Earthwork Computations 1

[nurhforward]

My kind greetings,
Right now, my Companay is working on 82km road project in Nasarawa, Nasarawa State, Nigeria; it is well known fact that earthwork quantities covers more than 35% of the Total Contract Sun on road projects.

Several CAD systems (including CIVILCAD,AUTOCAD etc.) has been empolyed by most Draft engineers on site to calculate volumes of earthworks done. None, seems to predict the 'actual' quantity or volume of earthworks carried out for defined section or chainages (stations).

These inaccuraries and errornous 'Computer Outputs' made the project consultants to advice the Employer to pay the Contractor on a linear basis; ie Lenght*Breath*Depth. Whereas the thickness of 'fill' or 'cut' for formations is clearly stated in the Project drawings; and was not followed when preparing Interiem Certificates.

The general implications/cost overruns now boils down to the Contractor who achived over 0.8 - 1m plus depth on earthwork and paid less for more work done on site.

Please, can anyone advice the Contractor and if possible CAD systems that is generally acceptable to the Industry in calculating volumes of earthworks.

Kind regards, Pls.

nurhforward, Gitto International.

 

[civilperson]

Your well known facts do not represent any of the highway jobs I am familiar with in Arizona, Nevada, Nebraska, or Texas. The earth moving, grading, blasting and sub-grade construction is much less than 20% of the total contract. The contract language requires payment to the neat lines and grade shown in profiles and typical sections as well as the pre-construction survey. Only changes ordered by the engineer require recalculation of soil quantities.

 

[davilara01]

Try Pizer Earth Software - can use average end area method or prismatic formula.

Remember GIGO Garbage in garbage out. If data is wrong so do output. Also consider creating close cross sections when abrupt changes do occur.

PIZER Sales: 1-800-222-5332 1-206-285-6100
FAX: 206-634-0624
E-MAIL: sales@pizer.com

PIZER Incorporated
4422 Meridian Avenue North
Seattle, WA 98103
U.S.A.

 

[cherrypicker]

In the UK a very good software package for earthworks calculations is LSS (check it out at

http://www.dtmsoftware.com).

I have used this on many jobs from the very small to (relatively) large jobs 10 million cubic meter excavations and has proven very quick, accurate and reliable. It can use various methods including complex vertical prisms, isopachytes, simple vertical prisms, square grid and cross sections (Simpsons Rule) and will even accept feet and yards as units.

I do agree with davilara01 that the accuracy of the calculations is purely dependant on the quality of the models.

cheerypicker

 

[TerryScan]

I believe the GIGO factor that davilara01 stated is more likely the root of the discrepancies than the software.

What are assumptions for shrink/swell? Are they based upon pre-design geotech work? How detailed was the geotech work? How far between testing? How much do the ground conditions vary over the 84km? Does the calculation input take all of this into account?

 

[LCruiser]

Borrow is typically at about 80% compaction (std proctor). If you are specifying 95%, you will 95 m^3 of borrow per 80 m^3 of fill. There is also haul density, generally around 60% to 70%. The math is the math - it's the easy part. The tough part is figuring out how much shrink you will have.

 

[Blas]

Google pay dirt, agtek, trackware or terramodel.

 

[cvg]

lack of accuracy in the design survey or the construction staking and as-built surveys can have a huge impact on the estimated excavation volumes, even if the computer model is done accurately. I agree that most cad systems, especially the ones that have been mentioned can all be used to obtain an accurate estimate of the quantities, assuming the cad operator knows what he is doing and is given the time and good data required to do his job. Poorly written specs can also create problems and all quantities should be based on in-place volumes without respect for shrinkage or swell. If you are working on soft ground, you may also need to estimate ground compaction (of the subgrade) which can increase the amount of embankment needed over the theoretical amount.

 

[mouradtraweh]

it is better to use autodesk - land desktop and make the alignment as approved alignment and follow the typical cross section .

 

[thegraduate]

blas - do you know of any software similar to this that has a free trial period?

 

[bank]

GEOPAKis used pretty widely down here, and I believe it is required by TxDOT for highway works. It is used for developing horizontal and vertical alignments, cross-sections, as well as earthwork cut and fill quantities.

 

[ladysueg]

I worked as earthwork coordinator for over 5 years, I used CAICE and before that CEAL civil software to do all my calculations, I felt these programs were extremely easy to use, gave cut/fill, shrinkage, etc. printed out cross sections, views could be represented in 3D. I will well over $65 million in earthwork.
I found that doing pit calculation to be the most accurate with survey before and after, show exactly what the contractor used to build the project.

 

[LCruiser]

I agree with ladysueg, borrow should be measured by before and after cross sections. You have to watch out that the contractor doesn't fatten up slopes though to increase his borrow quantity.

 

[sixaparrat]

I agree with the two posters above.
Terramodel with the "Roads" package is excellent at this sort of work.

 

[slyhoney1974]

I RECOMMEND LSS SOFTWARE