The old Allandale Bridge over the N1 in Midrand had to be demolished overnight to make way for the widening of the freeway between Johannesburg and Pretoria. South African demolition specialists, Jet Demolition, contracted by Grinaker LTA and using equipment supplied by High Power Equipment Africa (HPE), had just 16 hours to get the job done.
This section of the freeway was closed at 21h00 on a Friday in November 2009, until Saturday at 13h00. During this period, 22 items of demolition plant – including 15 Hyundai excavators and front end loaders – were used to demolish the old bridge and clean up the area before the interchange was reopened to traffic.
Jet Demolition managing director, Joe Brinkmann says, “This sort of work gets the adrenalin pumping, but there is a lot of planning that takes place first. We plan step-by-step in fine detail and have a clear understanding of exactly how we will take the bridge apart. The equipment we use is obviously vital to the success of the operation and, in this case, so much was needed that we brought in plant from five other sites across Gauteng, Free State and Mpumalanga.”
The bridge carried two lanes of Allandale Road and two pedestrian walkways over the N1. It comprised a four-span continuous post-stressed concrete voided slab deck, 13 m wide and 72 m long; in total 850 m³ of concrete and about 60 tons of steel reinforcement.
Jet Demolition’s site manager on the project, Dennis Oosthuysen says he is very pleased with the results, which were achieved according to plan and with the demolition works being completed within the given time span.
“We chose mechanical demolition over blasting for several reasons,” says Oosthuysen, “including limited access to prepare the bridge as it was in full service until shortly before demolition began. Furthermore, the use of excavators equipped with hydraulic hammers and demolition tools allowed for controlled incremental demolition without the risk of large concrete pieces dropping and damaging the road below.”
Brinkmann notes that the road beneath the bridge had to be covered for protection before any work could start and to assist with the cleanup operation post-demolition. “Our staff and the five tipper trucks took care of the removal of debris efficiently.”
Managing director of HPE Africa, Alan Grady says, “We have been the sole South African distributor of Hyundai earthmoving equipment since 2000 and have a long-term relationship with Jet Demolition. Their work is extremely demanding on the equipment and we ensure that they are supplied with equipment that will stand up to the task. By all accounts, it certainly did on this project.”