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Abstract
Researches on frozen soil are of great significance in climate monitoring, engineering construction, and oil exploration. Previous experimental studies on the properties of frozen soil were mostly based on 1D ultrasonic transmission waves. They failed to observe the differences in the waveform caused by uneven spatial distribution of ice content in frozen soil. Using an innovative reflected wave experimental system, we investigated the changes in ultrasonic reflected P-wave measured in a large volume unconsolidated sediment during the freezing process, and obtained 2D single-shot records and 2D zero-offset reflection records. Notable observations include the following: different ice contents in frozen soil can cause tilted reflection events at the bottom of the target layer; the amplitude and phase of the reflected wave at the top of the target layer vary with temperatures; the high-velocity layer caused by the high ice content in the upper part of the target layer hinders the downward propagation of waves and cause the loss of reflected wave at the bottom of the sample. We call this the shielding effect of the high-velocity layer (SEHV). Our experimental results showed that the main cause of SEHV is the large impedance contrast between the upper and lower parts of the target layer, resulting from the different ice contents. We quantitatively estimated the ice saturation in the sample using the measured velocity of the sample and a rock physics model. Meanwhile, we have also provided a quantitative estimate of the impedance difference that causes SEHV. Our experimental results can be used to study the propagation of reflected wave in spatially non-uniform media and guide on-site seismic exploration and engineering construction in frozen-soil areas.
Published Version
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