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Small Emplacement Excavator
QUESTION:I have this problem on a highway project. A section of cut slope is of sandy
silty material with direct shear phi angle of 35 degree and bulk weight of
17.
When i model the cut slope of 1 :2 , without presence of water, it stands
with Factor of safety way above 2. However, the insitu case is that water
level is high. So when i model it with water saturated the whole slope, the
cut slope would not stand!
I need help out there, as how such a slope can be protected and
stabilised?. Water is there for sure and it is the cause of all the failure
on site.
ANSWER: Locally we have about a 2x2'+ granite rock product called 'dropball,' which is just
rock shot out of the quarry that is a little too big for the crusher. It's dozed into
a pile and a crane drops an iron ball on it to make it small, hence its name. To
stabilize a wet slope, select angular dropball is countersunk by excavator 1 meter
below grade, and successive dropball courses rise toward the top, grading toward
smaller r-100 and then r-25 rip rap material. Lay your backslope down about 3:1, or
bench up every meter. Use geo-textile underneath it all to stop the mud from coming
in. To finish, get the excavator guy to 'sprinkle' the smaller r-25 over top of the
dropball. This is done to 'lock in' the dropball so water coming from behind or
sweeping beside it can't shake it out. Watch either end of the drop ball emplacement
for scouring. Heavy water flows collect and move through the countersunk portion.
Typically do this in brook rehab, brook creation, and road back slopes where active
springs exist. Key is having a fussy old operator who knows what water can do. Give
him lots of time to pick over the rock piles to find what he needs. He needs to be in
contact with the guy in the loader guy at the pit so he can call for the material size
and type needed. I think planting willow trees so they would root right in the stone
slope would also be a good idea. Probably have to iron bar a hole between the stone to
reach the dirt. Smash the end of the willow branch to a fiber pulp, toss some topsoil
into the hole and ram the plant into it.
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