Development of Excess Pore Water Pressure around Piles Excited by Pure Vertical Vibration

In this study, an assessment to excess pore water pressure generated around a single pile and pile group excited by two opposite rotary machines embedded in saturated sandy soil was considered experimentally. A small-scale physical model was manufactured to accomplish the experimental work in the laboratory. The physical model consists of: two small motors supplied with eccentric mass of 0.012 kg and eccentric distance (20 mm) representing the two opposite rotary machines, an aluminum shaft 20 mm in diameter as the pile, and a steel plate with dimensions of (160 x 160 x 20 mm) as a pile cap. The experimental work was achieved taking the following parameters into considerations: pile embedment depth ratio (L/d), spacing between piles (S) and operating frequency of the rotary machines. Twelve tests were conducted in medium dense fine sandy soil with 60 % relative density. In all these tests, the change in excess pore water pressure was measured around the pile at two spots: at the middle of the pile and at its tip. The results revealed that the generation of excess pore water pressure was affected by the following parameters: slenderness ratio of the pile, operating frequency of the machines, and the soil permeability. However, for all cases, it was found that the pore water pressure generated during operation was not greater than 20 % of the initial hydrostatic pressure. Using pile foundation reduced the amplitude of vertical vibration by about (300 %) for all operating frequencies, lengths of piles, pile spacings and number of piles. In addition, the presence of piles reduced the disturbance (fluctuation) in this amplitude by about (400 %). For single pile, and under the same operating frequency, a small decrease in the amplitude of vertical vibration resulted from increasing the length of the pile.