Effects of Driving Displacement Piles in Lean Clay

Investigations were conducted to determine the characteristics of foundation soils for two large pumping plants of the Bureau of Reclamation's Weber Basin Project near Ogden, Utah. Normal investigations showed that saturated lean clays of low strength and high compressibility would be encountered for appreciable depth below plant grades. Because a pile foundation, with embedment in lower firmer layers, was indicated, it was necessary to determine if the upper soils would be remolded during pile driving to the extent that they would consolidate under their weight and add load to the piles. Several special laboratory and field tests were conducted to investigate this possibility. These were one-dimensional consolidation tests on undisturbed and remolded specimens, three-dimensional consolidation tests in which model piles were driven into undisturbed specimens, model pile load tests in undisturbed samples, and vane shear tests adjacent to test piles driven at the site. The tests showed the clay soils to be borderline with respect to sensitivity, but the driving of piles did not cause significant loss of strength or increased compressibility. The behavior of the soils during and after construction confirmed this conclusion.