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Chai J.C.,Saga University | Shen S.L.,Shanghai JiaoTong University | Long P.V.,Vina Mekong Engineering Consultants JS Company VMEC | Chung S.G.,Dong - A University
GA 2012 - 5th Asian Regional Conference on Geosynthetics: Geosynthetics for Sustainable Adaptation to Climate Change | Year: 2012

Using geosynthetics in soft ground improvement is one of the main applications of geosynthetics. Firstly the recent developments on the methods for determining design parameters, and the methods for consolidation and deformation analyses in soft ground improvement using geosynthetics, especially prefabricated vertical drains (PVDs), are discussed. The current states of using electro-PVD(EPVD) and thermo-PVD(TPVD) in soft ground improvement are also reviewed. There are six (6) papers submitted to this session. The issues addressed by the papers are hybrid techniques for soft ground improvement; using suction induced by siphon to consolidate the soft clayey ground; deformation characteristics of PVD during consolidation process; a case history of an embankment on PVD improved subsoil and a case study of stabilizing a landslide using horizontal geosynthetic drains.

Long P.V.,Vina Mekong Engineering Consultants JS Company VMEC | Bergado D.T.,Asian Institute of Technology | Nguyen L.V.,Vina Mekong Engineering Consultants JS Company VMEC | Balasubramaniam A.S.,Griffith University
Geotechnical Engineering | Year: 2013

This paper presents the soft ground improvement using Prefabricated Vertical Drains (PVD) including PVD installation and preloading techniques, settlement and stability design calculations, observational methods and back analyses of monitoring data and performance of conventional preloading with surcharge fill and preloading using vacuum consolidation method (VCM) in combination with fill embankment. Several case histories were studied. The monitored data illustrated that the effectiveness of VCM is dependent on the method of applying vacuum pressure to the PVDs. Measured pore pressure in the PVDs at different depths indicated that the effective vacuum pressure inside the PVDs is distributed uniformly along the PVD depth with a magnitude of over 80 kPa for VCM using airtight membrane. Back-calculated ch values from measured settlement data using Asaoka method confirmed that with the assumed values of ds/dm = 2 and kh/ks = 2, the corresponding value of ch/cv,oed = 3 to 5 were obtained for both soft Bangkok (BKK) clay and soft clays in Mekong River Delta (MRD). Also, the linear relationship between compression index and water content for soft clays in MRD is similar to that of BKK clay. The settlements versus time calculated by 1-D method are in very good comparison with measured data for both conventional preloading and VCM considering the vacuum pressure as an induced vertical stress distributed uniformly in the PVD zone. From the results presented in this paper, simple procedures can be made for selection of soil parameters and design calculations of embankments on PVD improved soft ground using conventional preloading and vacuum consolidation.

Long P.V.,Vina Mekong Engineering Consultants JS Company VMEC | Nguyen L.V.,Vina Mekong Engineering Consultants JS Company VMEC | Bergado D.T.,Asian Institute of Technology | Balasubramaniam A.S.,Griffith University
Geotextiles and Geomembranes | Year: 2015

In order to investigate the performance behavior of soft ground improvement using different vacuum consolidation methods (VCM) and different PVD thicknesses, four trial sections namely C1, C2, D1, and D2 were constructed. VCM without airtight membrane using cap drains and direct tubing system (VCM-DT) were used for the first two sections with PVD thickness of 3 mm and 7 mm for C1 and C2, respectively. VCM with airtight membrane and band drains (VCM-MB) were applied for the last two sections for D1 and D2with PVD thickness of 3 mm and 7 mm, respectively. The soil conditions, construction procedures, instrumentation program, and monitored results of the above trial sections are presented in this paper. The results confirmed that the effective vacuum pressure in PVD mainly depends on vacuum consolidation methods and the assumption of uniform distribution of vacuum pressures along the PVD depth which can be suggested for practical design. For VCM-MB using PVD thickness of 3 mm arranged in triangular pattern of 0.9 m spacing, the degree of consolidation of more than 90% can be achieved in less than 8 months of vacuum pumping. However, for VCM-DT, further investigation is needed for preventing air leakage in vacuum system particularly for the case of thick soft clay deposits with large deformations during the preloading. © 2015 Elsevier Ltd.

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