As trenchless engineering specialists, we are often asked why our design drawings always follow a left-to-right, entry-to-exit convention. We’re asked why they don’t follow some of the general drafting conventions common in construction. Why not be like everybody else? Wouldn’t it be easier?

The answer is simple: the consistent left-to-right, entry-to-exit convention for trenchless designs minimises construction risk and communicates the method effectively and consistently to stakeholders prior to and during construction.

But how, and why? Many reasons. Let’s explore them below.

Trenchless designs, such as HDD profile and alignments, generally require detailed engineering to minimise risk and maximise constructability. Many standards and conventions apply to this engineering, and specialist software is required, all of which use or incorporate a left-to-right convention. For example:

• Hydrofracture Analysis is completed to determine allowable fluid pressures and resulting risk of frac-out. The pressure calculation incorporated in the analysis includes increasing pressure as frictional losses need to be overcome to return the fluid to surface. As such, the calculation must be completed starting with entry at 0, progressing towards exit. The result is a graph, produced with supporting software, which is plotted in the same convention: 0 at entry on the left, and exit at final length on the right. As such, both the Profile and Alignment and Hydrofracture drawings are illustrated in a left-to-right convention, aligning with the calculation convention.
• Installation forces are calculated via the Installation and Integrity Calculation as per an applicable standard. The standard specifies the ways that stresses are accumulated along the pipeline as it is installed. In order for the calculation to best correlate between the standard and the profile, the design drawing must be drafted in a left-to-right orientation.

Trenchless design documents are used extensively during project construction phases. The consistent left-to-right, entry-to-exit convention further aligns with construction as follows:

• Site mobilisation is faster for drilling crews when the HDD design drawings follow the same convention every time. By using a left-to-right design standard, crews can instantly orientate the design with the project – which is particularly relevant for projects with several bores, fast rates of progression, and shared management.
• Tracking of the bore, each pass, tooling positions, and final install are all measured by the driller from the rig at entry point. As such, for ease of use on site, the “for construction” documentation package is drawn left-to-right, with entry as the orientation – in line with the drilling convention.
• Steering of the pilot hole – one of the most crucial stages of construction – is conducted using proprietary specialist software. This software, into which the designed profile is imported, strictly requires each segment of the crossing to be input from entry to exit. A left-to-right drawing allows for a direct importation of data – while the opposite orientation would require conversion of the data, potentially presenting a risk of data error.
• A left-to-right convention also allows as-builts to be plotted incrementally by the steerer as the crossing progresses from entry to exit. Given the often fast pace of the steering phase, the data inputs to the steering software need to be optimised for quick and convenient use. As such, if a right-to-left drawing was utilised, the practical constraints of the time required to convert the data to reverse for segment-by-segment importation into the steering software would limit the ability to track the as-built effectively, potentially delaying steering progress. Such a situation could also significantly increase the complexity of steering and increase potential for error via the need to complete the steering calculations in reverse, in turn increasing the risk of steering deviation and potential for breaches to steering tolerances and proximity to boundaries and services.

As you can see, there’s many reasons that trenchless design drawings should follow a consistent left-to-right, entry-to-exit convention with trenchless designs. The bottom line is that this aligns consistently with key conventions and models used during detailed engineering and additional stages of construction – the vital stages which check if the pipeline is constructable, as well as actually complete installation. By designing for “real life”, with engineering and construction at the forefront, uncertainty is minimised – and several easily avoidable risks to the project can be completely eliminated.

Finally, one exception can be made to the left-to-right convention in relation to trenchless engineering documentation: the as-built. Given that this is a reference document for asset owners which is produced after construction, it is not utilised as a reference document during completion of the works. As such, it poses no risk to construction and can be produced in either direction, as per client/asset owner preferences.

Entry on the left, exit on the right: an HDD Profile and Alignment as per this standard leaves no room for uncertainty.