The $15.8 million Somers Middle School expansion and renovation project has been delayed before crews have even broken ground, thanks to a soil report that raised questions about the safety of the building design.
Architectural plans will need to be changed following the results of soil sample tests that showed wet, loose, sandy soil.
“That wet sand is highly susceptible to what we call soil liquefaction,” said architect Max Grebe of L’Heureux Page Werner, which typically occurs during earthquakes.
Joshua Smith of Slopeside Engineering described what happens during soil liquefaction.
“Basically if you shake the soil, it loses its strength and turns into a liquid for a short period of time,” Smith said.
As the pressure of groundwater held in the gaps, or pores, of soil drops, everything settles. The settling or sinking often results in structural damage.
The discovery of the sandy soil complicates the current architectural design and has resulted in questions about how the project should proceed.
Somers Middle School is situated on land that slopes downward to where a lower parking lot is located. New construction was to include a two-story addition built on the south side of the existing school — into the hillside. Plans included retaining about 10,600 square feet of an existing one-story wing built in 1993. Two older wings built in the 1950s and ’60s were slated for demolition in 2019.
As building codes have changed over the decades, they now include seismic requirements in areas vulnerable to earthquake damage. The new building needs to be designed and constructed to withstand a 6.0 magnitude earthquake with the epicenter a little more than six miles away from the school. This is referred to as a “design level” earthquake, Grebe said, basically the worst-case scenario architects design for.
So what is the chance that a 6.0 earthquake will hit the area?
“There’s what’s called the probability of exceedance, which works out to a one-in-500-year event, approximately,” Smith said.
Based on the soil makeup, settling of soil after a quake wouldn’t be uniform, and Smith estimates a 6.0 earthquake could result in the planned two-story addition settling 12-18 inches and the existing one-story wing settling 6-9 inches. That would put unacceptable stress on the building, and the “differential settlement” could even lead to structural collapse, Smith said.
There are ways to reduce the risk of differential settlement in new construction, Smith said. Soil can be amended to improve its stability, and architects can also design to improve stability. In coming up with feasible solutions, architects suggested the school district consider constructing a new stand-alone middle school and completely demolishing the existing building while sticking to the current budget, square footage and completion date.
The project, however, has to remain faithful to the wording on the ballots for the bond issue that voters approved in October 2017. Ballot language is essentially the contract between a school district and community.
The ballot stated that the bond issue funding was for “... designing, constructing, furnishing, and equipping additions and renovations to Somers Middle School, to include classrooms, a gymnasium, a kitchen and lunchroom, a shop, a science lab, upgrades to the main school office area, building-wide security enhancements, related amenities and improvements at the existing Somers Middle School campus...”
Somers Lakeside Superintendent Joe Price said he is currently checking with lawyers on how to proceed without invalidating the bond issue or jeopardizing the project. Price’s goal is to have design options ready to present at the next school board meeting in July.
Reporter Hilary Matheson may be reached at 758-4431 or email@example.com.