Driving Resistance as a Design Validation Tool: Observations from Small Displacement Piles Driven into Chalk at Dover Western Docks

Whilst there is a pressing need to update guidance for the design of driven piles within chalk, there is also a need to validate assumptions made during the development of ground models that inform the design of piles in chalk; a complex geological stratum an d geo - material. The Dover Western Docks Revival is one of the UK’s largest nearshore piling projects in recent years, comprising ~700.no large diameter piles driven in combination with AZ sheet piles to form a 2.3km combi-wall, retaining to 22.5 meters of reclamation fill material. Driving records were reviewed to confirm geotechnical design assumptions by correlating relative ‘resistance-set’ energies from piles driven adjacent to rotary cored borehole data. The review identified the critical interface between structured and structureless chalk required to validate pile design and discovered an unidentified dissolution feature which required the redesign of a ~35m cantilever section of quay wall. Driving records demonstrate the limiting shaft resistance is quickly reached within chalk and a lower bound ‘set-up’ factor of between 3.1 and 3.6 is estimated. 82.no pier piles installed with hydraulic impact hammer record increased mean driving resistance 238% between EoD an d time delayed over-drive, reducing to 174% where vibro-driving was undertaken to within several metres of the design toe level.