Resarch on transition of dynamic failure of soils.

通常，在设计土木工程结构时，工程师使用砂的内摩擦角f或粘土的内聚力c。然而，大多数土壤具有介于砂和粘土之间的各种粒度分布，称为中间土。考虑到结构的安全性，将其作为粘土处理。另一方面，自从1995年兵库县南部地震中风化花岗岩发生液化以来，一些研究人员对中间土的循环特性进行了研究。本研究通过一系列的静、动三轴试验和动扭转试验，探讨了中间土的静、动特性与土的性质之间的关系。结果表明，随着粘粒含量的增加，混凝土的静强度和循环强度均降低。此外，还进行了循环扭转试验中的弯曲单元试验，以研究中间土剪切模量退化与土性之间的关系。结果表明，在循环扭转试验过程中，由于孔隙水压力的增加，剪切模量在前20个循环中急剧下降。剪切模量衰减随粘粒含量的增加而减小。

Generally, in designing the civil engineering structures, engineers use the angle of internal friction f for sands or cohesion c for clays. Most of soils, however, have a various particle size distribution between sands and clays, which are called intermediate soils. They are dealt as clays taking into consideration safety of the structure. On the other hand, since the liquefaction took place for decomposed granite during Hyogoken-Nambu Earthquake in 1995, some researchers have investigated the cyclic behavior of the intermediate soils. However, their mechanical properties have not elucidated yet.In this research project, a series of both static and cyclic triaxial tests in addition to cyclic torsional tests of the intermediate soils to investigate the relationship between static and cyclic behavior of the intermediate soils and soil properties. As the results, the static and cyclic strength decreases as clay content increases. Also, mineral composition of clay has an influence of the static and cyclic strength of the intermediate soils.Also, the bender element tests during cyclic torsional tests were carried out in order to investigate the relationship between shear modulus degradation and soil properties of the intermediate soils. It was found that the shear modulus degrades sharply in the first 20 cycles during cyclic torsional test due to the increase of pore water pressure. The shear modulus degration decreases as the clay content increases.