基于旁压试验的常州地区典型砂土变形特性研究

Experimental study on deformation characteristics of typical sandy soil based on pressuremeter tests in Changzhou area

常州地区地基中第⑤层超固结砂土层是对各项工程影响最为显著的关键性土层,研究该土层的变形特性对各类地下工程土体和结构变形控制的意义重大。通过对该砂土层开展不同深度土体的原位预钻式旁压加载试验和室内三轴压缩试验,将砂土层加载变形分为初始阶段、弹性阶段和弹塑性阶段。根据应力—应变值得到土体剪切模量及其随剪应变的衰减规律,在考虑超固结比为1.5(OCR=1.5)时,三轴压缩试验结果与旁压试验最为接近。基于试验数据,对Stokoe和Hardin-Drnevich(H-D)方程对比分析发现,Stokoe方程能更好地描述该砂土层的变形特征。在小应变条件下土体的剪切模量衰减很快,进入大变形阶段后剪切模量衰减趋缓。原位试验对土体的扰动程度小于室内试验,旁压试验推求土体的剪切模量随剪应变的变化规律更为合理。研究结果可以为常州地区第⑤层砂土层相关的基础工程设计和施工提供参考。

The 5th layer of over consolidated sandy soil in Changzhou area is the most critical layer which has the greatest impact on various projects.The study on the deformation characteristics of this layer is significant for the controlling of the soils and structures displacement of underground engineering.Based on pressuremeter tests and indoor triaxial compression tests on the sandy soil specimens taken from different depth,the deformation of sandy soil is divided into three stages,which including initial,elastic,and elastic-plastic deformation.When over consolidation ratio is 1.5(OCR=1.5),the shear modulus value of the soil and its degradation law with shear-strain obtained from the triaxial compression tests are close to those of the pressuremeter test.By the comparative analysis of Stokoe and Hardin-Drnevich(H-D)equations,it is found that Stokoe equation can better describe the deformation characteristics of the sandy soil.Under the condition of small strain,the shear modulus of the soil decreases rapidly,and then decreases slowly in the stage of large deformation.The disturbance degree of in-situ test on soil is less than that of indoor test,and it is more reasonable to deduce the variation law of shear modulus of the soil with shear strain by pressuremeter test.The study will provide the relevant reference for design and construction of foundation projects.