Evaluation of strain and stress states of a compacted highly expansive soil using a thin-walled oedometer

Investigation of the volume change behavior of expansive soils typically utilizes conventional oedometer which provide estimates of vertical strain and swelling pressure under fully lateral restrained conditions. In this study, testing was conducted on compacted highly expansive clay using a thin-walled oedometer to evaluate the state of stresses during inundation in both vertical and lateral directions in addition to the vertical strain. First, calibration, correction, and verification of the thin wall oedometer were described. Second, an experimental program was developed to evaluate the volume change behavior during inundation for a wide range of vertical stresses at inundation (σi) under two conditions: (i) constant vertical stress at inundation and (ii) constant volume. Results of tests under constant vertical stress at inundation indicate the dependency of strain state of expansive soil on the inundation vertical stress. Moreover, the vertical stress at inundation (σi) was observed to affect the vertical stress state after inundation for constant volume condition. Investigating the equilibrium vertical stress state after inundation under constant volume condition showed that there is one relation termed as “Swell-Collapse Equilibrium Line, SCEL” that represents the equilibrium condition after inundation for specimens subjected to different initial sample conditions prior to inundation. General trends of strain softening behavior for the evolution of lateral stresses with time were observed, particularly for the swelling zone. Stress path followed by tested samples was depicted. Interpretation of results in light of Barcelona Expansive Model (BExM) was also performed. An enlargement of yield envelop after loading to stresses greater than past stress history was observed.