INFLUENCE OF DEGRADATION ON MOBILIZED SHEAR STRENGTH OF SILTSTONE FOR SLOPE STABILITY ANALYSIS

Abstract

This paper presents weathering behaviors of siltstone during cut and fill construction, which could affect the stability of slope. The siltstone specimen was taken from Mae Moh mine, Lampang province, Thailand. Construction activities and climate environments could alter the physical condition of siltstone. The physical alteration of siltstone had been simulated in laboratory by wet-dry process, and different loading magnitudes. The durability and degree of weathering of siltstone specimen was determined by slaking test, jar test and grain size distribution analysis. The weathering mechanisms significantly influence the shear strength of materialobtained by direct shear test and unconfined compressive strength test. Variation of drained and undrained shear strength parameters of siltstone were summarized and utilized for slope stability analysis of a dumped embankment. The results reveal that the factor of safety (F.S.) is mainly influenced by degree of weathering from Soft Rock to Hard Soil. Material consistency could affect drainage condition and shear-induced pore-water pressure. The slope stability could become unstable (F.S. < 1.3) if ru > 0.53 and su ≤ 460 kPa