MODEL STUDIES OF BOUNDARY EFFECT ON DYNAMIC SOIL RESPONSE

An experimental apparatus was developed at The University of British C olumbia, Vancouver, Canada, to investigate model pile dynamic response and soil-pile interaction. The model test apparatus comprised a conta iner of soil in which piles were inserted. The container was then moun ted on a shake table and subjected to simulated earthquake shaking. Hi gh stresses were obtained in the soil model by subjecting it to very h igh downward hydraulic gradients, a technique called hydraulic gradien t similitude (HGS). In this way, stresses simulating field conditions were obtained. This is very important in soil because the behaviour of soil is highly dependent on stress levels. This paper presents the st udy carried out on the effect of the soil container boundary condition s on the response of the soil within the box. The effectiveness and li mitation of placing soft material on the vertical boundaries of the mo del, averting wave reflections, are examined and discussed. This was e xamined directly in the model by placing soft material adjacent to the boundaries. it was also examined analytically using the FLUSH compute r code. Both experimental and analytical results indicate that respons e of the soil within the HGS device without sort material on the side walls (rigid boundaries) is closer to that in the free field condition s, and the HGS apparatus reasonably provides a high stress level that matches the field conditions.