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GEOPHYSICAL
ENGINEERING

Buried Foundations 

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Left : Exposed Foundations at Vindolanda Roman Fort – if only they were always this clear!

Buried foundations can create a costly obstacle when developing a brownfield site. Whether the footings of a demolished modern structure, or the buried walls of a Medieval house, unknown buried foundations can delay a project or even halt the works altogether.  

Historic plans exist for many sites, but there is often no record of how much of the foundations remain, or indeed how much has been removed by a previous contractor! Knowing about this risk at design stage should improve both the profitability and delivery timescale of your project.

From small private sites, to operational car parks and active construction sites, SUMO has an approach that can help. Using combined methodologies, a survey programme can be designed to give you the best information about your site in the most cost-effective way.

 

Ground Conductivity

 

On large sites, a Ground Conductivity Survey may be suitable. Penetrating up to 4m depth and collecting up to 1ha per day, this methodology can inform design works and/or enable anomalies to be targeted with higher resolution techniques such as GPR.

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Above : Ground Conductivity data in plan view, together with a basic Interpretation.

 

The Ground Conductivity data above, which was conducted at former gas works, revealed two extensive blocks of foundations, measuring approximately 35m x 10m. The in-phase (metal detecting) data shows a marked level of activity. This suggests the foundations may contain structural steelwork or heavy reinforcing.

Around the easterly foundation is a marked "halo" of lower conductivity readings. This is a possible pollution plume that may be associated with the former use of the site as a gas works.

 

Ground Penetrating Radar (GPR)

 

The most suitable technique on smaller and/or urban sites is Ground penetrating Radar (GPR). This is a higher resolution technique which offers depth information, measuring to the top of the foundation, and allows the data to be analysed in plan or section view.

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Above : Section view of GPR, showing a large anomaly which is likely to be the remains of a substantial foundation at 1m depth.

 

GPR data can be collected using High Density Radar. These systems provide high resolution data, collecting traverses every 8cm, which allows detailed plan views of the site to be displayed at various depths. Tracked by a robotic total station, the data can be positioned accurately to OS or the client’s grid. Additionally, instant 3D pictures can be produced on site.

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Above : Timeslice (plan view) of a Roman Villa collected with High Density GPR.

 

Detailed magnetic Survey

 

Magnetic survey can also be a useful tool to locate buried foundation. In the example below, Magnetic survey proved to be the most successful of three techniques employed on site. The survey detected three rectilinear shaped anomalies (M3, M5 and M6) that are clearly suggestive of buried foundations. M1 is likely to be a pipe.

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Above : Example Magnetic survey data, showing three sets of foundations.

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Geophysical Engineering Surveys
 

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Cellars & Basements

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Underground Storage Tanks

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Air Voids

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Chimney Flues

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Rebar

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Water Engineering

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Badger Setts

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Earthing Installations

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Sinkholes

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Burials

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Geological Application

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Soil Thermal Resistivity Testing

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Buried Foundations

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Landfills

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Structural Investigations

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Buried Manholes

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Mineshafts

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Tree Roots

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