Developing a universal tunnel span classification from global tunnel databases

Abstract Tunnel span classification differs across the literature and among national standards and codes, and no universally accepted standard currently exists. To address this challenge, this study introduces a universal tunnel span classification that incorporates tunnel span, cross‐sectional area, typical tunnel types, and intended uses. The classification is based on a comprehensive database of 450 tunnel profiles from 47 countries. The development process comprised three main steps: establishing the correlation between tunnel span and cross‐sectional area, determining cross‐sectional differences among classifications using geometric progression, and identifying typical tunnel types and functions for each span class. The universal tunnel span classification consists of seven distinct tunnel span classes: (1) Very small‐span tunnel, with a span less than 4 m and cross‐sectional area less than 15 m 2 ; (2) Small‐span tunnel, with a span of 4–7 m and cross‐sectional area of 15–40 m 2 ; (3) Medium‐span tunnel, with a span of 7–10 m and cross‐sectional area of 40–80 m 2 ; (4) Large‐span tunnel, with a span of 10–14 m and cross‐sectional area of 80–130 m 2 ; (5) Very large‐span tunnel, with a span of 14–18 m and cross‐sectional area of 130–200 m 2 ; (6) Super large‐span tunnel, with a span of 18–24 m and cross‐sectional area of 200–300 m 2 ; and (7) Cavern, with a span greater than 24 m and cross‐sectional area greater than 300 m 2 . The classification is consistent with standard practices in China and Japan, as well as The International Tunnelling and Underground Space Association (ITA‐AITES) classification, confirming its global applicability. The universal tunnel span classification contributes to ongoing research aimed at developing comprehensive guidelines for tunnel construction methods. These guidelines are intended to assist engineers in selecting appropriate construction techniques and ground support systems for various span classes and ground conditions. This study constitutes a substantial advancement toward this global objective.