Question

An 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.
What is the total duration of the rock cut project assuming 10 hours per day work?

Answer 1

Detailed solution is as follows,

Tractor 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

Quantity of rock

Given Length =15000 ft

Width = 85 ft

depth =3 ft

Volume of rock = 15000 x 85 x 3

                       =3825000 cft

Total duration required to cut

Per day productivity =productivity per hour x no of hours worked in a day

                             =560 x 10

                             =5600 cft

No of days required to complete the work = total volume/productivity per day

                                                            =3825000/5600       

                                                            =683 days