Numerical modelling of soft soil stabilized by vertical drains, combining surcharge and vacuum preloading for a storage yard

This paper presents a finite element analysis of a case study of a combined vacuum and surcharge load through prefabricated vertical drains (PVD) at a storage yard at Port of Tianjin, China. The top 15 m of soil at this site was very soft to soft and needed to be improved using preloading surcharges of more than 140 kPa. To avoid any stability problems associated with a high surcharge embankment, 80 kPa vacuum pressure combined with fill surcharge was applied (40 and 58 kPa for sections I and II, respectively). A plane strain analysis was performed using equivalent permeability and transformed unit-cell geometry. The converted (equivalent) parameters were incorporated in the finite element code ABAQUS, using the modified Cam-Clay theory. The performance of a trial embankment at the site of the storage yard is predicted on the basis of a constant vacuum pressure applied on the soil surface and distributed along the length of the drain. The predictions of settlement, pore-water pressure, and lateral displacement were compared with the available field data, and an acceptable agreement was found based on this numerical approach. The combination of vacuum and surcharge load can effectively shorten the preloading period, reduce the height of the embankment, and counterbalance excessive lateral displacements.Key words: consolidation, finite element analysis, plane strain method, soil improvement, vertical drains.

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Finite-element analysis of deep excavation in layered sandy and clayey soil deposits

Canadian Geotechnical Journal ◽

10.1139/t94-026 ◽

1994 ◽

Vol 31 (2) ◽

pp. 204-214 ◽

Cited By ~ 45

Author(s):

Chang-Yu Ou ◽

Ching-Her Lai

Keyword(s):

Finite Element Analysis ◽

Finite Element ◽

Clayey Soil ◽

Pore Water Pressure ◽

Water Pressure ◽

Deep Excavation ◽

Element Analysis ◽

Modified Cam Clay ◽

Soil Deposits ◽

Cam Clay

This paper presents an application of finite-element analysis to deep excavation in layered sandy and clayey soil deposits using a combination of the hyperbolic and the Modified Cam-clay models. In the analysis, the drained behavior of cohesionless soil and the undrained behavior of cohesive soil were simulated using the hyperbolic and Modified Cam-clay models, respectively. A rational procedure for determining soil parameters for each of the models was established. A simulation of the dewatering process during excavation was proposed. The analytical procedure was confirmed through an analysis of three actual excavation cases. Finally, analyses considering pore-water pressure dissipation during the actual elapsed time for each construction phase were carried out. The results indicate that the calculated displacement of a retaining wall during excavation is smaller than that given by undrained analysis. It was thought that some degree of pore-water pressure dissipation actually occurs during the intermediate excavation stages. This results in a decrease in the final deformation of the wall and ground.-surface settlement than would be predicted by undrained analysis. Key words : finite-element analysis, deep excavation, hyperbolic model, Cam-clay model.

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

Canadian Geotechnical Journal ◽

10.1139/t05-029 ◽

2005 ◽

Vol 42 (4) ◽

pp. 994-1014 ◽

Cited By ~ 89

Author(s):

Buddhima Indraratna ◽

Cholachat Rujikiatkamjorn ◽

Iyathurai Sathananthan

Keyword(s):

Finite Element ◽

Plane Strain ◽

Numerical Solutions ◽

Soft Clay ◽

Vacuum Pressure ◽

Excess Pore Pressure ◽

Soil Consolidation ◽

Vacuum Preloading ◽

Element Analysis ◽

Vertical Drains

A system of vertical drains combined with vacuum preloading is an effective method to accelerate soil consolidation by promoting radial flow. This study presents the analytical modeling of vertical drains incorporating vacuum preloading in both axisymmetric and plane strain conditions. The effectiveness of the applied vacuum pressure along the drain length is considered. The exact solutions applied on the basis of the unit cell theory are supported by finite element analysis using ABAQUS software. Subsequently, the details of an appropriate matching procedure by transforming permeability and vacuum pressure between axisymmetric and equivalent plane strain conditions are described through analytical and numerical schemes. The effects of the magnitude and distribution of vacuum pressure on soft clay consolidation are examined through average excess pore pressure, consolidation settlement, and time analyses. Lastly, the practical implications of this study are discussed.Key words: consolidation, finite element method, soft clay, vacuum preloading, vertical drains.

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