高温、高含冰量冻土中弹性波的传播特性

Propagation characteristics of elastic waves in warm ice-rich frozen soil

考虑了高温、高含冰量冻土在弹性波激励下表现出的冰晶黏滞性与未冻水流动性,并融入温度对介质物理性质的2种影响机制,通过结合Burgers黏弹性本构关系、BISQ模型和热力学理论推导了冻土中快P波、慢P波和S波传播的相速度及衰减因子的解析表达式,形成了针对该类冻土温度依赖的双相黏弹性孔隙介质理论。在此基础上开展了数值算例分析,明确了3种体波相速度和衰减因子的典型响应模式,并依次讨论了土孔隙度、冰晶黏滞性和地温等因素对它们传播特性的影响方式及敏感程度。证实了温度对快P波的相波速、衰减频带及峰值均有显著影响;对慢P波传播影响较小;对S波仅影响其相速度及低频衰减峰值。通过对比理论模型预测与实验室测试数据,证明了与传统基于弹性介质假设的冻土模型相比,基于黏弹性介质理论提出的新模型可以更好地描述高温、高含量冻土中弹性波的速度和衰减响应特征。

In this study,a novel rock physics model is proposed to simulate the coupling effect of wave-induced ice viscosity and unfrozen water mobility,as well as temperature influences on physical properties in warm and ice-rich frozen soil,by combining the Burgers viscoelastic constitutive relation,the BISQ model,and thermodynamic theory.The analytical expressions of phase velocity and attenuation factor of fast P-waves,slow P-waves,and S-waves in this frozen soil are derived,which extend the description range of conventional elastic models.Through numerical examples,the basic response modes of phase velocities and attenuation factors for these three body waves are simulated and studied in the frequency domain.On this basis,the effects of model parameters such as soil porosity,ice viscosity,and temperature on wave propagation are analyzed and concluded.It is confirmed that the temperature can affect the velocity and attenuation of the fast P-wave on aspects of central frequencies and intensities;the slow P-wave has almost no temperature dependency;and the S-wave attenuation has a clear dependency at low frequencies.Under laboratory conditions,the applicability of new model is well verified by comparing the theory with the measured data of a warm,ice-rich,frozen soil sample.