Calibration of Undrained Shear Strength Partial Factor Using Probability Theory

Filip Dodigović,Kristijan Grabar,Krešo Ivandić,Božo Soldo

doi:10.31803/tg-20201113132539

Filip Dodigović, Kristijan Grabar + Show 2 more

Open Access

https://doi.org/10.31803/tg-20201113132539

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Abstract

Design in accordance with Eurocode 7 applies the partial factors of geotechnical parameters to take into account uncertainties of various sources. The prescribed values of partial factors are unique, even though the degree of uncertainty can vary significantly. This can lead to an unequal reliability level of structures designed using the same procedures and methods. This paper analyses the influence of undrained shear strength variability on the reliability index (β), using reliability theory and statistical methods. Analyses were performed in the case of a shallow footing designed in accordance with Eurocode 7, design approach 3. It is shown that reliability indexes of a shallow footing could be lower than the target values prescribed in Eurocode. To meet these values, additional elaboration and calibration of undrained shear strength partial factor (γcu) was proposed.

Highlights

The measure of safety of geotechnical structures designed in accordance with Eurocode is regulated by the application of partial factors (PF) to actions, materials, and resistances
These studies can generally be divided into two groups: direct studies, which directly calculate the reliability of structures using the prescribed values of PF, and indirect studies, which calibrate PF values to achieve the target value of the reliability index (β) [7]
The unique value of the partial factor of the geotechnical parameter does not reflect the actual state of site-specific variabilities in a specific task

Summary

Introduction

The measure of safety of geotechnical structures designed in accordance with Eurocode is regulated by the application of partial factors (PF) to actions, materials, and resistances. In this way, instead of one uncertainty applied to the whole model, they are considered separately for each component of that model [1]. The influence of PF values on structural reliability has been investigated by several authors [2,3,4,5,6]. Almost all values used in modern codes have been calibrated against previous successful experience, with very little use of reliability methods [9]

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