SUBJECT: Homework Assignment #6
CMGT 120 Students
Introduction to Construction Management
March 18, 2015
SUBJECT: Homework Assignment #6
Estimating and Scheduling
Remember Joan? The owner representative for the Library project. The project has moved through design, the contract type selected, and the project was put out to bid. A variety of subcontracts were developed by the General Contractor for the project. One was for site work.
One particular work package in the site work subcontract involved foundation excavation and piping installation. This work package integrated with the foundation work package (footings are part of the concrete subcontract)
Joan was really getting into the construction activities associated with the project. As such, she wanted to verify some of the subcontract estimates. She chose the foundation excavation work package.
Joan called Chuck with several questions to get her started on estimating the cost of the trenching work package. Later that day, Chuck dropped off several tables with the rest of the information required to complete the bid estimate, along with a short note:
“We decided to use a truck with a trailer for hauling earth. Include this in the overhead cost and don’t worry about balancing it with the loader. Include the truck and trailer costs for all the hours worked by the foreman because they also include the cost for the time not used. The foreman should be on the job for about 172 hours. Also, the concrete footing, floor slab, and the insulation will be done by other contractors, so don’t worry about them. Enjoy!”
Table 1 Expected productivity and equipment cost
Activity description Productivity Equipment cost
Excavate trench 200 LCY/HR $148.00/hr including operator
Place Bedding Material 37.5 LCY/HR $32.40/hr
Compact Bedding Material 25.0 LCY/HR $6.40/hr
Lay & Joint Pipe 50.0 LF/HR $8.00/hr
Backfill Trench 144 LCY/HR $75.00/hr
Compact Backfill 115 LCY/HR $90.00/hr
*Note: Job Efficiency Factor is already included in these productivities
Table 2 Required Labor
Activity Description Labor
Place Bedding Material 2 1
Compact Bedding Material 1 0
Lay and Joint Pipe 5 1
Backfill Trench 0.5 1
Compact Backfill 0.5 1
Table 3 Cost Summary
Pipe Material $4/LF
Bedding Material $17/LCY
Excavation: Swell Factor = 25% (when excavated, the soil expands by 25% into Loose Cubic Yards)
Compaction: Bedding Material Shrinkage = 6.8% (when compacted, bedding shrinks 6.8%)
Backfill Shrinkage = 10.8% (when compacting backfill, it shrinks 10.8%)
Cross Section of Trench
Trench is 2000 feet long.
You are Joan, so: prepare a memo to Chuck for the foundation excavation work package estimate setting out your calculations, results, and suggestions for the estimate of the excavation. Your solution should include the following information:
• The total quantities of excavated material, bedding material, and backfill measured in LCY. LCY = loose cubic yards. The volume of material ‘after’ excavation.
• The unit price ($/ LCY) and total price of each item.
• The total price of the excavation. Don’t forget to add profit to your estimate.
• Go to the OSHA web site and find safety recommendations for trench excavation. As you finished the estimate, you checked the OSHA regulations for trenching and you found some very important information that you want to share.
• Attach all of your calculations as a supplement to the memo.
Foundation Excavation Work Items to be priced
Item # Description Quantity Unit Price Total Price
1 Trench Excavation
2 Pipe Material
3 Bedding Material
4 Place Bedding Material
5 Compact Bedding Material
6 Lay & Joint Pipe
7 Backfill Trench
8 Compact Backfill
9 Project Overhead
10 Profit 10% of Costs