Study On The Duncan-Chang Model And Nanshui Model's Parameters Based On Digital Image Processing System

In the dissertation, digital image processing system is used to study the. Duncan-Chang nonlinear model and Nanshui Elasto-plastic model's parameters, which are well-known and widely-used in the Geotechnical Engineering. However, the displacements resulted from the numerical analysis are generally bigger than the practical values, because the parameters can't be tested and applied exactly limit to the testing apparatus, testing methods, etc. Digital image processing system can overcome some limitations and shortages in triaxial tests, furthermore, with higher accuracy, compared with the traditional method. So it is necessary and worthwhile to use this advanced apparatus to study the constitutive model's parameters.The Fujian standard sand, the Shifo Si fine sand, the Maoying silty soil are chosen for the triaxial compression tests to study the parameters. Two main aspects of the research work are as follows:(1) The differences of the soil parameters on Duncan-Chang's model and Nanshui model made by these two methods are analyzed, which occupy large variation ranges, especially the parameters K, Kb and Cd even to double. The reasons areprovided to show the reasonability and veracity of digital image processing system. The displacement, adopting the parameters of the traditional method, is about two times of the value based on the parameters of the image processing method. Moreover, the characteristics of the parameters' differences with density are analyzed. Meanwhile, the sensitivity of soil parameters with respect to a ground settlement is studied by the Geo-slope program, and the results suggest that the displacements vary sensitively with the parameters Rf, K and n .(2) Based on digital image processing system, the hypotheses of the Duncan-Chang model and Nanshui model are tested and validated. Meanwhile, by analyzing the characteristics of soil lateral deformation, especially the relationship between axial strain and radial strain, the fitting expression of the tangent Poisson's ratio is discussed and provided. Compared with the Duncan-Chang model, the calculated curves are in good agreement with the test results.