Geotechnical design is evolving to adopt the limit state design (LSD) philosophy, also known as reliability-based design (RBD). This is evident by its inclusion in geotechnical design codes (e.g. Eurocode 7). Partial factors are often used in design codes to overcome the difficulty in performing probabilistic analysis suggested by the RBD. The increasing use of RBD suggests a need to investigate the applicability of design with partial factors for various rock engineering structures; this paper will investigate their application in the design of support for a rock wedge in an underground opening. The paper provides a critical overview of the design philosophy of RBD, the components necessary for its application, and the methods by which the probability of failure may be computed. In addition, it discusses how partial factors are calibrated from RBD and how code development can be subsequently performed. This is put into context with a design example for the support of a rock wedge.

1. Introduction

Rock engineering design customarily uses deterministic methods with factors of safety. However, this is inappropriate as these methods do not appropriately account for the variable conditions prevalent in rock engineering. In addition, it is known that factors of safety do not always lead to safe designs [1]. In the presence of variable conditions, probabilistic design - which asks "does the design satisfy a specified probability of failure given the observed variability?" - is known to be more appropriate. This has long been recognised by the structural engineering community, and fuelled the development of structural reliability - also known as reliability based design (RBD) or limit state design (LSD) - as a formal design philosophy that quantifies the probability of a structure behaving as intended. This includes ensuring stability and satisfying deformation limits, as well as any other requirements of the structure. Presently, this design approach is used globally in structural engineering, and is currently also being adopted by the geotechnical community [2, 3].

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