Influence of water on engineering properties of weathered rocks

Abstract

ABSTRACT The influence of groundwater on the engineering properties of rocks is well known. Because of its importance, rock mass classification methods include groundwater as one of the main classification parameters. Perhaps the best indication of the influence of groundwater on rock mass properties comes from the application of geophysical resistivity and seismic refraction techniques to investigate groundwater. When ground conditions change from an unsaturated to a saturated state, resistivity and velocity of the rock mass change markedly. In nature, groundwater affects rock properties either by changes in pore water pressure or by chemical reaction. While increase in pore water pressure decreases the total normal stress in the rock mass, chemical reactions cause rocks to weather resulting in changes in physical and mechanical properties. Pore water pressure is best evaluated in the rock mass by in situ measurements. However, the properties of weathered rocks are very often best studied in the laboratory. Over the last decade the influence of weathering on the engineering properties of mainly igneous and sedimentary rocks, under dry and saturated conditions, has been investigated. A great deal of test data has been accumulated on the index and engineering properties of fresh and weathered rocks from the UK and abroad. Analysis of the available test data shows that while certain rock properties increase with weathering and saturation, others decrease. In this paper changes with saturation in selected index and engineering properties of fresh and weathered porphyrites and andesites from the UK and Turkey are reported. Established relations between the dry to saturation index and engineering properties of weathered rocks will also be presented.