VIKTOR: “Getting a better understanding of the actual soil layout with the improved filter”

In many construction projects a cone penetration test (CPT) is converted to a soil layout. The data of such a CPT is often filtered based on the layer thickness, because very small layers (e.g. 4 cm) are not realistic.

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VIKTOR applications can soon make use of an improved filter algorithm, which is more accurate and detailed than the old one. Developer Roeland has worked on this algorithm, and says: “This improved method enables geotechnical advisors to get a better understanding of the actual soil layout.”

A CPT is a soil measurement, obtained by inserting a probe into the ground which measures the resistance. This resistance varies between different types of soil, allowing identification of the soils that are present. Roeland: “The difficult part is that the slightest measurement deviation can already result in a different type of soil, when the classification consists of many soil types.” In figure 1 you can see an example of an unfiltered soil layout on the left. The thin layers are not realistic and have to be filtered. In the old algorithm, the user could specify the minimum soil thickness (e.g. 10 cm) which have to be removed from the soil layout. These layers are replaced by the soil which is present on top, such that there are no gaps in the overall layout. “This method works well, but is rather coarse.”, says Roeland. This is visible in the center of figure 1.

Figure 1

VIKTOR is continuously improving, so when the request came in to improve this filter algorithm, Roeland accepted the challenge. He explains: “Now we do not simply remove the thin layers, but we mark which layers are smaller than for example 10 cm. These layers are clustered to form individual layers with a maximum thickness equal to the specified filter thickness.”

The way a cluster is replaced depends on the thickness. If the total thickness of the individual layers is still thinner than the filter thickness, the old algorithm is used. The layers are removed and replaced by the soil present on top. If the cluster thickness is larger than the filter thickness, a new layer is formed. “A soil type has to be assigned to this newly created layer. The soil which is the most occurent within the cluster is automatically selected.” This logic is visualised in the schematic of figure 2.

Figure 2

Roeland: “With the improved filter, the soil layout is classified less coarse.” The difference between the old and new algorithm seems large in figure 1, however Roeland states that this is not always the case. “In many cases it is not very likely to see such a large amount of different soil layers.” The old filter will not become obsolete, as many projects do not require the level of detail the improved filter offers.

Many projects make use of the soil layout classification, which may become more accurate with the improved filter. However, in the end the technical advisor will always be the one making the decision of how the soil layout should be interpreted. Roeland: “When it comes to classification of a soil layout, a lot of expertise is required. Based on geological knowledge, experience from previous projects, location data, etc. the advisor will determine the soil layout.”

This improved filter will soon be available in the VIKTOR platform. Roeland: “We are trying to continuously improve our product and I think this is a great example of such an improvement.”

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