The influence of face and shield annulus pressure on tunnel liner load development. (November 2021) - Epel, Tamir
Highlights: Analysis of segmental lining strain gauge field data using 3D numerical modeling. Simplification of TBM shield by modeling the pressurized shield annulus. Convergence prior to lining installation relays on the support pressure. Lining loads are controlled by face and shield annulus support pressures. Abstract: Three dimensional (3D) finite-difference analysis simulations together with rare field data from strain gauges installed in segmental lining rings at the Seattle Sound Transit Northgate Link tunnel project are examined to provide a better understanding of segmental liner loading developed during earth pressure balance shield tunneling. A simplified 3D numerical model is presented for pressure balanced mechanized tunneling, where the annulus between the shield and excavated ground is full of pressurized material, simplifying the shield shape, and the modeling of the annular gap. This simplified model is based on the assumption that the shield annulus pressure controls the tunnel convergence prior to lining installation. While the presented model simplifies the modeling of the TBM shield, it captures the important components in shield tunneling, including the jointed segmental lining, grout injection pressure, time-dependent grout hardening, and the non-liner soil behavior using the hardening soil constitutive model. The results of this study show that the final lining loads are controlled by the chamber pressure for pressure balance TBMs with pressurized material in the shield annulus. In the case study presented here, pressure drops of the chamber pressure (common in EPB tunneling due to excavation standstill), result in a significant influence on tunnel lining loads.