Technical Specifications
The Challenge
Why were the piles required? To support a brand new 10 storey student accommodation block for the University of Portsmouth as part of a regeneration programme for the Fratton area.
What were the tricky elements of the job? It became clear that plunging reinforcement into the freshly cast piles was troublesome, a combination of a layer of sand around 5m below ground level and a concrete mix that was susceptible to filtration led to initial problems on site.
What were the ground conditions? Ballast and sand over a silty clay at depth.
The Solution
What rig was used? SoilMec SF50
Was a specific concrete mix needed?
A review of the initial mix design found that the mix was lacking it smaller aggregate meaning the concrete was more susceptible to filtration in the ground, this is where some of the cement and water in the concrete filter into the surround sand creating a band of stiff concrete that reinforcement cannot be plunged through. The mix was altered by the Franki technical department which solved the issue.
What was the benefit of using Martello for this project?
A quick technical response lead to minimal delays on site
Any other interesting facts about the project?
We are planning a site visit for the University of Portsmouth Engineering Geology and Geotechnics MSc students, they can view how a CFA pile is formed and understand the geotechnical issues Franki have overcome on this project.
