Vacuum and surcharge combined one-dimensional consolidation of clay soils

Abstract

In this study, a vacuum and surcharge combined one-dimensional consolidation model is developed. Terzaghi's consolidation theory is revisited by applying the initial and boundary conditions corresponding to combined vacuum and surcharge loading on a soil. A test apparatus is designed, manufactured, and assembled to verify the model. The apparatus has the capacity of applying designated vacuum and surcharge pressures to a soil specimen, and it allows for the measurement of the excess pore-water pressure, settlement, and volume change during the consolidation process. Two series of tests are performed using the apparatus on two reconstituted natural clay soils, namely, the Welland sediment at water contents close to its liquid limit and the Orleans clay, reconstituted and consolidated under an effective stress of 60 kPa. The former test series mimics the strengthening of a very soft soil, such as the hydraulic fill used in land reclamation. The latter test series is designed to study vacuum–surcharge combined strengthening of a consolidated soil. It is demonstrated from the experiments that the one-dimensional vacuum-surcharge consolidation model describes the consolidation behaviour of both soils well. The consolidation characteristics of the soils show no discrimination against the nature of the consolidation pressure, namely, whether they are consolidated under the vacuum pressure alone, under the surcharge pressure alone, or under a pressure generated by the combined application of vacuum and surcharge. The study concluded that the soil consolidation characteristics obtained from the conventional consolidation tests can be used in the design of vacuum preloading systems, provided that the one-dimensional loading condition prevails.Key words: consolidation, soil improvement, vacuum pressure, surcharge pressure, excess pore-water pressure, soil consolidation parameters.

Analytical and numerical solutions for a single vertical drain including the effects of vacuum preloading

“…Gabr and Szabo 1997). Mohamedelhassan and Shang (2002) discussed the application of vacuum pressure and its benefits, but without any vertical drains. The simulation of vacuum pressure for the vertical drain system in analytical or numerical models requires further refinement to obtain better predictions in the field.…”

Analytical solutions and design curves for vacuum-assisted consolidation with both vertical and horizontal drainage

“…Hansbo (1981) and Onoue (1988) extended these solutions to take the smear effect into account. In terms of vacuum preloading, a rigorous solution for vertical consolidation was proposed by Mohamedelhassan and Shang (2002), whereas a solution for radial consolidation was introduced by Indraratna et al (2005). However, to the authors' knowledge, no comprehensive solution to vacuum-assisted consolidation with both vertical and horizontal drainage including the smear effect and well resistance is available in the literature.…”

Model Test Study on Dredge Slurry Vacuum Preloading

“…(3) Improve the dredge materials with the so called vacuum preloading technique [1][2][3][4][5][6][7][8]. The details and mechanism of vacuum preloading have been discussed by many authors [9][10][11][12][13][14] With the extension of reclamation work, the elevation of the initial ground surface becomes lower and lower, which makes the thickness of the filled dredge material become larger and larger. The water content of the dredge is usually more than 80% before vacuum preloading.…”