Quality of Conventional Fixed Piston Samples of Norwegian Soft Clay

Abstract

The UCD community has made this article openly available. Please share how this access benefits you. Your story matters! (@ucd_oa) Some rights reserved. For more information, please see the item record link above. ABSTRACT:It is well accepted that the quality of soft clay samples obtained using standard fixed piston samplers can be relatively poor and that block samples are necessary to yield very high quality samples. However for many practical projects it is not economically viable or physically practical to obtain block samples. In this project the quality of standard 54 mm composite piston samples of soft clay is examined by comparing six separate sets of 54 mm samples to parallel block sampling. Sampling and laboratory testing was carried out by three different organisations at a well characterised highly uniform soft clay site in Norway. As expected the work showed that the block samples behaved significantly differently from those obtained using the 54 mm sampler and were of higher quality. Block sample derived parameters were considerably different from those obtained from the 54 mm sample tests. However significant differences were also found between the different sets of 54 mm samples.Although the differences are less than when compared with block samples, the consequences of poor quality 54 mm sampling will be significant in engineering design. It is concluded that the differences are due to small details in the sampling operation such as the need to keep the piston effectively stationary at all times, to avoid overcoring and to handle the recovered sample carefully. If a well trained driller follows good quality practice, then relatively good samples can be obtained by the fixed piston sampler, which are suitable for analysis and design of routine engineering works.

Relationship between electrical resistivity and basic geotechnical parameters for marine clays

“…The displacement method is used; where the sampler is pushed down to the desired depth without pre-augering. Long et al (2009) describe a detailed study into the quality of samples retrieved using this procedure and demonstrate the resulting quality is acceptable for routine and medium sized projects. At a number of sites in the Mid Norway region the version of the sampler which uses a thin walled 54 mm tube only was used.…”

“…(See separate document). Extra refs: Long et al (2009), Bjerrum (1967 , Lunne and Lacasse (1999), Rømoen (2006), Gregersen (1981), Aasland (2010), Ottesen (2009), , Solberg et al (2011), Helle (2004), Multiconsult (2009 …”

Large-strain analysis of undrained smooth tube sampling

“…A piston is considered advantageous in all those phases (Osterberg, 1973): it prevents contamination during descent, helps recovery upon withdrawal, and, if the piston remains stationary during sampling, soil heave into the sampling tube is eliminated. Indeed, field experiments indicate that when a true stationary condition is not achieved sample quality is severely diminished (De Groot et al 2005;Long et al 2009;Lim et al 2018).…”