Norfolk County Council




Cocksedge Building Contractors


454 Bi-Modulus Columns installed

Project Details

A new primary school and nursery was to be built in King’s Lynn by Norfolk County Council to replace St Edmund’s Academy, located two miles from the new site. The works included significant earthworks (including upfill) and required therefore to control the settlements of the external areas surrounding the building supported by piles, and of the new drainage pipes to be installed in the ground.

Ground Conditions

The typical soil profile determined from the initial site investigation report and complemented by additional Cone Penetration Tests (CPT) comprises a layer of made ground above soft to firm clay down to about 1.8 mbgl underlain by very soft clay and peat (CPT cone resistance < 0.5 MPa) to a depth of up to 5 mbgl, then competent natural ground made of medium dense sand and firm clay above mudstone.


In order to control the settlements of the external paved and asphalted areas surrounding the buildings, Menard designed and installed a solution of ground improvement by Bi-Modulus Columns (BMC). The BMC technique, which consists of Controlled Modulus Columns (CMC) rigid inclusions topped up by Vibro Stone Columns (VSC) heads, combines the performance of rigid inclusions (high settlement reduction factor) with the flexibility of the VSC (excavation through the stone head possible) and was therefore perfectly adapted to the site to allow the installation of the numerous drainage pipes running across the external areas. The VSC heads also help to reduce the thickness of the Load Distribution Mattress required beneath the flexible pavements.

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