Geophysical techniques can be applied to a wide variety of sites to investigate numerous types of materials and structures below the ground. We’ve put together this list of features that can be found by geophysical survey techniques.
1: Air Voids and Cavities
Buried vaults, crypts, culverts, sewers and heating ducts are just a few examples of where voiding can occur. Voiding caused by burials and crypts can be identified within current or former ecclesiastical sites using an archaeological survey. Other indicators of voids are swallow holes and subsidence, which can be found in many locations such as greenfield sites, roads and brownfield sites. Typically, near surface geophysics techniques such as Ground Penetrating Radar, Ground Conductivity and Microgravity can be used to find these features.
2: Buried Mineshafts
The approximate locations of old mine shafts and adits are recorded on historic maps and records. Some may have been capped and others not recorded at all will be difficult to find. A geophysical survey can be the most cost-effective method of locating them before development work commences.
Buried mine shafts are interesting in that a range of geophysics techniques can be used to characterise the buried features. Initially we’d recommend to a client the use of Ground Penetrating Radar and Ground Conductivity. The use of magnetometry can be used to find the remains of any metal structures associated with the pithead gear.
Above: Example Radargram showing the location of a buried mineshaft.
3: Buried Fuel and Attenuation Tanks
The discovery of buried fuel and attenuation tanks can create health, safety and environmental concerns. As well as this, there can be significant cost implications. The identification of buried tanks and their location is therefore essential at the design stage and may be of particular relevance to the redevelopment of brownfield sites.
Buried fuel tanks should be easily identified using Ground Penetrating Radar, Ground conductivity or Magnetometry survey techniques.
Above: The image shows buried attenuation tanks.
Above: Radargram showing the location of buried attenuation tanks.
Above: This example of Ground Penetrating Radar data shows the location of buried attenuation tanks.
4: Air Raid Shelters
Throughout the UK thousands of air raid shelters were constructed during World War II. These varied from large public shelters built with bricks andreinforced concrete through to small private shelters using corrugated steel panels. Many of these were removed after the war, however, others remain buried and are often encountered during construction works. Ground Penetrating Radar, Ground Conductivity and possibly Electrical Resistance Tomography ERT would be the techniques we would use for identifying air raid shelters.
Above: This image shows the structure of a typical Air Raid Shelter that would have been used during the war.
Above: This example of Radar data shows the location of buried Air Raid Shelters.
5: Land Forms and Geomorphology
Before construction and infrastructure projects start, it often proves necessary to characterise landscape features to assess their suitability for design purposes. This could include attributes such as depth of drift cover to bedrock, body of water profiling and sediment thickness, or the extent of sink hole formation.
Ground conductivity and ERT has the ability to find Palaeochannels and near surface rock outcrops. The depth of rockhead can be mapped through the use of GPR. Lastly, Magnetic surveys can be used to detect igneous intrusions.
Above: Example of Seismic Refraction data. This cross-section of data shows the depth of conglomerate and limestone.
Above: Example of Seismic Refraction data. This Plan View of the site shows the depth to the Bedrock.
6: Waterfronts
Significant areas of voiding can be created where water under pressure has forced its way through masonry and brick linings. Typically, we would find this sort of voiding in harbour walls and quays by using Ground Penetration Radar.
7: Badger Setts
As a protected species, it is important to identify the existence and extent of any badger setts before commencing construction work. Often having deep and intricate tunnels, badger sets can be best discovered using Ground Penetrating Radar.
8: Rebar
Rebar can successfully be located by Ground Penetrating Radar and Cover Meters. It is often a survey technique we pursue when our clients have plans for drilling but are unable to obtain previous records of the rebar’s location.
Above: SUMO Geophysics can utilise a palm antenna to locate rebar. It is the ideal piece of equipment to locate features such as rebar and tension cables.
Above: Example of Ground Penetrating Radar Radargram showing the location of rebar.
9: Hidden Flues and Chimneys
Identifying building features such as these would be best suited to High-Frequency Structural Radar. This technique can also find similar embedded features and voiding caused by crumbling masonry and water ingress.
Above: This example of radar data shows the location of a former fireplace.