Research about the mechanism of surface slope failure in clear-cutting forest area

在本研究课题中，通过对清林采伐山地边坡的监测，评估清林采伐对地表边坡破坏力学的影响。1999年对监测边坡进行了全面采伐，2000年植树造林。监测系统获得的调查目标为：a)网络摄像机图像监测；b)气象水文数据（降雨、空气土壤湿度、地下水位）。在监测系统方面，我们开发了一套适用于无市电供电的天然边坡监测系统。与降雨事件同步的图像监测系统可以有效地给出地表边坡破坏前后的一般边坡情况的图像信息。从森林砍伐前后土壤湿度随时间变化的波动数据可以确定如下几点：1)毁林后坡面土壤水分总量总体上呈现出增加的趋势，主要是由于森林植被蒸散量的减少，但土壤水分的波动趋势随坡面位置的不同而不同。2)坡面上部表层土壤含水量呈下降趋势。另一方面，坡底中下层土壤含水率呈增加趋势。将入渗模型与利用土体强度参数的边坡稳定模型相结合，实现了按场地估算边坡失稳风险。

In this research topic, the monitoring of clear-cutting mountainous slope was carried out for the estimation of effect of clear-cutting on mechanics of surface slope failure. In the monitoring slope, clear-cutting was executed in 1999, and tree planted in 2000. The objectives of survey obtained by monitoring system are as follows, a) the image monitor with the Internet camera, b) Meteorological and Hydrological data (rainfall, air soil moisture, ground water table). As for the monitoring system, we developed the system which can be applied for the natural slope without the commercial power supply.The image monitoring system synchronized with rainfall events can effectively give the image information of general hill slope condition before and after surface slope failure occurrence.From the data of the fluctuation of soil moisture with the time lapse before and after deforestation, the following are confirmed. 1) The total amount of soil moisture in the slope after deforestation totally shows the tendency of increasing due to the decreasing of evapo-transpiration of forest vegetation, although the tendency of fluctuation of soil moisture varies by site of the slope. 2) The soil moisture content in surface soil layer at upper part of slope shows the decreasing trend. On the other hand, the moisture content in middle and lower soil layer at bottom part of slope shows the increasing trend.The estimation of slope failure risk by site is done by combining the infiltration model and the slope stability model which use the soil strength parameter.