Investigation of the end bearing load in pile group model in dry soil under horizontal excitation

A series of 94 laboratory tests were conducted to measure the response of pile foundation when subjected to dynamic loads. Eight tests were conducted on single pile in dry soil at relative density 30 % (loose) and 50 % (medium); 66 tests on group of piles with different spacings and patterns. All tests were carried out under operating frequencies 0.5, 1 and 2 Hz under horizontal shaking. All tests were achieved with one embedment ratio (L/d = 30). These tests were grouped in three different numbers of piles; 2 piles in row and line patterns, 3 piles and 4 piles; and three pile spacing ratios (s/d = 3, 4 and 5). The results of dry soil indicating the mechanism of dynamic response of piles and soil subjected to dynamic horizontal shaking include the variation and distribution of acceleration with time in different states of soil in addition to the vertical and horizontal displacements, end-bearing load, peak acceleration and the peak velocity of foundation. It was concluded that for a dry soil bed, the acceleration amplitudes increase with frequency for both soil relative densities (loose and medium) and different pile patterns (number; single or group and different spacing ratios s/d). The maximum acceleration in the foundation is lower than in the soil bed for all operating shaking frequencies, pile spacing ratios and soil states. The decreasing of the maximum acceleration recorded in the foundation as compared to that in the soil bed is between 10-100 % for loose and medium state of soil, and the decrease in loose state is more than in medium state. This means that there is damping effect or attenuation of vibration waves. The amplitudes of recorded acceleration in the pile cap are much higher than in the soil bed for single pile and pile group with different pile spacing ratios, also these amplitudes are increasing with increase of shaking frequency and relative density of the soil.