Is There Anything Better Than LRFD For Simplified Geotechnical RBD?

Geotechnical design codes, be it reliability-based or otherwise, must cater to diverse local site conditions and diverse local practices that grew and adapted over the years to suit these conditions. One obvious example is that the COVs of geotechnical parameters can vary over a wide range, because diverse property evaluation methodologies exist to cater to these diverse practice and site conditions. Another example is that deep foundations are typically installed in layered soil profiles that vary from site to site. These diverse design settings do not surface in structural engineering. If the performance of geotechnical RBD were to be measured by its ability to achieve a more uniform level of reliability than that implied in existing allowable stress design over these diverse settings (which is recommended in Section D.5, ISO2394:2015), then LRFD and comparable simplified RBD formats widely used in structural design codes are not adequate. While it is understandable for geotechnical RBD to adopt structural LRFD concepts at its initial stage of development over the past decades, it is timely for the geotechnical design code community to look into how we can improve our state of practice in simplified geotechnical RBD. This paper demonstrates that improved formats such as the Quantile Value Method coupled with an effective random dimension (ERD-QVM) can cater to a more realistic and diverse range of design scenarios. Specifically, ERD-QVM can maintain an acceptably uniform level of reliability over a wide range of COVs of geotechnical parameters and a wide range of layered soil profiles. It can achieve this while retaining the simplicity of an algebraic design check similar to the traditional factor of safety format and LRFD. ERD-QVM is a step in the right direction to develop geotechnical RBD for geotechnical engineers. More research is urgently needed for geotechnical RBD to gain wider acceptance among practitioners.