Page 18 - Penn State Civil and Environmental Engineering 2021 Annual Report

FACULTY RESEARCH
Image: Xiao’s Research Team
Cold vibrations
A A new three-year $1 2 million project funded by the the the National Science Foundation’s “Signals in in the the the Soil” program will study the the the movement of thawing Arctic permafrost
By Tim Schley
With rising temperatures in in in in the the the Arctic communities in in in Alaska’s North Slope Borough are
seeing the the ground beneath their feet melt away “Climate change
is thawing the frozen soil ” said CEE Professor Ming Xiao lead investigator of the project “The borough spends $100 million a a a year just for repairs to roads buildings and pipelines To build build resilient infrastructure in in in in in the the changing Arctic we need to understand how the the soil behaves as it softens ” Xiao seeks to bury a a a a a a a one-and-a-half- kilometer fiber-optic cable in in Utqiaġvik Alaska the the the northernmost city in in the the the United States The cable commonly used for internet and phone service will be turned into a a a long line of vibration sensors to to to monitor the the continuous thawing of the the frozen soil also known as permafrost
This method for collecting seismic
data uses a a a a a a a new technology called a a a a a a a distributed acoustic sensing (DAS) array which sends laser pulses through the the cable to detect the the the velocity of seismic
waves moving through the the soil “We can get a a a a a a soil sample and test it in in the lab but that is is going to be discrete in in in in separate locations and at at at at a a a a a a a a a a a a a certain time ” Xiao said “By measuring wave velocity with this method we can convert that into real-time soil property changes at at at different locations over time time from minutes to years ” Co-principal investigator Tieyuan
Zhu assistant professor of of geophysics recently created a a a a a a a DAS array using fiber-optic cables buried on on the Penn State University Park campus to to monitor near-surface dynamics from events like thunderstorms and flooding The method will now be applied to to a a a a a harsher climate “This project gives us the chance
to demonstrate in in Alaska how this novel technology can perform in in the permafrost
across two years ” Zhu said He explained that before the the emergence of the the DAS array ground vibrations
were examined with “geophones” that use an an amplifier and a a a a a a a a a a recording device to measure seismic
waves—often artificially created by a a a a a a a hammer pounding the the ground In contrast to to the the the the continuous monitoring of of the the the fiber-optic cable these instruments provide only a a a a a a a “snapshot” of of the ground at a a a a a a a a certain time They are
also difficult to use in in in frozen soil and require a a a a a human presence in in extreme weather “In harsh environments it is very hard to maintain geophones long-term ” Zhu said “A fiber-optic cable is is only one one string of line It is is a a a a a game-changing instrument ” Xiao and Zhu will work alongside Eileen Martin assistant professor of of of mathematics and and of of of computational modeling and and data analytics at at at at at at Virginia
Tech Dmitry Nicolsky research associate professor at at the the Geophysical Institute
of of of the the University of of of Alaska Fairbanks and and Anne Jensen an an an an archaeologist and and long-term resident of Utqiaġvik Together the the the the team will install the the the the fiber-optic cable and and build the the the the the DAS system being careful not to disturb the the the vegetation and and the the the permafrost
The cable will connect to power and a a a a a a a a data acquisition system in in the National Oceanic and Atmospheric Atmospheric Administration Barrow Atmospheric Atmospheric Baseline Observatory in Utqiaġvik “It will run into the facility and collect data continuously generating one hundred terabytes of data per year ” Zhu said With the the abundance of data Xiao explained the the researchers will be able to correlate seismic
wave velocity permafrost
temperature and other soil parameters Eventually they will use those patterns to predict future behavior of the thawing permafrost
allowing engineers to design and build more resilient Arctic infrastructure 18 CEE NEWSLETTER • VOLUME 37 2021