Excavation is a fundamental activity in construction and civil engineering projects. To estimate the cost of excavation accurately, a detailed rate analysis is essential. Rate analysis of excavation involves measuring the quantity of earthwork to be carried out and calculating the associated costs of equipment, labor, and other factors. This article explores how excavation rates are analyzed, the factors influencing these rates, and presents an example to illustrate the process.
Classification Based on Excavation Depth
The cost of excavation largely depends on the depth of the earth that needs to be removed. Excavation depths are generally classified into categories to simplify cost estimation:
- Up to 1.5 meters
- Between 1.5 meters and 3 meters
- Between 3 meters and 4.5 meters
- More than 4.5 meters
These categories allow for a structured approach to pricing excavation work. However, the required depth varies by project and site conditions, influenced by numerous factors such as foundation type, soil stability, and design specifications.
Rate Analysis Framework
Rate analysis is primarily based on two key variables: the type of soil and the lead distance—the distance soil is transported after excavation. Soil can be broadly categorized into soft soil and hard soil or rock, each requiring different effort and equipment.
For example, rate analyses may be structured as follows for a lead distance of 1 kilometer:
- Excavation in soft soil for depths:
- Up to 1.5m
- 1.5m to 3m
- 3m to 4.5m
- Excavation in hard soil or rock for depths:
- Up to 1.5m
- 1.5m to 3m
- 3m to 4.5m
This framework can be extended to accommodate various soil types, lead distances, and depths depending on project requirements.
Key Components for Rate Analysis
Before performing rate analysis, it is important to consider several factors:
- Type of Soil: Different soils require different excavation methods and equipment.
- Lead Distance: The cost to transport excavated soil varies with distance.
- Depth of Excavation: Deeper excavation typically increases costs due to additional labor and equipment requirements.
- Method of Excavation: Manual or mechanical methods affect productivity and cost.
- Labor Capacity: Productivity rates and wages for manual labor.
- Equipment Capacity and Cost: The efficiency and operating costs of machines.
- Water Charges: Costs related to water use during excavation, if applicable.
- Contractor’s Profit: A percentage added to cover contractor margins.
Example Rate Calculation
To understand rate analysis practically, consider the excavation of soft soil to a depth of 1.5 meters with a lead distance of 50 meters for 10 cubic meters of soil:
| Item | Unit | Quantity | Rate (Rs.) | Amount (Rs.) |
|---|---|---|---|---|
| Hydraulic Excavator | Day | 0.04125 | 5000 | 206.25 |
| Tractor/Dumper | Day | 0.04125 | 1500 | 61.88 |
| Unskilled Labor | Day | 1.20 | 311.2 | 373.44 |
| Total | 641.57 | |||
| Water Charges @1% | 6.42 | |||
| Contractor Profit @15% | 96.23 | |||
| Grand Total | 744.22 |
The gross cost per cubic meter (m³) for excavation up to 1.5m depth is Rs. 74.42.
Equipment Productivity and Costing
The productivity of equipment such as hydraulic excavators and transport vehicles is expressed as the volume of soil excavated per day. For example, if a hydraulic excavator takes 0.04125 days to excavate 10m³, its capacity is:
With a daily operating cost of Rs. 5000 (including fuel and operator wages), the cost for excavating 10m³ is:
0.04125×5000=Rs.206.25
Similar calculations are done for other equipment and labor based on their capacities and costs, then summed up to determine the total cost.
Summary
Accurate rate analysis of excavation involves considering many variables including soil type, excavation depth, lead distance, labor and equipment productivity, and contractor profit. By breaking down costs and capacities as shown, contractors and engineers can prepare precise bids and budgets. Different projects require different combinations of these factors, making a detailed and flexible approach essential in civil engineering tendering and project planning.