冻土超声波波速与冻土物理力学性质试验研究

TESTING STUDY ON RELATIONSHIP BETWEEN ULTRASONIC WAVE VELOCITIES AND PHYSICO-MECHANICAL PROPERTY OF FROZEN SOILS

超声波在介质中的传播速度反映了介质的物理力学性质。运用UVM-2型声速测定仪,测定不同密度的冻结砂土、冻结黄土和冻结粘土在不同温度下的超声波波速(纵波波速和横波波速)。对比分析不同土质的冻土,在温度和密度变化时超声波波速的变化,得出以下结论:土质颗粒的大小及组成成分在土冻结且在温度继续下降的过程中,通过影响结合水含量的变化而影响未冻水含量的变化,从而进一步影响冻土中的超声波传播速度,所以,可以在超声波波速与温度变化和未冻水含量与温度变化的基础上,建立超声波波速与未冻水含量的关系,通过测定超声波波速来量测冻土未冻水含量。密度的变化也影响着冻土纵、横波波速的变化,且冻结黄土的波速受密度变化影响较大,而冻结粘土则较小。冻土土质类型不同,透过它们的纵波波速和横波波速的变化范围也不同,可以通过对比表示压缩和剪切相对幅值的纵横波速比比值,来判定此冻土的土质类型,一般冻结粘土为1.07,冻结黄土为2.15,冻结砂土为0.7。根据弹性理论,泊松比与波速比有关,所以可以直接测量冻土的波速比研究冻土的强度及变形性能。

Ultrasonic wave velocity traveling in media reflects the physico-mechanical properties of the media. Velocities of the ultrasonic (dilatational and shear) waves in frozen fine sand, silt (loess) and clay with different densities are measured at different temperatures by UVM-2 ultrasonic measuring system. Then, the variation tendency of ultrasonic wave velocities with densities and temperatures is analyzed. The following results are obtained. (1) The ultrasonic wave velocities are influenced by soil particle size and soil composition which affect the variation of the bound water content and then the variation of unfrozen water content after the soil is frozen. Therefore, in terms of the ultrasonic wave velocities versus temperature and unfrozen water content versus temperature, the relationship can be set up between ultrasonic wave velocities and unfrozen water content. (2) The variation of dilatational and shear wave velocities is related to that of densities of soils, especially of frozen loess. (3) Different type of the frozen soil is of different scope of dilatational and shear velocities. The ratio of dilatational to shear velocities which express the relative range of compression and shear can be used to determine the type of frozen soils. Generally, the ratios are 1.07, 2.15 and 0.7 for frozen clay, frozen loess and frozen fine sand, respectively. In terms of elastic theory, the Poisson's ratio is related to wave velocity ratio, so that the property of strength and deformation can be determined by measuring the velocity ratio.