During the past decade, the application of vacuum pressure for stabilising soft coastal clay and other low-lying estuarine soils has become increasingly popular in Australia, mainly due to the proven costeffectiveness in view of the significantly reduced time for achieving a high degree of consolidation and enhanced shear strength. Due to an increase in trade activities at the Port of Brisbane, new facilities on Fisherman Islands at the mouth of the Brisbane River will be constructed on the new outer area (235ha) adjacent to the existing port facilities via land reclamation. A scheme of vacuum assisted surcharge load in conjunction with conventional surcharge and prefabricated vertical drains was selected to reduce the required consolidation time through the deeper subsoil layers. The design of the combined vacuum and surcharge fill system and the construction of the embankment are described in this paper. A comparison of the performance of the vacuum combined surcharge loading system with a standard surcharge fill highlights the clear benefits of vacuum pressure application. A comprehensive array of field data is presented to demonstrate how the embankment had performed during construction. A new analytical solution for radial consolidation considering both time-dependent surcharge loading and vacuum pressure is proposed to predict the settlements and associated excess pore pressures of the soft Holocene clay deposits in the Port of Brisbane, for future design of port infrastructure under increasing live loads over the next two decades.

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Performance and Prediction of Vacuum Combined Surcharge Consolidation at Port of Brisbane

A method is proposed for determining the optimum penetration depth of prefabricated vertical drains (PVDs) in cases where vacuum consolidation is combined with the use of PVDs in a clayey deposit with two-way drainage. The advantages of combining vacuum pressure with embankment loading are discussed in terms of reducing preloading-induced lateral displacement of the subsoil, increasing the effective surcharge loading, and reducing con- struction time in the case of road construction. A vacuum consolidation project conducted in Saga, Japan, is described, and the results from a fully instrumented test section are presented and analyzed using a two-dimensional finite ele- ment approach. The numerical simulations compare well with the field measurements. The validated numerical ap- proach is then used to examine the response of soft subsoil subjected to vacuum consolidation. The results confirm the usefulness of the proposed method for determining the optimum penetration depth of PVDs and the advantages of combining vacuum pressure with embankment loading.

http://toshi1.civil.saga-u.ac.jp/chai/PDF-New-J/J46.pdf

Vacuum consolidation and its combination with embankment loading

This paper presented a new approach for ground improvement of deep marine clay in which the conventional booster tube in the current air booster vacuum preloading technology was replaced by a boost...

/pdf/a-new-approach-of-vacuum-preloading-with-booster-pvds-to-3gp3uy74c0.pdf

A new approach of vacuum preloading with booster PVDs to improve deep marine clay strata

http://www.repository.rmutt.ac.th/xmlui/bitstream/123456789/403/1/Measured%20and%20predicted%20performance%20of%20prefabricated%20vertical%20drains.pdf

Measured and predicted performance of prefabricated vertical drains (PVDs) with and without vacuum preloading

This paper presents a three-dimensional (3D) and two-dimensional (2D) numerical analysis of a case study of a combined vacuum and surcharge preloading project for a storage yard at Tianjin Port, China. At this site, a vacuum pressure of 80 kPa and a fill surcharge of 50 kPa were applied on top of the 20-m-thick soft soil layer through prefabricated vertical drains (PVD) to achieve the desired settlements and to avoid embankment instability. In 3D analysis, the actual shape of PVDs and their installation pattern with the in situ soil parameters were simulated. In contrast, the validity of 2D plane strain analysis using equivalent permeability and transformed unit cell geometry was examined. In both cases, the vacuum pressure along the drain length was assumed to be constant as substantiated by the field observations. The finite-element code, ABAQUS, using the modified Cam-clay model was used in the numerical analysis. The predictions of settlement, pore-water pressure, and lateral displacement were compare...

/pdf/2d-and-3d-numerical-modeling-of-combined-surcharge-and-59bk3q7p27.pdf

2D and 3D Numerical Modeling of Combined Surcharge and Vacuum Preloading with Vertical Drains

The deformation characteristics of soil subjected to vacuum pressure are discussed and an approximate method is proposed for calculating settlement and lateral displacement of the ground induced by vacuum consolidation. Laboratory oedometer test results indicate that if the vacuum pressure alone is larger than the lateral stress required to maintain an at-rest (no horizontal strain) condition, there will be inward lateral displacement and the vacuum pressure will induce generally less settlement than a surcharge load of the same magnitude. In the case of field vacuum consolidation, the confining stress acting on a soil element can be regarded as consisting of two parts: Due to vacuum pressure and earth pressure. Assuming a value of the lateral earth pressure coefficient acting in the ground under vacuum consolidation ( kao ) , somewhere between the active and at-rest values, an equation defining the depth—below which there will be no significant inward lateral displacement—is derived. Further, assuming th...

S. Hayashi

Papers

Ground Deformation Induced by Vacuum Consolidation