Bentonite/soil rate lab test question
Bentonite/soil rate lab test question
(OP)
Ok, here's a fairly simple one. I have a contractor looking for us to run a proctor, perm, hydrometer, atterberg limits test on a sample of silt with a mix of bentonite for a liner material. The contractor wants to add 1.5 lbs of bentonite per square foot of surface area (6" lift) in the field and i need to duplicate that in the lab. The silt is at 103 PCF at 18% optimum and he wants 95% compaction at optimum moisture content. What I am trying to figure out is the amount of bentonite i need to add to a 2500g sample of the silt to get a equivalent sample. I got a number and so did another guy and he didnt match up with me so I want to check. Thanks for any help. This should be a simple one but I fear I am looking way too far into it.





RE: Bentonite/soil rate lab test question
40 pounds of moist soil
12 percent dry weight (as received)
35.7 pounds of dry soil
35.7*0.03=1.071 pounds (this is how much bentonite you'd add)
Now I can rant about the problem with the overall approach. What is "optimum" moisture content for 95 percent compaction? The correct answer is something greater than the optimum moisture content for 100 percent compaction. What you'll find is that the permeability of the sample prepared at 95 percent of the 100 percent optimum moisture content will likely be lower (maybe even much lower) than the permeability you'd acheive if you actually knew the optimum moisture content for 95 percent compaction. Jim Mitchell published quite an interesting paper on this - JSMF ASCE Vol 91, SM-4, July 1965, pp. 41-65. Please note that a soil compacted over optimum will often acheive a 10 fold decrease in permeability. This usually relates to compaction at about 90 percent saturation.
Hope this helps.
f-d
¡papá gordo ain't no madre flaca!
RE: Bentonite/soil rate lab test question
Don't forget that these samples will take a little longer to run as the bentonite needs time to fully hydrate.
RE: Bentonite/soil rate lab test question
RE: Bentonite/soil rate lab test question
There are other methods; however. . .
f-d
¡papá gordo ain't no madre flaca!