Cause of hill collapse known, but not cost of fix

Mother Nature, not the $45.6 million Port Washington High School project completed in 2018, is responsible for the collapse of a hill on the south side of the school this spring, experts have concluded.

But that doesn’t mean stabilizing the hill will be simple or inexpensive. 

“This turned out to be a significant challenge,” Port Washington-Saukville School Supt. Michael Weber told the Building and Grounds Committee last week.

With the support of the committee, the School Board voted to hire Miller Engineers and Scientists of Sheboygan to design and oversee the hill project, agreeing to pay the firm no more than $38,100 for work that will include drafting a request for proposals and reviewing them, as well as overseeing the work. 

School officials said they do not yet have an estimated cost of the project, which is expected to begin in October or November when contractors will likely be looking for work and conditions are dry, Director of Business Services Jim Froemming said. 

A section of the hill collapsed on May 18 after heavy rain, leaving the city road below that runs along the north side of the outdoor swimming pool and to the Parks and Recreation Department office covered with tons of mud and trees. 

The mudslide also damaged a section of the fence around the pool.

City officials who decided not to open the pool this year because of the coronavirus pandemic said damage to the fence also factored into their decision. They said they didn’t want to fix the fence and fill the pool until the hill was stabilized.

Froemming said last week that engineers are not immediately concerned about another mudslide.

“Miller does not see a risk to the (swimming pool) right now,” he said. 

Because the hill has shown no signs of collapsing in the past, even during floods, there was concern that work done on the high school in 2017 and 2018, which included the construction of a large gym and cafeteria on top of the hill, may have weakened the slope and changed the water runoff dynamics. 

But Miller Engineers and Scientists concluded that deposits of silt and sand in the lower two-thirds of the slope, which hold up a heavy layer of clay at the top, became saturated and unstable, causing the collapse.

To stabilize the slope, the firm is recommending the construction of a treated timber retaining wall tied into the top of the hill with earth anchors. Below that, geotextile fabric and coarse stone would be used to prevent erosion. 

A section of the hill immediately to the west of the area that collapsed is also unstable, and Miller Engineers and Scientists has recommended shoring that slope up as well. 

The district may seek bids for both parts of the project, then decide how to proceed based on the costs.