Lateral displacement under combined vacuum pressure and embankment loading

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.

Methods of vacuum consolidation and their deformation analyses

“…For a preloading project using a combination of vacuum pressure and embankment loading there is no well-established method for predicting the lateral displacement profile. Chai et al (2013) proposed a semi-empirical method for predicting the possible range of maximum net lateral displacement (ä nm ), where ä nm is defined as the maximum value of the net outward lateral displacement reduced by the maximum value of the net inward lateral displacement. The predicted range of ä nm corresponding to the end of embankment construction is included in Figure 14 also.…”

“…It is therefore uncertain whether the bending movement of the sheet pile might have affected the observed maximum lateral displacement of the soil in this case. Also there is one layer of very soft peat at the ground surface, and the prediction method may not be suitable for this kind of situation (Chai et al, 2013), and further study of this aspect is needed.…”

Sustainability of Combined Vacuum and Surcharge Preloading

“…However, the maximum value of lateral displacement due to embankment loading usually occurs at depth beneath the crustal layer, whereas under vacuum loading, the maximum inward movement occurs close to the ground surface. Therefore, since the mechanisms of lateral displacement for preloading under surcharge alone and vacuum alone are different, even the optimum combination of the two does not necessarily result in zero lateral displacement being uniformly achieved over the full depth profile (Chai et al, 2013). Nevertheless, for most clays, a combination of 40% surcharge and 60% vacuum generally appears to reduce the overall lateral displacement to a minimum (see Fig.…”

“…A method of computing the lateral displacement arising from a combination of vacuum and embankment loading for a soft clayey deposit has been developed by Chai et al (2013). It gives a direct relationship between the maximum net lateral displacement and the ratio of index pressure, p n (see Eq.…”

The Settlement Models of Deep Vacuum Dewatering Method

“…Vacuum consolidation has been extensively applied [1][2][3][4][5][6] and proved very effective in improving soft ground [7,8]. Vacuum consolidation usually applies a vacuum pressure into soil and a sealing membrane at the surface of the ground.…”