Every four years, the American Society of Civil Engineers (ASCE) puts together a Report Card for America’s Infrastructure that gives a general idea of the country’s infrastructure condition. Letter grades are assigned based on infrastructure condition and need for improvement. In 2017, ASCE gave the United States a D+ and found that while some infrastructure areas are improving, many others are declining and require additional investment.
While our infrastructure continues to age and the cost of maintaining tunnels, pipelines, and other facilities skyrockets, owners and operators of water, wastewater, and storm infrastructure will need to consider all available tools when determining how best to monitor the ongoing condition of these assets. It will also be important to understand the logistical and safety requirements necessary to complete a successful inspection program that yields results that are useful and contribute to the overall management of the asset.
Historically, an inspection has been conducted by a team that is put into the tunnel or structure to directly observe existing conditions. The level of detail obtained from these inspection teams is tremendous. The trade-off, however, is multifaceted. Manual inspections require that facilities be placed under restricted operation or removed from operation entirely. This can include the complete unwatering of a structure, which is time-consuming and could require putting backup systems into operation. These backup systems are typically not intended for extended use, and can come with a significant price tag in cases where equipment has to be rented. Unwatering could also place unknown structural stress on a facility that is not normally unwatered, adding a degree of risk for an owner as well as those who will be entering the structure to perform the inspection. In addition to the operational constraints caused by manual inspection, safety precautions are also required. These can be quite extensive depending on the configuration of the facility to be inspected. The target structure’s configuration and any local safety requirements that may supplement current safety regulations will likely necessitate staff and equipment to support a permit-entry confined space, fall protection measures, air monitoring equipment and processes, and remote communication equipment. Each of these safety procedures, as well as any others that would apply, will certainly add to the required manpower, cost, and logistical concerns to perform a manual inspection.
Inspections using remotely operated vehicles (ROVs) offer some attractive alternatives to manned entry. ROVs are underwater vehicles that can be controlled from the surface through an attached cable (umbilical) and flown into a watered structure to take still photos, video, and sonar data. An ROV control station provides power and control to the ROV and stores this information, as well as other collected data, on computers for later use and analysis. Multiple monitors are provided for both pilot and engineer to monitor the inspection in real-time. Safety requirements for ROV work are typically minimal and include protections for staff during the insertion and recovery of the vehicle. Mobilization and demobilization times are short when compared to manual inspections. That being said, ROV operations need to be carefully planned, and an understanding of the configuration of the target structure needs to be well understood before beginning any work so that one can plan for any operational constraints. This understanding will minimize the risk of the ROV or its umbilical getting caught on an obstruction within the structure.
Autonomous Underwater Vehicle (AUV) technology is an offshoot of ROV technology, and is similar to ROV with a few exceptions. Since these vehicles are autonomous, there is no umbilical connection to a control station. This means that the only constraints on how long an inspection distance can be are related to data storage capability and available battery power. These devices contain extensive sensor and camera arrays that allow them to maintain a preprogrammed distance from surrounding objects or walls, or even to navigate a predetermined route to complete an inspection without intervention from the surface. Once the device has flown its inspection path, it is retrieved. Data can then be downloaded and analyzed. Depending on the level of detail desired, post-inspection data processing and analysis can be quite time consuming. However, in locations with limited access, this technology may be one of the few tools capable of obtaining the necessary data.
Unmanned Aerial Vehicles (UAVs), also known as drones, can be used in a manner similar to ROVs to obtain remote inspection images and videos of facilities located aboveground. These vehicles can also be used to obtain photogrammetric data (georeferenced photographic images), which can be used to create three-dimensional point clouds. These point clouds can be employed to create digital surfaces in two or three dimensions and imported into CADD software for analysis. The data obtained from this type of scan are comparable to data from a LiDAR survey. UAVs are currently being used to perform many types of inspections. These include slope stability inspections where rope access is difficult, tunnel inspections where liner conditions are unknown and suspect, and inspections inside storage tanks. All of these locations, and many others like them, would require that extensive safety precautions be taken for a traditional manned inspection or, in the case of a cliff face, manned access would be nearly impossible.
When selecting a manual or a remote inspection, owners need to understand how each tool is best used. Manual inspection can be expensive and require the implementation of extensive safety precautions. The trade-off is the level of detail that can be obtained. Unlike the remote inspection methods discussed, there is not a concern for highly turbid water that can obstruct the visibility of a video recording, or a mechanical problem with a remote device shutting down an inspection run until it can be fixed. Since remote inspections are relying solely on what a camera or sensor can “see,” owners need to understand what type of information they are attempting to obtain and how best to get it so that they can then make educated decisions for maintaining critical infrastructure facilities.
Brian M. Lakin, PE, is an Associate with McMillen Jacobs Associates.