Highway tunnels are occasionally built under difficult ground conditions and technical limitations, in a surrounding ground mass with weak mechanical characteristics, specifically the Cretaceous soil, which is a significantly weathered and deteriorated rock exhibiting a scaly composition. These tunnels are typically dug with wide cross sections and commonly in double-tube configurations, maintaining a distinct gap between them to promote traffic flow and safety services. Tunnels with high sections often cause considerable stress changes and distortions that can lead to ground collapse under misinterpreted conditions of the ground mass, especially in freeway twin-tunnel with defined spacing. This study examines a paired 3-lane tunnel, which is a component of a nationwide freeway initiative covering approximately 1200 km, characterized by a horseshoe configuration with a cross section of 190 m2 each and a clear gap of 17 m. Considering the surrounding rock conditions, at a specific phase of the project, significant displacements peaked at 41 mm/day; additionally, concrete fractures were noted before a major failure extending up to 130 m toward the tunnel. This study suggests a back assessment for main disturbance factors before and after collapse, evaluates support force, and employs numerical modeling to reconstruct ground behavior. It has been observed that the decompression was quite significant, particularly above the tunnel's crown. The monitoring activities emphasized the effectiveness of both the original and enhanced support systems, showing a decrease in displacement from 47 to 64%. Given the surrounding rock's inadequate mechanical properties, the noticeable distance between the tunnels and the extensive excavation area raises concerns about support effectiveness. As excavation advances, the need for prompt responses is also highlighted to facilitate feedback contributions.

来源平台：INDIAN GEOTECHNICAL JOURNAL