A critical evaluation of proxy measures used to quantify excavation-induced damage in masonry buildings

Building response during nearby excavation activities (e.g., tunnelling or deep excavations) is traditionally monitored by conducting displacement measurements. These displacement data are then post-processed to determine proxy measures that are correlated to damage categories. For masonry buildings, commonly-used proxy measures include building deflection ratio, horizontal relative displacement and angular distortion; simple mechanical models and empirical rules are used to define limiting values for these proxy measures to identify and control the level of cracking in buildings during construction. This procedure has a profound influence on mitigation and construction activities, and a critical evaluation of its veracity is needed. To this end, results from a recent experimental campaign on the settlement response of half-scale masonry buildings are examined in this paper. During these tests, detailed optical measurements were conducted, allowing the calculation of absolute displacements across the façade, as well as crack opening displacements at specific locations. These measurements facilitate a direct comparison between the actual observed damage and the damage category that is indicated by the proxy measures. The comparisons highlight the limitations of existing techniques. A discussion is provided on how proxy measure calculations can be improved to deliver more reliable indications of building damage.