Safety Evaluation Analysis Of Deep Excavating Foundation Based On The Field Measured Data

With the development of urban rail transit network in Shanghai, the foundation pit of subway station is becoming more and more deeper, the scale of construction is getting larger, high integration of risks becomes a question for the subway constructors. This paper concentrates on the safety evaluation for the foundation pits of subway stations in Shanghai soft soil in the view of the condition of actual projects. By collecting millions groups of field measured data and project datum from the constructed subway stations in Shanghai, research on the reasonable deformation alarm value, risk identification and safety evaluation in the pits constructing has been made. Primary content includes several parts as follows.1.Based on the summarization of the engineering accidents and comparison of the common risk assessment methods, the paper give a preliminary study on the risk management of deep excavation, putting forward that fuzzy synthetic evaluation method is more suitable for excavation safety evaluation.2. This paper studied and summarized the judgment criterion of alarm value for monitoring items, such as measuring inclination of retaining wall, deformation of column, settlement of surrounding buildings and pipelines. On the basis of research mentioned above and practical cases in the Shanghai, a reasonable and effective series of deformation alarm value in the pits constructing was put forward.3. The paper made pointed statistics on dangerous cases which happened in subway foundation project in Shanghai recently, and concluded that the main risk sources were as follows: (1) over excavation, not supporting in time (50%); (2) unfavorable precipitation and waterproof for foundation pits (28%); (3) improper strengthening pressure of high pressure jet grouting piles (11%). Combined with engineering cases, it could be found that different risk source has different characterization of monitoring data. So process of risk identification based on the field measured data for foundation pits was established.4. According to the field measured data, the safety evaluation index and level were established. And also the safety evaluation model is established by using the fuzzy synthetic evaluation method, so as to give a quantitative safety evaluation for the ontology and peripheral environment of foundation pits.5,Process of safety evaluation for deep excavating foundation based on thefield measured data was put forward: abnormal measured data being found——maderisk identification based on the characters of field data (qualitative)——made riskevaluation using fuzzy synthetic evaluation method (quantitative)——control therisk combined with the development trend of field data.In the finality, the problems requiring further studies are discussed.