Hybrid Pile Definition

– A pile installed by combining driven and auger/drilled techniques.

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

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.

Case Study 2 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).

Case Study 2 Static Load Test Results

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Pile vertical load capacity of 3250KN was held but pile reached its serviceability level at around 2.75 x working load (2750KN).

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).

Case Study 3 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.

Hybrid Advantages Environmental Impact

– reduced spoil– mitigates risk of grout seepage– low vibration

Cost Effective– due to driven pile element

Versatility– can be employed in a wide range of

ground conditions