This article was published in the Spring 2019 edition of NC Currents Magazine.
Written by Matt Broderick, PE, Senior Project Manager, Hulsey, McCormick & Wallace, Inc. and Anne-Marie Moehring, Administrative Services Manager, Harper General Contractors
Three-dimensional (3D) technology is no longer just for large, complex projects. Advances in 3D scanning and modeling software have significantly reduced costs and increased accessibility across the construction industry. The upgrade
of the City of Hickory’s Water Treatment Plant on-site sodium hypochlorite generation (OSHG) system is a prime example of a smaller project significantly benefiting from 3D technology. Designed by Hulsey McCormick & Wallace (HMW) and constructed by Harper General Contractors (Harper), the project team used 3D design and modeling instead of traditional 2D design throughout the planning, design, and construction phases of the project. This method allowed the team to build the project twice, once in the model and once in the field, delivering the project within the $1.4 million budget.
Located in in the Western Piedmont Region of North Carolina, the City of Hickory owns and operates a conventional surface water treatment plant (WTP) that provides drinking water to over 28,000 service connections. With over 950 miles of water mains, the City provides water to numerous other municipalities across four counties. The WTP has a rated capacity of 32 million gallons per day (MGD) with average production around 13 MGD. The original facility, like most older facilities, used chlorine gas as a primary disinfectant. The City converted the gas chlorine system to an OSHG system in 2003 due to aging equipment and a desire to improve safety. This was the first OSHG system installed in a municipal WTP in North Carolina. After nearly 13 years of service, the OSHG equipment had reached the end of its useful life and required replacement. It was at this point that the City engaged HMW to evaluate options for replacing the OSHG system.
While 3D design software has been commercially available in the design and construction industries for several decades, its use has generally been adopted on larger, more complex Architectural, Transportation, and Civil/Environmental Projects. 3D design platforms have evolved from basic 3D dimensional modeling to advanced Building Information Modeling (BIM). Combined with advances in reality capture (360 photography + 3D laser scanning), highly accurate models can be created to closely model the existing environment. As demand for this technology has increased, the costs to acquire equipment and software have decreased, allowing designers and contractors to utilize 3D tools on smaller and mid-sized projects. In addition, manufacturers are increasingly providing access to 3D models of equipment, building materials, and other construction products, reducing the time designers spend creating 3D model components.
“Graphical interfaces utilizing parametric design have also evolved to become more user-friendly, reducing the learning curve required to utilize the software. These advances have made use of 3D design cost-competitive with conventional 2D design methods, while providing increased design accuracy and improved design visualization."
For this project, HMW proposed the use of reality capture and 3D modeling during the design phase of the project. The existing sodium hypochlorite room had several challenging factors that led to this decision, primarily limited space and inconsistent record drawings. The system utilized the majority of the room and plant operations required all work to take place within that space. Furthermore, there were numerous pipes and conduits with complex routing running throughout the area. In addition, modifications to equipment and room components after the 2003 construction project meant the record drawings had variations from the real conditions. In order to provide an accurate base model, HMW utilized a 3D laser scanner to provide a highly precise point cloud model of the existing hypochlorite room. The laser scanner captured over 68 million points, each with x,y,z coordinates, to re-create the existing space. The accuracy of the points for these scans was < 0.25 inch. The entire scanning process took less than 4 hours, including moving the scanner to 10 different locations to capture the entire project area. While the hourly cost of a crew to complete the scan was more than traditional measuring methods, the number of points captured, high level of accuracy, and reduced capture duration made this method of as-built documentation more cost effective than traditional methods because there was less demand for time spent on the backend creating, editing and confirming the plans.
The point cloud was used as the base to create the 3D solids of the existing building features. Any items to be removed from the room were not re-created as solids. Features that were to remain were converted to 3D solids. Once the base model was established, new equipment, piping, HVAC components could be designed. While 3D models provide very detailed design capabilities, the design for this model was limited to major equipment, piping, and building components (HVAC, Lights, Doors, etc.) because additional detail was not necessary to successfully complete the project. The ability to tailor the model for the Owner or project is an advantage of 3D modeling. The designer can easily turn layers on and off or limit the amount of detail included. During design, the model was shown to the City to allow for input. The enhanced visualization allowed the City to make informed decisions on the proposed design. Items such as maintenance access, code clearances, and piping conflicts were easily validated utilizing the 3D model.
From Model to Reality
Use of 3D is not just limited to the design phase of construction. Utility contractors are increasingly utilizing innovative technology to enhance project delivery. Harper Corporation is one contractor utilizing innovative technologies, such as 3D modeling, to improve project execution. For Harper, technology has become a staple on projects as both an educational tool and a practical planning exercise. 3D models allow an estimator or project manager to do a precise take off, decreasing the costs and increasing schedule efficiency. They also allow the project team the chance to literally walk through a new laboratory or chemical feed building before and during construction. Operators can discuss their needs as they see the virtual building and the design team and contractor are able to make changes before those changes involve significant cost or rework.
For the Hickory WTP, the original estimate during the bidding phase of the project was developed using data from the 3D model. The estimating team was able to use precise measurements and detailed visualizations of the existing and proposed equipment to develop a dialed-in cost, giving the City of Hickory a competitive and well-priced proposal. The model also informed the schedule because the project team was able to map out the installation plan using a detailed visual of the existing conditions. Because the initial estimate was developed using such precise images and plans, buyout was also very accurate, with limited excess materials and materials arriving onsite as needed, decreasing project down time. Pipe was a huge component of this project. Being able to visualize the vast amount of pipe and the small spaces for hanging the pipe allowed the team to do a more thorough and accurate buyout.
During construction, the project team regularly referred to the model for constructability questions. Pulling up the model during subcontractor meetings aided in communication and planning. For example, the HVAC system required detailed planning for installation due to existing conditions. Equipment had to be flown over the brine tank and retaining wall and then slid through the existing door. The team used the model and existing structure to plan a near seamless installation. Without that information and the ability to manipulate equipment on the computer, equipment installation would have proved much more time-consuming and would have potentially resulted in an increase in budget, either during estimating to cover risk or during construction due to unknown or unforeseen circumstances.
Results and Lessons Learned
Construction began in January 2018 and the OSHG system was brought online in July 2018. Overall, change orders were successfully minimized, primarily as a result of the increased planning information provided by the 3D model. Total change orders were less than 3% of the original bid price, with only 0.7% resulting from unforeseen conditions. Due to the low level of unforeseen condition changes, the remaining 2.7% of the change orders were additional work requested by the owner during construction to repair items that were not in the original project scope. Limiting change orders due to unforeseen conditions allowed the City to maximize their budget and make additional upgrades to the facility initially thought to be outside of the budget.
While the OSHG system was brought online within the original project milestone schedule, there were some coordination issues that delayed the overall final completion. For example, the 3D model greatly reduced project risk but there were some areas of the project execution that still require traditional communication. One specific example of field coordination was the HVAC installation. The HVAC subcontractor did not use the 3D model to plan and procure equipment. Therefore, conflicts arose that required re-alignment or use of different components than were originally planned or outlined in the model.
For instance, the HVAC ductwork plan changed during construction. A gas line that was included in the 3D model was planned to be removed. However, during construction it was mutually agreed to keep the line in place. The louver elevation had to be adjusted and ductwork re-routed to accommodate the new louver location. Another example related to the HVAC air handler drip pan. A drip pan was required below the air handler that was not included in the 3D model but shown on a 2D standard detail. The drip pan was several inches larger than the air handler, which caused a conflict with some process piping. Field modifications were required to avoid conflicts between the piping and duct work.
The Project Team used the above examples as learning opportunities. After construction, the team sat down and developed the following key takeaways from this experience:
- Even the most detailed models do not replace the need for frequent and detailed communication. Face to face communication is still the best way to discuss questions or concerns.
- The model should be continually updated throughout construction. As equipment submittals are reviewed, component dimensions should be updated and verified prior to releasing for purchase.
- The model didn’t include all project components. For this project, electrical conduits, disconnects, control conduits, and fixtures were not modeled. This was a decision made during design and communicated throughout the project. However, it is important for all members of the project team to remember the model is not a complete representation.
- Field measurements and verification can identify red flags. The model is able to measure and verify an almost infinite amount of points. However, there is no replacement for double checking measurements in the field.
- Some material sizes may not be readily available or cost effective at time of ordering. For example, some 3” fittings for HDPE piping shown on design were not readily available. The pipe size was reduced to 2” since it was available.
It’s easy for wires to get crossed no matter what department you’re in. Sending information through too many different people, or too many different channels, can end up diluting what would otherwise be a compelling piece of content. This is why Harper made sure to set up a direct line of communication between marketing and estimating. Being able to work with estimators so closely ensures that marketing truly captures the voice of the company, and strengthens the consistency of the company’s messaging as a whole.
3D design is a tool in the tool kit for project teams. It has the ability to decrease budget and schedule by facilitating pre-planning. Using 3D technology can increase communication using models to show exactly what will be built. However, it is not a magic elixir. While it can be applied across market sectors and to just about any size project, 3D technology does not replace traditional communication and planning methods. Models must be updated as construction commences, and face-to-face meetings are imperative when solving complex problems. However, 3D technology appears here to stay and is becoming an important part of the design and construction process.