一种大型循环单剪试验装置研究

循环单剪试验被认为是研究地震场地中土体动力特性最合适的方法。为减小尺寸效应影响及解决工程中广泛存在的加筋土及粗颗粒土动力特性测试问题，研究大尺寸循环单剪试验方法具有重要意义。基于此，介绍了一种大型循环单剪试验装置，采用竖向线性滑动轨道约束上加载板和采用水平滑动轨道约束下加载板，确保前者仅发生竖向平动，后者仅发生水平平动，采用层叠的、带层间橡胶膜、分离式4点支撑的钢筋环构成的柔性剪切箱为试验提供侧向边界约束，确保了对单剪土样加载边界条件的真实模拟。针对土工格室加筋橡胶砂的测试结果表明：大型循环单剪试验装置得到的土动应力-动应变关系较好地反映了土在循环荷载作用下的滞回性、非线性和棘轮特性，大型循环单剪试验装置得到的 - 和 - 曲线变化规律与常规尺寸试验基本一致，证明其具有可行性；大尺寸试验得到的动剪模量特性与常规尺寸试验之间的差异，与单剪试验尺寸效应结论相符；试验中阻尼比特性受尺寸效应影响的规律性不明显。

Development of a large-scale cyclic simple shear test apparatus

Cyclic simple shear test (CSST) is one of the most appreciative methods for studying the dynamic characteristics of soil in earthquake site. To minimize the size effect in the experiment and to monitor the dynamic properties of fiber-reinforced and coarse-grained soils, a testing system called large-scale CSST apparatus is developed. In the developed equipment, the vertical loading plate at the top of the specimen is constrained by a series of vertical linear guides so that it can translate vertically, the horizontal loading plate at the bottom of the specimen is constrained by a series of horizontal linear guides so that it can only translate horizontally, and the shearing box containing specimen is formed by laminated steel rings which are interlayered at four discrete bearing ears with rubber membrane. These features of the equipment ensure proper boundary conditions of the soil specimen during testing similar with soil element in seismic site. The developed CSST equipment is used to perform experiments on geo-cell reinforced rubber sand mixtures. It is shown that the relationship between the dynamic stress and dynamic strain of the specimen exhibits typical hysteresis, nonlinearity and ratchet characteristics, and the - curves and - curves gained from large- scale CSST show similar characteristics as those gained from normal size CSST, implying that the device works well; the differences of the dynamic shear modulus properties between results of large-scale and normal size CSSTs coincide with size effects of CSST; no obvious regularity of size effect on damping ratio is observed from the tests.