Ground Investigations (Geotechnical Applications)

A number of geophysical methods are now available to provide a means of non-invasive, non-destructive investigation of the physical and chemical nature of the subsurface. These types of technique may be included in many site investigations where powerful and cost-effective investigation can enable well informed decision making.

Engineering Sites

Determination of ground rip ability
Location of fractures and faults, voids & Cavities
Location of pipelines and services
Determination of overburden thickness, structure and stratigraphy

Landfills

Location and delineation of extents of buried landfills
Detection and mapping of leachate migration from landfills
Detection of buried drums

Mineworkings

Location of historical shafts and adits
Determination of void infill
Determination of groundwater levels
Location of tip and fill zones in the subsurface
Determination of spoil-tip structure.

Contaminated Sites

Location and mapping of water tables
Location and mapping of groundwater pollution
Detection of subsurface hydrocarbon leakage
Location of buried drums
Location of buried ordnance
Location of metallic and non- metallic underground storage tanks (UST's).

Water and Sewerage Infrastructure

Location of pipelines and services
Determination of liner integrity
Location of dam and revetment leakage
Determination of geotechnical conditions/voids

Miscellaneous

Archaeological investigations
Subsurface obstructions - buried foundations underground structures.
Forensic investigations - locations of unmarked graves or buried artifacts.

Geophysical techniques generally rely on the detection or measurement of physical or chemical contrasts that exist within the subsurface. In general, geophysical instruments respond to lateral and/or vertical variations in contrasts that are measured along traverse lines, within grids or down boreholes. Modern geophysical instruments record data in digital format for later computer processing and interpretation.

The most important properties that give rise to a geophysical response, the corresponding geophysical technique, and common application examples are outlined below:

Property	Geophysical Technique	Example Applications
Electrical resistivity	1-d Resistivity sounding Subsurface Imaging Cross-Hole Tomography	Ground earthing quality Contaminant plume mapping Geological mapping
Electrical conductivity	Electromagnetic Sounding Electromagnetic Profiling VFL Profiling Pulse Induction Surveys	Groundwater mapping Mapping landfill margins Bedrock fault mapping Location of buried UXO Electrical Polarisation (chargeability) Induced Polarisation (IP) Location of buried wastes
Magnetic susceptibility	Magnetic Profiling Magnetic Gradiometer	Location of buried pipelines, cables Location of buried wastes, drums
Density	Microgravity Profiling	Location of voids and cavities Tunnels Mine works
Dielectric Constant (relative permittivity)	Impulse Radar	Void Location Bedrock Profiling Archaeology UST Location
Seismic moduli (+ Density)	Seismic Reflection Surveys Seismic Refraction Surveys Cross-Hole Tomography	Delineation of overburden features Bedrock depth, rip ability, quality Geotechnical investigation
Gamma Ray Emission	Gamma Logging (Boreholes)	Borehole-borehole correlation

GBG Australia is able to provide a cost -effective service based upon thorough technical scoping of the project to meet the needs of the client. A single geophysical technique or, more commonly, a combination of techniques may be used to provide information about the subsurface from a few millimetres to several hundred metres beneath the site.

Field data is usually logged in a digital format for downloading and processing by geophysical workstations. Presentation of processed data, interpretations and ground models can often be readily integrated with pre-existing CAD drawings of site details and related structures in their one, two or three-dimensional formats.

GBG Australia have undertaken investigations of: