No abstract

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 (ä 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 ä 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.

No abstract

Surcharge load (e.g. embankment fill) will induce settlement and outward lateral displacement, while vacuum pressure will induce settlement and inward lateral displacement of a ground. Ideally, combination of surcharge load and vacuum pressure can reduce or minimize the lateral displacement. Laboratory large scale model (length: 1.50 m, width:~0.62 m, height: 0.85 m) tests and finite element analyses (FEA) were conducted to investigate the main influencing factors on lateral displacement of a soft clayey ground under the combination of vacuum pressure and surcharge load. For the conditions investigated, the results indicate that the outward lateral displacement increases with the increase of the ratio of surcharge load to vacuum pressure (RL) and the loading rate of the surcharge load (LR). Also, it is shown that for a given RL and LR condition, lateral displacement reduces with the increase of the initial undrained shear strength (S u ) of the ground. To predict the lateral displacement of a ground under the combination of surcharge load and vacuum pressure, the loading conditions in terms of RL and LR, and S u value of the ground have to be considered.