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?
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.
We always allow at least 30% for compaction and even then we run out of material at times. Rn'R
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.
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
Thanks I will keep that in mind.
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..
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... It turned out to be a pretty expensive estimate, didn't it?
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...
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.
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
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
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
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
just remember that the same rule aplies when your removing fill. As you dig it up, it removes the compaction and your 50 cu yards becomes 75 again. You also have to allow for this when you blast an area... no school like the school of hard knocks
differnt matierals have swell factores and will change you volumes as u put air into the matierals. each of them have a % that it will swell. and it will fill in compaction i have the numbers somewhere ill have to find them. and they might be online too
hahaha i just saw the link up top by trihonu
When I qoute these types of job's I always estimate the material and quote the labor. Because material is hard to get exact, I tell the customer that my labor will be a fixed price but material should be this but could be more or less and that is a fixed price per truck, how many trucks I bring is what he is going to pay for. When it comes time to pay I add the qouted price on labor to what ever the cost of material is and thats what he owes me. I have used less material than i said i would and the customer has paid less for the work , and I have used more for material and the customer has paid, sometimes the fill just compacts more because the site is wet, or I could use something else to get compaction, you don't know until you open it up. I have sold the customer on fabric after I have taken the topsoil off because of how wet the site is. My labor number never changes. All this is in writing before I start.
A bit late with a reply but havent had much chance to get on here. I was lucky enough to be given a "cheat sheet" from the local sand and metal guy which hasnt let me down yet. Sorry to most as its in metric but you should be able to follow it. Lenght x width x depth x compaction rate = tonnage needed. Depth 25mm = .025 50 mm = .050 100mm - .100 etc Compaction rate loam 1.78 rubbles and paving sand 2.25 stone 1.6. how it works for me is. I have a 10 metre by 15 metre area to be built up 75mm with rubble. 10 x 15 x .075 x 2.25 = 25.3 tonne. I have found this to be a big help, as one example I went out to do a quote for a 21m x 9m shed they have ordered 30tonne of rubble, but wanted to build it up 250mm so needed 130 tonne. While i wasnt paying for the rubble at least I made sure the right amount was brought on site to start with. Cheers all :drinkup