Traditionally construction of basement substructures involving hoists, conveyors and skips has been extremely labour intensive, dirty and environmentally disruptive. This has become such a problem in terms of congestion that many Local Authorities now prohibit the use of static skips or builders skips on the public highway overnight; preferring instead a ‘wait and load’ method of disposal where spoil arising is placed in 25kg bags, hoisted to the surface and deposited into a wait and load vehicle. For example, a relatively modest basement measuring 40 square metres, would amount to 8,900 bags of spoil arising which is a time consuming and expensive process to remove.
Over the last three years Room Below have experimented with alternative methods of excavation. We considered suction excavation, and although this was more efficient than using labour intensive methods, it was found to have a number of insurmountable drawbacks. Although cleaner than traditional excavation it was still messy and suction excavators, as used by Utility Contractors, are generally mounted on 26 or 32 tonne chassis cabs which are not compatible for use in London’s narrow streets.
Instead we have developed and now use the next generation of equipment, known as Vacuum Excavators, which can be mounted on a much smaller 16 tonne chassis cab. To enable efficient disposal of spoil, each site is fitted with a 150mm diameter static line with a number of manifold points to which the vacuum excavating pipes and tools are connected. The lorry mounted Vacuum Excavator then connects to the static line and vacuums a 6 cubic metre load in approximately 20 minutes. By comparison this would take almost four times as long using traditional conveyors, and a whopping 31 times as long using ‘wait and load’.
Excavation and the removal of spoil arising is a major part of basement construction. Vacuum Excavation is designed to improve and speed up the process while minimising environmental impact. Vacuum Excavation is cleaner and less disruptive and for these reasons will become the preferred method of excavation where safety and environmental impact are understandably of major concern.
Vacuum Excavation is faster, cleaner, safer and is less environmentally disruptive on the surrounding neighbourhood by negating the need for conveyors and skips which clutter the public highway.