Portsmouth Middle School
Building Deformation Monitoring
Doucet Survey initially started work at this Seacoast NH school in 2010, when we were retained by the School District’s lead Architect to perform a complete boundary and topographic survey of the school property and adjacent athletic fields. The objective was to provide the Architect and the project’s Civil Engineer with a base drawing suitable for the design of a 130,000 square foot expansion to the 80-year old facility.
Once the building and site design were complete, DSI was hired by the School District’s selected General Contractor to provide construction layout and other Surveying services. Part of the construction sequence involved the installation of numerous settlement plates, which are used to provide a means of measuring soil settlement. Between May 2013 and February of 2014, DSI took measurements twice each week on settlement plates in different phases of the building construction.
Deformation monitoring requires great care to ensure that the necessary level of accuracy and precision are achieved. DSI developed a procedure that was reliable and consistent. We established off-site control to ensure that our results were not compromised by the dynamic conditions of the site. Each visit included repetitive measurements to known points as “checks” on our data.
Once construction was complete and the school was in full-use, cracks and other signs of settlement became visible. The City reached out to us for assistance based on our prior knowledge of the site. For nine consecutive weeks in the winter of 2014, DSI took vertical measurements at 74 unique locations throughout the older portion of the building as well as the new addition.
As directed by the City, our monitoring interval then changed to monthly visits. For the next 14 months, we continued our measurements on the original 74 points, and added another 22 points to that list. Since June of 2015 we have been conducting bi-monthly visits, and our work for the City continues to this day.
Our data is promptly delivered to City officials, as well as their hired consultants in a Microsoft Excel spreadsheet. The spreadsheet identifies the change in measurement from the previous visit, as well as the cumulative change from the beginning of our monitoring effort. Any measurements exceeding the expected tolerance are highlighted.
The incorporation of the Trimble DiNi level, which we purchased in 2013, has enabled us to increase our efficiency as well as our level of accuracy on this type of work. The DiNi reduces errors with the use of digital readings, allows for effortless data transfer between instrument and office, and is up to 60% faster than conventional automatic leveling.
