negative skin friction - constant force?
negative skin friction - constant force?
(OP)
I am assessing down drag forces for a 170 foot deep manhole already in place, and buried in a ring of stone surrounded by municipal solid waste. The down drag force is easy enough to compute; however, I am curious about whether this is a transient or constant force. When the waste consolidates and there is relative motion between the waste and the backfill, this motion will impart a force on the manhole. What about when the waste is not in motion? Can we have a downward force acting on the manhole without motion? Does the force that is exerted on the manjole dissapate as the manhole resists the downward force?





RE: negative skin friction - constant force?
Practically speaking, you will probably end up with both conditions over the life of the manhole but will need to design for the long term force condition.
RE: negative skin friction - constant force?
Thanks for the reply. I'm thinking this "set" would be a residual stress built up in the stone/waste contact and translating to the manhole walls. This makes some sense to me, and I will evaluate the condition as you suggest. Thanx again.
RE: negative skin friction - constant force?
Good luck!
RE: negative skin friction - constant force?
Negative skin friction should be expected when the surrounding compressive soil is being compacted (under its own weigth) ; this down drag will cause the "tube" to settle, which will reduce the relative movement between the tube and the surrounding soil/waste, and in this way reduce the down drag.
Dimitri Timbremont
Geotechnical Engineer
Socofonda
(Belgium)