Vacuum excavation (VacEx) has become a routine working practice for utilities during their maintenance, repair and replacement of buried assets. Benefits in urban environments include more rapid exposure of the assets, particularly where multiple and congested services are present, smaller excavation footprint, reduced damage to assets, improver operative safety, and reduced disruption and delay to highway users.
In contrast to its successful (if limited) deployment in urban environments, the gas industry has made only limited use of the technology (on average three times per year over the last five years) for Local Transmission System (LTS) asset excavations in rural environments - despite its acceptance as an approved practice under current safe working guidelines. LTS challenges are different - gone is the requirement for a rapid, low intervention dig with minimal impact on road users, however the ability to safely displace hand digging operations in close proximity to higher risk assets does offer scope for VacEx to deliver substantial value to the business and its stakeholders.
A feasibility study (Stage 1) has been conducted under SGN’s supervision to understand the use and perceived attitudes within SGN towards vacuum excavation near LTS assets in rural areas and questions the technical, logistical and risk barriers restricting its use. This study identified what technology developments and modified working practices might facilitate its extended use, for example as a safe excavation practice around valves, standpipes and protective sleeves. The vision is to remove all hand dig operations around LTS assets.
The scope of work for the second and the third stages of the project following the feasibility study conducted in Stage 1 is outlined below. In Stage 2 of the project, an excavator head will be developed and go through laboratory testing and validation. The validated excavation head will then be integrated in the VacEx unit in Stage 3 of the project and the system will be tested and validated on site in the UK.
Benefits
This project will investigate the feasibility of developing an innovative solution to reduce costs, increase safety and improve efficiency when excavating on the Local Transmission System (LTS).
Learnings
Outcomes
After the initial design of each nozzle, using CFM models and computer simulations different variations of each part of the design were tested to find the most optimum combinations of dimensions to maximize soil agitation. The results were validated by numerical and mathematical techniques which were used to create the conceptual design of the excavator head.
Four different nozzles were manufacturing and tested which validated the effectiveness of these nozzles in agitating hard compacted soil. After finalizing all of the soil testing, nozzle 3 was found to be the ideal choice for moving the most amount of soil per blast. Nozzle 3 would remove most soil and would allow the compressor to run at a lower duty cycle by only using the low-pressure setting. Other factors were considered when choosing the most optimum nozzle for the VELTS excavator head such as weight, form factor, the footprint of equipment, and the volume of material the vacuum excavator can move.
After completing the detailed design of the prototype, all the materials were ordered, and custom-made parts were manufactured. For easy fabrication and assembly, the nozzles were integrated into the excavator head eliminating the need for a variety of fasteners and components.
3 different configurations of excavator heads were developed and fabricated to test these different configurations under different scenarios to establish the best possible solution. Different tests were conducted to see the effects of the following variables:
- Powering multiple nozzles
- Cycling nozzles on and off in different patterns
- The number of nozzles designed into the head.
- The excavation process
- Pattern to follow
- Starting height
- Velocity of excavation
Each prototype was tested from 200 to 500 PSI . Our findings showed that prototype 3 met all of the conditions outlined in the specification document. The prototype is light and has a compact design to allow free movement on site while being able to agitate hard compacted soil on mass using soft touch technology.
Lessons Learnt
The project progressed successfully from TRL 3 to TRL 5 which tested the prototype of the VELTS system. Following completion of the testing a number of observations were made which can be applied to other projects:
· It was vital to ensure design iterations were made after each round of testing which refined the design of the prototype.
· As the LTS soil types can vary from hard compacted clay to softer soil types, testing incorporated different environments to ensure system would be fit for purpose around LTS assets.
· As the project progressed, engagement was important to understand any other use cases that Velts could be utilized on. With the testing being shown live, the project team were able to specify other use cases in addition to the LTS excavation that Velts would benefit ie work in close proximity to HV cables within our rural environments to improve our safety in these high risk areas.
