By David Glover, Principal Geotechnical Engineer, Tonkin + Taylor
With many methods and technologies available for trenchless pipe installation, there is no one-size-fits-all solution – selecting the right technique for the right job is dependent on understanding the ground and groundwater conditions and basing your decision around that.
Gauging the ground
The best way to gain a thorough understanding of the ground conditions at any job site (or prospective job site) is to engage a geotechnical engineer prior to commencing work. A horizontal directional drilling (HDD) or other trenchless technology contractor will be able to advise on the right tool for the right conditions. However, accurately gauging those conditions is the challenging part.
Geotechnical consultants specialise in assessing the conditions of the ground and groundwater to determine the most effective method of installation. Although there is some publicly available information on ground and groundwater conditions – such as geological maps and GIS tools like “Visualising Victoria’s Groundwater” in Victoria – a geotechnical specialist will provide much greater insight.
Being informed about what lies beneath the surface is crucial for determining the most suitable tools for the job. It’s essential to note that geotechnical consultants vary in expertise, so ensure your consultant has extensive experience with trenchless technologies before hiring.
Geotechnical engineers work across many fields, so it’s important to hire a consultant with experience in your specific area of interest. It’s also recommended to check that your geotechnical consultant is appropriately accredited and a registered professional engineer to ensure compliance with current regulations.
Geotechnical assessment involves a combination of research and field analysis. Firstly, data will be gathered pertaining to the project area, looking at any previous reports on the ground conditions and soil composition. Then, the geotechnical consultant will conduct fieldwork by drilling boreholes into the ground and testing samples to gain a greater understanding of what lies beneath the surface. The combination of these methodologies provides the greatest insight into the prevailing ground conditions at any job site.
Going to market
Following the desk study and ground truthing, the geotechnical specialist will prepare a report on their findings. The report will advise on the conditions of the soil and groundwater, which will inform the drilling conditions that will likely be needed. Going to market with a ground condition report ensures you are equipped with thorough knowledge of the project requirements, and enables potential contractors to easily determine the correct tools for the job.
There’s a saying in the industry: “You pay for a geotechnical investigation whether you want it or not”. Without a geotechnical report, contractors are bidding for jobs based on only a surface understanding of the project conditions and requirements. This often results in big cost increases and project delays down the line, as there may be undetected surprises hidden underground.
Different ground composition can affect the performance and accuracy of drilling, such as unexpected surface conditions pushing the drill out of alignment. Changing course or equipment midway through a project can push contractor fees through the roof.
Understanding the ground conditions allows all parties to come to a project from an informed perspective, enabling the best decision-making for the conditions and promoting a collaborative approach to trenchless pipe installation.