Electrical resistivity and Ground Penetrating Radar for the characterisation of the internal architecture of Quaternary sediments in the Midlands of Ireland

Abstract

a b s t r a c t a r t i c l e i n f oGeophysical techniques Electrical Resistivity Tomography (ERT) and Ground Penetrating Radar (GPR) supported by traditional field methods are used for the geological mapping, description and interpretation of Quaternary unconsolidated sediments in a site located in the Midlands of Ireland. The site comprises a broad range of glacial and postglacial sediments (diamicton, esker sand and gravel, glaciolacustrine sand, glaciolacustrine silt/clay and peat). Preliminary fieldwork comprising, geomorphological mapping, lithostratigraphic analysis of exposures and borehole drilling and laboratory testing encompassing particle size distribution analysis were carried out to broadly characterise the geology of the study area. These data aided locating the geophysical profiles and supported the geophysical data interpretation. Five GPR radargrams were collected and permitted depicting the subsurface internal architecture within low conductivity unconsolidated sediments and aided to the classification and characterisation of sedimentological and deformational structures. Four ERT profiles allowed the depth to bedrock to be determined and lithological classification of the sediments. The use of these geophysical techniques in combination with geotechnical and geological data allowed (i) the determination of the lithological composition and detailed internal architecture of the subsurface, (ii) the characterisation and description of the geology of the site and (iii) understanding the depositional processes acting in the area during ice withdrawal. Diamicton and esker gravels were deposited subglacially by an ice sheet withdrawing westwards; glaciolacustrine sediments located along the south margin of the esker ridge were laid down in an ice marginal environment as a subaqueous fan composed of silt, sand and gravel, and as distal deposits composed of silt and clay in the lower ground area between the fan and the esker ridge. Peat developed during postglacial times and was partially cut away by anthropogenic action at a later stage.

Imaging and locating paleo-channels using geophysical data from meandering system of the Mun River, Khorat Plateau, Northeastern Thailand

“…A few millilitres of suspension are required to carry out the measurements. After that these samples were subsequently classified under the Shepard's classification system for sand, silt and clay for distinguishing the sedimentary type [3,32,33]. The lithological logs from boreholes were used to verify the lithologic types and boundary of GPR and ERT profiles.…”

“…ERT profiles show thickness of fluvial deposit from 5 to 30 m depth and clearly reveal vertical and horizontal changes. However, the detail of sedimentary internal structure cannot be recognised using this technique alone [3]; however, the GPR can be the supplement. Based on resistivity profile results from location 1 (Figure 4(a)), the upper most part, the cultivated soil with low moisture contents depicts high resistivity value (orange to purple color).…”

“…Electrical Resistivity Tomography (ERT) and Ground Penetrating Radar (GPR) techniques have been widely used in the past for describing lithological and sedimentological characteristics of Quaternary deposits [3][4][5]. GPR detects changing of dielectric constant properties of sediment layers; therefore, the data will show discontinuities in the shallow subsurface.…”

Time-lapse resistivity analysis of Quaternary sediments in the Midlands of Ireland

“…Field mapping, geophysical characterisation of the study area (Pellicer and Gibson, 2011) and borehole data (Fig. 2) permitted the tentative categorisation of five lithological classes within the profiles (Fig.…”

“…The lithology and the internal architecture of a site located in the Irish Midlands were characterised using the geophysical techniques Electrical Resistivity Tomography (ERT) and Ground Penetrating Radar (GPR) in combination with geomorphological, lithostrastigraphic and geotechnical investigations (Pellicer and Gibson, 2011). However, electrical resistivity research shows that porosity, moisture contents and temperature of the subsurface strongly influence the resistivity of soft sediments (Bernstone et al, 2000;Chambers et al, 2009;Guerin et al, 2004;Harmon and Hajicek, 1992;Hayley et al, 2009).…”