Eurocode 7 - Partial Factors of Safety and Design Approaches

Design Approaches Overview

There are three design approaches which should always be considered in Geotechnical Analysis to consider the uncertaintly in the strength of soil and applied load.

Soil strength such as cohesion, friction angle and dilatancy angle will be reduced using the partial factor. Load (surcharge) will be increased with the partial factor.

Design Approach 1 (DA1)

There are two combinations from Design Approach 1.

Combination 1: A1 + M1 + R1

Combination 2: A2 + M2 + R1

Design Approach 2 (DA2)

Combination: A1 + M1 + R2

Design Approach 3 (DA3)

Combination: (A1 or A2) + M2 + R3

Combinations are denoted by A (for actions or effects of actions), M (for soil parameters) and R (for resistances). They are selected according to the used Design Approaches.

Partial Factors Table

We use the following table of partial factors and assign the relevent factors for each Design Approach seen above.

Partial Factors on Actions

Partial Factors on Soil Strengths

Partial Factors on Resistance 

Resistance calculations are typically used in spread foundations and verifications of structural (STR) and geotechnical (GEO) limit state calculations

It's a little bit of work to run the calculation for each design approach, but considering every case ensures a thorough and well thought out design.