Effects of Cyclic Wetting and Drying on Physical and Mechanical Properties of Neogene Sandstones and Siltstones from Boso Peninsula, Japan

Abstract

This paper reports field observations and new experimental data designed to clarify the response of sandstones and siltstones to cyclic wetting and drying. A methodology is proposed to understand the mechanism of disintegration of rocks due to cyclic wetting and drying. These methods were chosen after critical analysis of field observations of coast typified by cliffs where frequent moisture changes to the rocks were observed to be operative. The importance of mineralogical composition and physical properties of rocks on the overall breakdown mechanism is emphasized. The experimental results showed that the water absorption capacity appears to exert highly significant control over the rate of disintegration of rocks investigated. The results also revealed that fracture induced deterioration only occur in siltstones. The proportion of the initial flaws in the rock fabric is important for determining the rate of disintegration. We suggested that the data are consistent with a model that assumes that the coupled relationship between the amount of swelling minerals and the small scale heterogeneity (flaws) of the material are major controlling factors for fracture initiation within the rock mass and the consequent repetitive breakdown. The findings obtained from this study may offer practical considerations in understanding the mechanism of rock mass breakdown, and enable design for the control of minor rockfall and cliff degradation to be made on a rational basis.