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Warning: before you dig anything call YOUR LOCAL DIG - ALERT!
I realize that this is just the estimating phase and that you must estimate and win the project long before dig alert is called. I really just want to remind you to add labor for layout of trenching and excavation plus labor for dig-alert. I do have my own horror story about not calling dig-alert before "turning a spade", which I will share on a special (horror stories) web page later. This pitfall cannot be solved with even the best electrical estimating software.
Learn to take-off for trenching and excavation - Take off excavations for power vaults, manholes pull boxes and hand holes for a complete electrical estimate. Check the shop drawing or catalog data of the pre-cast structures for outside dimensions and recommended excavation sizes. If the catalogs don’t give an excavation size you can usually figure the width + 18” on each side, the length + 18’’ on each end and the depth + 12’’ for gravel sub base. Hand holes 11”x17” or 12” x24” only require +12” extra excavation on each side and bottom. Calculate the width and depth of the trenches for the various conduit and duct banks. Verify the depths at various locations based on your observations of the civil drawings for depths of the wet utilities.
Make a sketch of the trench on the utility drawing - Determine the width and depth of each trench at the various locations on the site plans. Sketch the profile of the trench on the utility drawing. This will give you a record and reference of what size of trench that you took off and where you took if off. And, it will help with your estimate review. Remember to always allow extra depth of the sand bedding for the conduits (usually 3”) and the spacing in between layers of conduits (usually 1½”).
Determining soils conditions - Determine the soil conditions for the excavations and back fills. You can usually get the soil conditions from the soils report. If a soils report is not available check with your excavating contractor, site grading contractor or general contractor. If there is doubt about the soils condition, sub surface rocks, strata or other hidden obstructions carefully and clearly qualify your estimate proposal as to what conditions you based your bid on!
Calculate how much concrete is needed for encasement - Determine what conduits or duct banks have to be concrete encased either full encasement or concrete cover on top of conduits. Calculate the amount of concrete required and include it in your bid.
Determining backfills - Determine the type of back fill material is required, such as existing native soil if suitable, sand or gravel. Calculate the amount of fill material needed and what percentage of compaction is required (usually at least 90%). A tip for backfilling is it will usually take 1.25 yards of fill material for each yard excavated, as the fill material will be compacted down.
Determining excess material - Determine how much excavated material will be left over after the vaults, manholes and pull boxes are installed and all the trenches are backfilled and compacted. This excess material will be either left on site in stockpiles or removed from the site for disposal elsewhere. Qualify your proposal regarding removal and disposal by you or others. Carefully consider all of the above points so your electrical estimating is complete and accurate. Without accuracy you are less likely to be as profitable.
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