1. Hybrid Pile n Definition –A pile installed by combining driven and auger/drilled techniques. n Why use a ‘Hybrid’? –by incorporating a ‘driven element’, the pile installation costs are significantly reduced. –On many occasions in the UK and further afield expensive drilled solutions have been adopted where a cheaper and quicker hybrid solution would be more economical.

2. Case Study 1 n Major Bridge Project - Scotland Problems –Concerns with vibration and ‘drawing in’ of granular material with temporary cased auger/sub-artesion pressure causing blow back into pile bore –3.5m headroom Solution –344mm dia temporary cased and 300 dia auger in upper 4m - casing advanced ahead of auger. Install closed ended steel tube 273 dia then bottom drive to set at 15m.

3. Case Study 2 n Rail Project - Scotland Problems –Very dense material in upper 5-6m (SPT 30-50), major obstructions, overlying very loose material (SPT<5), rockhead at 25m. –Vibration Solution –In upper 6m we used a Symmetrix concetric ODS to penetrate dense material/obstructions. –The base of the pile was grouted to form a 1.5m deep plug. Pile was then left for three days, drained then bottom driven keeping vibration levels <8mm/sec (PPV).

4. Case Study 2 n Static Load Test Results 4 n Pile vertical load capacity of 3250KN was held but pile reached its serviceability level at around 2.75 x working load (2750KN). n The pile also withstood a significant horizontal test load of 300KN although its serviceable limit was reached at approx 2.0 x working load (200KN).

5. Case Study 3 n Environmental Project Problem –Highly contaminated ground Solution –Proposal is to install a 323mm dia bottom driven steel tube installed to rockhead at approx 3m below ground level. Pile toe is sealed using a 0.5m deep concrete plug. –Concrete plug will then be drilled out using water flush rock roller to form 3m long x 250 dia socket –Solution has to cater for seismic event.

6. Hybrid Advantages n Environmental Impact –reduced spoil –mitigates risk of grout seepage –low vibration n Cost Effective –due to driven pile element n Versatility –can be employed in a wide range of ground conditions