Question

A 36-inch wide trench is to be excavated for a 21-in.-dia. sewer pipe. The depth of the trench is 12 ft in hard tough clay. The ground material is stable and water seepage is not anticipated, nor is shoring required. These conditions will allow a ladder-type trenching machine. Examination of the path reveals obstructions that will reduce the digging speed to about 60% of the theoretical optimum 1 fpm. A crew consists of a worker ($20/hr), three common laborers ($15/hr), and a foreman for 50% ($30/hr). The hourly cost of equipment is $97.50. Find the cost of the crew labor and equipment per linear foot.

Modify this problem so it's a digging rate of 1.5 CY per minute with an 85% efficiency.

Answer 1

Ist part: 36 inch wide French to be excavated. Depth of French = 12t. Theoretical digging speed = 1 ft/min. Actual speed of machine = 60% = 0.6 ft/min. 1 No worker cost = $ 20/hr 3 no. labours = $ 15/hr foreman = $ 30/hr. freeman 50% means only half time equipment cost = $ 97.50/hr. Actual time for digging for 0.6 ft = 1 min Actual time for digging for 1 ft = 1/0.6 = 10/6 = 5/3 minutes so, we need to determine the labour cost for 5/3 minutes. Therefore cost = 5/3($ (20/60 times 1) + (3 times $ 15/60) + (1/2 times $ 30/60) + $(97.50/60)) = 5/3($ 1/3 + $3/4 + $1/4 + $ 97.50/60) = 5/3(20 + (15 times 3) + 15 + 97.50/60)$ = 20 + 45 + 15 + 97.50/60 times 5/3 = 177.50/36 = 4.93056 $/foot will be required.