Hundreds of dams and levees across the country that were built in the past century and a half are starting to show their age, with resulting wear and tear. Ensuring the resilience and reliability of these structures into the next century and beyond requires sustainable modernization of the critical infrastructure systems. Severe weather events, extreme temperatures, erosion and rising water levels are all straining the infrastructure and exacerbating the impacts of deterioration and aging processes. In many cases, simply replacing the dams and levees is not a viable option due to high costs.
The Science and Technology Directorate (S&T) has joined forces with federal, military and academic partners to tackle this challenge. In early 2022, S&T launched a five-year effort with the U.S. Army Corps of Engineers (USACE), the University of Kansas (KU), the Federal Emergency Management Agency, and the Cybersecurity and Infrastructure Security Agency to find solutions that will help extend the life of dams and other concrete flood risk management infrastructure in the U.S. in an environmentally responsible way. The solution lies in science, research, technology and structural engineering.
“This endeavor is all about our natural disaster resilience and climate change research agenda,” said Dr. David Alexander, S&T Senior Science Advisor for Resilience. “The goal was to look at new material innovations that can strengthen the disaster resilience of water infrastructure to shocks and stresses.”
Focusing on fiber to give a structural boost
This critical infrastructure effort will improve the performance of dams and levees using fiber-reinforced polymers (FRPs).
Different types of environmental stressors—for instance, chemical action, corrosion, freezing and thawing—have been causing the gradual deterioration of concrete infrastructure across the U.S. Weather-related disasters also place extreme pressure, causing systems to fail to function as expected. Many levees breached during Hurricane Katrina in 2005, and Hurricane Matthew in 2016 caused some levees in South Carolina to fail. The Oroville Dam in California failed after heavy rains in 2017.
This S&T effort has two goals: one, to research how FRPs can help reinforce existing concrete dams to improve their performance and extend their service life, and two, to monitor the condition of dams and levees using deep learning and sensors deployed on unmanned aerial systems.
“We are looking for new FRP innovations that could strengthen concrete dams and levees to withstand shocks and stresses from disasters and normal wear and tear,” said Alexander. “The solutions we find must have low-carbon emissions and be cost-effective.”
FRPs are composite materials that consist of two or more different constituent materials—carbon or glass fibers imbedded in an epoxy matrix. This makes the material tough, lightweight, and very strong, with some interesting structural properties.
“The FRPs can be formed and molded over many different geometries,” said Dr. Caroline Bennett, professor, and Glenn L. Parker Faculty Fellow at KU’s Department of Civil, Environmental, and Architectural Engineering, and principal investigator of the project. “FRPs have great potential for applications in dams. They are also durable, don’t corrode, and thus don’t need corrosion-prevention maintenance.”
Carbon and glass fibers are very lightweight and strong; stronger, in fact, than steel in strength-to-weight ratio. And for building repair, much less material is needed. FRPs come in different configurations, including sheets that can be used to stop surface crumbling, laminate strips to hold cracks together, and braces to stop vertical elements from sliding and joints from opening.
The research team will review recent scientific and engineering advancements to select the best FRPs for dam and levee improvements and will test them in KU’s laboratories. Researchers will then conduct large-scale strength tests of the selected FRPs; they will test FRP performance underwater, and they will use deep learning to make dam and levee surveying more efficient. Finally, the team will make the FRPs self-sensing by adding sensors that detect further deterioration of the dams and levees.
Ultimately, as USACE operates and maintains more than 700 dams and related structures nationwide, they have a huge stake in the outcomes of this FRP research and field testing.
“Our role is twofold—physically demonstrating the FRPs on a dam or levee and modernizing our playbook to improve the dams’ performance under future hazards, like extreme floods or seismic events with diverse climate-induced variations,” said Dr. Robert Moser, Senior Scientific Technical Manager at the USACE Engineer Research and Development Center.
Building in sensors for effective surveying and monitoring
Before engineers repair a dam or levee, they need to survey it. However, surveying a half-mile-wide dam spillway structure, for example, can be challenging and time consuming. After making multiple photos using a drone, engineers go through thousands of images to catalog and analyze the deterioration and plan repairs. Deep learning, which is training computers to learn by example, can make surveying more efficient by automating the photo processing to find images with deteriorating concrete, determine its severity and quantify its frequency.
KU experts will train artificial neural networks to differentiate between images with and without various types of deterioration. Once trained, a computer model will be able to automatically recognize deterioration and pinpoint its location on the dam.
The next stage after repair is monitoring. But the monitoring will be challenging if the concrete is covered with FRP fabric, so the fabric needs to be self-sensing. To achieve this, the researchers plan to test two possible sensors in the FRP fabric—the carbon fibers’ natural electrical conductivity as sensors or adding optical fibers as sensors. The sensors will collect baseline data of FRP performance or of what is happening underneath whenever the FRP material strains from concrete deterioration.
“The sensors will provide early warning for needed repairs,” said Alexander. “This monitoring will be useful for both naturally occurring deterioration and disaster impact, including terrorist attacks. You should get a notice pretty quickly after a structure retrofitted with self-sensing FRPs is attacked.”
Implementing environmentally sound solutions for a sustainable future
Through all this work, S&T and its partners at USACE and the University of Kansas are committed to considering its environmental implications.
“Any time we introduce an innovation into the environment, we must do an environmental assessment. If the FRP installation increases the carbon emissions budget, we must understand the tradeoffs,” said Alexander. “For example, if you don’t need frequent maintenance, you don’t have to send vehicles out. That could offset the production process emissions.” Additionally, by extending the life of existing dam or levee infrastructure, its carbon emissions decrease because no new concrete material is used, and no material is wasted from demolition of existing structures.
The results from this effort could be applicable to other types of concrete structures exposed to harsh underwater conditions as well.
“You may apply these innovations to make structures more resistant to deterioration, increasing their resilience to seismic activity and vibrations from increased road traffic,” said Alexander. “Our research could potentially trigger innovations in how we build and construct our roadways, bridges and other concrete structures.”