THE SCHEME
The Help for Heroes’ Recovery Centre, within Devonport Naval Base is a purpose-built facility for both veterans and service personnel coping with life-changing injuries and mental health issues. The £23 million complex includes specially adapted accommodation, rehabilitation equipment, a 25-metre swimming pool, a hydrotherapy pool, a physiotherapy suite with individual treatment rooms and a sizable gymnasium.
GROUND CONDITIONS
The project was located on land that was contaminated with asbestos, hydrocarbons and heavy metals. To ensure any risks were mitigated, the client undertook a programme of ground remediation prior to the piling works commencing. To manage the residual risk of material being left in the deeper areas of made ground, the team opted to use the Screwsol method, a continuous helical displacement solution, which would ensure no spoil arisings would occur during piling works.
OPERATIONS
The Screwsol technique resembles standard CFA methodology in terms of the tools used and concreting process. A Screwsol cut head auger is essentially 350mm in diameter with an additional cutting edge protruding a further 75mm. Subsequently this produces a 350mm diameter pile with 75mm helical flights protruding from it, resulting in an actual central core diameter of 350mm but an effective diameter of 500mm. This increases the surface area and geotechnical capacity of the pile.
As the bore progresses, the auger displaces the ground it is going through, increasing its relative density. This method eliminates spoil arisings and is therefore an excellent method to use in non-dense, non-cohesive or semi-cohesive and/or contaminated ground.
In total, 288 Screwsol piles were bored to an average depth of 14m across the site. The piles were a 350/500 combination, providing the optimum load bearing capacity for the structure.
LOGISTICAL CHALLENGE
Working inside the Naval base provided several logistical challenges for the team, including ensuring all personnel, vehicles and materials were booked in at least 48 hours in advance. To achieve this, close collaboration with the supply chain, site team and other stakeholders was essential.
