When two bores right a wrong

Experience and having the right equipment can be the difference between still getting the job done to specifications, and expensive delays. Edge Underground faced this situation when a laser on its AXIS laser guided boring machine was unknowingly faulty, resulting in a straight, but off grade pilot line.

Despite this, the company’s experience and the AXIS’ ability to retract allowed the bore to be re-shot, ensuring an on-grade line was achieved with no delays. In January 2024, Edge Underground was called in at the last minute by Connell Civil Group to install a 427OD GRP jacking pipe at 8.5m deep for a Clyde North project.

A pipeline installation contractor was already engaged for the project, but due to difficult ground conditions – high water table, and a clay and sand mix – they were struggling to meet the project’s tight timeframes.

An unexpected issue

When Edge Underground arrived on-site, the team set up and completed the pilot line, but it soon became clear there was a problem. “Once we completed the pilot, we surveyed the shot and found that it was 170mm higher than specified. It was a perfectly straight line, but the grade was wrong,” Edge Underground managing director and founder Stuart Harrison said.

“Despite the equipment being tested and checked beforehand, we discovered the laser had been damaged without us knowing.” Usually, this would have caused a problem because the only recourse would have been to dig up the pipe, resulting in additional expense and delays. However, thanks to Edge Underground’s unique microtunnelling technique and the retractable capability of the AXIS, the experienced team could overcome the hurdle.

“We explained what happened to Connell and they gave us a chance to fix it when we told them we had a solution that would still achieve an accurate installation without the need to excavate,” Harrison said.

Fixing the mistake

Harrison said the team retracted the pilot and re-shot the line in the same bore, adjusting it to achieve the correct grade. “Because we used a method where we were going from a 350mm pilot line to 450mm, we had space to adjust the line and get it right – and it came out on grade,” he said. “Mistakes happen on trenchless projects no matter how good you are.

Other contractors would pack up and leave if a mistake like this were to occur.” But the team at Edge Underground prides itself on getting the job done and doing it right. “Our experience, knowledge and market-leading equipment mean we have the ability to adjust and achieve a successful installation without impacting the project, even when a mistake occurs,” Harrison said. Edge Underground then quickly completed another two lines.

“The high-water table and unexpected pockets of sand created challenging conditions, and I understand why the other contractor was still struggling to complete their lines,” Harrison said. “Vacuum machines are generally considered to not perform well when there is a high-water table, but our modified AXIS gives us abilities beyond anything that could reasonably be expected of other machines. “Combined with our expertise, we successfully completed the project.”

Meeting expectations

According to Connell Civil Group managing director Pat Connell, Connell Civil Group prides itself on quality and providing its clients the outcome they paid for. “When we heard the line was incorrect, we fully expected to dig it up, but Edge Underground provided an alternative solution, allowing the project to be completed trenchless and meeting the client’s specifications,” he said.

“The willingness from Edge Underground to accept their mistake and fix it showed great professionalism.” Connell emphasised the competence of the Edge Underground team and its ability to get the job done. “Their knowledge, experience and equipment were clear in their ability to do a job to specifications even in challenging conditions,” he said. “We definitely want to work with them in the future.”

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