不饱和黄土的波速与质量含水率关系

Relationship between wave velocities and water content of unsaturated loess

黄土具有特殊的物理力学性质,且多具湿陷性.本文采用陕西省延安市南沟村的黄土研究不饱和黄土波速与质量含水率之间的关系.低场核磁的T2驰豫曲线表明黄土样品中水分主要为两种存在状态,一种是存在于小孔径中的结合水,另一种是存在于中孔径和大孔径中的自由水.随着黄土质量含水率的增加,结合水占比显著增高.黄土的中小孔含水占比与纵横波速度具有正相关关系.黄土样品的纵横波速度测量结果显示黄土的纵横波速在含水率小于8%时,随着质量含水率的继续增加,纵横波速度呈现出下降趋势;当质量含水率大于8%时,纵横波速度基本保持不变.土壤波速理论模型能较好描述质量含水率小于8%的纵横波速度变化,但质量含水率超过8%之后低估了黄土波速值.

Loess,which is collapsible soil,has unique physical and mechanical properties.This work focused on the loess in Nangou Village,Shaanxi province.The low-field Nuclear Magnetic Resonance(NMR)was used to examine the state of moisture and acoustic transducers were employed to obtain waveforms.The low-field NMR results show that there are two existence states of water in loess:bulk-water and free-water.With an increase in the water content,the P-wave and S-wave velocities and the ratio of bulk-water to free-water increase.The P-wave and S-wave velocities decrease with water content when the water content is lower than 8%and maintain stability when the water content is more than 8%.The theoretical model of soil wave velocity can describe well the wave velocities when the water content is less than 8%,while underestimate the wave velocities when the water content is more than 8%.