Investigating continual damage of a nineteenth century masonry tunnel

Abstract

The Shiqiling tunnel, an ancient masonry structure built during 1888–1890, is the first tunnel in Taiwan. Designated as an official monument, the tunnel comprises stone walls and brick or stone vaults. The continual flaking and spalling of bricks in the past two decades prompted thorough tunnel investigations. To avoid any artificial damage, non-destructive technologies are utilised to acquire tunnel data. Visual inspections and mosaicked images reveal prevailing lining anomalies, including spalling, leakage, dislocation and loss of pointing mortar between stones or bricks. Ground-penetrating radar and electrical resistivity imaging suggest that voids exist behind the lining in some areas, and that the water content of rock masses is high. Geodetic survey results show that although continual tunnel deformation produces irregular profiles, an inner boundary exists where masonry blocks crack and fall when surpassing this boundary. Investigation results indicate that the uniaxial compressive failure of bricks and stones accounts for the unusual damage pattern, and the squeezing deformation of the tunnel caused by weathered surrounding rocks is likely to be the cause of the continual spalling phenomena.