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

Cutting contamination


Stability and protection for the cut-off wall is provided by two parallel reinforced concrete diaphragm walls.

These are 0.8m thick and vary in depth from 4m to 10m, penetrating the top surface of the marl by 1.5m. The walls act as protection for the plastic cut-off in-between, particularly in the alluvium.

In some sections the cut-off wall is protected by an anchored micropiled wall. This Berlin-wall consists of a micropiled curtain - reinforced with single steel pipes and varying in depth from 11m to 15m. It is supported with a row of inclined ground anchors that range in length from 14m to 24m.

Trevi is using a rotary drilling system, since the use of rotary percussion systems is strictly forbidden. As company director Gianluigi Trevisani explains: 'The use of compressed air could cause the dispersion of the contaminated water and dust in the air.'

The slurry wall is excavated deep into the marl using a hydrocutter. A trench is formed 1m across and varying in depth from 8m to 16m, giving penetration into the marl of up to 12m.

This is filled with a plastic slurry mix of water, concrete and bentonite into which the HDPE sheets are carefully installed in panels to create a continuous watertight curtain. The target permeability for the slurry wall is 2 x 10 -8 m3/s.

The drainage diaphragm wall is located immediately upstream - in terms of groundwater flow - of the cut-off wall and the supporting concrete diaphragms. The 1m wide, and up to 9m deep drainage trench intercepts contaminated groundwater and collects it for treatment - so in theory no contaminated water actually reaches the cut-off wall.

It will be excavated under the support of a biodegradable mud and then filled with crushed stone.

Control and monitoring is provided by a network of piezometers placed both up and downstream of the cut-off.

They will provide a check that protection measures are working.

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.