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Long, Michael (Michael M.)
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Long, Michael (Michael M.)
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Long, Michael (Michael M.)
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Now showing 1 - 6 of 6
- PublicationSampling disturbance in soft laminated claySample disturbance effects in the laminated facies at the Bothkennar soft clay research site are examined by comparing the results of laboratory tests on specimens obtained from three fixed piston tube samplers. A significant feature of the results is that the sampling process associated with the conventional piston tube used in the UK and Ireland appears to increase the post yield stiffness and the CAUC triaxial undrained strength, reduce the preconsolidation stress, the pore pressure coefficient at failure and induce a strong tendency for dilatant behaviour post peak when compared to tests on specimens from a sampler with a modified (sharper) cutting edge angle. It is reasoned that these findings are caused by material destructuration during the sampling process with the conventional tubes. Increased densification of these specimens caused both by sampling and during anisotropic consolidation may also contribute to these effects. The results are supported by reference to recent analytical work and data for three other soils. It is recommended that the use of these conventional thin walled tubes with a crude cutting edge is abandoned and that some with improved cutting edge geometry replaces them.
1184Scopus© Citations 12 - PublicationCharacterisation of Norwegian marine clays with combined shear wave velocity and CPTU dataA database of research quality CPTU and shear wave velocity information for Norwegian marine clays has been assembled so as to study the small strain stiffness relationships for these materials and to examine the potential use of CPTU and Vs data in combination for the purposes of characterising these soils. Data for sites where high quality block sampling was carried out have mostly been used. Improvements have been suggested to existing correlations between Gmax or Vs and index properties for these soils. Recent research has shown that CPTU qt and especially u2 and Vs can be measured reliably and repeatably and are not operator or equipment dependant. Therefore a new soil classification chart involving Qt and normalised shear wave velocity (Vs1) or Vs1 and Δu/σv0' is presented. Using this chart it is possible to clearly distinguish between clays of different OCR.
3842Scopus© Citations 62 - PublicationIn situ shear wave velocity from multichannel analysis of surface waves (MASW) tests at eight Norwegian research sitesThe Multichannel Analysis of Surface Waves (MASW) technique, used to determine shear wave velocity (Vs) and hence small strain stiffness (Gmax), has recently generated considerable interest in the geophysics community. This is because of the ease of carrying out the test and analysis of the data. The objective of this work was to assess the repeatability, accuracy and reliability of MASW surface wave measurements for use in engineering studies. Tests were carried out at 8 wellcharacterised Norwegian clay, silt and sand research sites where Vs had already been assessed using independent means. As well as being easy and quick to use MASW gave consistent and repeatable results and for the clay sites the MASW Vs profiles were similar to those obtained from other techniques. Reasonable results were also obtained for the silt and sand sites, with the best result being obtained for the finer silt. This work also confirms that MASW Vs clay profiles are comparable to those obtained by correlation with CPT. For these sites there also seems to be a good correlation between normalised small strain shear modulus and in situ void ratio or water content and the data fit well with published correlations for clays.
4701Scopus© Citations 51 - PublicationGeotechnical properties of Dublin boulder clayGeotechnical characteristics of Dublin Boulder Clay (DBC) based on detailed site investigation and site experience from some recent large projects in Dublin are presented. This paper attempts to synthesise available information in parallel with recent work by Skipper et al (2005), who provide an updated understanding of the geology of the DBC. Having assessed the effects of sampling disturbance, the paper characterises the various formations and sub-units of the DBC. The interpreted material behaviour is related to observed engineering performance. It was found from the behaviour of earth retained structures that intact, clayey, DBC formations are 2 to 3 times stiffer than assessed from high quality laboratory tests on block samples. DBC is shown to be significantly stiffer than other well-characterised tills. Relatively inexpensive Multi Channel Surface Wave techniques (MASW) can give very reliable estimates of in situ small strain stiffness. High undrained triaxial compression strengths were measured and it appears that simple UU tests on high quality specimens give good results. Significant strength anisotropy was suggested by undrained triaxial extension strengths that were only 30% to 50% of the triaxial compression strengths. Field horizontal permeability values of the intact clayey till units have a representative mean of about 10-9 m/s and when compared to laboratory values suggest that the material may exhibit some degree of anisotropy of permeability. Overall, the measured engineering parameters for the DBC are favourable for many construction projects. Further work is required in order to understand the in situ horizontal stress profile and the stiffness anisotropy of the till. KEYWORDS: Glacial soils, In situ testing, laboratory tests, site investigation, strength, stiffness.
10694Scopus© Citations 53 - PublicationQuality of conventional fixed piston samples of Norwegian soft clayIt 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.
2670Scopus© Citations 19 - PublicationA comparative study between the NGI direct simple shear apparatus and the Mikasa direct shear apparatus(Japanese Geotechnical Society, 2007-02)
; ; ; ; A comparative study of the NGI Direct Simple Shear Test (DSST) and the Mikasa Direct Shear Test (DST) is reported. Samples from Norwegian Drammen clay and Japanese Ariake clay were subjected to both types of test. An evaluation of these test results and a theoretical consideration on the different shearing mechanisms has shown that although the DST give generally higher stiffness and strength than the DSST, these differences can mainly be accounted for by the different shearing mechanisms and shearing rates. Sample disturbance due to transportation and handling may also be the reason for some of the difference. Tests on undisturbed and remoulded Drammen clay consolidated to stresses much higher than the in situ effective overburden stress give almost identical results. Thus the effects of sample disturbance and in situ structure in the clay were eradicated.7747Scopus© Citations 23