Hybrid Pile n Definition A pile installed by

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.

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. 5 m headroom Solution – 344 mm dia temporary cased and 300 dia auger in upper 4 m - casing advanced ahead of auger. Install closed ended steel tube 273 dia then bottom drive to set at 15 m.

Case Study 2 n Rail Project - Scotland Problems – Very dense material in upper 5 -6 m (SPT 30 -50), major obstructions, overlying very loose material (SPT<5), rockhead at 25 m. – Vibration Solution – In upper 6 m we used a Symmetrix concetric ODS to penetrate dense material/obstructions. – The base of the pile was grouted to form a 1. 5 m deep plug. Pile was then left for three days, drained then bottom driven keeping vibration levels <8 mm/sec (PPV).

n Case Study 2 Static Load Test Results 4 n n Pile vertical load capacity of 3250 KN was held but pile reached its serviceability level at around 2. 75 x working load (2750 KN). The pile also withstood a significant horizontal test load of 300 KN although its serviceable limit was reached at approx 2. 0 x working load (200 KN).

Case Study 3 n Environmental Project Problem – Highly contaminated ground Solution – Proposal is to install a 323 mm dia bottom driven steel tube installed to rockhead at approx 3 m below ground level. Pile toe is sealed using a 0. 5 m deep concrete plug. – Concrete plug will then be drilled out using water flush rock roller to form 3 m long x 250 dia socket – Solution has to cater for seismic event.

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