Observed behaviour of reconstituted clay along stress paths typical of excavations

The paper presents experimental results from a laboratory investigation on reconstituted samples of a stiff and overconsolidated clay. The experimental programme was carried out using stress path triaxial cells to investigate the mechanical behaviour of the soil when subjected to stress paths typical of excavations. Samples were compressed along continuous drained paths under approximately K-0 conditions to different values of the maximum effective stress and overconsolidation ratio OCR. After compression to the desired values of OCR, pairs of samples were sheared along two different drained stress paths: compression with decreasing horizontal effective stress under constant vertical effective stress, and extension with decreasing vertical effective stress under constant horizontal effective stress. For OCR = 3, undrained compression and extension tests were also carried out. In the interpretation of experimental results, the effect of the direction of the stress paths on the shear stiffness is evaluated and distinguished from the influence of the previous stress history. The observed stress dilatancy and mobilisation of the shear strength are also discussed in the paper.