Effects of horizontal drains on slope stability under rainfall by three-dimensional finite element analysis

The effects of the horizontal drains on the ground water level during rainf all are predicted using a three-dimensional finite element analyses of tran sient water how through unsaturated-saturated soils. The slope stability is evaluated by the global safety factor, based on the three-dimensional elas to-plastic shear strength reduction finite element method. The following co nclusions are obtained: (1) the horizontal drains can effectively lower the ground water level and increase the slope stability under rainfall, but th e rate of the increase in the safety factor becomes smaller and smaller whe n the drains is extended beyond a critical length; (2) lengthening the hori zontal drains is more effective than making the spacing smaller and increas ing the number of the drains in a group in order to lower the ground water level and increase the slope stability; (3) the effects of the drains are m ainly influenced by the ratio of the rainfall intensity to the saturated hy draulic conductivity. (C) 1999 Elsevier Science Ltd. All rights reserved.