RELATION BETWEEN THE PLASTICITY INDEX AND KEY CONSOLIDATION PARAMETERS OF SOFT GROUND STABILIZED BY VACUUM PRELOADING TOGETHER WITH VERTICAL DRAINS

The soft ground improvement employing vacuum preloading is widely used in Tianjin. In the application of vacuum preloading, the bending of plastic vertical drains (PVDs) often occurs accompanying the large settlement of the soft ground or the significant shear strain at the ground surface. In order to investigate the influence of bending of PVDs on the ground consolidation, three different bending shapes of PVDs are assumed and a series soil-water coupled finite element analyses are carried out. It is found that: 1) the macro-element method is available to take the bending effect of PVDs into consideration; 2) the bending at the bottom of PVDs has much impact on the consolidation of ground even though the hydraulic gradient at the bottom is much smaller than that at the top; 3) Due to the bending of PVDs at the bottom the drainage capacity is much influenced and the volumetric compression only occurs at the first few layers of the ground.

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Numerical Investigation to the Effect of Suction-Induced Seepage on the Settlement in the Underwater Vacuum Preloading with Prefabricated Vertical Drains

Journal of Marine Science and Engineering ◽

10.3390/jmse9080797 ◽

2021 ◽

Vol 9 (8) ◽

pp. 797

Author(s):

Shu Lin ◽

Dengfeng Fu ◽

Zefeng Zhou ◽

Yue Yan ◽

Shuwang Yan

Keyword(s):

Practical Implication ◽

Soil Surface ◽

Small Strain ◽

Seepage Flow ◽

Excess Pore Pressure ◽

Combined Effects ◽

Vacuum Preloading ◽

Prefabricated Vertical Drains ◽

Vertical Drains ◽

The Difference

Vacuum preloading combined with prefabricated vertical drains (PVDs) has the potential to improve the soft sediments under water, however, its development is partly limited by the unclear understanding of the mechanism. This paper aims to extend the comprehension of the influential mechanism of overlapping water in the scenario of underwater vacuum preloading with PVDs. The systematic investigations were conducted by small strain finite element drained analyses, with the separated analysis schemes considering suction-induced consolidation, seepage and their combination. The development of settlement in the improved soil region and the evolution of seepage flow from the overlapping water through the non-improved soil region into improved zone are examined in terms of the build-up of excess pore pressure. Based on the results of numerical analyses, a theoretical approach was set out. It was capable to estimate the time-dependent non-uniform settlement along the improved soil surface in response to the combined effects of suction-induced consolidation and seepage. The difference of underwater and onshore vacuum preloading with PVDs is discussed with some practical implication and suggestion provided.

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Laboratory Model Tests on Dredger Fills by Vacuum Preloading with No Sand Cushion

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.170-173.655 ◽

2012 ◽

Vol 170-173 ◽

pp. 655-660

Author(s):

Ya Jun Wu ◽

Jian Bo Yang

Keyword(s):

Fine Particles ◽

Soil Strength ◽

Plasticity Index ◽

Laboratory Model ◽

Soil Parameters ◽

Grain Composition ◽

Vacuum Preloading ◽

Prefabricated Vertical Drains ◽

Water Contents ◽

Sand Cushion

It is difficult to operate on the hydraulic-filled mucky soil foundation which the water content is high, so the vacuum preloading method with no sand cushion is used to deal with the foundation in some areas in China. Although there are still many problems in it’s application, such as, the effective range of the prefabricated vertical drains(PVDs) is small, the surrounding soil is easy to be accumulated and the soil strength increases little. For these problems, a laboratory model test on dredger fills made from the 4th layer of the Shanghai mucky soil by vacuum preloading with no sand cushion is performed. The changes and distributions in the settlement, water contents, permeability, plasticity index and grain composition of the dredger fill are studied in the process of the vacuum preloading. It is found that the water contents and permeability of the soft clay near the PVD (the diameter is about 40 to 50cm) are much lower than the outside, while the content of fine particles, plasticity index and soil strength near the PVD is much higher than the others. The measured data shows that the fine particles gather to a soil column at the center of the PVD under the action of vacuum negative pressure, then the permeability and the grain composition of the soil around the PVD is changed. As a result, soil parameters are not evenly distributed. Finally, some suggestions about how to reduce the non-uniformity are proposed.

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

Geotextiles and Geomembranes ◽

10.1016/j.geotexmem.2009.08.002 ◽

2010 ◽

Vol 28 (1) ◽

pp. 1-11 ◽

Cited By ~ 60

Author(s):

J. Saowapakpiboon ◽

D.T. Bergado ◽

S. Youwai ◽

J.C. Chai ◽

P. Wanthong ◽

...

Keyword(s):

Vacuum Preloading ◽

Prefabricated Vertical Drains ◽

Vertical Drains

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Vacuum preloading consolidation of reclaimed land: a case study

Canadian Geotechnical Journal ◽

10.1139/t98-039 ◽

1998 ◽

Vol 35 (5) ◽

pp. 740-749 ◽

Cited By ~ 79

Author(s):

J Q Shang ◽

M Tang ◽

Z Miao

Keyword(s):

Land Reclamation ◽

Soil Improvement ◽

Large Area ◽

Vacuum Preloading ◽

Reclaimed Land ◽

Improvement Project ◽

Prefabricated Vertical Drains ◽

Vertical Drains ◽

Soft Clays

This case study presents the design, operation, and results of a soil improvement project using the vacuum preloading method on 480 000 m2 of reclaimed land in Xingang Port, Tianjing, China. The areas treated with vacuum ranged from 5000 to 30 000 m2. The effects of soil improvement are demonstrated through the average consolidation settlement of 2.0 m and increases in undrained shear strengths by a factor of two to four or more. The study shows that the vacuum method is an effective tool for the consolidation of very soft, highly compressive clayey soils over a large area. The technique is especially feasible in cases where there is a lack of surcharge loading fills, extremely low shear strength, soft ground adjacent to critical slopes, and access to a power supply.Key words: vacuum preloading consolidation, soil improvement, soft clays, land reclamation, prefabricated vertical drains.

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