Abstract:
A targeted jet grouting and compaction grouting project was successfully carried out to stabilise a section of the eastern retaining wall and the abutment foundations of the M1 / Oxford Road bridge, which were severely destressed as a result of more than 400mm of settlement of the foundations and the approach fills since construction in the early 70s. The remedial design was based on a detailed geotechnical investigation, which identified a deep weathered zone of soft silts and clays due to faulting beneath the epicentre of the settlement. The M1 motorway, which is a major arterial road leading into the Johannesburg CBD, had to remain open to traffic throughout the contract, while all construction work had to be carried out from on top of the motorway as the retaining walls defined the limits of the road reserve. Purpose made standpipes had to be installed on the outside of the walls in the neighbouring properties to control the drilling and grout returns being carried out some 3m to 5m above the ground level while working over the edge of the retaining wall and grouting beneath the toe of the foundations. Keywords: Jet Grouting, Compaction Grouting, Case Study, Settlement Reduction