Now showing 1 - 10 of 46
  • Publication
    In situ shear wave velocity from multichannel analysis of surface waves (MASW) tests at eight Norwegian research sites
    (NRC Research Press, 2007-05) ;
    The 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.
      4721Scopus© Citations 51
  • Publication
    Characterisation of Norwegian marine clays with combined shear wave velocity and CPTU data
    (NRC Research Press, 2010-07) ;
    A 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.
      3860Scopus© Citations 62
  • Publication
    Thermal response testing of compromised borehole heat exchangers
    (Oxford University Press, 2012-03-19) ;
    The results of five thermal response tests (TRTs) are presented. Three of the tests were carried out consecutively on the same borehole to illustrate the importance of allowing artificially imposed thermal gradients to dissipate prior to commencement or re-commencement of a test following testing issues. The two remaining tests carried out on separate boreholes confirm the results obtained by the first(uncompromised) of the initial three tests. The testing regime demonstrates the necessity of careful performance of TRT’s and shows the variation in costs/required borehole length which may occur if testing problems occur on site.
      617Scopus© Citations 3
  • Publication
    Engineering characterisation of estuarine silts
    (Geological Society of London, 2007-05)
    Guidance is provided for geotechnical engineers designing civil engineering works in silty soils. A detailed characterisation of two estuarine silt sites in Ireland is performed and the soil properties are linked to their geological origin. It was found that these soils are susceptible to densification by conventional and high quality fixed piston tube sampling and care needs to be taken when using laboratory derived design parameters, particularly for consolidation and shear strength properties. One dimensional consolidation and creep of these silts can be modelled successfully by the well known Janbu formulation. Settlement predictions from laboratory derived parameters match reasonably with measured data but tend to underestimate primary consolidation, consistent with a sampling densification effect. Vane data should be used with caution as measured strength values may be high and it seems more reliable parameters can be derived from CPTU tests. Conventional techniques for determining soil strength from triaxial tests in silt are inappropriate due to the dilational nature of the material and more reliable and logical strength estimates can be made from a limiting strain criterion.
      1047Scopus© Citations 10
  • Publication
    Design and development of a low-cost divided bar apparatus
    A divided bar apparatus is deemed to be the most accurate method of measuring the thermal conductivity, λ, (W/mK) of intact rock cores in the laboratory. The divided bar is a steady-state comparative method in which the temperature drop across a disk of rock is compared with that across a disk of standard material of known conductivity. Thermal conductivity test results obtained from rock cores can be used in software programs to determine the design requirements for any medium to large-scale ground-source energy system. This paper describes the design and development of a low-cost divided bar apparatus and compares the values obtained to those achieved by previous researchers and those recommended by EED, a commonly used borehole heat exchanger design software program. The divided bar was designed in accordance with the following principles: keep construction costs low by using readily available materials, develop a simplistic operating procedure to promote continuity of use and cater for the testing of different sized rock cores. As there are currently no recognised testing standards available for operation of a divided bar apparatus, the sample preparation procedure for samples tested on the UCD divided bar apparatus was developed as a proposed standard testing procedure. The proposed procedure amalgamates the developments and suggestions of previous researchers in addition to published test procedures in Ulusay and Hudson (2007), and could possibly contribute towards the development of a standardised procedure for testing on a divided bar apparatus. The test results presented in this paper demonstrate a strong relationship between thermal conductivity and mineral composition with the effects of porosity also having a notable influence on the thermal conductivity of the tested rocks.
      924Scopus© Citations 8
  • Publication
    Engineering characterisation of Norwegian glaciomarine silt
    Guidance is provided for geotechnical engineers designing civil engineering works in silty soils based on a detailed characterisation of a glaciomarine silt from Os in western Norway. It was found that these soils are susceptible to disturbance by good quality fixed piston tube sampling and care needs to be taken when using laboratory derived design parameters, particularly for consolidation and shear strength properties. A technique for assessing sample disturbance using shear wave velocity and suction measurements proved promising. Conventional techniques for determining soil strength from triaxial tests in silt are inappropriate due to the dilational nature of the material and more reliable and logical strength estimates can be made from a limiting strain criterion. Field vane data should be used with caution as measured strength, particularly remoulded values, may be high and it seems more reliable parameters can be derived from CPTU tests. One dimensional consolidation and creep of these silts can be modelled successfully by the well-known Janbu formulation. The behaviour of the Os silts does not fit easily into classical soil mechanics and published frameworks for soft soils. It seems the material is of “transitional” type and this work adds to the database of such soils which includes other natural silts and gap graded soils. For future work it is recommended that larger sample tubes (say 75 mm) with a very sharp cutting edge should be used in parallel with in situ CPTU testing.
      1732Scopus© Citations 20
  • Publication
    Interpretation of In Situ and Laboratory Thermal Measurements Resulting in Accurate Thermogeological Characterisation
    (Taylor & Francis, 2012-09) ;
    Growing worldwide interest in the exploitation of geothermal energy resources has led to a scenario where the technology routinely forms part of building-scale renewable energy feasibility studies. A thorough understanding of site-specific thermogeological parameters is a vital design requirement of such systems and accurate measurement and interpretation of these parameters is necessary in order to inform scientifically rigorous system design. An overview of the theory underlying a number of laboratory and in situ thermal characterization testing methods and the results from a number of testing regimes carried out using the various thermal characterization equipment constructed in University College Dublin are presented. Results from both the laboratory steady-state and non-steady-state thermal analysis systems and the in situ thermal characterization system are shown to provide accurate measurements of soil and rock thermal parameters. In addition, the settlement profiles of a number of the tested materials were investigated in order to gain an in-sight into this potential drawback of exchanging the backfill material placed around electricity cables to optimize thermal transfer efficiency.
      600
  • Publication
    Quality of conventional fixed piston samples of Norwegian soft clay
    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.
      2673Scopus© Citations 19
  • Publication
    Geothermal energy : settlement and water chemistry in Cork, Ireland
    (Institution of Engineers, 2011-07) ;
    Detailed analysis of potential water chemistry and settlement issues associated with the installation of open-loop geothermal systems is infrequently carried out. This has led to the failure of several previously installed systems. Chemical analysis of water extracted from beneath the Cork docklands, Ireland has been performed by the authors in order to assess the suitability of the area for the exploitation of open-loop geothermal energy. The possibility of settlement induced by pumping of groundwater for open-loop systems has also been examined. Current market penetration of ground source heat pumps in Ireland is discussed to illustrate the infancy of the technology in Ireland relative to other European countries and to highlight the necessity of approaching the possible installation of such systems with the care required. Water extracted from beneath the docklands shows that significant water chemistry issues exist. Laboratory and field tests confirm that optimal concentration levels of several water chemistry characteristics are significantly exceeded; leading to the conclusion that open-loop exploitation in the area may not be suitable. In addition, settlement induced by pumping of water could potentially lead to a consolidation settlement in excess of 30 mm due primarily to the existence of highly compressible alluvium.
      1484Scopus© Citations 6
  • Publication
    Difficulties with ground anchorages in hard rock in Dublin, Ireland
    (Springer-Verlag, 2003) ;
    Engineers in Dublin favour founding structures on the hard interbedded limestone, which underlies the city. Despite the apparent good ground conditions, problems have been experienced on several sites. A detailed description is given of the problems encountered during ground anchorage installation at the Jervis St. shopping centre site. In all, 72% of the 443 anchorages encountered some difficulty. The pattern of zones within this site, where the difficulties were encountered, and the location of all 5 sites whereproblemshave been recorded correlates well with the known bedrock conditions in Dublin. The case histories detailed here show that the process of construction (particularly drilling technique) and the effects of groundwater need to be carefully considered when designing underground works in hard interbedded limestone. Design and construction issues cannot be separated and this calls for more collaboration between designers and contractors.
      533Scopus© Citations 3