Retaining wall on the north side of the Library Lot partially failed, spilling a great deal of dirt into the hole. [photo] [photo]
Fifth btw William and Liberty
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Archived by the Ann Arbor District Library
Story here [link] credit to “new media watch”, I guess.
Update as of 10:30 this morning: Jersusalem Garden and Earthen Jar are supposed to be open for business today. I spoke with Ali Ralawi, owner of JG at the store, who described how the area where the sinkhole opened — as a result of the breach in the retention system — was actually used for vehicular traffic. An employee of his had driven across it about 10 minutes before it opened up. No one was injured in the event.
Based on conversation at the sinkhole, last night the breach was plugged with bagged gravel and capped with a pour of concrete. This morning, more gravel is being dumped into the hole from the sinkhole side. Additional repairs will need to be effected on the other side (the big-pit side) of the earth retention wall. The earth retention system on the north side of the pit, where this breach occurred, is a “tangent wall” system, which entails pouring three columns of concrete in a outwardly bowed formation between every pair of steel-beam-reinforced columns. The vertical steel beam elements were an obvious part of the earth retention construction phase that unfolded over the course of last summer. With this breach, it was the three-column bowed-array that failed in one location, not the steel beams.
The tangent wall system is used there, instead of the wood-lagging system used elsewhere, because of the close proximity of buildings – there was not enough room to excavate sufficient space to install a wood lagging system. The sanitary sewer system of the building behind Earthen Jar was damaged by the sinkhole, so that’s on the schedule to be fixed as well,
Engineers have completed a visual inspection of the perimeter and identified no other problems. The perimeter inspection will be repeated using some kind of more sophisticated imaging technology.
It’s an incredible turn of luck that that sinkhole didn’t open in a lightly different spot or grow just slightly bigger. 30 feet to the east and 312 E. Liberty (the red house peering over the hole) would be in serious trouble.
Pardon the typo, I meant “slightly”, not “lightly”.