HOW TO CALCULATE GEOTECH TAKEOFF USING CARLSON SOFTWARE?

Contents

What is Geotech takeoff?

Geotech Takeoff is the process of calculating the volume and area of different soil and rock layers below the ground, based on information from geotechnical reports and borehole logs. It involves creating 3D models of materials like clay, silt, sand, rock, fill, and groundwater, then comparing those models to the proposed finished surface to know how much material needs to be excavated or filled.

Why is it important?

Geotech Takeoff is very important in earthwork planning, cost estimation, and construction design, especially for foundations, roads, and underground utilities. It helps engineers and contractors understand what’s underground before starting excavation, so they can plan the right equipment, budget, and timeline.

Standard workflow of a Geotech takeoff

The standard models we will create for each project

Mass Rock (Auger refusal)
Possible Mass Rock
PWR= Partially weathered rock
Silt
- Per Grading takeoff
- 0 to 5ft below subgrade
- 5 to 10ft below subgrade
Clay
- Per Grading takeoff
- 0 to 5ft below subgrade
- 5 to 10ft below subgrade
Sand
- Possible Fill (Previous Fill or Man-Made fill)
- Per Grading takeoff
- 0 to 5ft below proposed or existing whichever is the lower surface
- 5 to 10ft below proposed or existing whichever is the lower surface
Wet Soils
Ground Water

Reviewing the Geotechnical report

This report provides detailed information about the subsurface conditions, including the type of soils and rocks (such as clay, silt, sand, fill, mass rock, and partially weathered rock), their depth ranges, and the borehole elevations. It also includes Standard Penetration Test (SPT) values, which are essential for classifying materials; for example, low N-values may indicate soft soils, while high values suggest rock or dense materials. Moreover, the geotechnical report identifies groundwater levels and any zones with potential moisture issues.

how to calculate geotech takeoff using carlson software 01 — Image 1- An example of geotechnical report

Locating boreholes on the Grading plan

Import the PDF to the grading plan, make sure the Geotech map is accurately aligned with the grading plan. For example, check any existing conditions (existing contour, existing buildings, existing roads or property line) or another existing conditions from the Geotech map.

Once the import is done, then we need to create points for each soil type. For example, assign information to each bore: borehole number, elevation, material name (B1-Rock, B2-PWR, …)

how to calculate geotech takeoff using carlson software 02 — Image 2-Location of boreholes on the grading plan drawing

Creating boundaries for each model

Below are some tips for creating an accurate mass rock boundary

Consider the mid-point to the next bore and create a linework around the mass rock/Auger refusal bores.
If there is no next bore, consider approximately 100ft and create linework.
If we still have cut after creating the boundary at around 100ft or mid-point, then consider the next bores where per the bore log the bore is terminated.
If there is a pond next to a mass rock bore, please assume the pond excavation contain the Mass rock excavation and consider creating a boundary around the pond.

Modeling soil layers in 3D

After elevating the boundary, next you have to create surfaces for all the material layers. To create a surface in Carlson, please follow these steps:

Go to Surface => Triangulate & Contour => A popup will Open => Select => save the files at a desired location.

how to calculate geotech takeoff using carlson software 03 — Image 3-An example of 3D surface modeling for mass rock.

Volume calculations

After preparing accurate data, the next step is to calculate the volume of each material layer by comparing two surfaces.

Below is the method for calculating the volume between the mass rock surface to the finish surface by Carlson software:

Go to Surface => Volumes by Triangulation => Two Triangulation Surface Volumes => a popup will open => select the Mass rock surface first => then Finished surface
After selecting the surfaces, Carlson will ask you to select the boundary, select the boundaries and then select exclusion boundary (if we have), Carlson will open a popup and with volume report.
After placing the volume, now place cut and fill labels and maps, following the below steps:
- To place cut and fill map, go to surface => cut/fill Utilities => cut and fill color map.
- To place labels, go to surface => cut/fill Utilities => cut and fill color map.
- Select boundaries to place them on the cad file.

Technical considerations

When doing Geotech takeoff, it’s important to follow some key technical rules. First, always check the N-values in the bore logs. These numbers help us decide what type of material we are dealing with. For example, if the N-value is less than 10, it usually means soft soil like silt or clay. If it’s 50/4″ or lower, we may be looking at possible rock. If it’s more than 50/4′, that’s typically partially weathered rock (PWR). Using the right classification affects how we build models and calculate volumes.

Second, we must be careful to avoid volume overlaps. Each model (mass rock, fill, clay, etc.) should have its own boundary. If the same bore has more than one material, we need to split them correctly, so they don’t double-count in the final report.

Lastly, make sure all CAD data is organized properly. Each borehole should be on the correct layer, with a clear name like “B1 – Rock.” This helps a lot when creating surfaces, checking data, and sharing files with the team or client.

Ready To Streamline Your Geotech Takeoff Process With Carlson Software?

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