Testmasters Construction Production Question

[Mike_NC]

This comes from a construction PDF I downloaded from a previous post. The problem involves calculating production of a piece of equipment (by use of volume of excavation required). I found the correct perimeter, however I suppose where I am missing it is how the 'layback' of excavation when digging for a grade beam.

If someone could skim over the attached problem, solution as well as where I described my thoughts.. maybe someone can explain to me why they use the numbers they do.

Any help would be great, Thanks!

Also, does anyone think this look like a good PM type question that could come up?

Mike

_41_Excavation_Productivity.pdf

 

[SPSUEngineer]

based on my experience with the April 09' exam, this is definitely a question that is representative of the types of questions you may see on the exam.

 

[Mike_NC]

Thanks..

Do you see why they would not do a 'sloped layback' as I sketched? It appears I guess due to the shallow depth it does not need to be sloped. Or possibly it is a difference in the terms 'layback' and 'sloped back'?

 

[Mike in Gastonia]

Thanks..
Do you see why they would not do a 'sloped layback' as I sketched? It appears I guess due to the shallow depth it does not need to be sloped. Or possibly it is a difference in the terms 'layback' and 'sloped back'?

Does it have to be wider than 3 feet before it starts sloping due to the fact that it's formed on both sides? IOW, make it 5 feet wide and then slope it back from there?

 

[EnvEngineer]

Seems to be another poorly thought out question dumped on those of us studying for the exam

Def from Construction Estimator

Layback

Layback for excavation is given in units of run to rise.

However, it can be specified in terms of either variable run to a constant rise of one (1) or it can be given in a constant run (1) to variable rise.

A layback of zero (0) is simply an excavation with vertical walls (no slope to it)

Here are some common laybacks and their equivalents:

1/2 :1 is the same as 1:2

3/4 :1 is the same as 1:1 1/3

1:1 is a 45° slope

 

[chess5329]

This comes from a construction PDF I downloaded from a previous post. The problem involves calculating production of a piece of equipment (by use of volume of excavation required). I found the correct perimeter, however I suppose where I am missing it is how the 'layback' of excavation when digging for a grade beam.
If someone could skim over the attached problem, solution as well as where I described my thoughts.. maybe someone can explain to me why they use the numbers they do.

Any help would be great, Thanks!

Also, does anyone think this look like a good PM type question that could come up?

Mike

Why the perimeter isn't 1200 ft?

 

[Mike_NC]

You have to add (50' x 2) for the inset at the top...

 

[IlPadrino]

Thanks..
Do you see why they would not do a 'sloped layback' as I sketched? It appears I guess due to the shallow depth it does not need to be sloped. Or possibly it is a difference in the terms 'layback' and 'sloped back'?

I think this question is OK... the point to understand is that in order to form the grade beam, you'll need to excavate wider than the beam. So you're GUARANTEED that the 1:1 layback doesn't apply the way you drew it - there's no room for the formwork and it'd be awfully hard to build the formwork in place.

But I concede there's definitely some confusion over what "layback" usually means in terms of excavation protection... which is all about slopes. But, then, you've got to ask yourself... does a 2' deep trench really require sloping for excavation protection?!? I'd think anything under 3-5' is OK for no slopes. What's OSHA say?

 

[Mike_NC]

IlPadrino,

I do agree with you...

I think the fact its a 'grade beam' that tells you that the top of the footing is at 0'-0'. So you know the trench is 2'-0 deep. I think OSHA says anything over 4'-0 has to have protection and require a ladder to get into/out of... I agree with you irregardless if you laid back is vertical or sloped, is should be 1/1 away from the footing.. From there on, how you cut it back determines your actual quantity of material..