土体含水率和吸力量测及其对边坡稳定性的影响

为研究暴雨诱发滑坡的机理 ,在香港进行了一次大型人工边坡试验。通过检查该边坡坡顶在 2 0 0 1年 6月至 2 0 0 1年 12月期间含水率和吸力与每天及每小时降雨变化曲线 ,及含水率和吸力随深度变化曲线 ,看到在雨季含水率和吸力变化或者“浸湿前锋”移动通常发生在边坡土体以上 3m以内 ,而且 ,在 2 0 0 1年的一次最大暴雨中在边坡土体 1～ 2m之内形成了瞬时地下水位。另外 ,还看到在2 0 0 1年旱季由于蒸发在边坡土体中形成了“干燥前锋”。通过对边坡开挖之前的自然边坡的稳定性分析 ,降雨入渗可以使边坡土体的安全系数急剧降低而蒸发则可以使边坡土体的安全系数缓慢升高。雨季含水率和吸力的浅层变化或者“浸湿前锋”的浅层移动可解释为何香港地区在暴雨期间极易发生浅层滑坡。而旱季由于蒸发形成的“干燥前锋”可说明吸力对非饱和土边坡抗剪强度的提高

Soil moisture and suction measurement and its effect on slope stability

In order to investigate the mechanism of rainfall induced slope failure, a full scale cut slope experiment is being conducted at a being constructed cut slope, Hong Kong. By examining the variations of moisture content and matric suction with daily and hourly precipitation, and the variations of moisture content and matric suction profiles at the crest of the cut slope from June 2001 to December 2002, we observed that the variations of moisture content and matric suction or the movement of “wetting front” during the wet season of 2001 was within the top three meter soil and a transient water table was developed at around one meter to two meter depth during the heaviest rainstorm. We also observed that a “drying front” due to evaporation was developed during the 2001 dry season. Slope stability analysis of the natural slope showed that heavy rainfall infiltration could decrease the factor of safety dramatically while evaporation could increase the factor of safety slowly. The shallow variations of moisture content and matric suction or the shallow movement of the “wetting front” may be useful in the explanation of many shallow slope failures occurred in this region during heavy rainstorms. While the “drying front” due to evaporation during the dry season may illustrate the contribution of the increased matric suction to the increased shear strength of unsaturated soil slope.