Water weakening in sedimentary rocks

During the previous 20 years, numerous experimental studies have documented the dramatic weakening of water free North Sea chalks when exposed to water. Recent laboratory compression tests provide compelling evidence that water weakening also occurs in poorly-consolidated, weakly-cemented, detrital, siliciclastic (e.g., quartz and feldspar) rocks as well as chalks. A series of experimental studies was undertaken to identify the mechanism of water weakening in rocks, including many triaxial compression tests and uniaxial strain compression tests with fluid injection. Experimental evidence indicates water weakening requires the presence of chemically active water molecules and intimate chemical contact between liquid water and the rock matrix. One model that appears to be consistent with experimental results is "stress-enhanced solubility" of matrix grains subjected to high grain-to-grain contact stress. Quantitative models indicate this to be a viable water weakening mechanism.