冻土超声波声学参数与冻土物理力学性质试验研究

Frozen soil as a special geotechnical materials containing ice, its physical and mechanical properties depends largely on the status of frozen soil temperature and moisture conditions, as well as sample preparation process, even if the frozen soil samples processed under the same conditionsare also likely to have different properties and characteristics of traditional physical and mechanical test methods for soil samples are destructive, the sample can not be reused, it is difficult to unify the analysis of all test results. With the development and wide application of ultrasonic technology, the ultrasonic instrument hardware and software development, its function of transmitting and receiving transducers has also been greatly improved, in particular, no longer need to slice the original sample for test Therefore, the ultrasonic instrument has reached many non-destructive testing can be of any size single experimental sample and the original sample to use this feature to further expand the depth the ultrasonic characteristics of the acoustic parameters of study permafrost and frozen soil physical and mechanical parameters. The project intends to improve ultrasonic velocity instrument in the study of frozen soil acoustic parameters on the basis of physical and mechanical properties of frozen soil, non-destructive testing in the full sense will have been made, and combined test results with the traditional method,in order to summarize and analyze the difference between the two, and further explore the mechanism of the ultrasonic velocity changes with the changes of the frozen soil temperature, pressure, water content, and et al.

冻土作为含有冰的一种特殊的岩土材料，其物理和力学性质很大程度上取决于冻土的温度状况及含水率状况以及制样过程等，即使在相同条件下加工的冻土样品也很有可能具有不同的性质和特点，同时由于传统的物理力学测试方法对土样都具有破坏性，样品不能重复利用，所以很难将所有测试结果统一起来分析。随着超声波技术的发展和广泛应用，超声波仪在软硬件方面得到发展的同时，其发射和接收换能器的功能也得到了很大的提高，尤其是无需再对原始样品进行切片后测试，所以，目前超声波仪已经达到了可以对任意大小的单一实验样品和原始样品的多次无损检测，利用这一特点可进一步拓展深入研究冻土声学参数与冻土物理力学参数之间的相互关系。本项目拟通过改良超声波波速仪，在研究冻土声学参数的基础上，对冻土的物理力学性质进行完整意义上的无损测试，结合已有传统方法的测试结果，归纳分析二者的差异，进一步探讨超声波波速随冻土温度、压力和未冻水含量等变化的机理。

冻土物理力学性质研究是冻土工程的热点之一。由于超声波测试具有快速性、无损性等优点，超声波测试技术已成为研究冻土物理力学性质的有效途径。项目组成员从理论和试验角度研究了冻土超声波声学参数与冻土物理力学性质之间的关系。在理论方面将冻土视作三相体，分析了声波的传播特性和推导了声波在冻土中传播速度的表达式；试验方面利用RSM-SY5(T)型非金属声波检测仪对不同土质、温度、含水率、干密度、外荷载以及冻融循环条件下的冻土进行了超声波测试，同时测定了其在不同温度下的未冻水含量和抗拉、抗压强度。基于试验结果，分析了不同因素对冻土波速的影响，建立了不同条件下冻土声波特性与其物理力学性质之间的关系。根据弹性理论，利用所测波速计算冻土的动弹性力学参数。建立了在单一影响因素变化条件下冻土波速与未冻水含量、强度之间的关系式，它们之间存在良好的相关性。最后利用短时傅里叶变换及小波分析研究了冻土加载过程中声波传播的波形、频谱等特征。声波的特征参数能在一定程度上反映冻土加载过程中损伤的发育情况。研究结果为利用超声波检测技术预测冻土物理力学性质奠定了基础。