“…In this context, fuzzy set theory could be applied to represent these uncertain characteristics more realistically. Since its introduction over 40 years ago (Zadeh, ), fuzzy set theory has been utilized to solve numerous infrastructure engineering issues (Adeli and Hung, ; Sarma and Adeli, , , ; Adeli and Karim, ; Samant and Adeli, ; Karim and Adeli, ; Jiang and Adeli, , ; Adeli and Jiang, , ; Bianchini and Bandini, ; Tagherouit et al., ; Anoop et al., ; Bianchini, ; Graf et al., ; Hsiao et al., ; Saliminejad and Gharaibeh, ; Li et al., ; Dell'Orco and Mellano, ), including tunnel‐related issues. For example, Harrison and Hudson () develop an expression for the fuzzy factor of safety and extend this method to evaluate the potential for underground rock spalling at the boundary of a circular excavation in terms of strength and in situ rock stress.…”