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.