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Cone clarification


Lankelma has recently completed a ground investigation for Rock and Alluvium at East Side Plaza, Gun Wharf Quays, Portsmouth, as part of a regeneration project by Berkeley Homes.

The contractor wanted to install 800 piles, and Lankelma was called in to determine the ground conditions, provide a detailed ground model of the site and optimise pile design.

Of particular interest was a dense to very dense sand unit at 22m depth that had been found by an earlier investigation.

Lankelma's 13 day investigation consisted of 76 cone penetration tests (CPTs), from ground level to depths up to 30m, carried out using a 22t 6x6 wheel mounted CPT truck.

The cone resistance and local side friction are measured by strain gauges attached to the cone. These records are transmitted to a touch screen computer that acts as a data logger and records the data at 100mm intervals.

Pile design was performed as the investigation progressed.

To aid the design process, undrained shear strength (S u) and equivalent standard penetration test N60 values were plotted against depth for each CPT.

The nal report included a 3D ground model showing depth to the dense sand, together with a contour plot detailing its thickness across the site.

www. lankelma. co. uk

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