Behavior of seepage pore-water pressure and its influence on slope stability in embankment by rainfall

本文研究了降雨作用下路堤中的渗流行为及其伴随的饱和湿区扩展特征和促进边坡失稳的孔压发展特征。利用一种能在坡面上提供均匀恒定降雨强度的装置，在基质中安装了小型孔压测量装置，对几种模型填土进行了离心机渗透试验。在试验采用的降雨条件下，对模型填土原型进行了非稳定饱和-非饱和渗流有限元分析。总结如下：(1)降雨引起的渗流特性受降雨强度r、渗透系数k、坡度和填土初始含水率的影响很大；饱和湿区的扩展受…差控制。(2)降雨过程中，湿润带正面逐渐从坡面下落，形成饱和湿润带，随着时间的推移，湿润带从坡脚向路堤内部逐渐扩大。(3)在降雨总量约150 mm、降雨强度30 mm/h的条件下，试验证实了边坡有破坏迹象，安全系数减小。(4)饱和湿区的扩展和填方安全度的降低在很大程度上取决于初始含水率；在初始含水率较高的填土中，如预先经历了长时间降雨的填土，在降雨初期，饱和湿区的扩大和相应的安全度降低非常迅速和强烈。(5)对于中等坡度的填土，即使饱和湿区的扩展很明显，降雨渗流对边坡稳定性的影响也很小，因为它们本质上具有更高的稳定性安全性。(6)对于非饱和土水分和渗透性的离心法，离心机试验和1G试验相结合的方法被证明是非常有利的，因为在试验中采用离心机加速使排水过程更快，并实现了相当大的试验周期，而且在从饱和状态到低含水率的相当大的范围内连续测量都是令人满意的。较少

The behavior of seepage flow developed in an embankment due to rainfall and its associated features of extension of the saturated wet zone and those of pore-water pressure development, which promotes instability of slopes., were studied in this research project. Centrifuge seepage tests were conducted on several model fills, in which small size measuring devices of pore-water pressure were installed in matrix, by use of a device which can supply a uniform and constant strength of rainfall over the slope surface. Finite element unsteady saturated-unsaturated seepage analyses were made on the prototype of the model fill for the same rainfall conditions as adopted in the tests. Concluding remarks drawn from the present study are summarized in the following.(1)Seepage behavior due to rainfall is strongly affected by the intensity of rain r, and the permeability k, inclination of slope and the initial moisture of the fill ; Extension of the saturated wet zone is controlled by the difference … More of seepage water flowing in and out from the fill.(2)During rainfall, the front face of the wet zone gradually falls down from the slope surface, making the saturated wet zone at the toe, and it enlarges from the toe to the interior of embankment as the time elapses.(3)A sign of slope failure and the reduction of safety factor were confirmed in the test at the total amount of about 150mm and the intensity of 30mm/h of rainfall, which is often experienced in the past case histories of slope failure.(4)Extension of the saturated wet zone and reduction of safety in the fill are largely dependent on the initial moisture ; in the fill having high initial moisture, like a fill which has experienced a long-term rainfall beforehand, enlargement of the saturated wet zone and corresponding reduction of safety are remarkably fast and intensive in an early stage of rainfall.(5)The influence of rainfall seepage on slope stability is rather small for fills with a moderate slope, even if extension of the saturated wet zone is remarkable, because they have essentially higher safety in slope stability.(6)As for centrifuge testing method on moisture and permeability of unsaturated soils, the procedure using centrifuge test together with 1G test is verified to be much advantageous because centrifuge acceleration applied in the test made the drainage process faster and realized a considerably large reduction of the test period, and because successive measurement was satisfactorily done in a fairly wide range from saturated state to a state of low moisture content. Less