Study On Risk Assessment And Disturbance Effect Of Deep Foundation Pit Excavation In An Intercity Railway

Revealing the risk level and disturbance effect in deep foundation pit excavation is a critical question in geotechnical engineering.With financial supports of National Science Foundation of China(E080506/51538550)and the Scientific research plan of the former Ministry of Railways ” Research on key technology of underwater shield railway tunnel(2011G013-C)”.Relying on the Working well deep foundation pit project at the exit section of FGZH-3 shield tunnel in Guangzhou South to Wanghong Section of Foshan to Guangzhou intercity railway,the risk of deep excavation construction was evaluated through the use of AHP,fuzzy comprehensive evaluation and other risk assessment methods;the disturbance effect of deep foundation pit excavation was studied through the combination of on-site monitoring and MIDAS/GTS numerical simulation;also the deformation law of foundation pit excavation is revealed in this paper,which can provides technical support for the safety of deep excavation and the safety protection of adjacent structures.The main study contents is shown as:1)The risk assessment index for deep excavation is established using the analytic hierarchy process;and the risk grade of deep excavation is quantified gradually from the single factor risk fuzzy evaluation through the fuzzy comprehensive evaluation theory;Finally,the risk level of deep excavation is determined.2)A displacement and internal force monitoring program was developed based on the surrounding environment,geological and hydrological conditions,and excavation plans for the foundation pit;Subsequently,the monitoring project,monitoring means,monitoring frequency,and measurement point layout standards were constructed,and the monitoring information was clarified and fed back to the construction in a timely manner.3)The on-site monitoring and numerical simulation of the entire excavation process of the deep excavation project,including the horizontal displacement of the wall,the settlement of the ground surface,the axial force of the support,and the horizontal/vertical displacement of the wall top were performed;the adaptability and rationality of the excavation model are verified through comparison and analysis of the two results;At the same time,the law and characteristics of deformation,the law and characteristics of force in the whole process of deep foundation pit excavation are obtained,which provides a basis for analysis of the law of deep excavation deformation and stress.4)Some calculations have been made on the parameters of the supporting system that affect the deformation of foundation pits,and the effects of various elements on the deformation have been summarized on the basis of ensuring the construction safety of ultra-deep foundation pits and the safety of adjacent structures;finally,recalculate the model calculations by taking the values within the reasonable range of each parameter;the calculated results were compared with those before adjustment,and the feasibility of this parameter adjustment was verified.