Monday, February 20, 2017

Shallow Soil Slab Failure

I had the chance to revisit  a steep slope I had assessed about a decade ago. The slope is a former steep shoreline bluff underlain by silt/clay glacial drift with a few boulders embedded in the unit. I say former shoreline bluff because the base of the slope is fronted by what has been a very stable accretion shore with a beach that has built well out from the toe of the slope. The slope is 55 degrees, steep enough to be a challenge to walk on.

This fall and winter has been very wet so landslides are not unexpected. In my previous assessment of this slope I stated "The primary source of slope movement on the slope appears to be root throw from occasional toppling trees and raveling associated with deer and thaw freeze. However, the upper slope is steep enough that shallow landslides should be expected on a periodic basis. If slides do take place, I anticipate that they would involve only a few feet at most of the upper soil horizon".   

This fall/winter combination of wet and cold caused the top soil layer to release on the slope. There may have been some enhancement as trees had been cut and slash left on the slope. 

All and all a fairly straight forward site compared to a few other recent slope assessments. But it is a good lesson to visit failed slopes to observes recent slope failures.   

Silt/clay glacial drift with a few cobbles and boulders embedded in the unit.

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