Distribution of contact pressure under rectangular shallow foundation subjected to different vibration modes

In this paper, extensive laboratory tests were performed to investigate the effect of different parameters such as load vibration mode, vibration frequency, foundation depth and soil relative density on the distribution of contact pressure under shallow foundations in dry sand. A test model box with dimensions (800x800x800) mm was used to perform the laboratory test. Three vibration load modes were applied to a rectangular foundation with dimensions 150x250 mm placed at surface, 75 mm depth and 150 mm depth in sand of 70% or 90% relative density. Vertical settlement and stresses under the foundation were recorded for each loading cycle through each test, five ultra-thin tactile sensors were evenly distributed along the foundation width and in contact with foundations base. It was concluded that contact pressure distribution under a foundation final shape is nearly formed after 5 to 10 minutes after the start of applying dynamic loading by increasing time (number of cycles), the contact pressure may change slightly in its values but the shape of the pressure distribution under the foundation will not be affected for nearly all test models that have been performed. An increase in contact stress under observation in the last quarter section of rectangular footing compared to the first quarter section by 25-100% when applying rocking vibration load and this increase is highly related to the increase in footing depth and lesser to the vibration frequency. This increase becomes greater at edges points to reach 50-200%.