Undrained dynamical behavior of Nanjing flake-shaped fine sand under cyclic loading

A series of dynamic behavior tests on Nanjing flake-shaped fine sand were performed by using the WFI cyclic triaxial apparatus made in England. The dynamic behaviors of Nanjing flake-shaped fine sand under different static deviator stress levels and cyclic stress ratios were studied. Through comparing the effective stress path under cyclic loading with static loading, the processes of liquefaction of saturated Nanjing flake-shaped fine sand with development of dynamic pore-water pressure, including the initial compact state, compression state and dilative state, were investigated. The variation of the shear stiffness with the number of cycles and cyclic strain was investigated by analyzing the secant shear modulus in each unload-reload loop of dynamic stress-strain relationship. And by means of the exponential function, the empirical equations of the relationship between secant shear modulus Gsec, shear modulus ratio Gsec/Gmax and cyclic strain ε were established based on series of test results. The results show that according to different combinations of static deviator stress and cyclic stress, two kinds of failure patterns with deviator stress reversal or no deviator stress reversal are observed in the samples tested in this series, including cyclic mobility and the failure of accumulation residual strain. In addition, the degradation of dynamic shear modulus is due to the development of vibration pore-water pressure and it is observed that the shear modulus reduces with the progressive number of cycles.     

苏州第四纪沉积土动剪切模量比和阻尼比试验研究

通过深入分析苏州第四纪土的海相、陆相沉积环境及土层分布特征, 对苏州第四纪土 311 个原状土样进行了土的动剪切模量比和阻尼比试验研究 ,结果发现：海侵作用和土层深度对苏州第四纪各类土的动剪切模量比、阻尼比与剪应变幅值关系曲线的影响有明显差异,深度 0 ～ 30 m 的海相黏土动剪切模量比和阻尼比曲线分别低于和高于陆相黏土的曲线,深度 30 ～ 100 m 的海相黏土动剪切模量比和阻尼比曲线分别高于和低于陆相黏土的曲线;土 层深度对海相黏土、粉质黏土和海、陆相粉细砂的动剪切模量比曲线 以及对海相黏土、粉质黏土和陆相粉细砂的阻尼比曲线的影响较为明显;对黏土、粉质黏土、粉土、粉细砂按土层深度 0 ～ 30 m 和 30 ～ 100 m 以及淤泥质土、中粗砂不区分土层深度,给出了苏州第四纪各类土的动剪切模量比和阻尼比曲线经验关系的拟合参数值及其平均关系曲线推荐值。     

远场大地震作用下深软场地设计地震动参数研究

针对苏州城区典型地层剖面，建立大尺度深软场地的二维精细化非线性有限元分析模型，研究了大地震远场地震动作用于深软场地的设计地震动参数。结果表明：①大地震远场地震动作用时的深软场地地表地震动峰值加速度（PGA）明显大于人工波作用时的地表PGA，输入地震动特性、土介质的横向不均匀性及其非线性，使不同地表位置的PGA存在明显的变异性；②深软场地的地表设计地震动参数α_max，β_max和T_g值远远大于现行国家规范或标准的取值，且β_max随地震动水平的提高而增大；③沿土层深度的PGA折减系数，对深度5 m以浅土层可取1，对深度35 m以深土层可取0.65，对中间深度土层可线性内插；④苏州深软场地土的最大剪应变幅值出现在土层深度10 m附近的窄带区域内，且中震、大震水平时，深度10～20 m的土介质处于弹塑性变形到大变形的过渡阶段，对该深度的地下结构，尤其是细长地下结构的抗震不利。对于类似苏州城区的深软场地，应充分考虑远场大地震效应的影响。