In construction earthwork, you need to perform accurate and frequent site surveys to ensure your project is managed well and completed on time. Earthwork surveys keep construction team members up to date and on target with project schedules. But keeping track of all that moving dirt is not easy.
Normally, earthwork surveys require someone to walk the entire site to measure cuts, fills, and stockpiles. This is a slow, time-consuming process. Even if you use truck-counting methods, your calculations will be imprecise. Trucks are rarely filled uniformly and the dirt with which they are filled often contains hidden air pockets. Such “fluff factors” can be very costly in the long run.
To get more accurate and frequent earthwork surveys that don’t rely on so many assumptions, you’ll want to invest in drone technology.
In this article, we’ll go over what exactly an earthwork survey is, how cut and fill volumes are traditionally measured, how drones can survey construction sites, and the benefits of using drones in earthwork construction. Let’s get started.
Table of Contents
Source: Wikimedia Commons
What is a Construction Earthwork Survey?
An earthwork survey is the collection of earthwork site data to plan, estimate, locate, and layout various construction phases. It involves marking important reference points to guide and monitor the construction project as it moves along.
Construction earthwork surveys go all the way back to the Egyptians who used some form of surveying to build perfectly oriented and square pyramids. But construction surveying has come a long way since then. Today, earthwork surveys are used at every phase of the construction process, including cut and fill measurements.
Traditional Cut and Fill Survey Methods
Cut and fill is the modern terminology for moving and removing dirt. In earthwork construction, you are constantly cutting and filling dirt. To optimize the amount of dirt that needs to be brought in or carried away, it’s important to have accurate measurements. The goal is to conserve as much mass as possible. Why bring in extra dirt when you’ll be excavating some from the site anyway? Cut and fill surveys help you stay on top of the amount of soil you have available, so you can export and import dirt as little as possible.
That said, there are different ways to measure cut and fill volumes. We’ll go over the three of the most common ways:
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1. Grid Method
The grid method survey requires drawing a grid over the entire survey area, calculating the cut or fill required for each node on the grid, multiplying the value by the area of the grid cell, and then adding all the cell’s volumes together to determine the total cut and fill volume. An example calculation with only two grid cells would look this:
Fill (height): 4m
Cell Area 50m x 50x = 2,500m2
Cell Volume: 4m x 2,500m2 = 10,000m3
Cut (depth): -3m
Cell Area: 50m x 50m = 2,500m2
Cell Volume: -3m x 2,500m2 = -7,500m3
This method is more accurate if you divide your grid into smaller cells. But the smaller the cells, the more calculations you’ll need to make and the more time it will take to complete the survey.
Video Credit: Buildsum
2. Cross-section Method
The cross-section method involves dividing cut and fill areas into parallel cross-sections, calculating the volume of each cross-section, averaging the area of all cross-sections, and multiplying the averages by the distance between them. An example calculation would look like this:
Average cut area: 100m + 150m / 2 = 125m2
Average fill area: 120m + 90m / 2 = 105m2
Distance between sections: 50m2
Cut volume: 50m x 125m2 = 6,250m3
Fill volume: 50m x 105m2 = 5,250m3
3. Triangular Prisms
The triangular prism method is more accurate than the previous two methods but it’s also the most technical. It involves triangulating the survey area with a continuous surface of connected triangles. The more irregular the surface, the smaller the triangles.
Together, the triangles form a Triangulated Irregular Network (TIN). You repeat the triangulation process for the proposed terrain and then overlap the two triangulated terrains to create a third triangulation. You then calculate the cut and fill volume of each vertex on the third TIN and add them together to find the total cut and fill volume.
The above calculations are too complex to perform by hand, so you’ll need specialized software to do them for you. The triangular prism method improves the speed and accuracy of the cut and fill survey, but it’s still nothing compared to what earthwork survey software can do when coupled with drones.
All three traditional cut and fill survey methods require complex workflows and a lot of time, especially without the help of software. As a result, many construction companies only complete a survey at the beginning and end of a project. There’s simply not enough time or manpower to perform surveys more frequently.
"The introduction of drones in earthworks has completely changed survey workflows across every job site ."
Using Drones for Construction Earthworks
Luckily, there is a better way. Drones can automatically survey a standard construction site in as little as 20 minutes with unmatched precision. Here’s how they do it:
Drones scan topography quickly and then upload the data to the cloud where it can be analyzed with special software. For example, drone pilots set up special markers on the ground called ground control points (GCPs). GCPs are large targets (often shaped like an X) positioned strategically around a construction site. They have known coordinates so that drone software can later match the GCPs to their geographical position and thereby create an accurate map of large areas.
Video Credit: Steel City Drones Flight Academy
You can think of them as little thumbtacks that mapping softwares use to orient drone footage. So long as the GCPs are visible from the air, drones will be able to capture them in the footage to later produce earthwork maps that are properly aligned.
Other drones use real-time kinematic (RTK) processing to correct location data midflight with the help of an active base station that sends GPS data to the drone while it is in the air. Here, it is important for the drone to stay connected with the base station at all times. Otherwise, signal loss can result in lost data that makes it harder to create an accurate survey.
Still other drones use post-processing kinematic (PPK) technology to geotag coordinates in the air while the base station records positional information independently. The two sets of GPS data are then compared after the flight to create an even more precise map of the site. This method benefits from two independent sources of data that combine to produce 1/10 ft (3cm) accuracy with only one drone.
The wealth of data that drones are capable of collecting coupled with different types of advanced software allows you to create maps and surveys in much more detail than you could get otherwise. Whether you use GCPs or opt for RTK or PPK processing, your earthwork surveys will be incredibly precise.
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The Benefits of Drones in Earthworks
In comparison to manual methods, there are many benefits to using drones in earthworks projects. Let’s go over some of the main advantages:
Frequent Cut and Fill Reports
Because drones are so fast, they can create frequent cut and fill reports. At any given time, you can know exactly how much earth you are moving and who should be responsible for moving it. Plus, drones’ real-time feedback can be made visible to all team members. That way, everyone can track their progress against project schedules and managers can ensure they only pay to move or remove dirt when necessary.
With frequent cut and fill reports, stakeholders can also identify minor issues before they get bigger. And by maintaining an up-to-date digital representation of the construction site, you save on unnecessary costs.
Reduce Unplanned Expenses
Speaking of costs, drones can help you reduce unplanned expenses. Traditional earthwork surveys tend to involve costly change orders, but with drones, you can significantly reduce your margin of error. Drones measure within 1 to 2% of true volume. Such precision allows you to create a full topographic map you can rely on to validate and develop an efficient schedule before a project begins. By sticking to a reliable schedule, you limit the time and resources spent on correcting mistakes. This means less lost time and money in the long run.
Drones can also reduce unexpected costs by tracking changes in soil stockpiles. With features like terrain filtering, drones estimate earthwork volumes more accurately and limit how much you over- and underestimate. This way, you don’t pay for soil you already have or find yourself needing to import missing soil at the last minute.
Complete Projects on Schedule
As in all industries, time is money in construction earthwork. So you need to make sure your projects are completed on or ahead of time. Drones allow you to take control of project schedules with better documentation and grade management. They can quickly document site conditions and improve project readiness. This is helpful because you usually only have a small window of time to perform a survey before a project begins.
Drones also help you adjust the schedule when necessary and sign off on project phases as you go. That way, you stay on top of your project’s progress and lessen the chance of it getting off schedule.
Getting Started with Drone Earthwork Surveys
Well, there you have the complete guide to drone construction earthwork surveys. If you have any more questions or want to hire a drone pilot to fly your next construction earthwork project, The Drone Life can help. We offer professional construction drone services that can accelerate your workflow and significantly reduce your construction costs. Don’t hesitate to schedule a free consultation with a drone pilot today.
What's included in YOUR GUIDE...
A Proven Roadmap of Success for Implementing Drones in Construction.
A List of Red Flags to Avoid When Hiring Drone Service Providers.
How to Persuade Your Leadership Team to Leverage Drones on Every Jobsite.
