Soils and Foundations 2015;55(3):600–613 HOSTED BY The Japanese Geotechnical Society Soils and Foundations www.sciencedirect.com journal homepage: www.elsevier.com/locate/sandf Mineralogy and geotechnical properties of Singapore marine clay at Changi Myint Win Boa, Arul Arulrajahb, Patimapon Sukmakc, Suksun Horpibulsukd,n aDST Consulting Engineers Inc., Thunder Bay, Ontario, Canada bSwinburne University of Technology, Melbourne, Australia cSchool of Engineering and Resources, Walailak University, Nakhonsithammarat, Thailand dSchool of Civil Engineering, Suranaree University of Technology, 111 University Avenue, Muang District, Nakhon Ratchasima 30000, Thailand Received 3 June 2014; received in revised form 8 January 2015; accepted 2 February 2015 Available online 8 May 2015 Abstract An engineering geological study was undertaken to determine the geotechnical properties and mineralogy of Singapore marine clay at Changi in the Republic of Singapore. This soft soil is a quartenary deposit that lies within submarine valleys cut in an old alluvium formation. The marine clay comprises a soft upper marine clay layer overlying a stiffer lower marine clay layer. An intermediate stiff clay layer is sandwiched between these two marine clay layers; it is believed to be the dessicated crust of the lower marine clay layer. In the present study, morphological and mineralogical observations of Singapore clay were taken by scanning electron microscopy, X-ray diffraction and photographic identification. The geotechnical investigation included physical, compression, permeability and field vane shear tests. The upper marine clay was found to be soft with undrained shear strength values ranging from 10 to 30 kPa, while the lower marine clay was found to have undrained shear strength values from 30 to 60 kPa. The sensitivity of the marine clay at Changi varied from 3 to 8 and is described as highly sensitive marine clay. The upper clay 2 2 layer had a coefficient of consolidation of 0.47–0.6 m /year due to the vertical flow (cv) and a coefficient of consolidation of 2–3m/year due to 2 2 the horizontal flow (ch). The lower marine clay had a cv of 0.8–1.5 m /year and a ch of 3–5m/year, while the intermediate stiff clay had a cv of 2 2 1–4.5 m /year and a ch of 5–10 m /year. The primary clay mineral was kaolinite, followed by smectite and mica. With this high kaolinite content, the activity of the Singapore marine clay was found to be low at approximately 0.5–1.3 and classified as inactive to active clay. With reference to the intrinsic state line, natural Singapore clay (upper, intermediate and lower layers) has been classified as structured clay and is in a meta-stable state. The compression behaviour can be modelled by the Intrinsic State Line and the destructuring framework. The predicted and the measured compression curves were comparable for various depths. The successful modelling of compression curves will be useful for settlement calculations and for further research on the development of a constitutive model for Singapore marine clay. & 2015 The Japanese Geotechnical Society. Production and hosting by Elsevier B.V. All rights reserved. Keywords: Marine clay; Soft soils; Field vane; Geotechnical; Geology; Hydraulic; Compressibility 1. Introduction Over the last two decades, extensive land reclamation and ground-improvement projects have been undertaken as part of the mega Changi Land Reclamation project. As part of these n Corresponding author. projects in the Republic of Singapore, the geotechnical in-situ E-mail addresses: [email protected] (M.W. Bo), testing (Bo et al., 2000, 2003, 2013; Chu et al., 2002; Arulrajah [email protected] (A. Arulrajah), [email protected] (P. Sukmak), [email protected] (S. Horpibulsuk). et al., 2004b, 2005, 2006a, 2006b, 2007, 2009a, 2011) and the Peer review under responsibility of The Japanese Geotechnical Society. field instrumentation (Arulrajah et al., 2004a, 2009b)ofthese http://dx.doi.org/10.1016/j.sandf.2015.04.011 0038-0806/& 2015 The Japanese Geotechnical Society. Production and hosting by Elsevier B.V. All rights reserved. M.W. Bo et al. / Soils and Foundations 55 (2015) 600–613 601 geotechnical projects have been reported in recent years. Department Singapore, 1976). This formation is underlain by However, there is still a lack of understanding of the engineer- old alluvium. The preliminary site investigation and geophy- ing geology, the mineralogical properties and the compressi- sical survey of the project site revealed that the Singapore bility of this particular marine clay, as these aspects have not marine clay at Changi consists of two marine members locally been previously reported. In various other countries, detailed known as the upper and lower marine clay layers. These soft to geological and geotechnical engineering characterisations of medium stiff clay members are recent deposits of estuarine marine clays have been undertaken, but they are still lacking origin. The upper and lower marine clays are separated by a for Singapore marine clay. layer of medium stiff to stiff clay with a thickness of 2–5m. Karakouzian et al. (2003) reported on shear strength mea- This layer, locally termed as intermediate clay, is reddish in surements taken in Norfolk, USA with the usage of field vane colour and is believed to be the desiccated crust of the lower shear tests. Jung et al. (2012) reported on stress–strain responses marine clay resulting from the exposure of the seabed to the of reconstituted glacial clays in Chicago, USA. Horpibulsuk atmosphere during the rise and fall of the sea levels in the et al. (2007) and Abuel-Naga et al. (2009) reported on the geological past. engineering properties and geological history of soft Bangkok The onset of the Wurm/Wisconsin glacial period, occurring clay, Thailand. The mineralogical, chemical and geotechnical approximately 75,000 years ago, brought about an extremely properties of Bangkok clay were compared with those of Ariake rapid drop in sea level to about 140 m below the present sea clay, a Japanese clay, by Ohtsubo et al. (2000). Kim et al. level approximately 18,000 years ago. There has been a (2012) reported on the engineering properties and geological tremendous transgression of the sea over the land in the last history of soft clays in Songdo, South Korea. Yan and Ma 10,000–20,000 years. With the further uplift of land and the (2010) characterised marine deposits in Macau. Liu et al. (2011) regression of the seas, more erosion and deposition have taken characterised marine clays in Lianyougang. The results of these place. The present marine clay formation in Eastern Singapore geological studies, which included the mineralogical and has been formed by these cycles of aggregation and erosion geotechnical investigation of shear strength, hydraulic conduc- throughout the geological ages (Public Works Department tivity and compression, are vital for research and design. An Singapore, 1976). This conclusion is based on evidence that understanding of the compressive behaviour is essential for desiccation occurred on the intermediate clay layer during the geological and geotechnical engineering purposes and is the recession of the sea level after the ice age. core basis for modelling the stress–strain relationships of soils (e.g., Pestana and Whittle, 1995; Hong and Onitsuka, 1998; Potts and Zdravkovic, 1999; Baudet and Stallebrass, 2001; Chai et al., 2004; Liu et al., 2011, 2013). 3. Site and laboratory investigations Along the same lines, authors' intention in this study is to report on the geological aspects of Singapore marine clay at 3.1. Site investigation Changi inclusive of the geological history, clay mineralogy and geotechnical properties such as physical, compression, Marine bathymetric surveys, together with marine geophy- hydraulic conductivity and shear strength. The research site is sical seismic reflection surveys of the project area, were carried located in the Eastern part of the Republic of Singapore where out with the help of a water surface-towed boomer profiling Singapore marine clay is prevalent. This soft clay is a system. The elevations of the bases of the compressible layers quartenary deposit that lies within submarine valleys cut in and the distribution of soft marine clay pockets deposited in an old alluvium formation and is locally known as the Kallang submarine valley cuts were determined from marine bathy- formation. The study area was submerged underwater with a metric and seismic reflection surveys. seabed elevation varying from À2 mCD to À8 mCD (Admir- The seismic survey vessel was fitted with a trisponder, an alty Chart Datum, where the mean sea level is þ1.6 mCD) and echo sounder and a boomer profiling system. The survey is underlain by marine clay up to 40 m in thickness in certain operation was run at lines with spacing of 50 m in alternate areas. Detailed geotechnical properties and a mineralogical directions. Cross lines were run at a spacing of 50 m in analysis of the Singapore marine clay were undertaken in this alternate directions. For horizontal control of the survey, a study. The in-situ stress state of Singapore marine clay was trisponder positioning system was used to control the location examined and the compression behaviour was analysed. The of the survey vessel along the pre-computed lines. For vertical destructuring framework, which was proposed by Liu and control of the survey, the tidal reduction of the survey area was Carter (1999, 2000) and verified by some soils, was adapted to carried out using tides observed with a tide gauge. Tidal data model the compression curves of natural Singapore marine was obtained from the Hydrographical Department of the Port clay. The predicted and measured compression curves were of Singapore. compared to illustrate the applicability of the framework. The echo sounder enabled the contouring of the seabed elevation profile, while the boomer enabled the plotting of the 2.