Civil 3D surface analysis is probably one of the most powerful capabilities of this engineering software. Yet many professionals may not know the full potential of this tool. If you are amongst them, do not panic – we’ve got you covered!

Once you have learnt how to model Civil 3D corridors and Civil 3D gradings, learning surface analysis is just the next natural step forward. Even if you have not learnt those tools yet, understanding surface analysis can help you get started with your project. For example, you can quickly get a better understanding of what your topographic survey looks like.

The surface analysis options currently available in Civil 3D are the following:

  • Contours
  • Directions
  • Elevations
  • Slopes
  • Slope arrows
  • User-defined contours
  • Watersheds

Let us look at each of them in more detail.

Contours and user-defined contours

Contours are probably the most widely-used surface feature in the construction and civil engineering industries. Any time that a client plans to build new civil infrastructure, everything starts with a topographic survey. And one of the most common ways of representing this survey is through contours. These contours represent the imaginary lines that have the same elevation across the site.

Thanks to the Civil 3D surface analysis tool, we can quickly specify a set number of ranges, and give each range a specific colour. We can also change the linetype (for example, we can make minor contours to be dashed), and lineweight (to make major contours thicker, for example), per interval. This way, it is very easy to look at the surface and understand its shape in a visual way, thanks to the coloured contours. Contours and user-defined contours are virtually the same, with the only difference that they are placed in different layers, allowing you to have a main display setting for major and minor contours, plus an analysis of user-defined contours for a set of specific elevations, for example.

civil 3d surface analysis contours

Analysing surface directions with Civil 3D

This analysis is less frequently used, as it may not be as helpful as others, such as the slope flow analysis. In a similar way to the contours analysis, we can set up a specific number of ranges with different colours representing different directions. Thanks to this analysis, we can see the surface triangles coloured according to how they are oriented in space.

surface directions

Civil 3D surface analysis: elevations

This is one of the most used analysis types, especially when it comes to cut and fill. In a similar way to the previous analysis, we can set a number of ranges with different colours. It is very similar to the contours analysis, but rather than showing lines (contours), it shows fully shaded areas for each interval.

The Civil 3D elevations analysis comes particularly handy when we work with volume surfaces to calculate earthworks volumes. When we create a volume surface in Civil 3D comparing 2 surfaces, we can create a surface elevations analysis with two intervals, one positive and one negative. That is, when the comparison surface (finished elevations) is above the base surface (existing topo), it means that we are in fill (green in the image below). And when the comparison surface is below the base surface, it means we are in cut (red in the image below). That way, in just a few clicks we can get a really good understanding of what the areas of cut and fill are in our site.

cut and fill volume analysis

Slopes and slope arrows

The Civil 3D surface analysis for slopes and slope arrows are very useful, especially when analysing the surface drainage. As their name indicates, this analysis shows a representation of how steep the gradients are on the surface triangles. Both the slopes and the slope arrows analyse the same – the slope gradient in percentage – but they display it differently.

If we choose the slope analysis, it will fill in each triangle with a solid colour, based on our set intervals. In contrast, if we choose the slope arrow analysis, it will show coloured arrows. This arrow analysis is particularly useful when doing drainage design and assessments. As we mentioned before, the direction analysis is not so widely used, similarly the slope analysis. The main reason is that the slope arrow analysis will give you both, the direction (with the arrow direction on each triangle) and the slope (with the colour of the arrow). As a result, engineers tend to use the slope arrow analysis more often, as it gives more valuable information.

civil 3d surface analysis slope arrows

Watersheds in Civil 3D surface analysis

Watersheds are slightly more complex to understand and analyse than the other analysis types. They are very useful again for drainage analysis, especially to identify catchment areas and streams of water. It analyses the water behaviour on the surface, giving us boundary points, boundary segments, depression, flat areas and multi-drain points.

Although it may be somewhat complex, this analysis can be really insightful and save loads of time on your project. It can help identify ponding areas and discharge points where appropriate infrastructure needs to be built.

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