The Application Of Spline Function In Inversion Of Foundation Pit's Soil Equivalent Parameters Of C And ?

In the foundation pit engineering,the deformation of the supporting structure is predicted according to the shear strength index c and ? of the soil The shear strength index of soil obtained by experiment often differs from the actual value,so many scholars have proposed a method to determine the equivalent values(c and ?)of foundation pit by back analysis.According to the fourth derivation of the quintic spline,the quintic spline function can not only fit the deformation curve of the supporting structure,but also realize the back analysis of the load concentration.In this paper,the application of spline in back analysis of equivalent parameters(c and ?)is studied,and a new back analysis method of equivalent parameters for foundation pit is proposed.The main contents are as follows:By studying the spline theory and the mechanical properties of beams,the mechanical interpretation of quintic spline is put forward,that is,the deflection curve of beams under continuous distributed loads.In order to popularize the mechanical interpretation of quintic spline function,an improved fitting method of quintic spline for beams under the concentrated discontinuous loads is proposedThe two problems existing in the application of the back analysis in practical engineering are discussed,namely the impact of the error of the soil interface on the result sensitivity and the impact of the deformation monitoring error on the back analysis of the spline.To solve this problem,firstly,the interpolation nodes of spline are enumerated considering the error of soil interface.Secondly,for each interpolation node group,the back analysis results satisfying the minimum of I=?i=1 n(yi caculated-yi measured)2 are output,and then the value of I is regarded as the judgement value,and the minimum valne of I in the enumerated interpolation node group are selected as the final back analysis results.The back analysis takes the elastic fulcrum method prescribed by the code as the calculation model,and regards the earth pressure as the discontinuous distributed load concentration.The support force provided by the anchor cable is regarded as the concentrated force,and the quintic spline function is utilized.The deformation curve of the supporting structure is fitted by the quintic spline,and the distribution load concentration(earth pressure effect)of the supporting structure is obtained by inverse derivative analysis.The equivalent parameters c and ? of the foundation pit are determined according to the actual engineering condition.The method of back analysis is applied to typical engineering cases and its feasibility is verified.According to the above back analysis method,the soil parameters of foundation pit are inverted.The parameters of back anal ysis are substituted into the mechanical calculation model of the foundation pit,and the deformation value is calculated and compared with the measure d values.The reliability and feasibility of back analysis are verified.