ABSTRACT
Secant bored pile walls are frequently used as retaining walls in trough excavation pits to cut off ground water aquifers and are subsequently exposed to ground water pressure loading in addition to earth pressure loads. In order to avoid the extra loading due to ground water pressure in soils with limited permeability, it can be useful to arrange drainage windows within the secant-bored pile walls by means of single primary piles filled with porous concrete without reinforcement cage, which usually has to be placed within the casing under submerged conditions. This concrete may serve as a horizontal arch between the reinforced secondary piles, but it must enable vertical draining between the load carrying construction beams to the bottom of the excavated pit.
In the present submission, the results of several material tests using different mix designs of porous concrete with certain admixtures are presented as well as first and important experiences with a well-suited placement technique for porous concrete in cased boreholes by means of small- and large-scale laboratory tests. It can be shown, that the usual placement technique of employing a tremie pipe is not suited for this type of unsaturated concrete. Instead, pouring with a particular kind of cone and an open conductor pipe has been proven to give satisfying results.
Additionally, special testing methods have to be developed in order to judge the suitability of the desired concrete mix design in preparation for an upcoming real-scale experimental pile installation in Germany.
