I have a L shaped dam that i need to find out how many cubic yrd. there are
150 ' 8 ft. tall 8 ' wide at top 38 ' at base..this is the biggest section.
the other 150 ftwill taper up to existing grade.
I am gettin mixed bids?????

Grant

The first thing you do is calculate the average width of the dam. You add the top and bottom widths and divide by 2. In your case this comes to 23 ft. (I'd actually recommend going with a 10-12 foot wide dam top if you plan on driving over it very often).

From your description it sounds like you have a 150 ft stretch that will be 8 ft tall. Thus you multiply 150 x 8 x 23 to get 27,600 cubic feet, or 1,022 cubic yards.

For the tapering end you divide the length of 150 by 2 to make this a rectangular box. Then also multiply by 8 and 23 to get 13,800 cubic feet or 511 cubic yards.

Thus your total fill would be 1,533 yds, but you should probably add in 5-10% for shrinkage.

You don't mention anything about the core trench and the fill for that, but in the dams I've built we've figured 10-12 ft wide, probably an average of 8-10 ft deep (this will depend on your substructure) and running the full length of your dam. Just estimating in your case, if you take 300 x 12 ft wide by 8 ft deep would be 28,800 cu ft, or 1,066 cubic yards. In my experience, contractors will charge 1.5 to 2 times the rate for the core trench excavation and fill, as they will for the general fill.

Do you have an engineered design of the dam showing the elevations, slopes, and calculations for the core trench and fill? If you do, then the contractor bids should be fairly easy to compare, since they should be able to show the rates for the various activities. Also the design should include the principal and secondary spillway structures, and how the inpoundment is to be protected from wave action.

On the other hand, if you've just got some stakes set out and it's up to the contractor to esimate all the yardages and determine what they want to do for the spillways, it would be understandable that you've got a range of bids. If the latter is the case, I'd sure recommend you to get your USDA NRCS folks out there to give you some advise and provide engineering. They used to do this for free. However if you need to pay a private engineer to do this, it will sure be worth the money.

as far as the trench goes I planned to start diggin the trench w/ dozer & simply push the clay dirt into trench to forming for the new trench?? I plan to dig core trenck 3x10 w/ dozer. the site is pure clay 3' feet ...then hardpan clay mixed w/ gravel.

Grant,

Is the gravel in your hardpan clay layered in veins, or is it just some gravel particles mixed in with the gravel. If it's veins of gravel, that could be bad news, and you'll want to make sure you cut through those layers completely until you have solid clay at the base of the core.

I'd also suggest that if you haven't already, check the soil conditions along the length of the dam, especially where it crosses the existing channel or drainageway. Often times the substratum changes significanly where the water flow typically is.

Compaction is critical on the core trench, as as you'll read on this site, fill in 6 inch lifts, and make sure the fill material has sufficient moisture to adequately compact. You'll want to pull a sheepfoot roller over the fill, as the tracks of the dozer won't provide the pressure needed.

the gravel appeared at 3 ft. deep & it was hard for the excavator to dig at this point?
How can i tell if it is veins of gravel?

Grant,

Was there any water flowing into the trench when you hit the gravel? In our country we have black dirt down the first couple feet, then it gets into a foot or so of sandy/gravel mixed with dirt sitting on top of the clay. The water seeps from the surface down through the black dirt and into this sand/gravel layer, through which it flows horizontally downstream. The clay serves as the base, preventing the water from flowing down. Thus we just make sure we dig through the sand/gravel and get down 2-3 feet into good yellow clay.

I'm surprised that it was hard for the excavator to dig when it got into your gravel material. You might try digging out a small hole in this layer and pour some water into it. If it's mainly clay, but with some gravel particles in it, it should hold water and you might be okay. However if water seeps right into this layer, you will want to dig through it and get into a water impermiable layer.

You might check with your NRCS office and see if they could come out and do some core trench borings for you. Most offices have access to a soil testing probe that is run hydraulically from the back of a pickup

I spoke w/ NRCS & he confirmed that the soil in this area would be just fine for the back side of the dam.
No water was running....I think I will be alright w/ this advise
Thanks