| The dynamic characteristics of frozen soil are reflected by the propagation characteristics of ultrasonic wave in frozen soil, by the speed test using ultrasonic velocity technology, the kinematics parameters of acoustic in frozen soil can be tested directly. The propagation velocity of ultrasonic in the frozen soil is significant affected by the unfrozen water content of frozen soil, but the result of experiment shows that ultrasonic velocity clearly related to the kinematics parameters of frozen soil model propagation (Kinematics parameters affect the ultrasonic amplitude, frequency). The experiment purpose of this paper is trying to find the possible relationship between the ultrasonic velocity and the unfrozen water content, thus provide the experimental basis for the ultrasonic velocity using for the engineering application of the unfrozen water content test.The free unfrozen water content of the frozen soil is different, the acoustic velocity in the frozen soil are not the same. So the moisture content of frozen soil will be controlled within a certain temperature range according to the different model materials when making the frozen soil model (the range of chengdu sandy soil is 25.32%-32.52%, and the range of Chengdu clay is 35.22%～42.42%), then according to the calculating formula of unfrozen water content, the Acoustic and Electromagnetic Testing corresponding the unfrozen water content in the frozen soil can be tested out, thus the determination of the temperature is especially important during the test. The frozen soil model are designed, and its freeze-thaw layer can change, its bottom is the heating system, its upper completed frozen, around and the top are wrapped insulation material, when the process of slow heating at the bottom, freeze-thaw interface will change and frozen soil inner will form a field of temperature. Electrode was stratified buried in the model and thermistor was embedded in its corresponding position, at the same time, real-time monitoring the temperature. Thus velocity corresponding to different temperatures can be obtain through calculate spreading speed of signal of adjacent electrode section, this method can receive enough collected of temperature records. The test can also study relationship between electric signal and other factors with frozen soil through change the model parameters of frozen soil (medium composition, moisture content). The experiment selected three kinds of models to carry on the analysis:the Qinghai-Tibet region clay model, the Chengdu sandy soil model, the Chengdu clay model. To contrast with the existing theory, the temperature takes negative parts.Study proves the following aspects, looking from the temperature test data, regarding models of different media, in the temperature range-10℃～0℃, rise same temperature and relatively need to absorb more heat, in the most obvious that is the Qinghai-Tibet region clay model, in the range of-10℃～0℃, the temperature-time changing curve of other frozen soil model (Chengdu sandy soil model and the Chengdu clay model), the slope also has apparent changed. The comparative analysis of received acoustic signal strength relative to unfrozen water content in the model show that along with temperature elevation, the unfrozen water content in the frozen soil model increase gradually, the energy of received wave decreases gradually, when the unfrozen water content is more than 7%, the frozen soil model is almost no model sound signal acquisition. Finally, according to data with different test of model medium, this paper found the relation function between the acoustic wave propagation velocity and the unfrozen water content.
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