Cut and fill is a practice in excavation.
It is often used in the process of constructing a road, railway, building, or canal.
In this process, the amount of material from cuts roughly matches the amount of fill needed to make nearby embankments.
By utilizing this practice, you can minimize the amount of construction labor.
If you’re planning cut and fill excavation in an upcoming construction project, read on to see what you may need to know.
1. What is cut and fill?
Cut and fill in construction is also known as excavation and embankment.
It occurs when excavators move and place volumes of material to create an optimal terrain for a building, railway, road or canal.
Here’s how each of the two terms is defined:
Cut: This is the earth that is removed from an area (excavated earth)
Fill: This is the earth that is brought into an area (embankment earth)
When canals, roads, or railways are dug out, the cut material is pushed to fill nearby hills and embankments.
Earthmoving equipment, such as bulldozers and excavators, will remove land from cut locations and transfer them to dump trucks.
These trucks then carry them to the fill locations.
After the fill is relocated, the earth is compacted with a roll-style or plate compactor.
The compaction process is intended to remove air before any construction takes place.
This is an essential step as it prevents the earth from moving and settling during or after the construction process.
If settling occurs after structures are built, then it can damage the foundation and building features.
2. What is the history of cut and fill?
Cut and fill was first widely utilized to construct tracks along rolling terrain across the British Isles.
It was also used to perform the construction of new dwellings for returning veterans in Ireland following the end of World War II.
Lachlan J. Boland, an Irish railway engineer, saw the application of cut and fill in railway construction and introduced it in residential projects.
3. What is the goal of cut and fill excavation?
The cut and fill process aims to conserve mass as much as possible.
When you have a project that has more cut than fill, it requires project managers to find somewhere to dump excess rock and soil.
On the flip side, when you have more fill than cut, it results in project managers needing to bring in dirt from another location.
Both these scenarios require additional material, labor, and equipment costs.
To avoid needing to fill in or remove the excess mass, the cut and fill process is planned in a way to keep both the cut and fill masses approximately equal.
Overall, a cut and fill operation is expensive.
As more land is moved and more equipment and labor are required, the cost of excavation increases.
Therefore, to maximize the use of earth, cut and fill maps are used by site planners to minimize any waste.
4. How are cut and fill maps used?
When cut and fill is required, areas are planned out using cut and fill maps.
Designers will create these diagrams that illustrate all the areas where cut and fill are required.
These maps are generated by taking highly precise measurements of the existing topography and elevation.
Then, a map of the desired topography is overlaid.
Here’s how cut and fill are defined in these maps:
Cut: Areas where the existing elevation exceeds the desired elevation have the “cut” material
Fill: Areas where the existing topography lies below the desired elevation line are the “fill” spaces
5. What are the two types of cut and fill maps?
Cut and fill maps are created in two different varieties.
There are 2-dimensional diagrams and 3-dimensional modeling software.
Here’s a more extensive description of each.
The 2-dimensional diagrams show a location along an X-axis with a positive or negative Y-axis.
They quantify the amount of cut or fill with a negative or positive number, respectively.
Because land exists in three dimensions, these diagrams are created for multiple cross-sections of the landscape at regular intervals.
On the other hand, 3-dimensional maps are a more modern solution for cut and fill excavation projects.
First, the terrain is measured using accurate surveying equipment.
The data points are used to create a software-generated model of the terrain.
When the base model is complete, the planner creates a model of the desired terrain and lays it over the existing terrain model to identify the cut and fill areas in three dimensions.
Software models may highlight cut vs. fill areas with different colors.
These colors will vary based on value ranges.
6. How do you know which type of cut and fill map to use?
Choosing whether to use a 2-dimensional model or a 3-dimensional model depends on the level of accuracy required for the project a hand.
Smaller-scale projects with limited cut and fill needs may not require more than 2-dimensional diagrams.
If you’re dealing with a larger (and thus more expensive) project, then it will usually require the accuracy of a 3-dimensional diagram.
Beyond this difference, the ability to use one type of diagram over the other depends on access to the site and equipment availability.
7. What terrain features are included in cut and fill maps?
Cut and fill maps include many of the same terrain features as traditional maps.
For example, they will often include elevations for the purpose of calculation.
Below, we’ll list out some of the common terrain features that are included in the cut and fill maps detailed below:
Hill: This feature is defined as an area of elevated ground where the ground rises at a slope.
Hills are shown on maps using contour lines that form concentric circles.
The smallest closed circle represents the hilltop.
Saddle: This feature is a low point between two points of high ground.
It may appear as low ground between two hills or a break or dip along a ridge crest.
This feature will be represented on a map with an hourglass shape.
Valley: This feature appears as a long groove in the land, and it usually contains a stream or river flowing through it.
On maps, valleys are represented using contour lives (either U or V-shaped) with the closed-end pointing upstream.
Ridge: This feature is an area with a steep slope and high ground on one side.
It will typically be shown with contour lines (either U or V-shaped) with the closed-end pointing away from the higher ground.
Sometimes, there will also be spurs from the ridges that appear as continuous lines of higher ground jutting out from the ridge.
Depression: This feature is a low point or sinkhole in the ground.
Maps usually show depressions only if they are significant enough in size.
A depression is shown on a map with closed contour lines with tick marks pointing to lower areas.
Cliff: This feature suddenly drops off and appears as a vertical or near-vertical change in elevation.
Cliffs normally appear as contour lines being drawn extremely close together or on top of one another.
When you have a complete map, you can plan cut and fill around any existing topographical features.
A map with any of the above features may be used as a base with the final project laid over it to determine the potential areas of cut and fill.
Then, once you’ve made the initial plans, cut and fill will be added based on the existing topographical features.
8. How do you calculate cut and fill?
If you’ve determined that you need to use cut and fill excavation in your project and you know which method you’ll be using to map your project, your next step is calculating the cut and fill area.
Once you’ve done this, you can plan out the labor and calculate your project costs.
Keep in mind that the calculation method depends largely on the method you’ll be using in your project.
To calculate cut and fill, there are numerous software products available.
These will generate cut and fill maps as well as automatically calculate and optimize projects.
There are also some cases in which a manual method will be required.
Here are some of the ways to calculate cut and fill:
This common method uses 2-dimensional mapping.
Cross-sections of the existing and proposed land levels are measured at regular intervals across the site.
Next, the cut and fill area is determined for each cross-section.
Then, adjacent cross-sections are compared and the averages of their areas are multiplied by the distance between them.
This process is done for each adjacent pair of sections.
The total volumes are then added together to create the complete cut and fill volumes for the project.
This method of calculation is more time-consuming than other automatic methods of calculating volume.
The accuracy is also dependent on the distance set between sections.
Closer sections result in greater accuracy.
That said, these take longer to calculate.
Further sections are less accurate, but they take less time to calculate.
This method involves drawing a grid onto the plan for the earthwork project.
For each node of the grid, you determine the existing and proposed ground level.
Then, you calculate the cut or fill required.
Once this depth is calculated, you multiple the value by the area of the grid cell.
Do this for each square of the grid and add the volumes together to determine the total cut and fill volumes for the project.
Just like the previous method, the grid method requires time to implement.
It’s significantly more time-consuming than other automatic systems.
The accuracy of this method also depends on the size of the grid cell.
Larger cells take less time to calculate, but they are less accurate.
Smaller cells are more accurate and take more time to calculate, so you’ll see that time-accuracy trade-off.
If you choose to use earthwork software, you may not need to use one of the manual methods above.
The software will run the calculations for you.
These are faster than the manual methods but not necessarily more accurate.
Some software calculations are based on high-density versions of the cross-section and grid methods.
Automated systems will often use more sophisticated calculation methods.
One of these methods is the triangular prism method.
The triangular prism method is a common calculation method for earthworks because it has excellent accuracy.
That said, it must be completed with software due to its technical complexity.
Here’s a brief overview of how it works.
The triangular prism method triangulates the existing terrain to create a continuous surface of connected triangles.
The same method is used to model the desired terrain.
Once both surfaces are complete, the triangulations are merged to create a third triangulation.
When these are merged, cut and fill are calculated by taking the volumes of these generated triangles and adding them together.
This method is a good option as it maps both existing and desired terrains.
As such, it represents an excellent representation of volumes for both cut and fill projects.
9. What do excavation and embankment mean?
As you’re reading up on cut and fill, you’ll likely see the words excavation and embankment quite a bit.
Here is the definition of these words.
Having the proper vocabulary can help you make informed decisions throughout this process.
Excavation: Material removal, typically of soil or rock, from its natural location
Embankment: The placement and compaction of layers of earth or rock to form a roadbed of the planned shape, density, and profile grade
10. Is there an alternative?
You don’t always have to do cut and fill depending on your situation.
In fact, there are some alternatives to cut and fill excavation.
For example, if a house is built on a slight slope, then you can build on top of the land with small piers at one end of the building.
This will provide a small (but useful) area under the house to use for tools or storage.
In this case, the house will have some sort of wooden or raised concrete floor (the more expensive option).
Cut and fill may be one of the first steps in a construction project.
Often, architects and engineers must consider the existing conditions of a site.
Use the information above to ensure you have all the information to make your project successful!
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Disclaimer: we are not lawyers, accountants or financial advisors and the information in this article is for informational purposes only. This article is based on our own research and experience and we do our best to keep it accurate and up-to-date, but it may contain errors. Please be sure to consult a legal or financial professional before making any investment decisions.