Cyclic Settlement of Footings of Different Shapes Resting on Clayey Soil

An experimental investigation is carried out to investigate the impact of the footing shape, when rested on clayey soil under cyclic loading condition. The model footings used in this study are circular, square and the area of footings is fixed. Cyclic load test is carried out on the cohesive soil with three undrained shear strengths (20 kPa, 40 kPa and 70 kPa). Two depths of foundation embedment (at surface and 5 cm) to know the effect of the depths of the foundations on the change of settlement and total vertical stress and two rates of loading (3 mm/sec and 6 mm/sec) are used. It has been observed that the bearing capacity varies in increasing order as Solid, Circular and Square. It is found that the cyclic settlement in the square foundation is less than the circular foundation. The results reveal that the shape of the footing has a significant effect on its bearing capacity and the settlement characteristics. The vertical stress reaches a constant value which is greater below circular footing and it is about (70.9 - 92.7) % greater than below square footing.

Pore water pressure accumulation and settlement of clays with a wide range of Atterberg’s limits subjected to multi-directional cyclic shear

In this study, normally consolidated specimens on four clays with a wide range of Atterberg’s limits were tested by applying several series of undrained multi-directional cyclic shear followed by drainage. The cyclic shear tests were carried out under the shear strain amplitudes (γ = 0.05%-2.00%), number of cycles n = 200 and the phase difference θ = 90o. Then the accumulation of cyclic shear-induced pore water pressure and the post-cyclic settlement in strain (εv, %) were observed and discussed. In conclusion, it is clarified that the pore water pressure ratio (Udyn/σ’vo) increases with g and the soils with higher Atterberg’s limits show lower Udyn/σ’vo, and under the multi-directional cyclic shear strain at γ > 0.4%, Hue clay and Kaolinite clay with relatively low plasticity suffer from cyclic failure. In addition, the post-cyclic settlement has a tendency of decreasing with the Atterberg’s limits in the range of plasticity index from Ip = 25.5 to 63.8, meanwhile when Ip < 25.5, different tendencies were observed e.g., Hue clay (with lower Ip) shows a smaller settlement compared with those on Kaolin (with higher Ip). Furthermore, the threshold number of cycles (ntp) and cumulative shear strain (G*tp) for pore water pressure buildup were then clarified.