Oguz Salih OkcuGeotechnical Engineer, DOLSAR Engineering Inc. Co.
Oguz Salih Okcu is a geotechnical engineer in Dolsar Engineering, Turkiye. He's holding a Bachelor of Science in Civil Engineering and a Master of Science in Geotechnical Engineering, focusing on geotechnical earthuqake engineering. He uses GTS NX in his projects extensively for two years, mainly on dam bodies and hydraulic tunnels in dam projects.
Tech Q1. What are the minimum requirements for a soil constitutive model for this analysis?
A. It actually depends on your analysis type and soil type. If you are loading-reloading soil, it's better to use a model to account that effect. Because elastic modulus should change with the normal pressure. Additionally in dynamic analyses, variation of shear strain is important and you can account the change in shear modulus with small strain stiffness model. If you don't have loading-reloading or dynamic load, you can just go on with Mohr-Coulomb. But apart from all of that, if your analysis type changes, you should use a model according to that (eg. PM4Sand in liquefaction analyses).
Tech Q2. Which major factors are considered when determining spectral acceleration values?
A. The first thing is, you have to base your record selection on a seismic hazard analysis and a resultant response spectra. Later on, with the geology that you've been provided, you can limit your records with Vs30 values, distance between site and fault and faulting type. Record selection is completely another topic of expertise. But generally choosing a close response spectra to the given hazard analysis response spectra works fine.
Tech Q3. In dynamic analysis, is pore pressure treated as a preset value based on the initial water level?
A. I define the pore pressure before the dynamic step and it stays constant in dynamic analysis. If you want to see the change in the porewater pressures within the dynamic analysis, you should perform "coupled" analysis.
Tech Q4. How is pore air pressure accounted for during or immediately after construction stability checks?
A. As far as I know, pore pressures (air + water) acts together in the software. You can account them with definition of porous material properties in material settings.
Tech Q5. If there are horizontal and vertical seismic acceleration components, are they applied over the same time period?
A. In GTS NX you can input horizontal and vertical components together as they act together in the nature. Failure modes of the dam are calculated in the eigenvalue analysis and they do not change according to orientation of dynamic load components.
Tech Q6. Can the “dead section” of the dam be neglected in this type of analysis?
A. If you mean appurtenant structures (eg. spillway) by "the dead section", yes we neglect these structures in dam body analyses.
Tech Q7. How can an ice lens on the reservoir surface be included?
A. In the regions that I work, ice loads are not accounted but in the manuals and guidelines there's no mention about the ice loads. Thus, there's no need to define it. However, maybe you can use sloshing medium material with the definition of bulk modulus of ice.
Tech Q8. Do we need to explicitly mesh the Groundwater Level (GWL) in the soil?
A. Actually you don't have to but I prefer to mesh again after defining the phreatic line. So that your meshes look better below and above the phreatic line.
Tech Q9. Construction stage analysis often becomes unstable or hard to converge. Any practical tips?
A. "If your model is somehow complex, estimating the inital stress of activated elements really helps to find a solution but always check your deformation results to stay in a realistic range. Another thing to put attention is ""Estimate initial configuration of activated nodes"" in embankment dams. This have to be unchecked in embankment dam construction stages, otherwise you'll have unrealistic deformation shape."
Tech Q10. How should dam–foundation base shear be modeled and interlayer drifts be checked?
A. Since I'm modeling an embankment dam (for this instance) I don't check the base shear between my foundation and the dam. But to check it in concrete dams, you should define an interface mesh set.
General Q1. Is this training program free of charge?
A. Yes! The Global Geotechnical Webinar Series 2025 is completely free of charge. Once registered, you’ll get access to all live and on-demand sessions, expert talks, hands-on tasks, and learning materials — at no cost.
General Q2. How do I get the training license?
A. Trial licenses for GTS NX and FEA NX are provided only to registered participants. You can find free trial information in the register confirmation email. If you can't find in your inbox, please contact us via the below link : 🔗 Click
General Q3. Where can I get the assignment files and how should I submit them?
A. There is no assignment for the session 2.
General Q4. How can I ask a question to MIDAS experts?
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General Q5. How can I receive the certificate of completion?
A. To be eligible for the certificate, please make sure to:
✅ Attend at least 2 live sessions
✅ Submit 2 or more assignments by October 8
Certificates will be emailed to qualified participants on October 15, 2025.