In situ testing of barrette foundations for a high retaining wall in molasse rock

Barrettes are common foundations for high-rise buildings, especially because of their high bearing capacity, for vertical as well as for lateral loads. In this paper, it is shown how these were adopted and tested for anchoring a 27 m high retaining wall in rock on a slope located in the centre of Zurich. The monolithic 10 × 1 × 25 m deep barrettes, excavated and built in layered rock (Upper Freshwater Molasse), are also intended to stabilise the slope. The main contribution to their bearing capacity is given by the contact strength between the reinforced concrete and the rock. Two full-scale pull-out tests, instrumented by distributed fibre-optical measurements, are carried out to investigate the contact strength between rock and reinforced concrete. The results show that dilatancy at the contact caused by the irregular excavated surface has a strong influence on the bearing capacity. Additionally, the distributed fibre-optic instrumentation allowed progressive crack propagation of the reinforced concrete in the barrettes to be detected during the test. Inverse analysis of the rock and concrete tensile properties are obtained within a finite-element calculation, which takes into account the non-linear properties of the reinforced concrete and the rock.