Effect of stress ratio on the volume change behavior of compacted highly expansive clay

This paper aims at emphasizing the influence of stress conditions on the volume change behavior of expansive soils. A series of triaxial tests were conducted on remolded highly expansive clay specimens inundated under different combinations of stress ratios, K (ranging between 0.5 and 1.45) and axial inundation stress, σ_ai (ranging between 50 and 800 kPa). Volume change characteristics obtained from these tests included axial inundation strain (ε_ai), volumetric inundation strain (ε_vi), and axial swelling pressure (σ_s). Results of the experimental program showed that the stress ratio had a significant effect on magnitude of axial inundation strain. Test results revealed that axial inundation strain decreased with increase in axial inundation stress. However, stress ratio had a negligible effect on the volumetric inundation strain–mean inundation stress relationship. Furthermore, the axial inundation strain and axial swelling pressure obtained from triaxial tests were compared with that obtained from one-dimensional oedometer tests conducted on identical specimens and applied axial stress. The differences between axial inundation strain and axial swelling pressure evaluated from triaxial and oedometer testing were quantified by using corrections factors. Using these correction factors, a systematic procedure was proposed for the realistic estimation of axial inundation strain in the field based on results of laboratory oedometer tests and knowledge of in situ axial stress and stress ratio.