The characteristics of regional soils in Kyushu and Okinawa, and soil improvement

九州和冲绳分布有有明粘土、风化花岗岩、Onjaku土、Shirasu土、Kuroboku土、Kunigami-maaji土和岛尻泥岩等区域性土壤。这些土壤表现出不寻常的岩土工程特性。与这些特性相关的问题已经出现在土壤结构的建设和保护以及农业领域的土壤保护中。在本研究项目中，这些土壤的性质进行了调查，并提出了土壤改良程序。以下是获得的结果。1.通过向特别敏感的有明粘土中添加水泥和石灰来改良土壤，使其性质变为类似于砂的性质，从而增加了抗剪强度。2.分解花岗岩、Onjaku土壤和Kunigami-maaji土壤具有高天然含水量和差的可操作性。通过降低土壤含水量和增加土壤密度，可以改善这些土壤的力学性质和可蚀性。3.将不适合作为填料的Onjaku和Kuroboku土与分解的砂石和Shirasu混合。这一过程对提高填充材料的可加工性是有效的。4.从风化作用对泥岩软化的影响出发，探讨了岛尻泥岩的长期稳定性。5.在冲绳广泛分布着可蚀性很强的国上-真治土。土壤结构发育不全，吸水保水能力差，是造成土壤可蚀性强的主要原因。6.开发了农田渠道开挖边坡稳定性分析的有限元程序。

The regional soils such as Ariake clays, decomposed granite, Onjaku soil, Shirasu, Kuroboku soil, Kunigami-maaji soil, and Shimajiri mudstone are distributed in Kyushu and Okinawa. These soils exhibit unusual geotechnical characteristics. The problems associated with these characteristics have arisen in the construction and preservation of soil structures, and soil conservation in agricultural field. In this research project the properties of these soils have been investigated, and the soil improvement procedure is presented. The following is the results obtained. 1.The soil improvement by addition of cement and lime to extra sensitive Ariake clays changes their properties into those similar to sands, resulting in an increase of shear strength. 2.Decomposed granite, Onjaku soil, and Kunigami-maaji soil have high natural water content and poor workability. The mechanical properties and erodibility of these soils can be improved by lowering the water content and increasing the density of the soils. 3.Onjaku and Kuroboku soil, which are not proper for filling materials, were mixed with decomposed sand stone and Shirasu. This procedure is effective to increase workability of the filling materials. 4.The long term stability of Shimajiri mud stone has been discussed in terms of the weathering effects on the mudstone softening. 5.Kunigami-maaji soil exhibiting high erodibility are widely distributed in Okinawa. High erodibility of this soil can be ascribed to the insufficient development of soil structure and low capability of water absorption and retention. 6.FEM programs to assess the stability of slopes in canal excavated in agricultural field heve been developed.