Study on Geotechnical Properties of Local Soils and Economical Land Reclamation

九州和冲绳地区存在多种土质，在垦殖过程中存在技术和环境问题。本工程的目的是为了保证填料和堤防的安全，并保护施工过程中的水土流失。研究结果总结如下：为了评估作用在圆筒形破坏面上的应力和孔隙水压力对边坡滑动的影响，提出了一种补充经典切片法的有限元方法，并成功地应用于实际分析。水泥搅拌稳定是改善珊瑚礁区弱钙质沉积物的可能用途之一。细筛大于0.075mm时，水泥掺量对砂土强度和变形特性的影响显著。混凝土配合比设计中的空灰比规律可应用于人工胶结钙质砂层的强度评价。提出了一种加固软土地基的稳定箱形基础方法。这种新方法是通过在将要建造结构的地面上重叠水泥柱来制作箱形垂直墙的方法。模型地基的加载试验结果与地基承载力理论值吻合较好。针对冲绳珊瑚礁地区的环境保护，防止国上马吉地区的红土流失具有重要意义。利用化学稳定剂制成的膜膜覆盖地表是一种有效控制复垦过程中地面采伐面土壤流失的方法。

Various local soils exist in Kyusyu and Okinawa, and both technical and enviromental problems occur during the land reclamation. The purpose of this project is to make the fill and dike safety, and to preserve the soil erosion under the construction. The results are summarized as follws.1. In order to evaluate the stress and pore water pressure acting on the circular cylindrical failure surface of slope with respect to sliding, the new finite element method that complements the classical slice method was proposed, and applied for practical analysis successfuly.2. The cement stabilization through mixing was one of the possible use for improving weak calcareous sediments in coral reef areas. The effect of cement mixing on strength and deformation behavior was significant in sand with fine passing 0.075mm sieves than those with no fine. Void cement ratio law for design of concrete mix proportion could be applied to the evaluation of strength of artifically cemented calcareous sand deposits.3. A stabilized box foundation method for reinforcing soft ground was proposed. This new procedure was a method to make box-shaped vertical walls by overlapping cement colums in the ground on which structures were to be constructed. The loading test results of the model fondation on clay were found to agree well with the theoretical values of bearing capacity of the foundation.4. The prevention of reddish soil loss in Kunigami Maaji area is very important in the light of enviromental conservarion of the coral reef region in Okinawa. The surface covering with a membrain made from a chemical stabilizer was a useful method to control the soil loss in a cutting surface of ground during reclamation.