The loss in uniaxial compressive strength between UCSdry and UCSsat for 35 British sandstone types is discussed. The difference between UCSdry and UCSsat for the clay-rich Cretaceous Greensand was 78% while for the Siliceous Sandstone the strength decreased by only 8%. Over the whole range of sandstones, however, the view that the weaker varieties are more sensitive to moisture content is not supported. The degree of sensitivity to moisture content is controlled primarily by the proportions of quartz and clay minerals present and to a lesser extent by the rock microfabric. Research indicates that the development of pore pressure during loading is negligible especially in pure sandstones and hence does not play a significant role in moisture related strength reduction.

The work has demonstrated a large variation in sensitivity to moisture content throughout the range of sandstones studied and has shown that an increase in moisture content of as little as 1 0.000000rom the dry state can have a marked effect on both strength and deformability. A classification scheme for moisture content sensitivity is proposed.

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