Creep behaviour in isotropic and k0 compression of the Venice Lagoon sand

The creep behaviour of the Venice Lagoon sand is here investigated. Triaxial tests were conducted in the Bishop & Wesley stress path cell and in a 'high' confining pressure apparatus on specimens trimmed from bore hole samples frozen on site. The general framework of behaviour was first built by means of triaxial tests with high confinement. It is shown that the sand undergoes three phases during isotropic compression which can be easily identified if the tangential bulk modulus is plotted against the mean effective pressure in a double logarithmic scale. This indicates that the stiffness evolution follows a power law, but different sets of parameters apply for the three phases. The two transition points also coincide with the boundaries of the higher curvature part of the isotropic compression curve when void ratio is plotted against the logarithm of the effective isotropic pressure. For mean effective pressures within phase I, creep strains increase proportionally to the logarithm of time both in oedometric and spherical compression. Also their magnitude is related to the tangential stiffness, confirming results of previous researches. However, when the confining pressure is within the phase II range, much higher creep rates are recorded.