Study On The Small Strain Dynamic Properties Of Saturated Sand

Dynamic properties of soils as the most important parameters in geotechnical engineering, play significant roles in analyzing not only the dynamic problems such as earthquake, machinery foundation design, but also the characteristics of static deformation. It is well recognized that the dynamic properties of soil are influenced by many factors, but there exists many contradictions in the previous studies. Hence, small strain dynamic properties were studied using bender-extender element tests, resonant column tests, cyclic triaxial tests. First of all, the mechanical of bender-extender element test was introduced. And then, the effects of saturation degree, dispersion, fabric and cyclic history on small strain dynamic properties were conducted by means of various measurements. Detailed researches were introduced as follows:(1) The structure, connection and combination of bender-extender element were first introduced in detail, which had been rarely reported at present. Deep analysis on received waveform and the effects on accurate determination of the travel time of shear wave velocity, compression wave velocity were discussed using wide range of frequencies. Therefore, the travel time determination is more reliable. In addition, shear modulus, constrained modulus and Possion’s ratio could be obtained through the S-wave and P-wave using bender-extender element tests. Meanwhile, the effects of confining pressure and relative density on Possion’s ratio were also analyzed. For practical, a relationship between Possion’s ratio and shear modulus was established.(2) Deep researches on the relationship between Vp and B were necessary due to the discreteness in the previous studies. Hence, three kinds of grading sand were used to study the Vp-B relationship considering the pore water type, relative density and grading. At last, reasonable explanations were given for the test results.(3) Bender element tests and resonant column tests were performed on two clean sands and two nature sands under different confining pressure and relative density in saturation condition. And then the deviation results between the two kinds of tests were explained through the dispersion of shear wave. Additionally, BE tests and RC tests were conducted on saturation Nanjing sand with different fine contents to study the effect of fine content and hydraulic conductivity on the bender element tests. The results will give useful advice on testing small strain shear modulus of saturated sand using bender element test.(4) Different fabric could be obtained using two common methods for preparing remolded sand. And then, BE tests and RC tests were conducted on the different fabric saturated sands to study the shear modulus and damping ratio. The results were compared with the previous studies and explanations were given from the micro perspective.(5) The effects of cyclic loading history on small strain dynamic properties were performed on saturated sand in drained condition using dynamic triaxial tests combined with bender element tests. And the influence of initial mean principal stress, initial deviatoric stress, deviatoric stress amplitude and fabric were also discusse.Above all, many factors affect the dynamic properties (small strain shear modulus, damping ratio, Possion’s ratio, et al.). Although extensive researches have been conduced in the past, deep researches still need to solve the problems. The results will play an important role on understanding the dynamic properties. In addition, as a convenient measurement, the results will facilitate the application of bender element tests and extender element tests.