Investigation the design criteria of umbrella arc system based on the instrumentation data and numerical simulation

One of the main challenges of tunnel excavation in urban areas is subsidence control, which can affect surface and underground structures. Nowadays, the performance of the umbrella arch system is accepted as an effective solution for controlling subsidence and tunnel excavation in conditions where face of tunnel is unstable. In this research, using the Birgel tunnel instrumentation data and its construction method, the numerical model has been calibrated and the three scenarios of cantilever beam, critical strain and reinforced zone have been investigated applying numerical simulation. The first scenario showed that if the internal forces of the pile element are examined, the stability factor 1 should be used as the design criterion. In the second scenario, using the level there of Sakurai warning is proposed as a design criterion. In the third scenario, relationships are developed to calculate the geometry and geomechanical parameters of the reinforced zone considering the second scenario. Based on the analysis results, the internal friction angle in the reinforced zone could be kept unchanged and just the modulus of deformation and cohesion in the reinforced zone are raised up according to the proposed relationships.