Dynamic response of pile group model in sandy soil to lateral excitation

Abstract

This study offers an understanding of cyclic response of piled foundations in dry and saturated sand with different relative densities. The results of dry soil reveal the mechanism of dynamic response of piles and soil subjected to dynamic horizontal shaking including the variation and distribution of acceleration, bending moment along the pile, and vertical soil pressure with time in different states of soil; and the vertical and horizontal displacements, end-bearing load, peak acceleration and the peak velocity of foundation with time. 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 (R.D.) 30% (loose) and 50% (medium); 66 tests on group of piles with different spacings and patterns in dry soil at relative density 30% and 50% were conducted, too. All tests were carried out under operating frequencies 0.5, 1 and 2 Hz under horizontal shaking. Twenty tests for single piles and pile group with different patterns and spacings at relative density 30% were performed in saturated sandy soil under frequencies 0.5 and 1 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 main conclusion is that the manufactured vibrating box can simulate accurately the earthquake motion induced on foundations and, especially pile groups. The values of soil pressure decrease with increasing frequency and relative density. The soil pressure shows slight change with increasing frequency, while no clear changes appeared between pile groups with different pile spacings. The pile spacing is an important indicator that affects the acceleration and time-frequency characteristics of the displacement at pile top. With the increasing of S/D, the internal forces are slightly reduced.