Structural Reliability Analysis of NATM Tunnel Face Stability in Soft Ground

In spite of enhancement in modeling techniques as well as site investigation methods, uncertainty exists seriously in the process of construction of underground structure in soft soils. These uncertainties arise from limited data of geological data, measurement errors, interpolation of spatially geological properties, and extrapolation of results of experiments and natural analogue studies over times and conditions relevant to the project. Robust and optimize design of tunnel support pattern consists many important parameters including advance rate and excavation method. However, quantitative definition of these parameters is difficult because of restricting in site investigation data and uncertainties related to them. Furthermore, erroneous evaluation in these parameters can affect in incorrect projection of tunnel stability or economic loss. In this study, a probabilistic hypothetical elasticity modulus approach, based on Monte Carlo simulation algorithm (Latin Hyper Cube sampling), has been employed to evaluate the uncertainty in lining design of a NATM tunnel located in Tehran region. A parametric finite element model based on ABAQUS and a MATLAB interface program has been introduced to evaluate the performance of supporting system to limit the settlements induced by tunnel excavation in the different magnitudes of lifetime probability of failure. The tunnel has a horseshoe shape, excavating in a soft soil for subway purpose.