Evaluating slope stability with respect to pore-water pressure and suction variation with rainfall: A case study of fill granitic slope in northern Thailand

Abstract

This paper reports on the study of slope stability with respect to pore water pressure and suction variation with rainfall for highway No. 1009, Km 42, in Doi-intanon, Chaingmai, Northern Thailand. The slope consists of granitic residual soil fill that suffered from soil erosion and shallow failure. The KU-tensiometers were installed at depth of 0.5, 1, 2 and 3 meters to monitor both positive and negative pore water pressure along the slope and its variation with rainfall was discussed. Shear behavior and soil water characteristic curve of recompacted soils collected from the site were also studied in the direct shear box and with tensiometers. Stability analysis was also performed for a failed slope based on observed failure surface and shear strength using the effective stress analysis in order to determine the value of pore water pressure at failure. In this regards, the pore water coefficient, ru, was varied in the analysis until it was found that for Factor of Safety to be 1, the ru value was about 0.43 which would have responded to a total daily rainfall of about 100 mm and 3-day antecedent rain of about 180 mm. This value of pore water pressure agrees reasonably well with the measurement of pore water pressure shortly after the failure indicating the plausibility of study results.