Opened in 1970, the 3.2 km‐long Belchen Tunnel is a key element of Switzerland's north‐south national road network. The two tunnel tubes pass through highly swelling rock formations such as Gypsum Keuper (anhydritic swelling claystones) and Opalinus Clay. Mitigation measures had to be taken even during construction. However, only a few years after commissioning, damage to the tunnel structure became evident, attributable to the swelling properties of the rock, which subsequently required regular rehabilitation measures. The increasing and closely monitored progression of the damage ultimately necessitated a concept for a comprehensive rehabilitation. A full closure of one of the tunnel tubes for several years was not an option due to the high volume of traffic. According to the operator, 2 × 2 lanes must remain in operation at all times. This constraint led to the decision to first construct a third tunnel tube, enabling the sequential rehabilitation of the existing tubes under full closure while maintaining full traffic capacity. In 2022, the third, machine‐bored tunnel tube was put into operation. Subsequently, the extensive rehabilitation works on the existing tubes, which are still ongoing, began in 2024. This paper describes the history of damage development in the two old tubes of the Belchen Tunnel in swelling ground conditions, presents the key technical parameters of the third tunnel tube, and outlines the structural design of the rehabilitation of the two existing tubes.
Zingg et al. (Fri,) studied this question.