As an example, the following illustrates preparation of an estimate for a trench excavation. The estimate can be regarded as a baseline type or higher type. The discipline approach and crew development technique is used.
The estimate begins with a study of information available for the project: From the design documents, the estimator takes off such information as trench depth, length, slopes, soil conditions, and type of terrain. Wages for the locality in which the trench is to be excavated are obtained from standard handbooks, local labor unions, and the U.S. Census Bureau. The wage figures influence determination of the level of mechanization to be used for the project.
Crew Operation Calculation Sheet. With the basic information on hand, the estimator can now prepare a crew operation calculation sheet (Fig. 19.1). This sheet indicates the work to be done, how it will be done, who will perform it, and duration of the tasks. (The crew operation calculation sheet is normally the first item developed in a cost estimate.)
Crew Worksheet. The items, quantities, and units for the first three columns of the crew worksheet (Table 19.1) are obtained from Fig. 19.1. Unit costs for materials and subcontractors for columns four and five are obtained by direct quotations from vendors and subcontractors or from standard price lists. The worker-hours listed in Table 19.1 are based on data in Fig. 19.1. The wages in Table 19.1 are part of the basic information.
To obtain equipment costs, the estimator either gets quotations from rental yards or performs equipment ownership and operating cost analyses (Table 19.2). These costs include labor and material costs for owning and maintaining the equipment.
The equipment costs in Table 19.1 are assumed to be supplied by a subcontractor.
The total cost for one hour of production is calculated as the sum of the products of the quantities and the unit prices given in Table 19.1. The estimator obtains the unit cost for materials, labor, and equipment by dividing the cost for one hour of production by the length of the trench.
Estimate Worksheet. Table 19.3 gives the estimate for the total cost of the trench.
The quantities and units for the trench are taken off the contract documents. The costs are derived from the crew worksheet (Table 19.1), to yield the total direct cost for the excavation. To the direct cost, the estimator adds contingency costs (for rain, striking concealed utility lines, excavating in unexpected subgrade conditions), indirects (30% of labor cost), and company-wide costs and profit (10%). The sum is the total price of the project.
The estimator then makes two parametric checks to determine the reasonableness of the result:
1. By trench volume. The estimator compares the estimated price with that for similar projects with similar restrictions and requirements. A review of published bids for similar projects shows unit prices of $60 to $100 per cubic yard. This indicates that the estimated price of $73.65 is within that range.
2. By time clock. The estimator verifies that the specific equipment and personnel can be made available by the contractor. This is done by consulting the contractors work schedule for the equipment and personnel.