Centrifuge modelling of monotonic and cyclic lateral responses of monopiles in quartz and carbonate sands

This study evaluates the soil-structure interaction of monopiles subjected to monotonic and cyclic lateral loading by means of centrifuge modelling. The monopile were installed in two types of dense sands: quarts and carbonate. To evaluate the static and dynamic properties, the two soils were characterized by index tests, as well as triaxial, resonant column and bender element tests. The triaxial tests showed that angles of internal friction were higher for the sand with higher carbonate content (CaCO3). Also, curved shear strength envelopes were observed in both soils, i.e., peak friction angles decreasing with confining stress. Regarding the dynamic soil properties, the stress history appears to affect the stiffness of the carbonate sands more than the quartz sands, i.e., the higher CaCO3 content soil exhibited greater shear modulus degradation. In the geotechnical centrifuge tests the lateral loading capacity about doubled after 4800 loading cycles, slightly more for the carbonate sand than for the quartz sand. Also, as a function of the cycling process, the secant stiffness increased for both sand types, especially in the first 500 loading cycles where the increase occurred exponentially.