January 23, 2024

Prokon SUMO Subgrade Modulus – Part 2

Jacobus Oberholster | AEC Engineering Technical Consultant (Prokon)

In Part 1 we discussed the basics pertaining to the Subgrade Modulus parameter, its’ application and typical values. Understanding how you can determine a more “site-specific” value is important. In Part 2 we will delve into the formula for calculating the Soil Subgrade Modulus.

Section 9-6 of JE Bowles’ “Foundation Analysis and Design” – 5th Edition (McGraw-Hill) approximates an equation for calculating k (Subgrade Modulus) as k = 40 x SF x qa.

SF = Safety Factor (typical foundation safety factors apply).
qa = Allowable soil bearing capacity.

For the above equation, SF can be omitted as your Load Combination factors will perform the same function.

Consider a set of DCP results, indicating an average bearing capacity/pressure of 712kPa, which will place that soil in the Very Dense category. Calculating the Subgrade Modulus: k = 40 x 712 = 28 480 kN/m³. This can then be used as your Subgrade Modulus value in SUMO for a more accurate model.

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About the Author

Jacobus Oberholster | AEC Engineering Technical Consultant (Prokon)

Jacobus is an AEC Technical Consultant at Micrographics, specialising in the Structural Engineering industry. He focuses on optimising structural workflows in Revit, Prokon, and IDEA Statica, streamlining processes through the integration of various software packages. Jacobus holds a BTech in Civil Engineering and is a Professionally Registered Engineering Technician with the Engineering Council of South Africa. With close on 10 years of experience, he has served as a designer, quality controller, and project manager in both the public and private sectors, demonstrating his extensive expertise and commitment to the field.