Friday, August 21, 2009

Solution 1


From the figure (notice red lines) provided above,
Coefficient of uniformity, Cu = D60/D10 = 0.2/0.025 = 8
Coefficient of gradation (also known as coefficient of curvature), Cz = (D30)^2/(D60 x D10) = (0.12)^2/(0.2 x 0.025) = 2.88

What do these values mean?
Cu > 10 : Well graded
Cu < 4 : Uniform
Cu = 1 : All grains same size
1 <= Cz <= 3 and Cu > 4 : Well Graded Gravel
1 <= Cz <= 3 and Cu > 6 : Well Graded Sand

Also, Gravel sizes are usually > 4.75 mm
0.075 mm <= Sand <= 4.75 mm
silt and clay < 0.075 mm
By looking at our solution chart above, we don't see any gravel, and we have less than 35% fines. Also, Cu > 6 and 1 <= Cz <= 3. Moreover, since the given sample has more than 12% fines, we can, therefore, classify the soil as Silty Sand (SM).


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4 comments:

  1. chess5329August 21, 2009 at 11:38 PM

    Thanks layad, I really appreciate your help!

    ReplyDelete
  2. chess5329August 21, 2009 at 11:45 PM

    When we have a question in the PE exam to calculate qult. Is the formula of Terzaghi approved by the NCEES to get the closest result?
    qult=c(Nc)(Sc)+ (d)(den)Nq+ 1/2 B(den)(Ny)(Sy)
    d=Unit weight
    for sand c=0 1st. term canceled
    for clay friction=0 3rd term canceled.

    ReplyDelete
  3. geotechieAugust 22, 2009 at 1:56 AM

    Yes, this is the basic equation to evaluate the ultimate bearing capacity of shallow foundations.

    ReplyDelete
  4. AnonymousMay 25, 2015 at 4:23 PM

    You should qualify this question with the type of soil qualification system (AASHTO, USCS).

    ReplyDelete

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