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

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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