Reliability Assessment on Deep Braced Excavations Adjacent to High Slopes in Mountain Cities

Abstract

Due to rapid urbanization, the land available for city construction and development becomes more and more scarce. Within a built-up environment, the construction safety of a deep excavation becomes more crucial with the ever-increasing building density. For deep excavations in mountain cities, the areas of the foundation pit to be excavated are generally the passive soil pressure zones for the upper existing slope. Construction disturbance, weakening of the passive area, as well as the formation of even higher slope through the superposition of foundation pit to the existing upper slope, will result in more deformation and even failure of the slope. This study numerically investigates the influences of excavation geometries, the system stiffness and the distance between the excavation and slope and develops simplified ultimate and serviceability limit state surrogate models with regard to the overall factor of safety and the maximum lateral wall deflection of the supporting system, respectively. Considering the uncertainties of the design parameters, a probabilistic framework combining the estimation models with First-Order Reliability Method (FORM) is proposed to determine the probability that a threshold factor of safety or the pre-defined maximum wall deflection is exceeded. The study presents preliminary guidelines for reliability assessment of ultimate and serviceability limit state designs for deep braced excavations adjacent to high slopes in mountain cities.