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Bo M.W.,DST Consulting Engineers Inc. | Arulrajah A.,Swinburne University of Technology | Sukmak P.,Walailak University | Horpibulsuk S.,Suranaree University of Technology | Leong M.,Geofrontiers Group Pty Ltd.
Marine Georesources and Geotechnology | Year: 2016

An engineering geological study was undertaken to determine the engineering properties, and mineralogy of ultrasoft soils (USS) obtained from a nearshore mine tailings sedimentation pond. The USS is a high plasticity clay of high water content and low shear strength. Marine bathymetric and seismic reflection surveys were undertaken in the sedimentation pond located in the foreshore of the Eastern part of the Republic of Singapore. Specimens collected from the bore holes were tested to determine the engineering and mineralogy properties of the USS. Field vane shear tests were undertaken just adjacent to the sampling bore holes to determine the shear strength properties of the USS. The mineralogical properties of the USS were determined using X-ray diffraction and scanning electron microscope techniques. The USS is under consolidated soil where higher density and lower water content were found at deeper depth. The USS had three different compression indices under three log cycles of effective stress between 1–10, 10–100, and 100–1,000 kPa. This is the main characteristic of USS, which diverts from reconstituted soil. The outcome of this research is fundamental for understanding the compression behavior and subsequently the development of a constitutive model for USS, typical found in sedimentary pond. 2016 Copyright © Taylor & Francis Group, LLC

Bo M.W.,DST Consulting Engineers Inc. | Arulrajah A.,Swinburne University of Technology | Leong M.,Geofrontiers Group Pty Ltd. | Horpibulsuk S.,Swinburne University of Technology | Disfani M.M.,Swinburne University of Technology
Engineering Geology | Year: 2014

In-situ tests were undertaken with a BAT permeameter as part of a hydrogeological study to determine the horizontal hydraulic conductivity of Singapore marine clay at Changi. BAT permeameter tests were undertaken in marine conditions prior to land reclamation at a Test Site. An additional series of tests were undertaken after land reclamation and subsequent ground improvement works with prefabricated vertical drains after 23. months of surcharge loading. The BAT permeameter results were compared to laboratory test results carried out using a Rowe consolidation cell as well as hydraulic conductivity tests interpreted from other in-situ dissipation tests including Piezocone Penetration Test (CPTU), Dilatometer Test (DMT) and Self-Boring Pressuremeter Test (SBPMT). The BAT permeameter was found to be suitable for horizontal hydraulic conductivity measurements. The BAT permeameter has the advantage that it measures horizontal hydraulic conductivity directly whereas other in-situ test methods require the introduction of additional parameters to evaluate the hydraulic conductivity indirectly. The horizontal hydraulic conductivity measured using the BAT permeameter was however lower than that expected which is attributed to smear effect. The horizontal hydraulic conductivity was found to decrease in the vertical drain treated area as compared to the prior to reclamation results which is attributed to the significant void ratio reduction at the vertical drain treated area. © 2013 Elsevier B.V.

Arulrajah A.,Swinburne University of Technology | Bo M.W.,DST Consulting Engineers Inc. | Leong M.,Geofrontiers Group Pty Ltd. | Disfani M.M.,Swinburne University of Technology
Engineering Geology | Year: 2013

Piezometers are commonly used for monitoring the dissipation of pore water pressure and therefore the determination of degree of consolidation of soft soils after ground improvement in land reclamation projects. This paper compares the degree of consolidation obtained using pore pressure monitoring data from vibrating wire piezometers and pneumatic piezometers installed in a test site in the Changi East Reclamation project in Singapore. The test site consisted of a vertical drain sub-area at which prefabricated vertical drains were installed at 2.0. m. ×. 2.0. m square spacing as well as an adjacent control sub-area where no prefabricated vertical drains were installed. Pneumatic piezometers were installed at the same elevations as the vibrating-wire piezometers in both sub-areas for comparison purposes. During the surcharge period of 32. months, the piezometer monitoring data were analysed at various periods to determine the degree of consolidation of the underlying soft marine clay. The degree of consolidation values interpreted from both types of piezometers were compared with predictions from neighbouring settlement plates to evaluate their performance. The findings of the comparison between pneumatic and electric vibrating-wire piezometers indicate that both types of piezometer are suitable for monitoring the consolidation behaviour of soft soil under land reclamation fills. © 2013 Elsevier B.V.

Bo M.W.,DST Consulting Engineers Inc. | Arulrajah A.,Swinburne University of Technology | Horpibulsuk S.,Swinburne University of Technology | Horpibulsuk S.,Suranaree University of Technology | Leong M.,Geofrontiers Group Pty Ltd.
Soils and Foundations | Year: 2015

The quality management of Prefabricated Vertical Drain (PVD) material installation in ground improvement works in land reclamation projects is a critical task for designers, contractors and clients alike. Only if a good quality management system is established, can the expected performance of the PVD improvement works in the field be ensured. A case study of quality management of PVD materials in the mega Changi East land reclamation Project in the Republic of Singapore is presented in this technical report. The quality management of PVD works consisted of several processes, starting from selection of the type of PVD, properties of the PVD materials and ultimate performance verification in the field. This paper describes selection of PVDs against the comprehensive specification adopted in this project. The paper also describes the selection of the PVD installation rig and accessories based on the in-situ ground conditions. Test results from quality control test laboratories such as tension, permeability and discharge capacity are also presented and discussed. This paper seeks to set a benchmark for material quality management of PVD works in large-scale PVD ground improvement projects. © 2015 Japanese Geotechnical Society.

Bo M.W.,Sarafinchin Associate Ltd. | Arulrajah A.,Swinburne University of Technology | Horpibulsuk S.,Swinburne University of Technology | Horpibulsuk S.,Suranaree University of Technology | And 2 more authors.
Soils and Foundations | Year: 2016

The discharge capacity is a critical parameter controlling the performance of Prefabricated Vertical Drains (PVDs). The laboratory measurement of the discharge capacity is of the upmost importance when it comes to assessing the performance of proposed PVDs prior to their usage in the field, and hence, the significance of this paper. However, the laboratory measurement of the discharge capacity required to obtain the optimal performance of PVDs by laboratory testing methods is still uncertain. This is because there are various apparatus for discharge capacity testing currently in use by various commercial and research organizations, all of which provide widely varying values of discharge capacity for the same type of PVD under the same hydraulic conditions. The measured discharge capacity of PVDs in the laboratory, with and without surrounding soils, is affected by factors such as the dimensions of the apparatus, the test duration, the hydraulic gradient, the type of surrounding materials, the applied confining pressure and the deformation configuration of the vertical drains. The effects of these factors are investigated, reviewed and discussed in this paper. The relevant equations for obtaining the required discharge capacity of PVDs by laboratory methods are also presented and discussed in this paper. The test results indicate that a small tester results in the underestimation of the discharge capacity particularly for PVDs with a high discharge capacity. A reduction in PVD thickness, the clogging of the filter, the deformation of the PVDs, due to an increase in the duration of the tests (creep), and vertical pressure all cause a reduction in the discharge capacity for a particular hydraulic gradient. Softer surrounding soils and lower PVD stiffness cause a large deformation of the soils surrounding the PVDs. For a particular PVD, the creep effect on the decrease in discharge capacity is significant with a short duration, but becomes insignificant after a long duration. The deformation of PVDs under folded conditions is found to be the most critical factor in the resulting decrease in discharge capacity. © 2016 Japanese Geotechnical Society.

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