The Rif mountains are situated in the far north of Morocco - it is a harsh environment in which to live and in which to build new infrastructure.
'The area is known for its spectacular and catastrophic landslides. They put human life in danger and cause significant disruption to the region's infrastructure, ' says Pennine Vibropiling senior design engineer David Preece.
The firm is carrying out extensive ground improvement in advance of construction of the 54km Tangier Oued R'mel highway that will run east-west to connect the port with the main road south from Tangier to capital city Rabat. Main contractors for the project are Turkish firms Mak-Yol and Tekfen.
Pennine managing director Arwel Williams says the construction of the Tangier Oued R'mel highway will include 120,000m of stone columns, 800,000m of vertical band drains and 2,000 bored piles, including those installed under bridge piers.
Pennine is installing stone columns on which two 15m high, 100m long embankments are to be built, flanking a viaduct. These will help minimise differential settlement between viaduct and embankment. Ground conditions consist of valley deposits over shales and mudstones. The valley deposits are typically 20m thick but locally increase to 36m, comprising fine and coarse-grained soils with variable engineering properties.
The fine-grained element tends to be soft to firm in consistency and the coarse-grained deposits vary from loose to dense.
Significant pockets of organic clays and silts are also present.
Client and engineer for the scheme, Autoroutes du Maroc, Morocco's Highways Agency, predicted embankment settlement of 0.4m to 1m.
'Stone columns beneath the approach embankments will reinforce the weak valley deposits and speed up the rate of consolidation within the fine-grained soils, ' says Williams.
'The rate of consolidation will mean that the vast majority of the embankment settlement occurs during construction.' The 0.8m-diameter stone columns are being installed on a triangular grid with spacings varying from 1.8m to 2.25m. The design requires that they go through the full thickness of finegrained valley deposits onto competent coarse-grained valley deposits or bedrock.