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Vibro Menard uses CMC technique


UK-based geotechnical contractor Vibro Menard, working with engineering and construction group Costain, has completed the ground improvement work for the new Manchester Waste Private Finance Initiative (PFI) building in Bolton.

The contract was worth approximately £250,000 and used the controlled modulus columns (CMC) technique, which is new for the UK market.

Vibro Menard installed 1,793 CMCs, up to 3-12m deep and 320mm in diameter. “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,” Gabriel Portillo, one of Vibro Menard’s senior estimators, continued. “We offered the CMC solution to help reduce the settlement by transferring load to the stiffer layers within the underlying geology.”

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 into 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 0.4m and 0.8m thick, to efficiently transfer load from the structure to the CMC/soil matrix. The CMCs are realised using concrete with a minimum compressive strength of 12MPa, and will be 3m to 10m long, depending on the local characteristics of the soil.

Vibro Menard’s CMCs are used to improve the soil’s characteristics in weak ground and to reduce imposed settlements caused by the proposed structure.

“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 be thicker and need more reinforcement,” Gerry Crawford, Vibro Menard’s general manager, said.
Courtesy GeoDrilling

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