Review of OptumG3

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Review of Geotechnical Software

Updated 06.10.18

review of OptumG3

INTRO
Brinch Hansen proposed in a 1968 paper to include a shape factor to account for 3D effects for drained conditions. At the same time, he expressed the lack of 3D theory of plasticity solutions to determine a more accurate shape factor. Since then, all offshore design codes have included the shape factor. Today 50 years later Brinch Hansen would be delighted! Now there is a plasticity 3D software available. In the following, I will test the FELA software OptumG3 (version 2018.07.30 (1.3.0.14261)) with an offshore foundation initial vertical loaded followed by a horizontal load causing torsion and overturning.


OptumG3 is the first commercial available 3D finite element limit analysis FELA software commercial available. It must be mentioned that Oxford University Professorial Research Fellow Chris Martins developed OxLim both 2d and 3D FELA before the release of OptumG3. OptumG3 has both FELA and some soil models in FEA. It is currently relatively new and the user manuals are not yet available, but there are a high number of great demo videos on youtube. User manuals should be available in 2019 along with more advanced FEA soil models. OptumG3 uses adaptive mesh, which means that it makes an initial mesh and improves the mesh over a few iterations to determine a more accurate solution. Compared to Plaxis, where the user must define the mesh and the solution depends on how well the user defines the mesh. Hereby, OptumG3 reduces the possibility of user errors.

CASE
Foundation is 6 x 20 m and 3.5 m high. The software is easy to use, like a very simple drawing program. It is very critical to understand how the geometry select function works. There are good youtube videos to help to get started. The first case I tested was bearing capacity for vertical load. To compare it best with bearing capacity formulations, I chose to use phi=30 and submerged unit weight of 11kN/m3 and a c = 0.01. I have used the mixed element and the MOSEK solver (also used by OxLim). In 4 min I get 58,691kN, compared to Brinch Hansen bearing capacity of 59.677kN (shape factor=1), 52.515kN (shape factor=0.88). I compare to Plaxis 3D and get 59,700kN after approx. 2 hours of FEA. I believe that Brinch Hansen would have been very pleased to be able to be reduce uncertainty in the design and that he would probably have modified the shape factor.



The second case I have tested is a load is applied to upper corner at 20deg to horizontal. The load is 661kN. The soil strength is c=3.2kPa and a friction angle of 29.7deg with a submerged unit weight of 11kN/m3. I start of with a submerged weight of 2400kN on the foundation and reduce the weight until failure. I get 2473 I OptumG3 and 2780kN in PLAXIS 3D. I am a bit surprised over this relative large difference. The OptumG3 analysis is approx. 5 min while PLAXIS need to generate the full load displacement curve and the time is 1.5 hours. I am using an older version of PLAXIS which may cause this difference. The analysis is illustrated below.



COMMENTS
The OptumG3 software is a great tool to determine the ultimate capacity of a foundation. It is based on FELA which makes it very fast compared to FEA analysis. The software is very user friendly. Manuals are yet not available, but they will be here soon. Most geotechnical engineers have gotten used to the FEA load displacement approach which is in fact not the origin of the ultimate capacity analysis. This software does to some extend bring us back to basic back to what Brinch Hansen did not have available when he proposed his bearing capacity formulation above. It has been 50 years since he expressed the lack of a 3D plasticity solution to the bearing capacity and I believe this software is finally here.

FURTHER READING
If you find the concept of FELA interesting but want to know more before you want to implement, then I propose to read Helen Dunnes excellent and very well written phd thesis which is found here The thesis explains the FELA theory in further detail and presents results of several very relevant offshore aplications.


Evaluation

Evaluation 1-6 (6 highest)

Ease of Use

Accuacy

Technical Support

Speed of Analysis

Grafics