Studies on the Control of Slope Failure and Soil Loss by Rainfall due to Land Development in the Red Soil Area in Okinawa

在冲绳红壤地区，边坡的破坏主要受层面、节理等软弱层面的走向控制。沿软弱面的抗剪强度降低到接近剩余强度的水平。峰值强度在不存在弱面的剪切带中被调动。使用三轴压缩装置测量了来自斜坡破坏的未受干扰的试件的峰值强度。用环形剪切仪测定了扰动样品浆液的完全软化强度和残余强度。峰值强度参数为cf=3.0kPa16.1kPa.phi=28.5？A1-43.5？A1.完全软化强度参数为c&lt；sf&gt；=0kPa7.9kPa.phi&lt；sf&gt；=35.0？A1-40.0？A1.剩余强度参数为：cr=0kPa.Phi=16.5？A117.9？对于高粘粒含量、高粘粒含量的蚯蚓土，c_r=0kPa，Phi_r=19.8？A1-33.3？对于石英和小砾石为主的土壤，A1都高于潮土或滑坡土壤。这是因为Cla…针对红壤地区Makiya边坡的现场抗剪强度(沿滑动面的平均抗剪强度)和土体抗剪强度参数，采用考虑残馀因素的稳定性分析方法，对该滑坡的现场抗剪强度(沿滑动面的平均抗剪强度)和抗剪强度参数进行了估算。利用反分析方法和基于土体抗剪强度参数的图解计算了控制工程的设计强度参数，并利用降雨模拟器进行了土壤流失试验，以明确有机物质对红壤的侵蚀控制作用。径流流失量由大到小依次为木炭混交土>有机物质混交土>木屑混交土>原始土。10%的木炭混合土对土壤侵蚀的控制效果比原土高70%。较少

In the red soil (commonly called Kunigami Maaji) area in Okinawa, slope failures occur controled by the strike of weak planes such as bedding and joint plane. The shear strength along weak planes is lowered to the value close to residual strength. The peak strength is mobilized in shear zones where weak plane does not exist. The peak strength was measured for undisturbed samples from slope failures using a triaxial compression apparatus. The fully-softened strength and residual strength were measured for slurry of disturbed samples using a ring shear apparatus. Peak strength parameters were c_f=3.0kPa16.1kPa, phi_f=28.5? A1-43.5? A1. Fully-softened strength parameters were c_<sf>=0kPa-7.9kPa, phi_<sf>=35.0? A1-40.0? A1. Residual strength parameters were c_r=0kPa, phi_r=16.5? A117.9? A1 for soils containing vermiculite and high clay content, and c_r=0kPa, phi_r=19.8? A1-33.3? A1 for quartz and small gravels-dominated soils, both higher than thosef or landslide soils. This is because cla … More y particles in the red soil are poorly oriented, and, furthermore, the quartz and small gravels in the soils affected to make the residual strength high.The field shear strength (a average shear strength along the slip surface) and shear strength parameters of the soil from the slip surface were evaluated for the Makiya slope failure occurring in the red soil area based on the stability analysis method in which the residual factor was incorporated.A back-analysis of this slope failure showed that feild shear strengths are greater than residual strengths but smaller than peak strengths. The design strength parameters for control works were calculated by the proposed method and also by the graphic solution based on the back-analysis and shear strength parameters of the soil.The soil loss testing was performed by using a rainfall simulator in order to clear up that organic materials have the effect of erosion control on red soils. The quantity of runoff soil loss was small in the order of charcoal mixed soil, organic material mixed soil, wood shavings mixed soil and original soil. 10%charcoal mixed soil showed the more effective erosion control than original soil by 70%. Less