"Centrifuge model tests were made to find out the most effective installation distance of the vertical drains and to examine the influence on heaving damage of the thickness of the impermeable surface layer and the increasing rate of water level. The results revealed that the impermeable layer shows a greater expansion according as the drain distance becomes wider, which leads to higher pressure head in the layer by lowering the influence of drains. The tendency usually observed in the expansion increase of the impermeable layer with the decrease of its thickness was not confirmed in the tests. Also noticed was that the increasing rate of water level has little effects on the heaving process. It was then concluded that the heaving phenomenon is largely dependent on the drain distance and gives a significant influence on the stability of the permeable base foundation overlaid by the impermeable layer."