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RE: Epoxy Grout and Rock Anchors

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Caution ! I have experience with a major failure of an in-ground basin floor 
involving epoxy grouted rebar use as rock anchors in somewhat fractured rock. 
According to the drawings: Number 6 rebar embedded in 2 inch diameter holes 
drilled 6 ft. deep into rock was grouted with "BRUTEM 15 EPOXY GROUT OR 
EQUAL". The 15 ft. deep basin floor is 70 ft. x 140 ft. x 14 in. thick, 
reinforced with #6 at 12, EWEF. The floor cracked and was (permanently) 
deflected up 12  in. by 7 ft. groundwater head acting on the slab bottom, 
giving 268 psf net pressure on the slab. Based on analysis of the possible 
causes of the failure, I believe it has to do with the epoxy grouted rebar. 
Either (1) the particular epoxy used was not suited for the constant wet 
condition that exists and it failed by  loss of shear strength or debond, 
and/or (2) the two inch diameter hole is too large for epoxy grouting rebar 
in that over time the grout creeps under load and eventually fails in shear. 
Also, two inch hole diameter seems to be too large considering that all epoxy 
manuf. I see recommend the drill hole in concrete be only 1/8" larger on the 
diameter than the particular rebar size being grouted. I believe that a 
cementitious grout is better for rock anchors like this.