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Construction Estimating for Infrastructure Projects

A cost estimate is the first definitive dollar figures for a project and must be based on accurate data. This can be sourced from numerous organizations that provide cost data through online databases and cost estimating books/guides.

The estimates may be conducted at different levels of detail. An early estimate may simply serve as a rough indication of potential costs to help in funding or design decisions.

Site Investigation

For any project, site investigations are an important part of the planning process. These investigations help determine the current sub-soil conditions, allowing the design professional to plan the construction of the project to suit the site conditions. This is especially true for infrastructure projects, where risks are significant and can be extremely expensive.

The first stage of the site investigation is reconnaissance, which involves a visual inspection of the area. This includes checking for the presence of drainage ditches and dumping yards, geological and topographical features, the quality of the water table, and utility lines.

A preliminary conceptual site model (CSM) is then created based on the results of this reconnaissance. This is based on examination of existing data, such as maps, a walkover survey, and information from the local building control department. It is also based on an understanding of the history of the land use and the presence of known engineering abnormalities such as compressible ground, running sands and naturally occurring voids.

The next phase of the site investigation is intrusive, which involves digging and drilling to assess the current sub-soil condition. This can include trial pits, trenches and boreholes to examine the soils, sample in-situ measurements and take samples for laboratory analysis. It can also be used to check for the presence of buried hazards, such as coal mining legacy and contamination.

Equipment Requirements

The cost of building infrastructure projects is largely driven by the quantity and type of equipment required. This can result in large expenditures for specialized equipment and materials, especially in highly populated or environmentally sensitive locations. For this reason, project sponsors may conduct research to identify potential equipment requirements and associated costs. Ultimately, the goal of this research is to optimize construction productivity and reduce environmental impact.

Once the engineering team prepares a list of required equipment, contractors may use the information in a bid package to create their estimates. Depending on the complexity of the project, this may include performing a manual takeoff by using paper copies of drawings, rulers, digital measuring tools, and pencils to count the quantities of each item. More commonly, estimators rely on digital takeoff software that uses a variety of sources to gather accurate data. With a definitive list of material and equipment requirements, specialty contractors then begin to work with equipment vendors to get pricing information for each item.

The resulting estimate includes all direct field costs, equipment rentals and purchases, indirect field costs, overhead, and contingency. In a competitive bidding process, it is important to provide an accurate estimate that covers all necessary costs and returns a reasonable profit margin. Often, businesses add anywhere from 5-10% to the total cost of construction for contingency.

Labor Costs

Regardless of whether you’re creating an estimate for a single construction project or the total cost of all projects in your company, calculating labor costs is a critical part of the estimation process. There are several ways to approach this task, and each has its advantages and disadvantages.

The bottom-up method involves breaking a project down into tasks or work activities and estimating the number of hours required to complete each task based on historical data, industry benchmarks, expert knowledge, or consultation with experienced professionals. This information is then multiplied by a standard labor rate to calculate a project’s direct labor cost.

Direct labor costs are expenses that are directly associated with completing physical construction tasks, such as wages and salaries for carpenters, masons, electricians, plumbers, and other skilled workers. They may also include tool and equipment costs. Indirect labor costs are expenses that support construction activities, such as the salaries for project managers, foremen, supervisors, and administrative personnel. They may also include the wages for safety officers and quality assurance personnel who ensure compliance with project standards.

Bonding and insurance are necessary to mitigate risk for contractors, but they come with a price tag that must be included in project estimates. These expenses are annual, and they are generally spread across all of a contractor’s projects each year.

Safety Compliance

A safe work site is crucial for the project to run smoothly. This includes the use of proper equipment for each job and ensuring all workers are following safety guidelines to prevent accidents that could slow down productivity and increase costs.

Equipment and materials are important elements in the overall cost of a construction project, but they are not the only factors that need to be taken into account. Many projects also require the mapping or excavation of existing utility lines, which can be a costly and time-consuming process. Using ground-penetrating radar or electromagnetic detectors and leveraging public utility maps can minimize the need for excavation and improve project timelines and feasibility.

Historical cost data is essential for preparing cost estimates, but it must be carefully collected and organized for future use. This will ensure the accuracy and consistency of unit cost information and reduce the risk of errors due to changes in relative prices over time.

The final estimate for the construction of infrastructure requires a review of the project scope and a detailed breakdown of all of the items that will be needed to be constructed. This may include items such as the design technology, major structural systems, production equipment, and various miscellaneous overhead costs like permitting, on-site facilities, fuel, and other indirect costs. The estimate will also need to factor in the expected price for these items at the time of purchase, which can be difficult to predict and is why it’s best to include a contingency amount in the estimate.