Residual shear strength of tertiary mudstone and influencing factors

Abstract

Extensive research done on the residual shear strength of the Tertiary mudstone showed that mudstones are rich in expansive clay minerals. Those clay minerals are responsible for making the mudstone highly weathering susceptible, which is the main cause for excessive landslides in the mudstone formations. Because of high brittleness, residual shear strength is more important in analyzing the landslides occurred in such formations. Research results showed that average liquid limit, plasticity index, activity, and clay sized fractions in the mudstone from the Niigata Prefecture of Japan are 72%, 36%, 1.4, and 26%, respectively. Dominating clay mineral in mudstone is smectite with an average proportion of 15%. Dominating clay mineral oxide of mudstone was aluminum oxide with an average value of 18%. Average residual friction angle was observed to be 13°. At the presence of saline pore water the strength can increase up to 40%, depending on the nature of soil and site condition. If it is hard to get the soil specimens in sufficient quantity from the mudstone area, residual friction angles can be approximately estimated with index properties. However, if the mineralogical composition is known, residual friction angle can be estimated with up to 90% accuracy, using the diagram proposed by Tiwari and Marui (2005). This paper deals with the chemical, mineralogical, and mechanical properties of the Tertiary mudstone from the Niigata Prefecture of Japan, as well as the methods to measure residual shear strength in conventional soil testing devices. © 2007 Springer-Verlag Berlin Heidelberg.