Influence of Weathering on Physical and Mechanical Properties of Mudstone

Abstract

Majority of the landslides in Niigata prefecture, Japan are occurred at Neogene sedimentary soft rocks. Weathering of such rocks is an important geological, environmental and engineering process. In order to study the chemical and physical weathering and their impact on the shear strength of the soil mass, soil samples were collected from ground surface to 15 m depth at two dierent drainage wells in the Mukohidehara landslide area. We carried out several laboratory tests like Atterberg’s limits, particle size analysis, X-ray diraction analysis, slake durability test, X-ray fluorescence analysis. We also conducted drained simple shear test, and drained ring shear tests on the soil samples to measure the strength characteristics. Test results showed that fully softened shear strength of the less weathered rock sample was very close to the peak shear strength of the disintegrated sliding surface sample. Because of insignificant dierence in mineralogical composition, residual shear strengths of the soil and rock samples from dierent depths were very close. The research results suggested that physical weathering in terms of slaking plays major role in the reduction of shear strength of mudstone. They also suggested that chemical weathering was not significant compared to the physical weathering at the shallow depths in the mudstone formations.