Effects of overconsolidation ratio on tunnel responses due to overlying basement excavation in clay

Due to shortage of usable spaces in congested urban cities, deep basements for buildings are frequently constructed above or at a side of existing tunnels. Although much attention was paid to the basement-tunnel interaction, previous studies mainly simplified it as a plane strain problem and focused on excavation-induced tunnel responses in sand. In this study, three-dimensional centrifuge tests were conducted to investigate long-term tunnel responses due to overlying basement excavation in lightly (overconsolidation ratio (OCR) = 1.7) and heavily overconsolidated (OCR = 6.0) kaolin clays. Immediately upon completion of basement excavation, the measured heave and tensile strain of tunnel in heavily overconsolidated clay are up to 25% smaller than those in lightly overconsolidated clay. This is because a smaller void ratio in a stiffer clay possesses large soil stiffness around tunnel lining. Due to dissipation of excess negative pore water pressure, the maximum heave and tensile strain of tunnel increase by up to 210% and 50%, respectively, in heavily and lightly overconsolidated clays. To ensure the safety and serviceability of existing tunnel, special attention should be paid to long-term rather than short-term tunnel responses.