Study On Experimental Technology Obtained Dynamic Modulus And Damping Ratio Of Soils

Dynamic modulus and damping ratio, the two main parameters describing dynamic deformation of soil, are of great importance in the analysis of soil layer and its seismic response. The two parameters are determined by many factors, of which effective mean principal stress, void ratio and structure of soil are the most important factors.The apparatus used in the experiments, soil static and dynamic universal triaxial and torsional shear apparatus, is made by Dalian University of Technology and Seiken Inc., Japan. In this apparatus, two measuring systems are equipped: one is un-touched displacement sensor and corner sensor installed in the triaxial cell, the other is touched displacement and corner sensor. In order to improve the precision of experiment, both the un-touched and touched displacement sensor are used together. The curve that dynamic modulus of the sample varies with the amplitude of dynamic strain can be obtained simultaneously by touched displacement sensor and un-touched displacement sensor, avoiding the disadvantage that the vertical large displacement sensors is inaccurate under small strain amplitude and the measure range of small displacement sensors is narrow.In this paper, the methods and techniques that dynamic modulus and damping ratio are measured by cyclic triaxial tests and cyclic torsional tests are discussed. Through comparing the dynamic deformation behavior measured by conventional methods with results coming respectively from the test 1, i.e. sample under three different mean effective confining pressures and test 2, i.e. sample under dissipating pore water pressure frequently, the damping ratio property and the methods by which dynamic modulus and maximum dynamic modulus are measured are studied. The conclusion is that the results from testl agree with those from conventional methods when initial confining pressure σ₃ equals 100kPa, 200 kPa or 300 kPa. Furthermore, this method can guarantee the stability of the sample during experiment and effectively decrease the time of making and saturating samples. The comparison also shows that dynamic modulus and damping ratio from test 2 is close to results from conventional methods.In order to explore the effect of fly ash consolidation stress ratio on its dynamic modulus, cyclic triaxial tests are performed on fly ash whose relative density of D_ris 60%, under the condition that consolidation stress ratio K_c equalsl.0, 1.5 and 2.0 respectively. Result shows that, as illustrated by the curve of E^ε, under different consolidation stress ratio, the dynamicmodulus decreases consistently as the amplitude of dynamic strain increases. When consolidation stress ratio Kc equals 2.0, the maximum dynamic modulus under different initial consolidation stress is descending.