Case study: Safe excavation in congested footways

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 and it was important that safe excavation practices were carried out throughout.

Liverpool Vacuum Excavator Hire

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 vac ex 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

  • Time
  • Money
  • Reputation
  • Life

Primary benefits

  • 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
  • Water

Commercial

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.

Liverpool Vacuum Excavator HireLiverpool Vacuum Excavator Hire

Method of excavationLabourPlantExcavated soil (m3)Cost per m3
Vacuum Excavation2VacEx14.080£106.53
Hand dig3None1.495£301.00

Therefore the suction excavator 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.

Liverpool Vacuum Excavator Hire

Environmental Impact

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.

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 vac ex 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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