“Uncovering Boston’s Wooden Foundations”
John Rahill, S.B. ’18, environmental science and engineering
Advisor: Miaki Ishii, Professor of Earth and Planetary Sciences
As Boston grew from a small settlement on an 800-acre peninsula into a bustling metropolis, developers used man-made land to expand the city’s footprint. For decades, structures erected on landfill were built atop underwater wooden pilings to provide extra support, but due to groundwater depletion, pilings are now being exposed to air, causing them to rot. Rahill used reflective seismology as an affordable and non-intrusive method to detect the depth of pilings and help assess structural vulnerability. His technique involved emitting a wave pulse from the surface and capturing the resulting ground motion with an array of seismic sensors. Rahill developed a mathematical model that can assess reflections of mechanically transmitted subsurface waves, tracking wave speed and arrival time to effectively estimate groundwater and piling depth.
“The most challenging aspects of this project were modeling the subsurface geometry and setting wave propagation parameters accurately in simulations,” he said. “There is a wide range of factors at play that can contribute to wave behavior in the subsurface. Narrowing down on the optimal settings took a great deal of time and effort.”