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Abstract The similar materials representing the softening feature of the soft rock in water were prepared and the similar model for the thick red-bed soft rock slope was built in order to study the disaster caused by the failure of the thick soft rock under the rain condition in Southern China. The softening process was monitored and its mechanisms were studied under different rainfall patterns，including the medium-weak(Id＜25 mm，Id is intensity of rainfall)，heavy(25 mm≤Id＜50 mm) and torrential rainfall(50 mm≤Id＜100 mm). The failure of the slope was found to be closely related to the rainfall patterns. Heavy and the torrential rains tended to soften rocks on the slope. At first，the bottom of the slope was saturated and then the initial cracks were generated. Along with the expansion of cracks，local failure occurred due to the influence of the gravity and seepage forces，caused the collapses of the upper part and finally resulted in the pull-type landslide. The infiltrating process of rain water includes three main steps，i. e. the unconfined seepage，the confined seepage and the saturated seepage. The cracks on the surface of the slope were mainly generated during the unconfined seepage and gradually expanded during the confined seepage. The failure of the slope occurred during the saturated seepage. The accumulation and dissipation of the excess pore water pressure in the thick red-bed rock layer slope changed the distribution of the effective stress field during the raining process and caused the movement of the slope. The response of effective stress and water pressure in pores was more sensitive than displacement，displacement rate and other parameters to the failure of slopes near the sliding stage. The safety precaution in terms of slope disaster was proposed on the basis of the effective stress and water pressure in pores.
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2016, Vol. 35 
