Thornton Tomasetti Vice President, Michael Oakland, and Pierre Gouvin, president of GEO-Instruments, recently authored an article in the May/June 2016 issue of the Deep Foundations Institute magazine.
The article discusses the monitoring system used to evaluate and mitigate cracks that had developed in Boston’s historic Old South Church from a construction project nearby.
We recently spoke with Michael Oakland about his involvement in the Old South Church restoration project and how this article came about:
How did the article come together?
We initially wrote a paper for the annual Deep Foundations Institute (DFI) conference where it was presented as a poster session. A few years later we were contacted by one of the writers at DFI Journal who thought it would make a good article.
Please give us some background about Old South Church and the purpose of monitoring systems during historic restoration projects.
In this case damage had occurred to the façade during construction of a handicap access to the adjacent Green Line subway. The Old South Church is one of the original churches in Boston and its façade, constructed of Roxbury Puddingstone, is a unique landmark feature of the church. In addition to cracks that reached the full height of the church walls, the cracks went through the vaulted ceiling and cracked a corner of the historic stained glass window, which threatened the massive pipe organ mounted against one of the church walls. The stained glass is one of the oldest in New England, imported from a famous manufacturer in England at the time of the church’s construction which was completed in 1873. The pipe organ, the premier asset of the church, is one of the oldest in the country and massive in size. The monitoring was conducted to confirm that conditions were stable and that no further damage would occur during underpinning or other repairs to the church, which could threaten the façade and stained glass. The organ was dismantled and stored during all repairs.
How important is easy real time data to stabilizing structures?
The damage occurred quickly, lifting the church by inches and dropping it under the pressure of the jet grouting in less than a second. Conventional readings by optical survey can be taken only at 24 or 48 hour intervals and even then would require additional technical hours to reduce and post the data. Real time monitoring with readings taken every 10 to 15 mins and reported directly to a website is the only way to know if activities are causing damage in a time frame which allows reasonable response. The readings are linked to warning systems that send text messages or emails immediately if present movements or vibrations exceed a specific threshold to allow the engineer, contractor or owner to take prompt action.
What did you enjoy most about the project?
I conducted the work with GEO-Instruments, who I have worked with on numerous projects over 30 years of my career. The part I enjoyed the most was jumping into action – we received a call the afternoon after the event. I called Pierre Gouvin at GEO -Instruments immediately who was just getting off a plane at LaGuardia Airport. He drove straight to the site from the airport and we met the contractor that evening. We worked the better part of the night in a restaurant to develop a plan for instrumenting the structure. Geo-Instruments mobilised a crew the next day to start setting up the instrumentation. I felt I was working with a team I could trust, which is such a critical part of the job under these time-sensitive circumstances.
To see the May/June 2016 Deep Foundations article, click here.