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The ground engineering challenge

Work on the Kent History Centre in Maidstone has begun, housing historic material dating back to 699AD. Client Waring contractors employed piling specialists Central Piling as it became evident that the soil conditions would pose significant ground engineering challenges.

Work on the Kent History Centre in Maidstone has begun, housing historic material dating back to 699AD. Client Waring contractors employed piling specialists Central Piling as it became evident that the soil conditions would pose significant ground engineering challenges.

Limestone and sandstone bands were present at seemingly random depths starting from just 1m beneath ground level. This precluded the use of a driven piling technique. The presence of the high sand content within the Hythe Beds prevalent to the site meant that a rotary technique with coring equipment would be too expensive.

CFA piling

A continuous flight auger (CFA) system was the most attractive alternative. But penetration of the bands of rock was not straightforward.

Despite advances in drilling head equipment, machine torque and pull down strength, conventional CFA drilling heads would have been unable to clear all of the limestone, as its strength and size varied significantly. A different approach was agreed with the client’s managing engineer. This involved a rig probing, using a rock drilling head to penetrate obstructions up to a 10m depth. Once through the rock, a CFA rig with a concrete exit flap would follow and complete the construction of the piles.

In the event that rock could not be penetrated at pile locations, Waring’s site engineer would set out alternative pile locations based on cap layouts predetermined by the on-site structural engineer.
Two 40T Soilmec CM50 machines were used to install 350 number piles of 350mm and 400mm diameter to depths of between 13 and 25m. Works including three expendable test piles were completed in 10 weeks under the £230,000 contract.

 

 

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