The impact of partial water saturation on rock strength: an experimental study on sandstone

Abstract

The mechanical properties of sandstones are a critical parameter and of vital importance for several topics in the applied geosciences. For a systematic study eight sandstone varieties (Bad Bentheim, Bebertal, Obernkirchen, Sander, Schleerither, Tambach, Weser grau, Weser rot) were selected. All lithotypes were studied with respect to the mineralogical composition and its fabrics. They differ in composition, porosity (from 6 to 26 %) and in the pore radii distribution. The impact of partial water saturation on the uniaxial compressive strength (UCS) is highly variable and is a function of the micro to macro pore ratio. Sandstones belonging to the intermediate and low porosity group show higher values of the UCS and a pronounced sensitivity to the water saturation. The reduction in the UCS with increasing water content is significant, with values of up to 50 % strength loss. In general, if weakening occurs, it occurs when the water saturation is below 30 percent. Bad Bentheim and Obernkirchen sandstones are less sensitive to the water saturation/UCS relation. The proportion of pores below 0.1 mu m could have a significant control on the strength loss and hygric expansion. The correlation observed between the reduction of the UCS and the hygric expansion could be explained by swelling clay minerals or be caused by the disjoining pressures within the small pores.