STUDY ON RHEOLOGICAL CONSTITUTIVE MODEL OF CILILIN VOLCANIC CLAY, INDONESIAIN RELATION TO LONG-TERM SLOPE STABILITY

Abstract

: Ground movements do not remain constant over time but it is a time-dependent phenomenon in the form of long-term deformations due to in-situ stresses acting all the time on the slope body. Therefore, the time-dependent behavior of soil mass is an important factor that influences long-term slope stability. To understand the long-term slope stability, research on soil rheological characteristics is required so that the time-dependent soil strength reduction can be known. The result of the research will be very useful for the policymaker in disaster mitigation and regional planning.  To determine the rheological characteristics of Cililin Volcanic Clay, a laboratory shear creep test was carried out on soil samples taken from the Cililin area, West Java, Indonesia, which is well known as landslide-prone areas. Fifteen undisturbed soil samples were prepared for laboratory shear creep tests. The level of shear stress applied to the shear creep test is 50% - 95% of the peak strength. Then, the soil rheology constitutive models were established which are used to understand the creep behavior of the soil, determine the soil long-term strength, estimate the reduction of soil parameters as a function of time and calculate long-term slope stability. The result shows that the long-term strength of soil is reduced 48.80% from its peak strength after 16 years. The cohesion and internal friction angle reduced from 44.72 kPa and 30.34^o become 21.82 kPa and 15.94^o, respectively, and the slope safety factor is reduced from 2.16 to 1.04. Rheological modeling also shows that slope stability is a function of time.