Your browser is no longer supported

For the best possible experience using our website we recommend you upgrade to a newer version or another browser.

Your browser appears to have cookies disabled. For the best experience of this website, please enable cookies in your browser

We'll assume we have your consent to use cookies, for example so you won't need to log in each time you visit our site.
Learn more

Ground studies

Spotlight - Geophysical testing

Geophysical methods of investigation offer a number of alternative means of detecting and mapping buried karst features, says TerraDat UK's director Nick Russill.

Microgravity, for instance, is a powerful tool for identifying the presence of voids and sinkholes, exploiting the fact that their density is significantly lower than the host bedrock.

However, in some instances it can prove difficult to distinguish between solution features and localised rockhead depressions using only the gravity method.

As a result it is best to use an additional geophysical method to confirm the interpretation. A key control factor is knowledge of the depth to bedrock, which can be derived using resistivity tomography or seismic methods.

Under favourable site conditions, resistivity can be used to map karst features in cross-section, although it is recommended that any identified anomalous zones are targeted using follow-up microgravity to determine whether they relate to fracture zones or broader cavities.

Without the additional gravity data, conclusive interpretation can be less certain, particularly in areas that have variable soil cover and/or laterally unhomogeneous rock resistivity due to water or clay content.

Seismic refraction surveys are generally not suited to mapping sub-rockhead solution features. The method provides a powerful means of accurately determining soil depths for input to the gravity modelling process or for identifying sinkholes beneath selected traverse lines, however.

In summary, individual geophysical methods can provide a total solution at some sites but more commonly a combination of two carefully chosen methods measuring different physical properties will provide a better result.

Have your say

You must sign in to make a comment

Please remember that the submission of any material is governed by our Terms and Conditions and by submitting material you confirm your agreement to these Terms and Conditions. Please note comments made online may also be published in the print edition of New Civil Engineer. Links may be included in your comments but HTML is not permitted.

Related Jobs