Earthwork Balance Calculations ª Subsidence
Earthwork Balance Calculations ª Subsidence
(OP)
I am preparing an estimate for grading work for a commercial retail development and the site requires significant import. The soils report says: "We have estimated that shrinkage may range between 10 and 15 percent, and a subsidence value ranging from 0.10 to 0.15 feet my be used for preliminary earthwork calculations." Can anyone give me some pointers as how to apply the subsidence value to the earthwork balance calculations? I don't want to come up short on my estimate of import!!





RE: Earthwork Balance Calculations ª Subsidence
http://www.insitesoftware.com/091999.htm
In the case of import material, you need to find the ratio of loose hauled material to in place material. Normally the quarry the material is coming from will know this.
A soils report usually refers to core samples taken on site, and since your concerns are about import, they probably don't apply.
Clear as mud.....right?
Take Care
Steve Warfle
Insite Software Incorporated
(877)746-7483
RE: Earthwork Balance Calculations ª Subsidence
Preparation and compaction of subgrade may also cause the ground to subside since the in-situ density may be low. Simply driving the scraper over the site a number of times may cause some compaction of the subgrade. Rolling with a sheepsfoot will almost certainly result in additional subsidence.
As stated above, a soils report is needed for the "borrow site" (probably not a quarry) to determine the following:
a)suitability for use
b)shrinkage or swell when excavated, placed and compacted
c)maximum density and optimum moisture content for compaction
However, unless you are working for the contractor, location of a borrow site and precise estimation of the quantity at the borrow site is usually left up to the contractor. Bidding and payment is usually based on accepted quantities placed on the job.
For this job, I would assume that you move existing dirt around on the site, achieve desired subgrade compaction using rollers or scrapers and then calculate some subsidence amount. This will give your subsided subgrade elevation. Then just calculate the theoretical amount of fill required to achieve the finished grade.
RE: Earthwork Balance Calculations ª Subsidence
When estimating the earthwork, keep in mind that the excavation will be generally removed as soils with insitu densities of 100%. Borrow will be hauled in by a volume measurement or scaled. If by volume, then you must be aware and calculate the lighter density of the material in the truck box, which will be different than in the loader bucket, which will yet be different still than compacted onsite. Case in point.
We scaled our gravel utilizing a scale affixed to our loader. The truck boxes were 20 yard capacity and the loader had a (heaped) 5.5 yard bucket. In three loads, the loader would load the trucks. That means, if one used density as a constant, the loader used a 6.6 yard bucket. The material in the truck was 1.24 tonnes/yard, while in the bucket was 1.5 tonnes/yard and 1.61 compacted onsite.
Using this premise, I now caculate my borrow based upon weight, not volume. My estimated balances have been remarkably close to the final values in the contract, resulting in confidence in my methodology and cost savings in contingencies. I don't guess anymore and fiddle with "shrinkage" or settlement values, per se.
KRS Services
www.krs-services.com
RE: Earthwork Balance Calculations ª Subsidence
Fluff and shrinkage will depend on the fill material and its moisture content at time of excavation. If the pay quantity is embankment compacted in place, it is determined by topo and the number of truckloads is the contractor's problem. The contractor likely is familiar with local materials and will be including these issues in his bid.
Regarding the uncertainty of the soils report, call the engineer and ask.
Good luck.
RE: Earthwork Balance Calculations ª Subsidence
RE: Earthwork Balance Calculations ª Subsidence
RE: Earthwork Balance Calculations ª Subsidence
RE: Earthwork Balance Calculations ª Subsidence
RE: Earthwork Balance Calculations ª Subsidence
Are there any reference, technical papers or historical documents I can get hold of regarding the subsidences, particularly the subdivisions. It soounds like a very interesting read with applications throughout North America in terms of establishing public policies.
Any direction will be sincerely appreciated.
KRS Services
www.krs-services.com