Selection Of Supporting System Of Deep Excavations In Soft Soil Area Based On Risk Analysis

In recent years, it's a trend to assess environmental impact of main building project. There has been an increasing concern on deep excavations in urban area because of it's frequent accidents and huge losses. As a consequence, how to reduce the accidents and losses of deep excavations has become an important task. Risk analysis theory maybe a feasible way. In general, this paper includes three parts.In the first part, based on the statistical data of deep excavations accidents, accidents cause of deep excavations are analyzed by survey error, design error, construction error, monitor error, supervisor error and owner error. According to 342 deep excavations accidents, statistical analysis is done through different accident responsibler, different retaining structures, different excavation depth. Frequency distribution and statistical law of failure deep excavations is obtained in different situation.The second part is risk analysis of retaining structures of deep excavations. Firstly, according to the analysis result of deep excavations accidents, fault tree of drilled piles, soil mixing wall, composite soil nailing, cement-soil retaining wall and diaphragm wall are established. As a example, a triangular fuzzy number is introduced to represent the failure probability of a basic event. The fuzzy failure probability of SMW retaining structures in deep excavations is calculated by a fuzzy fault tree. Main basic events affecting the occurrence probability of the top event are verified by a sensitivity analysis, which can be applied in the risk analysis of SMW retaining structures in deep excavations.Secondly, based on deformation of retaining structures in deep excavations, failure mode is analyzed, and corresponding limit state equation and reliability model is established. Variability of affecting parameters, including cohesion, internal friction angle, soil gravity, extra load, calculation mode uncertainty, external load, physical dimension, material performance are analyzed. Failure probability of retaining structures in deep excavations is calculated by Monte-carlo FEM and failure loss of retaining structures is analyzed. Finally, time-dependent risk of retaining structures in deep excavations is obtained and the whole analysis procedure is presented with a example.The third part is environmental impact risk analysis of deep excavations...