Question

n earthwork contract requires to cut and move excavated rocks. The site is a typical limestone rock formation in a cut section, which is 15,000 ft long, 85 ft wide, and 3 ft deep. Seismographic tests indicate a seismic wave velocity of 5,000 fps for the rock layer material. The contractor proposes to rip the rock with a 370-hp crawler tractor. Answer the following questions.

As a Construction Manager for this site development project, prepare detailed cost estimate for the project, and bid documents.

      Assume 10% time value cost of money, bonds, insurance, and storage over total direct cost, contingency at 2% of total direct cost, indirect overhead cost at 5% of total direct cost (additional on top of the equipment and operator costs), and 10% fee (on subtotal total of direct and indirect cost).

Answer 1

Detailed solution is as follows,

Productivity

For the given seismic wave velocity,ie., 5,000 fps and using 370 hp tractor ,referring the tractor production chart,

Productivity =560 bcy/hr

Volume of rock = 15000 x 85 x 3

                       =3825000 cft

Total durationto cut the rock = 3825000/560

                                        =6830 hours

Estimation

The normal cost for the tractor per hour = $ 96 per hour(including operator charges)

Total direct cost = 96 x 6830 =655680

Other costs are as follows

Cost for fee =10% of Direct and Indirect cost

                 =10% of 767145

                =76714.56

Total Estimation =(Total Direct +Indirect cost) + Cost for fee

                           =767145.6 +76714.56

                           =$832860