Chapter 10 – Excavation and Earthwork: Comprehensive Notes
Excavation and Earthwork – Comprehensive Notes
Purpose of the module: understand how to estimate earthwork quantities for excavation, including types of excavation, soil conditions, swell/shrinkage, site plans, cut-and-fill methods, topsoil handling, and equipment implications. Emphasizes checking specifications, on-site verification, and coordination among contractors.
Core units and conversions to use throughout: bank cubic yards (BCY), loose cubic yards (LCY), and compacted cubic yards (CCY). 1 cubic yard = 27 cubic feet.
Key idea: estimators often work with feet and decimals but must translate between different volume states (bank, loose, compacted) using swell and shrinkage factors.
Major concepts and definitions
Excavation types (three major types):
Rough grading: bringing the site close to its final grade
General mass excavation: removal of large dirt quantities for basements, rolled cuts, etc.
Special excavation: small quantities, often by hand
Related tasks in excavation specifications: watering, finish grading, slope requirements, bracing/shoring, groundwater pumping, and disposal of excavated material.
Questions an estimator must resolve in excavation scope:
What is the extent of work covered?
What happens to excess excavated material?
Can material be left on-site or must it be removed? If removal, where to dispose?
Who does clearing and grubbing? Who removes trees? Topsoil stockpiling for future use?
If owner uses separate contracts, what work does each party perform? Coordination responsibilities if there is a General Contractor (GC) with/subcontractors vs owner directly hiring.
Site-specific items to consider:
Type of soil to be encountered (soil borings on drawings/project manual)
On-site verification of soil conditions (geotechnical investigations) and notes on drawings/specs
Access and logistics for clearing, hauling, and disposal
Importance of geotechnical input: sometimes a geotechnical report is required, and the estimator should coordinate with the geotechnical engineer to confirm soil conditions and required remediation.
Observational/onsite checks: bring basic tools (e.g., long-handled shovel, post hole digger) to verify soils and record observations in a project notebook.
Relationship between drawings and field work: soil conditions, gravel/rock layers, and site plan elevations influence how the excavation is performed and priced.
Soil properties and density references
Weight references (when available):
Undisturbed soil weight ≈
Rock weight ≈
When possible, tests should determine the actual weight/density of soil and rock.
Site plan as the primary drawing for determining earthwork quantities; typically scaled in feet and decimals of a foot.
Typical on-site practice: keep units in feet; convert inches to decimal feet when needed (e.g., 8 inches = 0.666… ft).
Swell, shrinkage, and related volumetric factors
Bank materials (in their natural state) swell when disturbed, becoming loose materials. This swelling is called the swell factor. It increases volume from bank to loose state.
After soil is placed and compacted, the material may shrink in volume. Shrinkage is the reduction from loose to compacted volume.
Common terms:
Swell factor SF: increase from BCY to LCY
Shrinkage factor SR: reduction from BCY or LCY to CCY
Typical behavior (conceptual):
BCY → LCY (swell): LCY = BCY × (1 + SF)
LCY → CCY (compaction/shrinkage): CCY = LCY × (1 − SR) or CCY = BCY × (1 − SR)
Figure references in course material: Figure 10.1 shows common swell/shrinkage factors for various soils (e.g., sand, gravel, dense clay, solid rock).
Example calculations (illustrative, using these concepts):
Example 1: 1000 BCY with SF ≈ 0.10 (sand/gravel range) → LCY ≈
If the final compacted volume is specified as CCY, and shrinkage SR ≈ 0.05, then CCY ≈
Practical note: swell factors often range from about 10% to 18% for typical granular soils; some mixtures can be higher. Shrinkage factors depend on soil type and compaction target (e.g., pavement subgrade vs. building fill).
Volume units, measurement, and rounding rules
Excavation is measured by the cubic yard (quantity takeoff) and conversions are common:
1 cubic yard = 27 cubic feet
1 foot = 12 inches; convert inches to feet when converting to decimals for site plans.
When estimating quantities, do not expect an exact answer; keep some rounding in mind and use accuracy that is appropriate for bidding, often rounding to the nearest whole cubic yard or two decimals for intermediate steps.
Site plans, contour lines, and elevation concepts
The site plan is the primary drawing for earthwork. It typically shows contour lines and spot elevations and locates all site improvements.
Contour line conventions:
Contour lines indicate equal elevation; existing (on-site) elevations are usually shown with dashed contour lines.
Proposed (design) elevations are shown with solid contour lines.
Water flows perpendicular to contour lines and from higher to lower elevations.
Spot elevations provide exact elevation at specific points to improve accuracy between contour lines.
Cross-section method and grid-based methods (for grading) are used to determine cut and fill quantities by breaking the site into manageable pieces.
Cross-section and grid-based methods for cut and fill
Cross-section method (grid-based refinement):
Divide the site into a grid; determine current (existing) and proposed elevations at grid intersections.
Compute the elevation change across each grid and determine cut (to lower elevations) or fill (to raise elevations).
For grids that contain both cut and fill, separate those areas and estimate costs for converting cut to fill separately.
The grid size should be chosen based on the magnitude of elevation changes; smaller grids yield more accurate results.
Labeling and referencing:
Grid intersections are designated with a combination of horizontal and vertical identifiers (e.g., numbers for horizontal, letters for vertical, or a mixed alphanumeric system like C3, D3, etc.).
Within each grid, document current elevation, planned elevation, and the resulting cut/fill quantities.
Volume calculations within a grid:
For a grid with both cut and fill, compute cut and fill volumes separately, then sum over all grids to obtain total cut and total fill.
When a grid has no change in elevation, it contributes zero to both cut and fill.
Average end-area method (for long, narrow projects like roads):
Divide the project into a series of end areas; estimate the average cross-sectional area along the route and multiply by the length to obtain volume.
Special case: finished pavement and rough grade adjustments
The top of rough grade may be different from the top of pavement; thickness of asphalt/bases affects the rough-grade target.
Example scenario: if the top of pavement is at elevation E_pavement and the rough grade is to be 0.4–0.5 ft below, adjust volumes accordingly.
Practical example workflows and calculations
Example: topsoil removal (typical spec inclusion)
Suppose a building footprint requires topsoil removal, and the removal area is expanded by 5 ft around the footprint to account for slope and accuracy.
Depth of topsoil to remove: 9 inches = 0.75 ft.
Footprint area (footprint expansion area) might be, for example, area A = 110 ft × 70 ft = 7700 ft^2.
Bank cubic feet for topsoil: BCF = A × thickness = 7700 × 0.75 = 5775 ft^3.
Bank cubic yards for topsoil: BCY = BCF / 27 ≈ 214 CY.
Example: cut and fill in a single grid (grid 10) with both areas present
Use corner elevations to determine cut and fill for the grid, e.g., corners have proposed elevations (plan) and existing elevations; compute changes such as ΔE across corners.
If in grid 10, you find that some corners require fill and others require cut, partition the grid into subareas where only fill or only cut occurs, and compute volumes for each subarea.
For a grid, the fill area could be calculated by integrating the elevation differences across the grid (often using an average of corner elevations to approximate the middle). Example approach: if the change in elevation across a grid is small, the average difference may be used and multiplied by the grid area to obtain volume. If you need more precision, subdivide further.
Example: pavement and rough grading adjustment (Figure 10.x cases)
The top of rough grade is typically below the top of pavement by the thickness of the pavement structure (asphalt/base).
Calculate cut and fill volumes relative to the rough-grade target rather than the pavement top to reflect actual earthwork before paving.
Example: determining the distance and slope within a grid for a cut/fill line
When the elevation change occurs along a line between grid corners, compute the per-foot elevation change (slope) as the difference in elevations divided by horizontal distance.
Use similar triangles to determine the length along the grid where cut vs fill transitions occur and estimate area accordingly.
Topsoil removal in more detail
Topsoil removal is often included in specifications and must be quantified separately because it impacts subsequent grading and rooting. Steps commonly followed:
Determine the area to be stripped (often larger than building footprint to account for slope and drainage).
Determine depth of topsoil to remove (e.g., 9 inches).
Compute the volume in bank cubic feet: Area × Depth.
Convert to bank cubic yards: divide by 27.
Stockpile topsoil area and plan for future use in finish grading.
Example continuation (from transcript):
Footprint expanded by 5 ft on all sides; topsoil thickness 9 inches (0.75 ft).
Area approximation (rectangular): e.g., footprint area + expansion = 110 ft × 70 ft → 7,700 ft^2.
Topsoil volume = 7,700 × 0.75 = 5,775 ft^3.
Topsoil BCY = 5,775 / 27 ≈ 214 CY.
Equipment and construction logistics
Equipment types mentioned and typical uses:
Trenching machine and dozer for trenching and initial grading
Power shovel / excavator for rapid excavation and loading into trucks
Front-end loader: used for basement excavation and direct loading into trucks; works well for closer distances
Bulldozer: used for shallow excavations and spreading material near the excavation
Scrapers (self-propelled) for large grading and fill operations
Backhoe/excavator: general utility for trenches, footings, catch basins, utilities
Clamshell bucket: for material removal in certain conditions; adjustable via telescopic arms
Key planning considerations related to equipment:
If material must be hauled a considerable distance, trucks or tractor-pulled wagons may be needed.
The choice of equipment depends on the site layout, access distances (e.g., >100 ft may favor trucks over crawlers).
The estimator should coordinate with the GC to determine available equipment and any constraints due to other ongoing work.
Practical note from the instructor: keep a balance between on-site operations and estimation work; avoid over-recording in class and ensure future sessions revisit any discrepancies with the book or slides.
Cut and Fill planning in site development
Cut and fill are the core components of grading work:
Cutting: removing soil to reach a lower grade
Filling: bringing in soil to reach a higher grade
The aim is to achieve the required final grade with proper drainage and structural support.
The relationship between cut and fill:
When materials from cuts are reused for fills, distance and logistics for moving material must be considered, including potential need for spreading and compaction equipment.
Shrinkage factors affect the volume of materials that must be moved or placed, so plan for excess material and stockpiling if reuse is intended.
Practical notes on planning:
It is often efficient to arrange for on-site material to act as fill rather than importing new soil, when feasible.
The site plan, geotechnical data, and structural requirements will determine how much soil needs to be cut and how much must be filled.
Grading layouts and grid layout approach:
A grid is laid over the site to organize calculations and identify locations where cut-only, fill-only, or mixed behavior occurs.
For mixed grids, separate the volumes for cut and fill and compute the required material for each portion.
The grid labeling system (e.g., C3, D3; 17, 11, etc.) helps reference specific grid intersections in plan and elevation discussions.
Finish grading and pavement preparation:
The finish grade must consider pavement thickness and base layers; rough grading and pavement elevations may differ, requiring adjustment of the cut/fill plan accordingly.
Practical calculation workflow summary
Step 1: Gather data
Review drawings and specifications, soil borings, and geotechnical reports
Visit the site to observe soil conditions and take notes in a project notebook
Step 2: Define volumes and units
Decide if you’re using BCY, LCY, or CCY; apply swell and shrinkage factors as appropriate
Use conversions where necessary:
Step 3: Decide on methods
Use site plan contour elevations and grid-based cut/fill calculations
For long roads or stretches, consider average-end-area method
Step 4: Perform calculations in steps
Compute swell: LCY = BCY × (1 + SF)
Compute compacted volume: CCY = BCY × (1 − SR) or CCY = LCY × (1 − SR)
For topsoil removal, use area × depth to get BCY, then convert to BCY
Step 5: Evaluate disposal or reuse strategy
Decide what material is removed off-site and what is reused for fill; plan stockpiles accordingly
Determine if additional hauling or truck capacity is required
Step 6: Coordinate with stakeholders
Confirm contractor responsibilities (GC, subs, owner), and ensure clear communication about tasks (clearing, grubbing, tree removal, topsoil stockpiling)
Step 7: Document and present
Use cut-and-fill worksheets, grid references, and elevation tables to present quantities clearly for bidding and construction planning
References to figures and pages (as cited in the lecture)
Figure 10.1: Swell and shrinkage factors for various soils
Figure 10.3: Sample site plan illustrating contour lines and elevations
Figure 10.4, 10.6, 10.12, 10.16, 10.17, 10.18, 10.19, etc.: Examples and layouts for cut/fill calculations, grid intersections, and pavement adjustments
Figure 10.8, 10.12: Parking lot/site plan scenarios showing rough grading vs finish grade alignment with pavement
Page references (course material): discussion of cut/fill grid labeling, average end area method, cross-section method, and site plan labeling conventions
Ethical, philosophical, and practical implications
Accurate quantity estimation is essential to project budgeting and scheduling and reduces change orders and disputes.
Clear delineation of responsibilities (GC vs subs vs owner) minimizes coordination problems and delays on site.
On-site verification and dialogue with geotechnical engineers ensure that the proposed earthwork plan is feasible and safe, protecting workers and future users of the project.
The choice between leaving material on-site vs. hauling away has environmental, logistical, and cost implications; decisions should balance cost, site constraints, and long-term site performance.
Quick reference formulas and reminders (LaTeX)
Conversion:
Swell to loose:
Shrinkage to compacted: or equivalently
Topsoil volume (bank cubic feet): where A is the plan area (ft^2) and t is thickness (ft)
Topsoil volume (bank cubic yards):
Example: topsoil area 7700 ft^2, depth 0.75 ft → →
If you’d like, I can tailor these notes to a specific section (e.g., the grid method, or the topsoil calculation) or add a short, problem-focused practice set to drill these concepts before the exam.