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Case study: Vacuum Excavator
Safe Excavation in Congested Footways
A565 North Liverpool Key Corridors (NLKC)
The NLKC project team in Liverpool are working in conjunction with Liverpool City Council on the £18 million road scheme. The works include improved paving, traffic signals and street lighting, involving a lot of digging around existing buried services.
What is Vacuum Excavation
Vacuum excavation is a safe means of excavating around underground utilities, using an Air Lance to agitate the ground.
Prior to the decision to use a Vacuum Excavator there had been a number of cable strikes in various locations throughout the project. Each of which have inflicted a number of negative implications.
Cost of a cable strike
- Reduction of utility damages
- Self contained excavation, leading to increased site cleanliness
- Excavation sizes reduced up to a third compared to the use of a mini-digger
- Hydraulic powered arms with extension tubes to increase manoeuvrability
- P.E insulated pipe to insulate vehicle and workforce in high risk areas
- Increased productivity compared to convention methods in highly congested areas
Vacuum Excavation versus Hand Dig
- Normal soil conditions
- Heavy soil
- Dry and heavy soil
- Wet and heavy soil or clay
- Moderately heavy soil
- Muddy soil, gravel and crushed rock
- Sandy soil
The table below shows a comparison against the labour and plant costs for the varying excavation methods in locations of comparable conditions on site over the course of a single 9-hour day.
The average cost of a labourer is £150.00 per day, with the associated costs.
The total cost of a Vacuum Excavator is £1,200.00 per day, including the associated labour.
|Method of excavation||Labour||Plant||Excavated soil (m3)||Cost per m3|
Therefore the VacEx would require 4.98 m3 of soil available to excavate in order to remain economically viable.
This table excludes the costs associated with cable strikes and the delays incurred which the risk of which are significantly reduced through the use of a Vacuum Excavator.
The areas in which the unit is used can take advantage of the machines self-contained excavation. This means that the spoil associated with the works is immediately removed, leaving a tidier site on display to members of the public.
- Minimised damage to tree or shrub roots as the vacuum is able to remove the ground between them in conjunction with the Air Lance, therefore not affecting the underground environment.
- Less lorry movements to and from site –providing a reduction in the carbon footprint.
- Self contained excavating team leading to increased site cleanliness, by tipping up to 8 cubic metres of spoil in a designated on site area.
- Reduction of Grab loader time on site, minimising disruption to Customers and local traffic and significant reduction in 3rd party damages.
- Excavation sizes reduced by up to a third compared to use of conventional methods.
Lessons Learnt / Advice / Review / Conclusion.
The Vacuum Excavator has proved itself as a much safer and more productive method of excavating around buried services, however some conditions were identified to ensure optimal performance can be achieved.
For all the units capabilities, labour is still required for breaking out areas of hard ground, such as tarmac, where neither the main suction tube or Air Lance will suffice.
Therefore, a good run-up of available and prepped work is required in order to ensure that the machine is able to work at the levels of productivity required, as it is too expensive to have standing around.
The locations in which the VacEx is most effective for use would be the areas of excavation close in vicinity to buried cables, where works would usually be limited to hand-dig. This is where the biggest increase of productivity can be achieved.
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