Delayed compression and breakage of crushed mudstones due to the drying/wetting and temperature cycles

Institute of Industrial Science, University of Tokyo, Japan

^* Corresponding author: nihaaj@iis.u-tokyo.ac.jp

Abstract

Soft sedimentary rocks, especially mudstones, disintegrated or crumbled when subjected to cyclic drying and wetting, known as slaking, which was the cause of severe slope failures and ground settlement. Drying/wetting and temperature variation are the influential factors of the slaking. In this study, a conventional oedometer was modified to make a drying/wetting cycle with temperature variation to examine the effects of slaking for four materials with different slaking ratios. Further, one of the four materials (Hamamatsu mudstone), showing higher vertical strains along the drying/wetting cycle, was experimented with under three loading conditions (100 kPa, 200kPa & 500 kPa) and drying/wetting cycles, in which the particle breakage was also measured along the drying/wetting cycles. In addition, a needle penetration test was conducted along the drying/wetting cycles. In the continuous drying/wetting cycles, the occurrence of particle breakage was higher in lower-stress conditions, where the void ratio became a governing factor for the breakage over vertical stress. The needle penetration resistance is dependent on two factors which are density and particle size, and there was a trade-off between them along the drying/wetting cycles. After a couple of drying/wetting cycles, the particle crushing resulted in a noticeable reduction in penetration resistance in lower stress conditions.