Rheological approach to determine the behavior of mass movement in Pengalengan, Indonesia

Abstract

Landslide and mudflow movements are usually be “triggered” under two different states of soil behavior. Landslide movement usually occurred when the soil reaches a plastic state or Liquidity Index (LI) is less than one. On the other hand mudflow movement occurred when the soil reaches a viscous liquid state or LI is greater than one. Pangalengan landslide in 5 May 2015, an Indonesia case study we have been involved in has been chosen as we undertook a rheological approach to determine the behavior of mass movement. This paper will discuss the comparison between numerical simulation using a Flo2D computer software and actual event of the mass movement. The rheological parameters which comprise of viscosity and yield stress were obtained from a laboratory flow box test and a fall cone penetrometer together with mini vane shear, respectively. In relation to the water content, which ranged from 45% to 85%, the viscosity values appear to be in range between 14.66 to 0.03 Pa·s while the yield stress values appear between 25.48 to 0.18kPa. These laboratory results were then used as input parameters for the Flo2D software to simulate an actual flow mass movement. In addition, soil parameters including a solid concentration, specific gravity, water content, and Atterberg limits were also incorporated to simulate and verify the duration, volume, length, source area, and deposition area of mass movements. The numerical simulation has shown that the rheological parameters are affecting the simulated behavior of mass movement and it was quite similar to the soil deposition on site.