Predicting volumetric behavior of compacted clays during compression

Compacted clays are one of the most frequently used materials in the construction of geotechnical infrastructure. Clays, after compaction, typically stay in an unsaturated condition. Their volumetric behavior is the key information for the geotechnical design but is quite complicated to describe or predict due to the coupled hydro-mechanical interplay among the solid, water and air phases. This paper proposes a model for predicting the volumetric behavior of compacted unsaturated clays during compression (compression line), which consists of the pre-yielding elastic deformation (recompression line) as well as the post-yielding elastoplastic deformation (normal compression line). The model is convenient to use as it only requires limited soil information to calibrate, including the conventional saturated compression line and one unsaturated compression line. Experimental investigation was conducted to determine the volumetric behavior of a compacted expansive clay collected from Nanyang, China during constant water content compression. The performance of the proposed model is reasonably validated against the testing data of the expansive clay, as well as literature data of several clays obtained from constant water content or constant suction compression. It is demonstrated that the model predictions are capable of capturing the non-linear characteristics of the unsaturated compression lines and allow smooth transitions (i) from elastic deformation to elastoplastic deformation at yielding (gradual yielding) and (ii) from unsaturated condition to saturated condition at high stress level (pressurized saturation).