Effect of rainfall on the triggering of the devastating slope failure at Malin, India

A study on a devastating rainfall-induced landslide at Malin, India, which resulted in 160 deaths including the destruction of an entire village in July 2014 has been presented. The area was under a massive rainstorm which lasted for 3 days before the tragedy. The seepage into the slope due to the rainfall infiltration and the corresponding factor of safety of the slope at Malin has been quantified using a two-dimensional numerical model. The study indicates that the continuous rainfall infiltration develops a perched water table near the slope surface which results in the saturation and the positive pore water pressure build up at a shallow depth. With the increasing intensity and the rainfall duration, this depth of saturated zone increases rapidly. Though the Malin slope has an adequate factor of safety of 1.6, initially, but with continuous rainfall and increase in rainfall intensity, the factor of safety reduces to less than one on the day of tragedy. The parametric study indicates that the factor of safety of the Malin slope is adequate after 24 h of 2 mm/h, 5 mm/h and 10 mm/h of rainfall. But it drops rapidly to less than 1 after 7, 6, 6, 3, 2 and 1-h of 20 mm/h, 30 mm/h, 40 mm/h, 50 mm/h, 60 mm/h and 70 mm/h of rainfall, respectively. The slope, on which the Malin village is located, is initially safe but the debris from the upper portions of the slope moves downward destroying the residential area of the Malin village.