Government agencies and construction firms are recognizing the significant benefits of an accurate map of underground infrastructure for construction projects. Here we describe how accurate models of underground infrastructure bring practical benefits to construction projects. Sydney Light Rail is particularly interesting because a consulting firm hired to study this five year project concluded that if a complete and reliable 3D map of underground infrastructure had been available at the project planning stage, the project could have been completed at least one and a half years sooner. The Alabama Department of Transportation estimated that it saved $10 million by using 3D modeling of underground and above-ground utilities on a major highway interchange project. Perhaps more importantly the project remained on budget and on schedule. The Expo Milano project estimated that it saved about €16 for every euro invested in improving the reliability information of underground infrastructure. This includes direct costs only and does not include non-quantifiable, benefits such as better safety for both workers and the public as well as fewer traffic disruptions. One of the innovative aspects of a highway revitalization project in Cedar Falls, Iowa was the development of a 3D model of underground utilities before the start of the design phase. This enabled the detection of 200 utility conflicts prior to beginning construction. Avoiding utility conflicts during construction was the primary reason that the project completed on schedule and 3% under bid saving the City $700,000. From a public safety perspective. Furthermore, it was estimated that accurately knowing the location of underground utilities resulted in an 89% reduction in personal injury accidents. For a gas pipeline project along a busy highway in Washington State, an accurate 3D model of underground infrastructure was created using GPR and potholing prior to design. Using the 3D model 170 conflicts were detected, representing points of intersection of the design for the new pipeline with other utilities. Several alternative routes were assessed and the costs and benefits of each were computed and compared in order to determine the optimal routing for the new pipeline. 3D visualization of the alternative routes helped the designers show stakeholders the advantages of alternative routes.
Sydney Light Rail
The Sydney Light Rail Project is a $2.1 billion PPP project for 12 km of light rail to be completed by 2019. Prior to awarding the contract for construction the Department of Transport for New South Wales undertook 12 months of night work to map 5,000 subsurface utilities along the route. 500 existing subsurface utilities were identified for relocation to make way for the new light rail infrastructure.
The first problem that was encountered was that as-built information from utility providers was frequently unreliable - incorrect location, incorrect materials, and so on - which caused disruption and delays with construction. The second problem was that during construction an additional 400 unknown services, not on the DoT maps, were found. Each of the unknown utility services that was encountered had to be treated as potentially live and all utilities in the area had to be contacted to try to identify the service, a process that typically required a month. Of the 400 unknown services that were found, a few were claimed by one of the utilities, but most of the unmapped services were found to be no longer in service. Unnecessary costs to the construction program were incurred as a result of these unforeseen delays. In addition completing the relocation of utilities was delayed by 5 months.
ACIL Allen (3D QLD Road Map - preliminary findings. Brisbane: #D QLD Task Force 2017 reported in Economic Value of Spatial Information in NSW 2017) has estimated that if a complete and reliable 3D map of underground infrastructure had been available at the project planning stage, the project could have been completed at least one and a half years sooner, at less cost with a much lower level of risk. While the project at that time of the study remained ‘on time and on budget’, ACIL Allen says that this is only because the risk of delays and additional costs resulting from unidentified underground utilities were included in the contract pricing and schedule.
Construction folks will not be surprised by this. It once again points out the advantage of 3D models replacing unreliable as-builts because it enables a process that speeds up project development because it leverages existing engineering data rather than requiring a "complete resurvey" (usually incomplete with respect to underground utilities) at the beginning of every project.
Alabama DOT I-20/I-59 Corridor
For the largest construction project in the state of Alabama's history, the Alabama Department of Transportation (ALDOT) used ground penetrating radar (GPR) and other technology to create an accurate 3D model of underground infrastructure prior to designing a replacement for one of the busiest interchanges in the state. ALDOT estimates that the 3D model, which was provided to all contractors bidding on the project, saved millions of dollars and reduced the risk of budget and schedule overruns.
The location of existing underground utility infrastructure is more often than not poorly known which creates significant risk for infrastructure and highway construction projects. Typically on highway construction projects, the right of way is chosen, the highway designed and the project readied for construction before the one-call centre is contacted and the affected utilities arrive to detect and locate their underground facilities, usually in 2D. The utilities that have been detected are then moved to make way for building the highway. Not infrequently the location of the identified utilities turns out to be unreliable and during construction other unidentified utilities are encountered both of which can lead to delays and to budget overruns.
The I-20/I-59 Corridor is the largest construction project in the State of Alabama’s history with a cost of $750 million. The project had a very tight timeframe. ALDOT's Design Bureau’s Visualization Group was tasked to provide a complete 3D proposed model for building information modeling (BIM). The BIM model needed to provide the information necessary for multiple uses including: visualizations, design checks, construction analysis, clash detection, right-of-way negotiations, lawsuits, and aesthetics. The model had to be very accurate because it was intended to be provided to the construction bidders to enable more accurate cost estimates and lower bids.
One of the important challenges faced by this project was utility coordination because the interchange is situated in Birmingham's business district. Realizing that underground utilities can make or break a project's schedule, ALDOT invested a considerable effort in locating utilities and creating a 3D model of above and below-ground utilities. Potholing and scanning with ground penetrating radar augmented existing as-built records to enable ALDOT to create an accurate 3D model of underground utilities. 3D is important because what may appear to be clashes in 2D may not actually be. Also it was much easier to explain to utilities in 3D that a costly move of a utility line is not necessary. ALDOT’s Visualization Group was tasked with detecting clashes between the proposed design with the existing conditions. Every contractor bidding on the project got the full 3D model. Because of the reduced risk associated with underground infrastructure ALDOT estimated that it saved over $10 million by using 3D modeling of underground and aboveground utilities. To date the project is on budget and on schedule. After completion of the project ALDOT plans to retain the 3D model which can be reused for other projects in the same area.
ALDOT found other advantages of 3D modeling as well. Public and stakeholder perspectives of the project were a major concern and using the 3D model allowed the Visualization Group to provide accurate photomatches, renderings, and animation to relay project impacts to all stakeholders. While the project is under construction the 3D model is also being used by inspectors in the field so that construction details are relayed accurately to the workers.
This project provides further evidence of the significant benefits of a 3D model of underground infrastructure which can be used during design and construction to reduce the risk of utility hits, reduce the cost of utility relocations, and avoid unnecessary utility relocates.
Expo Milano
A ground breaking project to map underground infrastructure as undertaken in the Region of Lombardy in Northern Italy. This project was kicked off by a pilot project to map all underground infrastructure on the site of Expo Milano in preparation for the 2015 event in Milan.
For the Milan pilot project all underground infrastructure in the project area (230 000 square meters) including electric power, water, sewers, gas, district heating, street lighting, and telecommunication were mapped both from historical records and using IDS's ground penetrating radar (GPR) technology. A data model for underground infrastructure was developed for the different types of underground networks based on the Italian DigitPA and the INSPIRE US utility standards.
The key part of the project was the comparison of the historical records with the results captured by GPR. The analysis revealed significant discrepancies in the historic record including thousands of meters of unknown infrastructure. For the known infrastructure the average error in geolocation was about 30%, but much larger errors of up to 100% were also recorded. The conclusion is that even in Europe the record of underground infrastructure can be highly unreliable. That GPR can identify previously unknown underground infrastructure provides a financial motivation for municipalities to invest in GPR because utilities are taxed by municipalities based on the total infrastructure the utilities maintain within city limits.
The other ground breaking part of the pilot project was an economic analysis of the costs and benefits of applying GPR to detect the location of underground infrastructure. The analysis estimated that the return on investment is about €16 for every euro invested in improving the reliability information of underground infrastructure. The analysis emphasized that there were other important, but non-quantifiable, benefits including better safety for both workers and the public as well as fewer traffic disruptions.
Highway revitalization project, Cedar Falls, Iowa
For a $38.9 million highway revitalization project in Cedar Falls, Iowa it was estimated that an innovative design including roundabouts would save the community $32 million over 25 years by reducing the number of accidents, decreasing travel time, lowering fuel usage and emissions, increasing property values, and leading to greater economic growth. Most importantly a 3D model of all underground infrastructure in the right-of-way was created prior to engineering design. This was an important factor enabling the project to complete on-time and 3% under budget.
University Avenue in Cedar Falls was an Iowa Department of Transportation (DOT) six-lane, divided highway which the City of Cedar Falls took ownership of in 2014. Built over 60 years ago, the corridor carries 20,000 vehicles per day and was suffering from deteriorated pavement, a crash rate 20% above the state average, a lack of pedestrian and bicycle accommodations, a pedestrian death, and inefficient traffic operations.
Innovative, advanced traffic designs were developed; multi-lane roundabouts, a dogbone interchange, and complete streets – which allowed for a reduction of lanes that still decreased congestion and increased overall traffic flow. Technical innovations included use of drone and mobile scanning utilized for reality modelling, a building information (BIM) for creating 3D models and fostering collaboration, and 3D visualization and traffic modelling for communicating alternative designs to stakeholders and the public.
One of the most innovative aspects of the projects was the development of a 3D model of underground utilities before the start of the design phase. This enabled the detection of 200 utility conflicts during the design phase avoiding utility conflicts during construction and was the primary reason that the project completed on schedule and 3% under bid saving the City $700,000.
From a public safety perspective, Foth estimated an 89% reduction in personal injury accidents. As owner of the highway, the City is projected to realize $27 million in benefits from economic growth, corridor improvements, avoided traffic signal maintenance, and reduced lighting costs. Reality modeling including mapping underground utilities prior to design, innovative highway design, and digital design technology based on BIM saved $521 thousand in project costs by eliminating utility conflicts and the resulting change orders, enhanced public engagement, and design acceleration.
Despite facing aggressive schedules, the challenge of information coordination, complex utility coordination, intense public involvement, and a very tight design schedule involving public participation, Foth was able to deliver the project on time and below budget.
Natural gas pipeline, Washington State
In a major Puget Sound Energy gas line construction project, an eight inch high pressure natural gas pipeline along a major highway SR510 managed by the Washington Department of Transportation, the design engineers Utility Mapping Services (UMS) diverged from normal construction practice by first creating a 3D model of the existing underground and above ground infrastructure. During construction there were no utility strikes and as a result there were no change orders and the construction project was completed in 7 instead of the expected 10 weeks.
A major risk for the project was that the corridor includes complex utility infrastructure woven through dense commercial and residential areas with limited right-of-way and heavy traffic congestion. Because of the complexity of the underground utility infrastructure it was decided at the beginning of the project to develop a 3D model of the existing underground infrastructure. The model enabled the design team to adjust the pipe elevation and horizontal alignment to avoid potential utility conflicts during the design phase. The 3d model of existing utility infrastructure avoided unnecessary utility relocations and the associated construction delays and contractor change orders. It also allowed for tighter contractor bid estimates by providing a more accurate design to the contractors.
UMS' subsurface utility engineering (SUE) services group were familiar with new remote sensing technology such as ground penetrating radar (GPR) and electromagnetic detection which allowed them to acquire 3-D location data for underground utility infrastructure. Application of new SUE technology created much greater value for the customer because UMS could now clearly convey to the client the issues presented by existing infrastructure and work with their design and construction teams and the utility infrastructure owners to minimize utility relocations and avoid surprises from buried unknowns.
Starting with a 2D basemap, the underground survey was conducted using several technologies, including electromagnetic and GPR, and potholing for validation. In addition to the expected utility infrastructure, the survey detected undocumented abandoned utility lines which highlights an important advantage of the new remote sensing technologies. The data was captured and integrated to create a 3D model.
The 3D model formed the basis for the design for the new gas pipeline. The 3D model detected 170 conflicts, points of intersection of the design for the new pipeline with other utilities. Several alternative routes were assessed and the costs and benefits of each were computed and compared in order to determine the optimal routing for the new pipeline. 3D visualization of the alternative routes helped the designers show Puget Sound Energy and the Washington DOT the advantages of alternative routes and allowed changes to be made to the design live in front of the customer. One interesting wrinkle is that the design had to avoid conflicting with a new sewer line which had not been built yet. One of the existing sewer lines was scheduled to be replaced by a significantly larger one in the near future.
A major advantage of the 3D model is that it reduces the risk of utility strikes during construction. On projects where automated construction is used, exclusion zones can be created from the underground 3D model that prevent the machinery from striking utility infrastructure.
The 3D model helped in other ways. The project required two variances from the Washington DOT which were granted in record time because the 3D model showed so clearly why and where they were required. The 3D model helped to minimize highway disruptions to the public. Most critically from a safety as well as cost perspective, there were no utility strikes on the project. As a result the 3D model is credited with reducing construction time from 10 to 7 weeks. Most importantly from a budget perspective, there were no change orders and the total cost of the project came in at 10-15% less than estimated in the absence of a 3D model.
Conclusion
These examples show that an accurate model (preferably in 3D) of underground utilities can not only reduce the risk of underground utility damage and the associated project delays and budget overruns but can also reduce the cost of infrastructure by designing to reduce unnecessary and costly moving of utilities.
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