Vertical drains
Vertical Drains are used to accelerate the consolidation of soft, low permeability soils. Drains are installed in a grid pattern designed to achieve the optimum time v. cost outcome. The most common forms of drain are strip or “Wick” drains and are introduced into the ground using a mandrel containing the drain material being pushed into the soil. The mandrel is pushed to the design depth, where it releases the drain and is withdrawn leaving the drain in place. Menard Bachy has developed the use of small diameter circular plastic tube drains, which are more efficient than the flat Wick” drains. These circular drains have particular application in the Vacuum Consolidation process.
Menard Bachy has developed its own range of purpose made drain installation equipment to cope with a variety of ground conditions. The picture below shows a static 45m cable leader rig which can be equipped with a vibrator to enhance installation rates.
Ground inclusions of columns of sand or other granular materials are also used to create, generally, larger diameter and shallower vertical drains.
Often, surcharge in the form of a temporary embankment is used in conjunction with vertical drainage to enhance its effectiveness and to target the achievement of total primary consolidation and limit long term secondary consolidation.
Vertical Drains are an integral part of the Vacuum Consolidation method.
RABAT/TANGER Motorway (MAROC)
The route planned for the RABAT-TANGER motorway constructed on behalf of the Autoroutes du Maroc company crosses the Loukkos wadi where it is about 100 m wide.
The wadi is crossed by a bridge, access to the bridge is via embankments up to 5 m high which are to be constructed over a depth of 30 m of compressible soil. In order to solve the problem of residual settlements beneath the embankments MENARD has installed 630,000 m of vertical drains to speed settlement and stabilize the embankment foundation.
Instrumentation has been installed over the whole site to provide continuous monitoring of the soil's behavior. MENARD was responsible for this monitoring in order to allow the height of the embankment to be raised near the wadi as quickly as possible while ensuring the stability of the embankment.
