Bi-directional Static Load Testing – State of the Art

The use of static load testing in optimising design and providing verification of suitability and constructability continues to be unsurpassed in the foundation industry. The utilisation of top load reaction testing appears to be that with which most European engineers are familiar, but a variation on this, which has become just as conventional in some parts of the world, is the use of bi-directional testing allowing tests to near ultimate capacity to be performed more conveniently, economically and safer. A purpose build jack, (such as an Osterberg Cell) is cast within the pile at a chosen location typically half way down the “capacity length” of the pile in a manner in which the upper and lower portions of the pile are tested against each other. Techniques for computer controlled loading and remote control by GSM links can readily be applied and the quality of data recorded and reliability is excellent. The numerous applications and methods of analysis are described. Where the confidence in prediction of capacity is not high, a technique using O-cellsTM arranged at two different levels maximises the information that can be retrieved from a single test pile by sequentially loading from one level and subsequently loading at the other. A review of the advantages and disadvantages is presented and how some of the perceived shortcomings have been overcome together with an appraisal of current usage around the world.