Research in the top few metres of the ground beneath our feet has traditionally been split between
soil science, geology and several sub-disciplines. This has lead to different working practices,
classifications and boundaries as well as inconsistent approaches to databasing and modelling. A
significant uncertainty lies within the “transition zone” between the pedosphere and geosphere. The
British Geological Survey (BGS) set out to investigate this zone through multidisciplinary field surveys
at both a site specific and catchment scale in representative soil-geoscapes across the UK. The spatial
3D soil-geology model is developed by the combination of spatial soil and geoscientific findings.
Whilst undertaking these studies the BGS were particularly interested in investigating whether
technologies developed to map geology in 3D can be used to routinely develop spatial models of the
soil-geology environment, and if technologies used in digital soil mapping can assist in reducing
uncertainties associated with such models at a variety of scales.
The presented soil-geology model is an example of recent work carried out on an area of
approximately 2 km2 near Shelford, Nottinghamshire, UK. The site lies on the River Trent floodplain
and an adjacent gentle slope of Triassic mudstone. The whole site is underlain by typical red
mudstones of the Triassic Mercia Mudstone Group with some interbedded greenish grey siltstones
and sandstones.
This is overlain by up to 5 m of Pleistocene and Holocene river terrace deposits, varying from sand to
coarse gravels and Holocene alluvial and colluvial deposits. Fieldwork was orientated along several
parallel traverses running from the hilltop, downslope towards the River Trent.
The study of the survey area comprised of two main stages. Firstly a field survey which included
techniques such as a detailed soil and geological survey, pitting and drilling, installation of
piezometres, soil moisture tests, high-resolution electrical mapping, electrical resistivity tomography,
ground penetrating radar, magnetic susceptibility, gamma spectrometry, remote sensing and terrain
analysis.
The second stage involved the digital assembly of data, processing, and the development of the 3D
soil-geology model. Each survey delivered its own results in form of maps, tables and property
models which were collated into one software package (GSI3D by INSIGHT GmbH).
Developing a solid 3D soil-geology model in GSI3D utilizes a Digital Terrain Model, mapped geological
and soil line work, downhole borehole and augerhole data, and geophysical data. This enables the
geoscientist to construct regularly spaced intersecting cross-sections by correlating boreholes and
the outcrops-subcrops of units to produce a fence diagram of the area. Mathematical interpolation
between the nodes along the sections and the limits of the units or horizons produces a solid model
comprising of a series of stacked triangulated volume objects.
The final 3D model shows several top- and subsoil horizons in conjunction with the underlying
Holocene, Pleistocene and red Triassic Mercia Mudstone parent materials.
These models can aid studies of near surface processes including the movement of water, dissolved
agricultural nutrients and associated eroded soil particles
