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
    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.
      4719Scopus© Citations 51
  • 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
    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.
      3856Scopus© Citations 62
  • Publication
    The Application of Distributed Acoustic Sensing for Shallow Marine Investigations – an Intertidal Case Study
    (European Association of Geoscientists & Engineers, 2021-09-02) ; ; ; ;
    Typically, there is a paucity of geotechnical information available to designers of offshore foundations for marine renewable structures, which often results in highly conservative designs. Recent innovations offshore (e.g. McGrath et al. 2016; Long et al. 2020)) seismic surface wave (SW) measurements have highlighted their potential for providing offshore geotechnical information, thereby reducing design uncertainty. There is also an increasing recognition of the value of these measurements from the geotechnical industry, with Lunne (2013) recommending that measurements of seismic shear wave velocities (Vs) should be standard practice for important offshore site investigations. Vs is related to the small strain shear modulus Gmax, which is a critical input parameter for several applications, including static and dynamic analysis of foundation systems, soil liquefaction analysis and input for advanced constitutive soil models. The main disadvantage of current offshore SW practice is a relatively slow data acquisition procedure, which, in turn reduces the spatial coverage of the approach.
      316Scopus© 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.
      337Scopus© Citations 12
  • Publication
    Time-Lapse Monitoring of Moisture Induced Landslide Using Surface Waves at Hollin Hill Landslide Obsevatory
    (European Association of Geoscientists & Engineers, 2021-09-01) ; ; ; ; ;
    For about fifteen years, the Hollin Hill site has been used as a landslide research site to test different geophysical characterization and monitoring methods, to assess temporal and spatial stability, and the following methods are regularly evaluated on site: ERT resistivity mapping (Chambers et al. 2010, Uhlemann et al. 2017), self-potential methods SP (Chambers et al. 2008), more recently seismic refraction tomography SRT (Whiteley et al. 2020, Uhlemann et al. 2016). The dynamics and ongoing subsurface processes of the Hollin Hill landslide are therefore relatively well described in literature (Whiteley at al. 2019a). Seismic methods based on characterization of P-wave (Vp) and S-waves (Vs) propagation and in particular on Vp /Vs ratio are commonly used in a landslide context (Grandjean et al. 2009, Mainsant et al. 2012). Since mid-2000, methodological improvements have led to increased routine use of dispersion inversion of Vs in hydrological applications (Pasquet et al. 2015; Dangeard et al. 2016) and in geotechnical applications (Donohue et al. 2011, Bergamo et al. 2016). This abstract therefore discusses current geophysical research to monitor seasonal variations using surface waves content (Rayleigh waves) from SRT acquisitions, in the context of moisture induced landslide monitoring, at the Hollin Hill Landslide Observatory.
  • 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.
      276Scopus© Citations 41
  • Publication
    Multi-method geophysical mapping of quick clay
    Marine clay deposits in coastal, post-submarine areas of Scandinavia and North America may be subjected to quick clay landslides and hence significant efforts are being taken to map their occurrence and extent. The purpose of this paper is to assess the use of a number of geophysical techniques for identifying quick clay. The investigated area, Smørgrav, located in southern Norway has a history of quick clay sliding, the most recent event occurring in 1984. Geophysical techniques that are used include electromagnetic conductivity mapping, electrical resistivity tomography, seismic refraction and multichannel analysis of surface waves. These results are compared to geotechnical data from bore samples, rotary pressure soundings and cone penetration testing. A number of these approaches have proved promising for identifying quick clay, in particular electrical resistivity tomography and electromagnetics, which delineated a zone of quick clay that had previously been confirmed by rotary pressure soundings and sampling. Seismic refraction was useful for determining the sediment distribution as well as for indicating the presence of shallow bedrock whereas the multichannel analysis of surface-waves approach suggested differences between the intact stiffness of quick and unleached clay. It is observed that quick clay investigations using discrete rotary pressure soundings can be significantly enhanced by using, in particular, electrical resistivity tomography profiles to link together the information between test locations, perhaps significantly reducing the need for large numbers of soundings.
      888Scopus© Citations 54
  • 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.