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

4

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