UK: Altrad RMD Kwikform says it used ‘revolutionary’ techniques as part of a complex project to assist High Speed 2 contractor Mace Dragados with the construction of a London Underground traction substation at Euston station.
Altrad RMDK says this approach meant ‘more could be done with less’, with fewer and smaller props used on a 20 m deep excavation which meant more working room, less to transport and lower overall costs.
The excavation required three levels of temporary propping. This had to be designed to allow for daily fluctuations in forces due to ambient conditions; props in full sunlight behave differently and attract more load than those in shaded areas.
Current design guidance is aimed at above-ground permanent steel structures, but Altrad RMDK felt a novel approach taking depth into account could achieve a more economical design.
Drawing from its experience in previous projects where actual total prop loads are typically 40% to 60% of design loads, Altrad RMDK proposed that the temperature ranges for each level be determined individually based on weather records and actual installation/removal dates. This made use of the diminishing effects of solar gain at depth, which resulted in load reductions of around 30% compared to conventional design codes.
A digital twin of the excavation including models of all surrounding buildings was used to better understand the effects of sunlight throughout the construction period.
