Study On Back Analysis For Bending Moment Of Retaining Wall And Safety Evaluation Based On Monitoring Data

The massive construction of subway station for urban railway transportation in recent years has not only brought increase in economy and social development but also resulted in rapid rise of risk in engineering projects. How to evaluate the real-time status of foundation in the process of excavation and classify its safety level is becoming an increasingly valuable and large research task. If it is possible to estimate whether its deformation and performance is normal, determine its safety level, and judge how far it is from being dangerous, the accidents can be reduced to a large extent.As an overall system of 'foundation safety evaluation and classification', the internal force of the retaining structure is a necessary research item. How to obtain its real bending moment in the process of excavation has become the key to its internal force. This thesis particularly focuses on the research of bending moment.After detailed analysis, the procedure of determining bending moment can be considered as that the deformation curvature is first calculated by surveying data of the retaining structure, and then the bending moment can be determined by fundamentals of material mechanics. This thesis, which is developed gradually by solving the deformation curvature of the bending moment, can be summarized as three parts on the whole.In the first part, analysis is conducted to explain why the curvature oscillates when determined by the method that three points make a circle. Meanwhile, the impact of density of surveying points on this algorithm is studied. Further, how the surveying error is propagated through this algorithm is examined.In the second part, the deformation curvature, which is determined by second derivative of curve fitting of the deformation of the retaining structure, is proposed. Followed by dimensional analysis, the dimension relationship between the curve fitting function and the bending moment and load is determined. Then the computational method, in which the curvature is obtained by method of least square and natural spline curve fitting of the deformation of the retaining structure, is derived. Based on this method, Specific dimension relationship and the propagation rule of survey error are deduced in detail. In the successive study, the function, which not only resembles natural spline segmented function but also satisfy the approximation function of method of least square, is searched to solve the issue of curvature oscillation. The computational method, in which the curvature is obtained by smooth spline curve fitting of the deformation of the retaining structure, is also presented.In the third part, the bending moment calculated by method of least square andsmooth spline curve fitting of the deformation of the retaining structure is compared with that determined by stress of reinforcing steel bar. The accuracy of method of least square is also contrasted with that of method of smooth spline. Further more, engineering projects is employed as testing examples. Method of least square method of smooth spline is simultaneously applied to calculate the bending moment of the retaining structure, which provides a basis for evaluating its internal force. The 'long-distance supervising and managing system' is proposed to concurrently control the safety of its internal force.