Now showing 1 - 10 of 22
  • Publication
    Rapid, cost effective and accurate determination of in situ stiffness using MASW at Bothkennar
    The measurement of the small strain shear modulus, Gmax of a soil is important for a range of geotechnical design applications. This usually involves strains of 10-3 % and less. According to elastic theory Gmax can be calculated from the shear wave velocity. Recently several researchers e.g. Donohue et al. (2003, 2004), Long and Donohue (2007) and Park et al. (1999) have shown that Vs (and hence Gmax) can be obtained cheaply and reliably using the Multichannel Analysis of Surface Waves (MASW) method. An opportunity arose to test and further assesses the technique at the UK National soft clay research site at Bothkennar. The purpose of this note is to summarise the data recorded and to compare the resulting Vs measurements to other parallel data.
  • Publication
    Examination of a novel wavelet based approach for bender element testing
    Accurate determination of shear wave arrival time using bender elements may be severely affected by a combination of near field effects and reflected waves. In most cases, the nearfield effect masks the first arrival and it makes its detection difficult in the time domain. Nevertheless the arrival of a shear wave creates a detectable singular point. This paper tests a recent approach for the assessment of shear wave arrival time by analysing the output signal in the time-scale domain using a multi-scale wavelet transform. Indeed, one can follow the local maxima lines of the wavelet transform modulus across scales, to detect the location of all singularities leading to detection of the first arrival.
  • Publication
    Assessment of ultrasonic signals to determine the early age properties of concretes incorporating secondary cementitious materials
    Secondary cementitious materials (SCMs) such as ground granulated blast-furnace slag (GGBS) are used in increasing quantities in concrete practice internationally. While these materials offer benefits such as reduced CO2 and a more dense microstructure, they also have drawbacks in terms of slower initial gain of strength. There are significant financial implications associated with this, as it can lead to delays in the construction process. Key to overcoming this challenge is the development of a methodology to assess the early-age stiffness development in concretes manufactured using GGBS. This paper presents the results of a study into the application of ultrasonic sensors to assess the early age concrete stiffness. A novel wavelet-based approach is used to overcome the difficulties associated with wave reflections and classical wave theory is used to determine the concrete small-strain stiffness based on P and S wave velocities. It was found that the results are largely in agreement with those obtained using standard strength testing, suggesting potential practical applications of this method.
  • Publication
    4-Dimensional Electrical Resistivity Tomography for continuous, near-real time monitoring of a landslide affecting transport infrastructure in British Columbia, Canada
    (European Association of Geoscientists and Engineers, 2020-08) ; ; ; ;
    The Ripley Landslide is a small (0.04 km2), slow-moving landslide in the Thompson River Valley, British Columbia, that is threatening the serviceability of two national railway lines. Slope failures in this area are having negative impacts on railway infrastructure, terrestrial and aquatic ecosystems, public safety, communities, local heritage, and the economy. This is driving the need for monitoring at the site, and in recent years there has been a shift from traditional geotechnical surveys and visual inspections for monitoring infrastructure assets toward less invasive, lower cost,and less time-intensive methods, including geophysics. We describe the application of anovelelectrical resistivity tomography (ERT) system for monitoring the landslide. The system provides near-real time geoelectrical imaging, with results delivered remotely via a modem, avoiding the need for costly repeat field visits, and enabling near-real time interpretation of the 4D ERT data. Here, we present the results of the ERT monitoring alongsidefield sensor-derived relationships between suction, resistivity,moisture content, and continuous monitoring single-frequency GNSS stations. 4-D ERT data allows us to monitor spatial and temporal changes inresistivity, and by extension, in moisture content and soil suction. The models reveal complex hydrogeological pathways, as well as considerable seasonalvariation in the response of the subsurface to changing weather conditions, which cannot be predicted through interrogation of weather and sensor data alone, providing new insight into the subsurface processes active at the site of the Ripley Landslide.
      161Scopus© Citations 25
  • Publication
    Assessment of Skempton's pore water pressure parameters B and A using a high-capacity tensiometer
    Saturation of soils is a prerequisite in many laboratory tests involving consolidation, permeability and stress-strain behaviour. The saturation process is usually time consuming, particularly in clay-rich soils, and this can incur substantial cost and potential delays in reporting findings. The saturation of samples is assessed using the well-established Skempton's pore water pressure parameter B. In a situation where the soil is fully saturated the B-value is approximately one. It is often the case that fine soil samples extracted from the ground, particularly those from below the water table, remain saturated. However, current testing protocols require evidence to verify a complete saturation prior to subsequent laboratory investigations. This paper reports experimental results exploring the hypothesis that, if the sample is ‘perceived’ to be saturated, then further saturation procedures may not be necessary to obtain reliable geotechnical parameters. Laboratory investigations were conducted on three different clays (Kaolin Clay, Belfast Clay and Oxford Clay) in a testing chamber instrumented with a high capacity tensiometer. The confining pressures were applied in a ramped fashion under undrained conditions. The response of the tensiometer confirmed that the samples were saturated from the very beginning of the loading process, as implied by the B-value being close to one. Further supplementary investigations were carried out to assess the Skempton's pore water pressure parameter A and the stress-strain behaviour of the soils. The combined finding provides further evidence to suggest that the saturation process as suggested in standards may not be necessary for fine grained soils to establish reliable geotechnical design parameters.
      167Scopus© Citations 2
  • Publication
    Hydrogeological and geophysical properties of the very-slow-moving Ripley Landslide, Thompson River valley, British Columbia
    (Canadian Science Publishing, 2020-08-20) ; ; ; ;
    Landslides along a 10 km reach of Thompson River south of Ashcroft, British Columbia, have repeatedly damaged vital railway infrastructure, while also placing public safety, the environment, natural resources, and cultural heritage features at risk. Government agencies, universities, and the railway industry are focusing research efforts on a representative test site — the very-slow-moving Ripley Landslide — to manage better the geohazard risk in this corridor. We characterize the landslide’s form and function through hydrogeological and geophysical mapping. Field mapping and exploratory drilling distinguish 10 hydrogeological units in surficial deposits and fractured bedrock. Electrical resistivity tomography, frequency domain electromagnetic conductivity measurements, ground-penetrating radar, seismic pressure wave refraction, and multispectral analysis of shear waves; in conjunction with downhole measurement of natural gamma radiation, induction conductivity, and magnetic susceptibility provide a detailed, static picture of soil moisture and groundwater conditions within the hydrogeological units. Differences in electrical resistivity of the units reflect a combination of hydrogeological characteristics and climatic factors, namely temperature and precipitation. Resistive earth materials include dry glaciofluvial outwash and nonfractured bedrock; whereas glaciolacustrine clay and silt, water-bearing fractured bedrock, and periodically saturated subglacial till and outwash are conductive. Dynamic, continuous real-time monitoring of electrical resistivity, now underway, will help characterize water-flow paths, and possible relationships to independently monitor pore pressures and slope creep. These new hydrogeological and geophysical data sets enhance understanding of the composition and internal structure of this landslide and provide important context to interpret multiyear slope stability monitoring ongoing in the valley.
      141Scopus© Citations 11
  • Publication
    Retaining wall behaviour in Dublin's fluvio-glacial gravel, Ireland
    Practising engineers in the Dublin, Ireland, area have significant experience in dealing with the Boulder Clay which underlies much of the city. However, the 45 m deep buried pre-glacial channel north of the River Liffey is infilled with fluvio-glacial deposits which behave very differently from an engineering point of view. Case history data from eight sites and a detailed examination of the retaining wall behaviour at two of the sites show that retaining wall movements appear to be governed by system stiffness (i.e. a combination of wall stiffness and support configuration). It seems that relatively simple beam–spring type computer programs will provide data for reasonably accurate designs of retaining walls for basements of up to two levels. Input parameters such as K 0, φ‘ and soil stiffness need to be carefully specified. Groundwater inflows can be significant but can be dealt with by providing a good cut-off into the underlying glacial till or bedrock and by conventional pumping techniques. Geophysical techniques such as multichannel analysis of surface waves, S/P waves and resistivity can be very useful for the determination of soil properties, such as degree of saturation, density and stiffness, and for material characterisation (i.e. distinguishing the presence of these materials in contrast to the Boulder Clay).
      600Scopus© Citations 13
  • Publication
    Suction Measurements as Indicators of Sample Quality in Soft Clay
    (ASTM International, 2009) ;
    Soil samples removed from the ground during sampling possess a suction in their unconfined state. This suction may vary depending on the degree of disturbance induced during the sampling process. The objective of this work is to examine the feasibility of using suction measurements for sample quality assessment. A number of suction measuring techniques are reviewed and examined on samples of varying quality from two well-characterized soft clay sites, Onsøy in Norway and Ballinasloe in Ireland. Most of the techniques tested gave comparable results, although the cell pressure loading method provided the most variable measurements. The Japanese and University of Massachusetts Amherst suction probe techniques provide relatively quick and consistent suction measurements, requiring less than half an hour to stabilize. In terms of sample quality the Sherbrooke block samples consistently exhibit higher suctions than the 76 mm, 54 mm, and continuous soil samplers for the Onsøy test site. Suctions measured on the Japanese 75 mm samples are similar to those measured on the block samples. The 5° displacement sampler provides the highest suctions on the Ballinasloe samples. It is observed that the quality of samples indicated by suction measurements is similar to that inferred from the normalized change in void ratio (Δe/e0) criterion.
  • 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.
      3668Scopus© Citations 58
  • Publication
    Academic Advising in Civil Engineering: design and evaluation of a hybrid model
    A project to formalise and expand Academic Advising has been implemented at the UCD Civil Engineering School. The goals of this project were twofold: on the one hand, it aimed at training faculty members in Academic Advising roles and providing them with the necessary resources. On the other hand, the project sought to expand student interaction, in particular by engaging students informally in order to build a rapport between them and the academic advisors that we expect will bring long term benefits. The resulting model combines elements of both the prescriptive, e.g., formal training, informative talks on key topics, and developmental approaches, e.g., coffee mornings for students and faculty members. The evaluation of the project was carried out through questionnaires and focus groups. It highlighted very positive feedback from the students, who find these new lines of communication with the academic staff to be useful and productive.