Prediction versus performance on the behavior of soft clay ground improved by vertical drains

To assess the adequacy of the technique of vertical drains combined with surcharge precompression for improving the soft clay stratum of more than 30m thick beneath airport runway, a field test was conducted at the Ningfeng plain, southwestern Ningbo city, where Ningbo airport, the first airport on such weak ground in China was to be constructed. In this paper, the performance of the test and the prediction of the consolidation behaviour of the ground by finite element method are described. A nonlinear stress - strain relationship taking account of dilatancy of clay is proposed based on laboratory tests and used in the prediction. Back analyses are also performed for determining some relevant soil parameters. The efficiencies of the ground improvement technique and the prediction by FEM are illustrated and emphasized.