Resarch on transition of dynamic failure of soils.

通常，在设计土木工程结构时，工程师使用砂土的内摩擦角f或粘土的内聚力c。然而，大多数土壤在砂土和粘土之间具有不同的粒度分布，这被称为中间土。考虑到结构的安全，它们被当作粘土处理。另一方面，自从1995年日本南部地震中分解的花岗岩发生液化以来，一些研究人员研究了中间土的循环特性。在本研究项目中，除了对中间土进行循环扭转试验外，还对中间土进行了一系列静力和循环三轴试验，以研究中间土的静力和循环特性与土性之间的关系。结果表明，随着粘粒含量的增加，土体的静强度和循环强度降低。此外，粘土的矿物组成对中间土的静强度和循环强度也有影响，并进行了循环扭转试验中的弯曲单元试验，以研究中间土的剪切模数退化与土性之间的关系。结果表明，由于孔压的增加，在循环扭转试验的前20次循环中，剪切模量值急剧下降。剪切模量值随粘土含量的增加而减小。

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.