Lateral displacement under combined vacuum pressure and embankment loading

Based on examination of existing field results, an empirical equation has been suggested for estimating the likely range of the maximum value of the net lateral displacement (δ_nm) of ground improved by the installation of prefabricated vertical drains (PVDs) and subjected to the combined effects of vacuum pressure and embankment loading. The effects on lateral displacement of the magnitudes of embankment loading, as well as the vacuum pressure, the loading rate, and the undrained shear strength and consolidation properties of the soil deposit, have been explicitly included in a newly defined parameter, which is given by the ratio of an index pressure to the representative soil shear strength (RLS). The ratio of δ_nm to the surface settlement under the embankment centreline, S_f, is also defined as the normalised maximum (net) lateral displacement (NLD). A direct relationship between RLS and NLD has been proposed, with a prescribed range, based on the results of 18 field case histories from 12 different project sites in five countries. It is suggested that the proposed relationship can be used as a preliminary design tool for preloading projects involving combinations of a vacuum pressure and an embankment pressure as well as PVD improvement.