How To Create Cut And Fill In Civil 3d

The processes involved with building roads, railways and canals often involve adding or removing large masses of dirt and stone. This addition and removal of mass is called cut and fill in the excavation industry. Cut and fill is a common process where the movement of the earth is handled in a logical manner.

The goal of cut and fill is ultimately to conserve energy and maximize the use of existing materials to avoid bringing in or shipping out dirt mass. While common, it can be an exhaustive process — moving earth takes a great deal of labor, and mistakes can lead to costly rework. To avoid such problems, project planners use detailed and intelligent cut and fill maps, providing exhaustive plans to help guide excavation teams to the most efficient use of mass and labor.

What Is Cut and Fill?

So what exactly does cut to fill mean? Cut and fill excavation is also known as excavation and embankment. It's a process where excavators move and place volumes of material to create optimal terrain for a road, railway or canal. The two terms are defined as follows:

Cut: Earth that is removed from an area is considered "cut" or excavated earth.
Fill: Earth that is brought into an area is considered "fill" or embankment earth.

When railways, roads or canals are dug out, the cut material is pushed to fill out nearby hills and embankments. This process is usually accomplished with earthmoving equipment. Bulldozers and excavators remove land from cut locations and transfer it to dump trucks, which carry it to fill locations. Once the land is transferred to the fill location, the filled earth is compacted with a roll-style or plate compactor.

This compacting process removes air before any construction takes place. It's essential, as it prevents the earth from moving and settling during or after the construction process, which can damage the foundation and building features.

loader being used to pick up fill

In cut and fill excavation, the ultimate goal is to conserve mass as much as possible. Having more cut than fill results in project managers needing to find somewhere to dump excess rock and soil, while having more fill than cut results in the manager needing to bring in dirt from another location. Both of these outcomes result in extra material, labor and equipment costs. To avoid bringing in or removing excess mass, cut and fill processes are planned in a way to keep cut mass and fill mass approximately the same.

While effective at conserving mass, cut and fill is an expensive process. The cost of this kind of excavation increases as more land is moved and more equipment and labor are needed to do so. To help maximize the use of earth, equipment and labor, site planners often use what is called a cut and fill map.

How Are Cut and Fill Maps Used?

When they're planning areas where cut and fill is required, designers create drawings called cut and fill diagrams. These diagrams illustrate all the areas where cut or fill are required. Such maps are generated by taking highly precise measurements of the existing topography and elevation, then overlaying a map of the desired topography. In these maps, cut and fill are defined as follows:

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.

Cut and fill maps are typically created in two varieties. The most basic maps utilize 2-dimensional diagrams, while more modern solutions use 3-dimensional modeling software. These two options are explained in more detail below:

2-dimensional diagrams: At their most basic, cut and fill diagrams show a location along an X-axis with a positive or negative Y-axis, quantifying the amount of cut or fill with a negative or positive number, respectively. Since land exists in three dimensions, these diagrams must be created for multiple cross-sections of the landscape at regular intervals.
3-dimensional diagrams: 3-dimensional maps are more modern solutions for cut and fill excavation projects. The terrain is first measured using accurate surveying equipment, and the data points are used to create a software-generated model of the terrain. Once 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 that vary based on value ranges.

Choosing to use a 2-dimensional model over a 3-dimensional one should depend on the level of accuracy required for the project. Smaller-scale projects with limited cut and fill needs may not require more than 2-dimensional diagrams. Larger and more expensive projects, however, will usually require the accuracy provided by a 3-dimensional diagram. Beyond this difference, the ability to use one type of diagram over another depends on access to the site and equipment availability.

Terrain Features in Cut and Fill Maps

Cut and fill maps contain many of the same terrain features as traditional maps, though they often also include elevations for the purpose of calculation. Some of the common terrain features included in cut and fill maps are detailed below:

Hill: A hill 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 closed circle that's smallest represents the hilltop.
Saddle: A saddle 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 is typically represented on the map with an hourglass shape.
Valley: A valley appears as a long groove in the land and usually contains a stream or river flowing through it. On a map, valleys are usually represented by contour lines in a U or V shape with the closed end pointing upstream. Draws are less prominent versions of valleys and are notated in the same way.
Ridge:A ridge is an area with steep slope and high ground on one side. Usually, ridges will be shown with contour lines forming in a U or V shape with the closed end pointing away from the higher ground. Sometimes, spurs form from ridges, appearing as continuous lines of higher ground jutting out from the ridge. They're noted similarly, though they may affect the shape of the ridge.
Depression: Depressions are low points or sinkholes in the ground. Maps usually show depressions only if they are significant enough in size, and these features are notated by closed contour lines with tick marks pointing to lower areas.
Cliff: A cliff is a sudden drop-off, appearing as a vertical or near-vertical change in elevation. Cliffs usually appear as contour lines being drawn extremely close together or on top of one another.

From the complete map, cut and fill can be planned around existing topographical features. Commonly, a map with these features may be used as a base, with the final project laid over it to determine areas of potential cut and fill. Once initial plans are made, cut and fill plans are added based on the topographical features.

How to Calculate Cut and Fill

So you've determined that you'll need to use cut and fill excavation in your project, and you have an idea of what method you'll be using. How do you calculate cut and fill area so that you can plan out the labor and calculate your project costs? The calculation method depends largely on the method you'll be using in your project.

A number of software products are available for generating cut and fill maps, and many of them automatically calculate and optimize cut and fill projects. However, if you're using more manual methods, a manual calculation may be required. A variety of calculation methods are used to calculate cut and fill values, and some of these methods are detailed below.

1. Cross-Section Method

The cross-section method of calculation is a common method used with the 2-dimensional method of mapping. With this method, cross-sections of the existing and proposed land levels are measured at regular intervals across the site. The cut and fill area is determined for each cross-section, then adjacent cross-sections are compared and the averages of their cut and fill areas are multiplied by the distance between them. This is done for each adjacent pair of sections, then the total volumes are added together to create the complete cut and fill volumes for the project.

The cross-section method of calculation is considerably more time-consuming than automatic methods of calculating volume, and the accuracy of the method depends on the distance set between sections. Closer sections result in greater accuracy but take longer to calculate, while further sections are less accurate but take less time to calculate.

2. Grid Method

The grid method of calculation involves drawing a grid onto the plan for the earthwork project. For each node of the grid, determine the existing and proposed ground level and calculate the cut or fill required. Once the cut or fill depth is calculated, multiply the value by the area of the grid cell. Do this for each square of the grid, then add the volumes together to determine the total cut and fill volumes for the project.

Like the cross-section method of calculation, the grid method takes time to implement and is significantly more time-consuming than any automatic systems. Additionally, the accuracy of the grid method depends on the size of the grid cell. Larger cells take less time to calculate but are less accurate, while smaller cells are more accurate but take more time to calculate.

3. Automated Methods

If you're using an earthwork software, you may not need to use one of the manual methods above. Instead, the software will run the calculations for you. It should be noted that these software systems are faster but not inherently more accurate — for example, some software calculations are based on high-density versions of the cross-section or grid methods. However, automated systems often use more sophisticated calculation methods, such as the triangular prism method.

The triangular prism method is a common calculation method for earthworks, and it's favored for its excellent accuracy. However, it must be completed using software due to its technical complexity.

The triangular prism method starts by triangulating 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. Once merged, the cut and fill is calculated by taking the volumes of the generated triangles and adding them together. Because of the excellent representation of both the existing and desired terrains, this method presents an excellent representation of volumes for cut and fill projects.

Work With the Data Preparation Experts

The cut and fill process is an extremely useful process for excavation in residential, commercial and roadwork projects. However, while cut and fill makes use of existing terrain, it requires detailed planning to be as effective as possible. To accomplish this goal, project planners need detailed cut and fill maps — that means they need survey equipment to get terrain information and software to process and visualize data in a meaningful way. Take-off Professionals can help.

Take-off Professionals prepares 3D models and performs related services for a wide variety of industries, from commercial construction to civil engineering projects. Our innovative data services are available to help take your terrain data and turn it into meaningful models that you can use for your next cut and fill project.

TOPS works with a wide range of systems, so we can provide services to as many companies as possible. We work with data from Carlson, Leica, Topcon and Trimble equipment and can provide models in any format you need, whether your engineers use Civil 3D, MicroStation or another design software. We can even work with multi-brand fleets.

When you work with us, you can trust our decades of knowledge and experience as well as our innovative GPS and 3D machine control services technology. With our tools and services, your business can gain detailed insights into your project to help make the most of your cut and fill terrain.

Want to learn more about our models and how they can help on your next cut and fill project? You can get in touch with our team of data preparation experts right away by completing our online contact form or calling us at 623-323-8441.