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 problems


The shaft was constructed through 26m of London Clay, 18m of Lambeth Group gravels, clay, sand and pockets of water, and a few metres of Thanet Sand.

Water in the ground below London Clay had to be dewatered to prevent flooding the shaft during excavation.

Contractor WJ Groundwater installed pumping wells to dewater the Lambeth and Thanet layers five months before excavation.

'Our biggest fear would have been a power cut and all the dewatering pumps turning off, ' admits Skanska project director Matt Cova.

'It takes just two hours for the water level to recover 2m. If this happened while [digging] in the Lambeth beds, the shaft would have flooded. So we always had a standby generator on site, just in case, ' he adds.

Skanska's geotechnical engineer Andy McNamara adds: 'The danger was that the dewatering wells missed an area of locked in water [in the Lambeth Group]. The only solution was to dig trial holes to check for water'. In the event of hitting water, secondary well points would be installed through the shaft lining.

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.