Subsurface utility strikes continue to be a significant challenge for AEC stakeholders. The strikes not only hurt monetarily but also are a considerable cause for loss of life of workers, and people who are either using that utility or are in the vicinity when strikes happen. Project owners increasingly realize this challenge. To mitigate this, there have been dedicated efforts by stakeholders to develop policies and standards and implement technologies to create accurate models of underground infrastructure to bring long-term benefits to construction projects.
The Sydney Light Rail Project, a PPP contract worth $ 2.1 billion, was a 12-km-long light rail project with the Department of Transport South Wales to be finished by 2019. To evaluate and assess the existing underground infrastructure and prepare for its relocation, to make space for the new rail light infrastructure, the Department of Transport of New South Wales undertook the initiative to map 5,000 subsurface utilities using traditional potholing technologies around the proposed site. During the planning stage, the Department concluded that 500 existing subsurface utilities needed to be relocated for the light rail to be constructed.
During the construction of the Sydney Light Rail Project, a number of challenges related to the project surfaced. It was found that that as-built data provided by the utility owners and the location and the material information was often incorrect, which lead to significant delays. Also, an additional 400 utility lines were found which could not be traced on the utility maps provided by the DoT of New South Wales.
Before the second underground mapping exercise for the Sydney Light Rail project, the project owners consulted ACIL Allen Consulting to conduct a research on the economic impact , which specified the need and the economic impact of having an accurate 3D map of the underground utilities. Based on Allen’s study and the importance realized of underground mapping, it took nearly one month for the contractors to cross-check each unidentified utility using new technologies such as Ground Penetrating Radar etc., of which some utility provider claimed few, but the majority of them were no longer in service. By way of geolocating the subsurface utility networks in the second phase, the stakeholders involved in the project were able to digitally map the surface and prepare accurate digital 3D maps based on the systemic surveys. The 3D models were created using the BIM principles to initiate the construction process and improve construction productivity.
Further, ARUP developed a GIS-based utility clash detection system, which presented an automated interaction of the proposed rail infrastructure with the existing subsurface utilities, helping the contractors to plan well-ahead their construction plan and process around the utility networks. The system incorporated inputs from over 100,000 individual underground utilities (in varied formats) bringing them together into a single usable and readable interface. This enabled stakeholders to make informed decisions and increase efficiency during construction.
Since the first underground mapping exercise failed, the Sydney Light Rail project did not achieve significant value-proposition as it would have had accurate 3D maps of the underground utilities were available before the study. According Allen Consulting, if these maps were available and the project did not have to spend additional money and hours in rechecking and re-evaluating the ground-beneath conditions, the work would have completed “at least 1.5-year prior with lesser cost and reduced amount of risk”. This is also to say that there were no additional costs incurred and timelines crossed — as the possibility of such a scenario was already accounted for in the project plan and schedule.