Effect of air-drying duration on the engineering properties of four clay-bearing rocks in Texas

The engineering properties of clay-bearing rocks may degrade upon exposure to the air; the engineer needs to know quantitatively the effect of the exposure duration on the rockʹs strength and deformability. This paper quantifies the effect of air-drying duration on the engineering properties of four clay-bearing rocks in Central Texas, USA, known as: Del Rio Clay, Eagle Ford Shale, Taylor Marl, and Navarro Shale. Their shear strength decreases upon exposure to the air when the liquid limit is greater than 56% and the cation exchange capacity is greater than 29 Meq/100 g (Taylor Marl and Navarro Shale), otherwise it is not affected by exposure to the air (Del Rio Clay, Eagle Ford Shale). After 48 h of air drying, the elastic modulus was approximately 35%, 10%, 15%, and 25% of the maximum value for Del Rio Clay, Eagle Ford Shale, Taylor Marl, and Navarro Shale, respectively (most of the reduction took place within the first 4 h of drying). Expressions are given for the strength and the Youngʹs modulus as a function of air-drying duration. In the jar slake tests, degradation occurred only when the material was first air-dried, and the degradation extent increased with increasing drying duration. Degradation in the jar slake test may not necessarily imply shear strength loss when the material is gradually rewetted. The slake durability index cannot be used to distinguish which material loses strength and does not correlate with loss of stiffness upon exposure to the air.