Investigation on Ultrasonic Wave Properties of Clay-Sand Mixture under Triaxial Compression Condition
In order to investigate the ultrasonic wave characteristic of buffer/backfilled material of the geological disposal for high level radioactive nuclear waste with highly buried depth,triaxial compression test including two different stress loading paths and OCRs,complying with ultrasonic test,are carried out by using the rock triaxial compression servo-controlled testing apparatus and the ultrasonic wave testing device.The stress loading paths performed correspond respectively to confining compression test and convention triaxial compression test.The OCR is set to be 0.83 and 2.9.The results show that the curves of velocity of compression wave and shear wave Vp and Vs can be also divided into three phases similar to that of stress-strain curve obtained from confined compression test.However,a hysteresis phenomenon can be observed from the curve of Vp.In the condition of deviatoric loading,the Vp increases with a gradually attenuation rate,the Vs seems to decreases linearly.The changes of both Vp and Vs are related to confining pressure.The evolutions of dynamic shear modulus and Poisson rate (Gd and μd) are similar to those of Vs and Vp,respectively.The Gd depends on confining pressure.A square polynomial correlation is proposed to describe the correlation between Vp and Vs and effective mean pressure p',which can reveal the influence of p on Vp and Vs.In terms of the analysis on spectrum and time-frequency spectrograph of the result obtained from the conventional triaxial compression test with effective confining pressure equal to 7.0 MPa,the main frequency of S-wave signal raises increasingly,but the main amplitude decrease firstly and then increases.It becomes ambiguity to identify the main frequency.The higher confining pressure,the stronger the attenuation of S-wave signal.A coalescence between the Ⅰ and Ⅱ time intervals can be observed,which refers to the abatement of the S-wave splitting effect.The findings obtained in this study can provide the basis for the design of buffer/backfilled material,and can also be used as a reference in other engineering projects.
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