Controlled Water Tests to Preload Tank Foundations

Long-term water testing of oil storage tanks can result in significant savings in foundation costs at sites underlain by soft soils. Settlements of a few inches to two feet were observed at four tanks sites of widely varying soil conditions during water tests of one month to one year. Reasonably good agreement was obtained between observed settlements and the calculated elastic plus consolidation settlements when appropriate time-rates of consolidation were used. Field time rates were generally faster than that obtained using average laboratory values of the coefficient of consolidation. Some plastic flow of the soft clays was believed to have occurred at one site at water loads that imposed foundation pressures approximately one-half the bearing capacity of the clay. Piezometers and inlinometers were installed in the soft soils at another site to permit safe loading of the tanks at the maximum rate. The differential settlements that developed during the water tests at two sites due to nonuniform soil conditions required relevelling of some tanks. The cost of such relevelling was only a small fraction of the cost of pile foundations.