Ground Improvement Specialists.

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Category Archives: Completed Projects

Soletanche Bachy – 2014 Portfolio

Vibro Menard uses new technique in Manchester Waste PFI ground improvement

Working with main contractor Costain, ground improvement specialist, Vibro Menard has successfully completed the ground improvement work for the new Manchester Waste Private Finance Initiative (PFI) building in Bolton. The contract is worth approximately £250k and uses CMC a new technique for the UK market.

Vibro Menard is installing 1793no. Controlled Modulus Columns (CMC), up to 3-12m deep and 320mm in diameter. The soils below the Waste Intake and Maturation building weighbridge area and amenity building present soft conditions composed of made ground over clay. The area that needs to be improved is approximateley 90,000m2.

In the area where the buildings will be built, some earthworks cut and fill was required, with a maximum fill of approximately 3.5m and a maximum cut of 3m. Construction of the structures without soil improvement or soil replacement would lead to unacceptable post construction settlements and deformation. The completed slab at the Bolton site will measure 89m by 260m. The 250mm thick concrete slab will be built on a 600mm thick load transfer platform, formed in two layers of high-quality granular fill with the first 300m placed ahead of the ground improvement work to act as a working platform for Vibro’s rig.

Vibro Menard’s Controlled Modulus Columns (CMCs) are used to improve the soil’s characteristics in weak ground and to reduce imposed settlements caused by the proposed structure. CMCs are installed using a specially designed auger that displaces the in situ soils laterally, with virtually no vibration or spoil, and reduced risk of contamination.

The auger is screwed in to soils to the designed depth, which increases the density of the surrounding soil, and as such increases its strength and/or bearing capacity. When the auger is extracted a column is developed by pressure grouting, at less than 5 bar, to improve the surrounding soils. The result is a composite ground improvement solution offering enhanced stiffness characteristics, allowing the CMCs and the surrounding soil to share the imposed loadings. After installation, CMCs are covered by a designed load transfer platform, between 0.4 and 0.8m thick, to efficiently transfer load from the structure to the CMC/soil matrix.

Gerry Crawford, Vibro Menard’s General Manager, said:

“Using ground improvement was more cost effective for the client; a piled solution would have required spoil disposal and a suspended floor slab that would have had to have been thicker and need more reinforcement. We were also extremely confident that the work could be delivered in three weeks rather than the originally proposed seven, representing an additional time saving benefit.”

Gabriel Portillo, one of Vibro Menard’s senior estimators, continued:

“Costain originally asked us to price a conventional vibro stone column solution for the site but analysis showed that the differential settlement from this approach was too much. We offered the CMC solution to help reduce the settlement by transferring load to the stiffer layers within the underlying geology.”

The CMCs are realised using concrete with a minimum compressive strength of 12 MPa, and will be 3 to 10 m long, depending on the local characteristics of the soil. CMCs were developed by Menard in 1994 and are now used in many countries around the world. Current practice is to install CMCs with a diameter of between 250 and 450mm.