Embankment - Water Content

[Blu1913]

SITUATION

Sand backfill used to construct an embankment has the following properties:

Moist unit weight: 122 lb/ft3

Relative density: 65%

REQUIREMENT

If the maximum dry density is 120 lb/ft3 and the minimum dry density is 90 lb/ft3, what is the moisture content of the sand backfill?

A. 13.5%

B. 15.6%

C. 11.22%

D. 12.8%

SHOW WORK!!!

 

[Blu1913]

The answer is 13.5%.

I have no idea how they got the answer. Its a problem from the Civil CD review course i have and unfortunately they dont give a FREAKIN SOLUTION!!!

We need a Geo Eng for this one....

 

[Blu1913]

did everyone give up on this one? Shall we call it a busted question?

 

[GTScott]

did everyone give up on this one? Shall we call it a busted question?

I will see if I can get an answer on it tonight.

 

[EL Nica PE]

Here is the answer

Dr= [(Gammadry-GammadryMin)/(GammadryMax-GammadryMin)]x(GammadryMax/Gammadry), Solve for Gammadry/

0.65=[(Gammadry-90)/(120-90)]x(120/Gammadry)

Gammadry=107.46pcf

then

Gammadry=Gamma/(1+w)

solve for moisture (w)

107.46=122/(1+w)

w=.135=13.5%

 

[Blu1913]

Awesome, can you tell me how you got the Dr equation....i cant find it anywhere...(or maybe im just slow...)

 

[EL Nica PE]

Just sub in the emin and emax formulas and then rearrange to solve for

gammadry of course that is the hard way.

Das has the equation.

 

[EL Nica PE]

please check your numbers, makes no sense ....according to your equation, the water content is negative w=-11.9%. Thanks.

3gorgesdam,

Check your Math.

I solved it by hand and then I ckecked with my TI-89

solver to see i my answer were right.

They are...

GammaDry=107.46pcf

w=.13531=13.5%

 

[EL Nica PE]

solve for moisture (w)107.46=122/(1+w)

w=.135=13.5%

The equation above will not give you a positive number for w. It is obvious, don't need any calculator. I think you put gama dry in the wrong side, should be on the right side of the equation.....

3gorgesdam,

Here is step by step:

start with

107.46=122/(1+w)

1)107.46x(1+w)=122

2)107.46+107.46w=122

3)107.46w=122-107.46

4)107.46w=14.54

5)w=14.54/107.46

6)w=0.13531

I hope this help and you were truely in trouble and just didn't waste 5 min of my time....

 

[3gorgesdam]

Dr=(emax-e)/(emax-emin)=0.65

rdry=SG*rwater/(1+e)

substitue e with r, then solve for rdry. Again, found my errors.

w=13% :ZZZ:

 

[EL Nica PE]

just being nice...

 

[3gorgesdam]

just being nice...

El Nica, thanks for the input, I found my errors. Keep up the good work!!!