上海地区软土旁压加卸载变形特性试验研究

Experimental researches on in-situ loading and unloading deformation characteristics of soft soil based on pressuremeter tests in Shanghai area

软土具有强度低、压缩性高的特点,在不同应力状态、应力路径下其变形呈现明显不同的非线性特征,研究软土的原位变形特性对各类地下工程土体变形的控制具有重要意义。通过对上海地区不同深度土体进行原位旁压加卸载试验,从加载及卸载两个维度对原位土体的变形特性进行描述。通过旁压加载试验结合室内小应变三轴试验,获取了土体剪切模量G随剪应变γ的变化规律;通过旁压卸载试验研究软土原位卸荷回弹变形特性,探讨了各层土不同卸载前载荷水平及卸载等级下,土体模量比E;与卸载比R之间的内在关系。研究结果揭示了软土在加载情况下的刚度衰减规律及卸荷条件下影响刚度特性的关键因素,为控制地下空间开发中的土体变形问题提供借鉴。

The quality of the soft soil includes low strength and high compressibility,and the deformation shows obviously different nonlinear characteristics under different stress states and paths.It is of great significance to study the in-situ deformation characteristics of soft soil for controlling the deformation in various underground projects.In this study,such deformation characteristics are well described from two aspects of loading and unloading through PMT in Shanghai area.The relationship between shear modulus G and shear strainγis obtained by the pressuremeter loading tests combined with laboratory small-strain tests.At the same time,the internal relationship between modulus ratio Ev and unloading ratio R is studied under different maximal unloading pressures and unloading levels by the pressuremeter unloading tests.The results reveal the stiffness degradation law for loading tests and the key factors determining the stiffness characteristics for unloading tests,which will provide the relevant reference for controlling soil deformation in the development of underground space.