A contractor has a contract for the construction of a high-rise office building with an underground parking garage. The size of the excavation required for the parking garage is 100 feet long, 45 feet wide, and 25 feet deep. The contractor plans to use a tracked hydraulic front shovel to excavate the soil and load 15-cubic-yard dump trucks. The rated heaped capacity of the shovel bucket is 6.8 cubic yards and the optimum digging depth for the shovel is 15.5 feet. The material to be excavated is bank clay with a swell of 35%. The contractor plans to excavate the foundation in two 12.5-foot layers and has determined the average angle of swing will be 120o .

a. What is the estimated productivity of the excavator in bank cubic yards per hour, if the ideal cycle time is 24 seconds and the operational efficiency is 40 minutes per hour?

b. If adequate dump trucks are used to eliminate excavator idle time, how long will it take to complete the excavation for the parking garage?