土,但以往对准超固结土研究较少,因此也有必要对准超固结土的固结特性展开进一步研究。本文着力于在考虑次固结的理论基础上分析堆载预压的预压持续时间,并同时考虑准超固结土在沉积过程中形成的“预固结”对软土固结所带来的影响,开展一些研究工作。首先引入充分考虑软土次固结和预固结现象的Yin-Graham等效时间流变模型来作为全文研究的理论基础,其次分别按砂井等效为一维均质土层、砂井等效为砂墙地基、砂井地基轴对称固结三种情况来编制有限差分程序来数值模拟并分析次固结对准超固结土固结特性的影响。最后在相关固结特性分析结果的基础上提出确定预压持续时间的计算方法。研究结果显示,当软土地基的预固结绝对等效时间较大时,准超固结软土在固结前期,存在着次固结系数ψ越大,孔压消散越快,固结度越大,沉降越小,达到同样沉降所需的时间也越长这一现象,并对现象产生的物理根源进行了定性分析。随着初始绝对等效时间T0的增大,软土预固结效应越显著,固结越快,长期沉降随着初始绝对等效时间的增大而减小,因此在软土固结特性分析和堆载预压设计时要充分考虑软土“预固结”水平的影响,不考虑预固结效应会对固结特性分析和堆载预压设计带来较大的影响。在上述研究结果的基础上提出了在准超固结软土地基上进行堆载预压设计确定预压持续时间的计算方法。更多还原

【Abstract】 When building the highways and railways in soft soil the surcharge preloading method has been widely used in the treatment of the soft soil foundation for its economic and effective, but some built highways through preloading treatment showed the post-construction settlement was much bigger than theory predicts during the traffic operation period, this indicated it will lead to the post-construction settlement exceeds than expected and bring hazards if using the primary consolidation theory to predict the post-construction settlement of soft soil foundation and put forward the preloading duration. If there are high requirements on settlement it will limit the application of surcharge preloading method in the treament of soft soil foundation. Another issue that didn’t get enough attention in the past was the preconsolidation phenomenon of soft soil, most soft soils in natural are quasi over-consolidated soils but previous research on it was few. therefore it is necessary to study further on the consolidation properties of quasi over-consolidated soils.This master’s thesis focuses on analysising of preloading duration based on the theory that considering secondary consolidation and carrying out some work about the impact of "preconsolidation".which is formed in the sedimentary of the quasi over-consolidated soils, on the consolidation characteristic. Firstly, introducing Yin-Graham equivalent time rheological model that considering the secondary consolidation and preconsolidation phenomenon of soft soils as the theoretical basis of research of full text. Secondly, compiling the finite difference programs to numerically simulate and studying the impact of secondary consolidation on consolidation characteristics of quasi over-consolidated clay according to equivalent conversion between sand wells and one-dimensional homogeneous soil, equivalent conversion between sand wells and sand-wall, axisymmetric consolidation of sand wells separately. Finally, proposing the calculation method of determining the preloading duration on the basis of the related consolidation properties.The results show when the absolute equivalent time of preconsolidation of soft clay is large, at the early stage of the quasi over-consolidated soft soil consolidation the larger the creep coefficient is, the faster the pore pressure dissipates, the greater the degree of consolidation has and the smaller the settlement gets, to reach the same settlement the soil that has less creep coefficient will require more time, the physical reason of this phenomenon is then qualitatively analyzed. The results also show that the larger the initial absolute equivalent time is. the more obvious the preconsolidation effect of soft soil shows, the faster the consolidation has. and the greater the long-term settlement gets, therefore "preconsolidation" level of soft soil should be taken into consideration when analysising the consolidation properties of soft soil and designing the surcharge preloading, if not considering the preconsolidation effect it will bring great influences on consolidation properties and surcharge preloading design. On the basis of previous study the calculation method to determine the preloading duration for the design of surcharge preloading in quasi over-consolidated soft soil is put forward.更多还原