| Rapid economic development,rapid population growth,land resources are very scarce,the rapid development of the city caused a surge in traffic pressure,hindering the future development of the city.The development and utilization of underground space has become an important method for humans to expand the living space,and the application of artificial freezing method has become more extensive.However,it is difficult to predict whether a complete frozen wall has been formed during the construction of the artificial freezing method.Therefore,it is necessary to study and analyze the propagation characteristics of waves in frozen soil,so that the theoretical research can be better applied to artificial freezing method.Through the restoration and analysis of the existing wave propagation characteristics theory,and the shortcomings of the existing models are analyzed Therefore,the non-free unfrozen water volume outside the macropore which is not considered in the existing model is added into the calculation model,to modify the theoretical calculation model of wave propagation characteristics in frozen soil the theoretical calculation model of the wave propagation characteristics in frozen soil.The model of wave propagation characteristics in saturated permafrost was successfully reduced to the model of Biot.In addition,the effects of frequency,temperature,porosity and other factors on the wave propagation characteristics in saturated frozen porous media are analyzed.Considering the unsaturated characteristics of soils in practical engineering,based on the modified model theory,a model of wave propagation characteristics of quasi-saturated frozen porous media is proposed to analyze the difference of wave propagation characteristics between saturated and quasi-saturated frozen soils.The influences of frequency,temperature and saturation on wave propagation characteristics are analyzed.Considering the characteristics of saline soil in underground engineering in coastal cities,based on the modified model theory,a model of wave propagation characteristics in porous media with salt saturation and freezing was proposed to analyze the differences of wave propagation characteristics between saline and non-saline saturated permafrost.The effects of frequency,temperature and salt concentration on wave propagation characteristics were analyzed.Considering that the soil mass in the actual underground engineering in coastal cities also has the characteristics of unsaturated,based on the above modified model,a model for studying the wave propagation characteristics in the porous medium with salt saturation is proposed to analyze the difference of the wave propagation characteristics between saturated and quasi-saturated saline permafrost.In addition,the influence of frequency,temperature,salt concentration and saturation on wave propagation characteristics was analyzed.Due to the complexity of the existing research on the freezing wall related problems of artificial freezing method,the theoretical research on wave propagation characteristics was applied to artificial freezing method,and the correctness of the modified model was verified by comparing the theoretical calculation results of wave velocity with the experimental results of Peng Wanwei.Some Suggestions are given for frequency selection during ultrasonic testing in actual experiments or practical engineering.In the low and middle frequency bands,wave velocity is unstable,so it is better to choose the high frequency band in the actual testing process.Finally,based on the change of ultrasonic wave velocity with the development of frozen permafrost region,it can be judged whether a complete frozen wall has been formed in the project,and the expansion thickness of frozen permafrost in a certain area can be simulated to predict whether the soil in this area is completely frozen,so that artificial freezing method can be better applied to practical engineering construction. |
