Abstract
Soil under the engineering seismic base layer is treated as elastic material in the engineering practice, however, evidence that its nonlinear behavior affects surface response begins to appear. Test data on dynamic deformation characteristics and tri-axial compression test on sedimentary soft rock are collected and compiled to consider its nonlinearity. In addition, nonlinear characteristics of soft rock and note on practical use are described. Static tri-axial compression test of the sample taken by means of diamond core drill is first carried out by using a LDT (Local deformation transducer), and shear modulus is found to keep nearly constant up to strain of about 10-3 for the undisturbed sample, whereas that decreases significantly even at strain of 10-5. Secondly, dynamic deformation test data on Pleistocene and Tertiary soft rock with SPT-N value greater than 30 or shear wave velocity greater than 300 m/s is collected and compiled. It is found that there exist data that shows similar behavior of static test described in the preceding. These samples is supposed be undisturbed, which means there exists many disturbed samples even if they are retrieved by, so called, undisturbed sampling method. Shear modulus at shear strain of 10-3, which is used as index of nonlinearity, is independent from effective confining stress, but it has positive correlation with plastic index. Finally, dynamic deformation characteristics of undisturbed samples are shown to be modeled by Ramberg-Osgood model well.
