calculating error ?????

[BIGDAN315]

I just finished a small job building a gravel pad for a 30 X 40 pole barn. I went 32'x 42' with the pad. My problem is I was way off on my estimate on the amount of material I needed to bring the site to level.ops Take to mind the site was fairly dry and firm. I took a reading at each corner and came up with 14",8",10",4" then added 4" for removal of the sod. Came up with an average of 1 foot. So I multiplyed 32x42=1344 sq foot divided that bye 27 cubic feet in a cub. yard=50yardsx1.5 tons in a yard= 75 tons OK. Well it took 106 tons of material to do the job which I will probably have to eat not to mention the extra for trucking and time to sread and level. Am I doing some thing wrong ? I sugested doing time and materials but the owner wanted a concrete est. I havn't asked him for more money yet..:Banghead but I don't like to do that because it was my mistake. What do you guys think?

 

[Bob Horrell]

Two things come to mind. If there was a flat plane between the 4 corners then removing 4 inches of sod would yield 13 inches of material to become a level plane. If the shape was concave in the center, it would take more than 13 inches and just the opposite if it was convex in the center. The second point is that the material added will shrink when compacted requiring more than estimated. Depending upon the material used, it could shrink anywhere between 10 and 30% when compacted. 106/75 equals a 41% difference. My guess, without actually seeing what was done, is that both of what I mentioned above was in play (it was somewhat concave and there was significant shrinkage).
I find a lot of people omit shrinkage when calculating the amount of imported material required for a job - and this includes the engineers calculating the job. It is an easily forgotten piece of the puzzle.
Hope this helps.

 

[RocksnRoses]

We always allow at least 30% for compaction and even then we run out of material at times.

Rn'R

 

[Dwan Hall]

Consider the extra cost an education..

Next time if they want a concrete price pad it by at least 30% in materials and 50% in labor/equipment.

You stated a concrete estimate? an estimate is just that an estimate, it is variable that is why it is just an estimate. A concrete price you have to eat the additional costs.

 

[digger242j]

I have to question why you didn't level the pad by cutting and filling the dirt, then just put down a uniformly thick layer of stone, say 8". Then you'd have gotten away with less stone than your original estimate...

 

[BIGDAN315]

I have to question why you didn't level the pad by cutting and filling the dirt, then just put down a uniformly thick layer of stone, say 8". Then you'd have gotten away with less stone than your original estimate...

I don't normally use cut and fill on a pad, I have always used gravel to fill in with over a foot out of level then top it off with crusher run..:beatsme. I've just always thought stone is better.Is this a excepted method? Thanks

 

[BIGDAN315]

We always allow at least 30% for compaction and even then we run out of material at times.

Rn'R

Thanks I will keep that in mind.

 

[BIGDAN315]

Two things come to mind. If there was a flat plane between the 4 corners then removing 4 inches of sod would yield 13 inches of material to become a level plane. If the shape was concave in the center, it would take more than 13 inches and just the opposite if it was convex in the center. The second point is that the material added will shrink when compacted requiring more than estimated. Depending upon the material used, it could shrink anywhere between 10 and 30% when compacted. 106/75 equals a 41% difference. My guess, without actually seeing what was done, is that both of what I mentioned above was in play (it was somewhat concave and there was significant shrinkage).
I find a lot of people omit shrinkage when calculating the amount of imported material required for a job - and this includes the engineers calculating the job. It is an easily forgotten piece of the puzzle.
Hope this helps.

I did not check the center with and instrament except by eye and it looked flat. I took measurment on 4 corners . I did not want to get out the laser for a free estimate. Maybe I should have..

 

[digger242j]

I don't normally use cut and fill on a pad, I have always used gravel to fill in with over a foot out of level then top it off with crusher run..:beatsme. I've just always thought stone is better.Is this a excepted method? Thanks

Well, there's an awful lot of stuff out there that's been built on properly compacted fill. That's what would determine whether it was acceptable or not. Certainly, one would need to weigh the cost of doing a proper fill with the native material against the cost of using stone...

I did not want to get out the laser for a free estimate. Maybe I should have..

It turned out to be a pretty expensive estimate, didn't it?

 

[Orchard Ex]

I took a reading at each corner and came up with 14",8",10",4" then added 4" for removal of the sod.

I did not want to get out the laser for a free estimate.

Just curious, what did you take the initial reading with if you didn't use the laser? Maybe it's out of calibration. I used to use a "Mk 1 I-Ball" but it got out of cal and burned me a few times so I went to the laser for most Firm Fixed Price jobs

 

[BIGDAN315]

Just curious, what did you take the initial reading with if you didn't use the laser? Maybe it's out of calibration. I used to use a "Mk 1 I-Ball" but it got out of cal and burned me a few times so I went to the laser for most Firm Fixed Price jobs

The home owner had a string around the pad area and was level so just took measurments to the ground from the string...

 

[nedly05]

was the string put in level?

 

[BIGDAN315]

was the string put in level?

He said it was..:Banghead When I finished the job today he had the check already writtin out for the original estimate I gave him . I asked for extra but nothing doing.

 

[atgreene]

We all get burned from time to time. Learn from it and allow for extra next time. You may get more work from him in the future or be refered by him if you keep it professional and eat the loss.

I have found that by eating my mistakes that I have gained a reputation for sticking to my price. A couple other contractors near me ALWAYS charge for extras, customers hate that, and they don't forget it.

 

[BIGDAN315]

We all get burned from time to time. Learn from it and allow for extra next time. You may get more work from him in the future or be refered by him if you keep it professional and eat the loss.

I have found that by eating my mistakes that I have gained a reputation for sticking to my price. A couple other contractors near me ALWAYS charge for extras, customers hate that, and they don't forget it.

Can't agree with you more I know I don't like suprises either specially if cost me money..:ban

 

[dumptrucker]

I always figured that a yard of compacted material equal about a yard and a half of uncompacted material. That is what the state engineers alway told me the rule they go buy.

Ever notice at a pit they turn the material before loading, that is to take the compaction out and fluff it up.

 

[BIGDAN315]

I always figured that a yard of compacted material equal about a yard and a half of uncompacted material. That is what the state engineers alway told me the rule they go buy.

Ever notice at a pit they turn the material before loading, that is to take the compaction out and fluff it up.

So your telling me you loose about 1/3. I guess thats what I am getting from every one else to.

Thanks for every ones inputs...:notworthy

 

[TriHonu]

I have attached an extract from an Army Manual. On page 3 you will find the conversion factors for some soil types. This will give you a starting point for your calculations since different soils swell and compact differently.


For example, using Table 1-1 for Loam (common earth), the conversion factor from loose to compacted is 1.39

You calculated you needed 54 yards compacted.

54 x 1.39 = 75.06 yards loose.

75 yards x 1.5 tons per yard = 112.6 tons

 

[TriHonu]

Here is another conversion chart that gives the weights of different materials in bank, loose and compacted states.

You figured you needed 54 yards compacted.

Using the value of 4000 lbs per compacted yard for Pit Run Gravel that is some where between dry and wet would give you:

54 x 4000 = 216,000 lbs or 108 ton.

 

[BIGDAN315]

Here is another conversion chart that gives the weights of different materials in bank, loose and compacted states.

You figured you needed 54 yards compacted.

Using the value of 4000 lbs per compacted yard for Pit Run Gravel that is some where between dry and wet would give you:

54 x 4000 = 216,000 lbs or 108 ton.

Thats a good rule of thumb I think, 2 ton for every yard loose figured for the job...Thanks