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或粘土的黏聚力c。然而，大多数土壤的颗粒大小分布在砂土和粘土之间，称为中间土壤。考虑到结构的安全性，将其作为粘土处理。另一方面，由于1995年小古根-南部地震中分解花岗岩发生液化，一些研究人员开始研究中间土的循环特性。然而，它们的力学性能尚未得到阐明。本研究通过对中间土进行静力和循环三轴试验以及循环扭转试验，探讨中间土静力和循环特性与土性之间的关系。结果表明，随着粘土掺量的增加，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。为了研究中间土剪切模量退化与土性的关系，进行了循环扭转试验中的弯曲单元试验。研究发现，由于孔隙水压力的增加，在循环扭转试验的前20次循环中，剪切模量急剧下降。剪切模量的退化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.