| The mechanical parameters of soil in head chamber of shield machine are the prerequisites in the studies of emulation and control of pressure field in head chamber. The traditional way for the parameter identifications of soil are the method of regression analysis, of which the test is carried out either in the current location or the laboratory. Due to the influences of the test methods and equipments, it is quite difficult to get the parameters of soil which are in correspondence with the practical situations. However, the back analysis of the parameters of soil is on basis of the collected data in the current location. Since it is a combination of optimization theory, numerical analysis and observation techniques, the method of back analysis can make a much preciser identification of the parameters.The method of back analysis is proposed to identify parameters of nonlinear constitutive model of soil in head chamber of shield machine by using genetic algorithm.The objective function is defined as minimization between strains obtained from finite element method and ones observed from tri-axial compression test in laboratory, of which the finite element model is simulated by the employment of ANSYS. In order to reduce programming time, the approach of calling ANSYS by employment of genetic algorithm tool of MATLAB is proposed. By using such method, six parameters of Duncan-Chang E-v constitutive model of soil are identified.The research shows that calling ANSYS by employment of genetic algorithm tool of MATLAB can be realized by use of MATLAB system functions. Through the comparison between the predicted curves and the observed ones from the test, it shows that the predicted curves from identifications are much closer to the observed ones from the test compared to the curves from regression analysis. It is proved that the method of back analysis has faster convergence speed, and the data obtained by that method agree better with the observed ones in laboratory.
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