Blog | Eurocode 7: Geotechnical Design - How to apply Eurocode7 to FEM software?

Written by MIDAS GEO TEAM | 2020.12.01

If you haven't read the Eurocode series >>

1- What is Eurocode?2- Design Approach and Partial Factor

03- Verification

The partial factors in EC7 (1997-1) can be applied to analysis with hand calculation or automatically considered in the analysis program. From the load (surcharge), it needs to multiply the partial factor from the original load (surcharge). From the soil parameters (strength), they need to be divided by partial factor from original parameters.

For example, if design approach 1 combination 1 (DA1C1) is applying to the FEM analysis as below,

If design approach 1 combination 2 (DA1C2) is applying to the FEM analysis as below,

They should have the same results, such as displacement and forces from the analysis when the partial factor has been applied with hand calculation and function from the FEM analysis program.

04- Apply to FEM Program

Now a day, FEM programs are supporting the partial factor function, and it will be automatically considered factored values in the FEM analysis. But, there is something that we need to make engineering judgment. For example, FEM analysis for excavation works.
“where do we need to apply partial factor during the excavation stage?”

There are different concepts from different engineers as below,

If the original analysis stage is,

Concept 1) Perfectly consider design approaches to analysis stage

[Normal Case]		[DA1C1 Case]		[DA1C2 Case]
Initial Stage	↓	Initial Stage	↓	Initial Stage
Cast RW and Surcharge	↓	Cast RW and Surcharge	↓	Cast RW and Surcharge
1^st Excavation	↓	1^st Excavation	↓	1^st Excavation
Install 1^st Reinforcement	↓	Install 1^st Reinforcement	↓	Install 1^st Reinforcement
2^nd Excavation	↓	2^nd Excavation	↓	2^nd Excavation
Install 2^nd Reinforcement	↓	Install 2^nd Reinforcement	↓	Install 2^nd Reinforcement
Final Excavation		Final Excavation		Final Excavation

Concept 2) DA1C1 is assumed by SLS (Serviceability Limit State) case and partially consider design approaches to analysis stage

[DA1C1 Case]		[DA1C2 Case]
Initial Stage
Cast RW and Surcharge
1^st Excavation	→	1^st Excavation
Install 1^st Reinforcement
2^nd Excavation	→	2^nd Excavation
Install 2^nd Reinforcement
Final Excavation	→	Final Excavation

From the above concepts, we cannot say whether it is correct or not. Those are done by engineering judgment from the geotechnical engineer who is carrying out the FEM analysis with partial factor.

And from concept 2), Applying surcharge and excavation stages are extracted as substages. Those stages are critical stages from the FEM analysis so that ULS (ultimate limit state) will apply to those stages. It is just for your reference, and no need to apply forcibly.

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