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Bank vs. Loose Hauling


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#1 wstahlm80

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Posted 31 March 2011 - 04:06 PM

Attached is a problem regarding hauling dirt from a construction site and determining the productivity rate. The solutions manual says that you should use the "Bank Density" for the calculation. However, my first instinct would be to use the "Loose Density" since the dirt in the ground (bank) would be disturbed and have swell introduced.

As you can see in my work, using either of the two densities given provide an answer which is shown. The solutions indicate that Answer D is correct.

Can someone explain why you would use bank density instead of loose?

Let's be careful with copywrited material. Just reference people to their copy of the sample exam. Thanks. SapperPE

Edited by Highway to Hell, 31 March 2011 - 07:15 PM.
Don't put copywrited material on here.


#2 sac_engineer

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Posted 31 March 2011 - 04:53 PM

The loose density is irrelevant because you're not asked about how the material will be reused. You're given the max capacity of the truck (27000 lbs) and you need to relate that to the bank material only.

Your steps are correct, but think of it as a weight transfer problem rather than a density (bank vs loose) issue.

3.24 trips per hour @ 27000 lbs per trip = 87480 lbs/hr

The bank weight of the soil is 2970 lbs/yd

Thus, the bank productivity is 87480/ 2970 = 29.45 yd/hr



#3 sac_engineer

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Posted 31 March 2011 - 05:05 PM

In addition to the above, the problem provide a maximum volume capacity of the truck. Even as the material becomes loose as it is loaded on to the truck (i.e. 2700 lbs/yd), this meets the maximum struck capacity of 10 cubic yards. So, this question can be approached either by mass (bank density) or by volume (loose density).

#4 wstahlm80

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Posted 31 March 2011 - 08:46 PM

QUOTE (wstahlm80 @ Mar 31 2011, 11:06 AM) <{POST_SNAPBACK}>
Attached is a problem regarding hauling dirt from a construction site and determining the productivity rate. The solutions manual says that you should use the "Bank Density" for the calculation. However, my first instinct would be to use the "Loose Density" since the dirt in the ground (bank) would be disturbed and have swell introduced.

As you can see in my work, using either of the two densities given provide an answer which is shown. The solutions indicate that Answer D is correct.

Can someone explain why you would use bank density instead of loose?

Let's be careful with copywrited material. Just reference people to their copy of the sample exam. Thanks. SapperPE



Again, sorry for the improper scan. Please refer to:

PAGE 38 the NCEES Civil PE Construction sample Questions & Solutions book.

#5 jrf500

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Posted 31 March 2011 - 09:56 PM

I was struggling with this problem too. Thanks 'sac_engineer'. This is one of those problems that is frustrating when you see the solution cause it's so darn simple....yet when I read it and tried to work thru it....I made it WAY more complicated than needed.

Thanks for the help. even though this wasn't my thread, I was curious on the same problem.




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