Geotechnical seismic isolation system to protect cut-and-cover utility tunnels using tire-derived aggregates

Abstract

Utility tunnels in urban areas are generally constructed using the cut-and-cover method, with shallow depths and large dimensions. Given their high seismic vulnerability, especially in soft soils, proposing feasible mitigation measures is a matter of great concern. Tire-derived aggregate (TDA) is an engineered construction material produced from recycled scrap tires and is widely used in geotechnical seismic isolation (GSI) systems. In this study, a series of nonlinear numerical analyses were performed to investigate the geotechnical seismic isolation for utility tunnels using TDA backfill. Two-dimensional numerical models were developed incorporating site profiles, structural features, and geotechnical parameters of a real project. Three configurations of the TDA backfill were investigated and their isolation efficiencies were compared under horizontal input motions. The contributions of the inertial effect of the soil cover to the isolation efficiency of the TDA backfill and the isolation mechanism were also presented. This study showed that TDA backfill was an excellent alternative for risk mitigation during strong earthquakes. The racking deformation, seismic-induced bending moment and shear forces were reduced by approximately 50%, 65% and 75%, respectively. The proposed system may lead to the avoidance of costly seismic mitigation measures when the earthquake effects on utility tunnels need to be considered.