Providing an Introduction to Ground Investigation and Engineering in Chalk

Southern Testing staff visit coastal chalk outcrops for training in logging, overcoming common engineering problems and assessing cliff stability.

One of the key objective of any site investigation is to assess the ground conditions prior to development, in an effort to reduce potential hidden risks that may cause delay or impact on costs. With this in mind, Southern Testing recognise the importance of providing our engineering staff with suitable training, particularly our graduate engineers; gaining relevant site experience is essential to their development and ensures that our teams provide clients with quality and objective technical advice.

Southern Testing provide a formal in-house graduate training scheme which is accredited by the Geological Society of London. The Geological Society offers Endorsement for Company Training Schemes, whereby it acknowledges that a company scheme provides an opportunity for participants to gain the necessary core skills, experience and competencies to facilitate a pathway to Chartership status (Chartered Geologist CGeol or Chartered Scientists CSci).

As part of this training we undertake field courses to provide our Engineers with experience of regional geologies across the UK, their relevant engineering properties, and the relative benefits and problems of different ground investigation techniques; this ensures that they are competent in undertaking logging in accordance with British Standards. Logging provides the detailed information on which other engineering decisions depend. It is therefore vital that experienced geologists are used for this purpose.

The recent focus of our in-house training has been coastal chalk outcrops, which has helped to develop an understanding of chalk in terms of ground engineering situations. Topics covered included:

• Chalk stratigraphy.
• Logging chalk to CIRIA C574 ‘Engineering in Chalk’
• Assessing cliff stability
• Superficial deposits related to the chalk
• Common engineering problems, and their solutions.

Some staff have also attended external Chalk logging courses presented by Professor Rory Mortimore to provide further experience; this has included the identification of features such as marker beds and natural fractures, along with looking at engineering grade.

Field Experience

Our staff practiced identifying different grades of chalk, using the logging system of CIRIA C574 ‘Engineering in Chalk’. They demonstrated a clear understanding of the weathering processes that give rise to changes in the engineering grade of the chalk. Flint layers, fossils, faults and fractures were all logged in detail.

Using these skills, our Engineers made assessments on the stability of the cliffs. This was based on the relationship between different discontinuities (natural features in the rock, such as bedding planes, fractures, jointing, and faults). They were able to identify different failure mechanisms, including planar slides, wedges and toppling failures.

After determining potential instability problems, they observed and discussed potential engineering solutions to reduce and mitigate the risk of future cliff failures. The relative merits and challenges presented by schemes such as cliff regrading, rock catch nets, retaining walls, sea defences and rock bolting were considered in relation to the risk posed by the cliffs.

Particular attention was given to common superficial deposits associated with chalk, with staff noting the way in which these deposits are formed and the engineering problems related to them. Solution features, weathering of the chalk, and slope instability were all assessed in detail. Our Engineers presented their ideas for safe ground investigation methods in each soil type observed. We also discussed what testing, using our own in-house soil testing laboratory, we would specify to help produce robust engineering recommendations.

How we can help you?

If you’ve got a development on a site which is underlain by chalk we’d love to hear from you. Please get in touch at enquiries@southerntesting.co.uk, or call us on 01342 333100.