Subsurface Information Modeling: Using LiDAR to Build on SUE, SUM + BIM
Building on SUE, SUM, and BIM to Advance Underground Stewardship
by Mike Twohig
The use of Subsurface Utility Mapping (SUE) dates back to the early 1980s. In 1991, SUE gained an official endorsement from the Federal Highway Administration (FHWA). A few years later, the famous Purdue study proved its value by leading to the creation of the ASCE C-I 38-02 Standard Guidelines for the Collection and Depiction of Existing Subsurface Utility Data. What started as a solution to project delays, unexpected encounters with underground facilities, and frequent utility relocations, later evolved into an industry best practice.
Yet still, underground damage happened, and projects went off-schedule and over-budget. Even with SUE, studies both in the United States and abroad have documented that project pitfalls are caused by a lack of comprehensive subsurface mapping before excavation. Failing to map the underground site conditions often results in costly claims, major delays, tarnished reputations and, all too often, physical harm.
Today, Subsurface Utility Mapping (SUM), a precursor to any SUE project, is one of the fastest growing practices in the geospatial industry. Professionals from various sectors are joining utility surveyors to locate, map, and document the underground site conditions. LiDAR, a common tool in SUM, has become an invaluable asset in improving project deliverables and the safety on site, leading an enhancementof data acquisition and management, now referred to as Subsurface Information Modeling (SIM).
The History of Marking Underground Assets
In the 1800s, the newly implemented Boston Transit Commission began to seek solutions to alleviate congestion in the busy streets of Boston. As contractors planned to break ground on the new transit system, designers uncovered that not only were the streets above ground congested, but the streets underground were also crowded. Engineers worked tirelessly with utility owners to compile plans of the underground assets but were left empty-handed. Insights from the Boston Transit Commission 1895 report state, “The records of most of the underground pipes, sewers, and other structures laid years ago were imperfectly kept, in fact, many such structures were built without any records of their location being made.”
One hundred years later, the FHWA continued projects across the nation and noticed a common theme. The primary cause of project delays and design changes were due to a lack of accurate and reliable utility information on the original project designs. Following a strategic study in many state transportations programs, the FHWA started developing a standardized program that included subsurface utility investigations along with other required surveys such as boundary, topography, geotechnical, and environment investigations. While this was a great step forward in improving industry best practices and workflows, these practices were quickly forgotten.
Inadequacies in Our One Call Dig Laws
Today, the vast majority of projects in the United States rely on the respective One Call paint and flagging mark-outs by the underground asset owners as the primary source of information to identify utility information. But the majority of underground assets are privately owned by utility companies, municipalities, railroads, and state DOTs, and are exempt from One Call laws. The APWA estimates that 65% of underground facilities are privately owned. This puts the contractor, crew and the general public at risk.
In addition, many land surveyors and engineers locate the paint and flags from obtaining a free One Call design ticket request, instead of the routine excavation ticket. Although not available in every state, Design Tickets are meant to be used to develop construction drawings that are inclusive of the underground asset owners understanding of underground facilities rather than for excavation purposes. This flawed workaround leaves a high risk for errors and omissions in the final contract plans and specifications if some asset owners do not respond, and numerous asset owners fail to participate in One Call programs. Given the opportunity for errors and omissions, it is not uncommon for Design Ticket mapping programs to fall short of their intended goals.
In 2018 in Sun Prairie, Wisconsin, workers struck an underground gas line. The cause of this explosion—digging without proper site markings and an expired One Call ticket. This incident damaged a section of the city’s downtown and claimed the life of a first responder. If the telecommunications design team, employed by a utility surveyor, had properly located and mapped the underground facilities, they wouldn’t have designed a directional drill bore patch that was in conflict with a gas line. The town would have remained intact, and the first responder would still be alive.
Fatal projects, like Sun Prairie, and other very similar fatal incidents completely violate specific US Health and Safety excavation requirements noted in the Code of Federal Regulations (CFR) 1926.651, demonstrating that One Call laws are not enough. Laws and regulations must push beyond One Call and design tickets to create a safer industry.
Advancing Technologies: Improving Upon Building Information Modeling (BIM)
It is commonly known that the construction industry trails other industries with technical advancements. Innovative technologies like drones, augmented reality, and virtual reality were initially slow to gain momentum in the construction industry. However, these innovative solutions, including Building Information Modeling (BIM), are now being accelerated into current workflows and platforms to push the industry forward.
Building Information Modeling (BIM) gives architecture, engineering, and construction professionals the insight and tools to more efficiently plan, design, construct and manage buildings and infrastructure above ground. But it does not highlight the importance and the connectivity of the subterranean environment.
Subsurface Information Modeling (SIM) will help to fill that gap and provide insight on potential conflicts that lie below the surface. This innovative term, crafted by Michael A Twohig, DGT’s Director of Subsurface Utility Mapping, mimics the advancement of GeoBIM. GeoBIM has become a term that links the individual projects or structures with a broader, more global geospatial perspective.
True SIM combines the best practices of SUM with the sophisticated data modeling of BIM. With SIM, utility surveyors rely on terrestrial LiDAR to map the surrounding streets in the design phase of the project. LiDAR can also be used to map the inside of underground vaults, chambers, and tunnels. Utilizing LiDAR technologies in unison with subsurface utility mapping is a best practice when investigating convoluted underground environments. Data gathered can then be used to identify any possible utility conflicts and assist in making final design adjustments, if needed. One of the greatest future applications of LiDAR will be bridging the gap between designers and planners, and the contractors and One Call responders. The future use of LiDAR, by contractors who want to capture the precise details of a site to create their own “Digital Twin” for the purpose of Dilapidation Surveys and documenting One Call responders mark-out, will be a vital step forward over current best practices. Moreover, the digital 3D model can be used to improve site safety by using clash detection software to identify discrepancies between the construction plans, the mark out performed by Utility owners and their representatives, a contractor’s team looking to protect the underground assets, the site workers, and the general public.
In a world of change, the need to use a different approach to solve fatal flaws in our industry is inevitable. Albert Einstein once stated, “We cannot solve our problems with the same thinking we used when we created them.”To solve the current industry challenges we need engineers, surveyors, and builders to return to traditional best practices—similar to those employed by the team building the Boston underground subway in the late 1800s—and locate and map the new facilities we install. Utilizing LiDAR technologies in unison with subsurface utility mapping and 3D imaging should be considered a standard practice because it allows us to capture the vital details we need before burying another 100 years of history.
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