Assessing the Dynamic Behavior of Step Footing Placed on the Surface of Sandy Soil

Numerous factors, including soil type, moisture content, foundation type, and excitation intensity, have impacted how soil responds to excitation forces. An accumulation of underlining soil deformation caused by the machine's vibration may exceed the limit. An experimental investigation was conducted to evaluate the effect of machine-induced vibrations on four prototype footings positioned at the soil's surface. Among the four footing models, three were designed with stepped areas, while one had a uniform rectangular section. The stepped footings were constructed with varying bottom-to-top area ratios (A₂/A₁) of 1.0, 1.2, 1.5, and 2. Three operating frequencies (10, 40, and 70 Hz) were applied to each of the four footings. The soil used was sand with a medium relative density of 50%. Dynamic response data include vertical amplitudes (displacement, velocity, and acceleration), settlement, and pressures at various depths. Despite different in magnitudes, it was found that the stepped footings significantly reduced the machine-foundation system's pressure, settlement, and amplitude movements. For instance, the stepped footing with area ratio of (A2/A1=2.0) displayed the lowest dynamic response. The pressure decreased by an average of 14.5% when the area ration changes from (A2/A1=1.0) (A2/A1=2.0), while the total settlement, amplitude displacement and acceleration were reduced by about 30%, 42% and 54%, respectively. Further, compared to a uniform footing, stepped footing is more cost-effective with high-performance.