基于Martin-Darvidenkov模型的冻结粉质黏土动力特性研究

冻土作为一种由固体矿物颗粒、冰晶体、未冻水及气体组成的多相结构体系，其动力学性质相较融土更为复杂。为了研究冻土动力特性的演化规律，探究等效线性黏弹性模型对冻土的适用性，以青藏粉质黏土为对象开展了一系列分级循环加载条件下的低温动三轴试验，深入分析冻土动弹性模量和阻尼比随振次、围压及动应变幅值的变化规律。研究结果表明：冻结粉质黏土骨干曲线的初始斜率随围压的增大而减小，体现了围压的强化作用；分别采用H-D模型和M-D模型对冻土的骨干曲线进行描述，结果显示相比H-D模型，采用M-D模型可以较好地模拟冻结粉质黏土骨干曲线在高动应变幅值下的软化现象；冻结粉质黏土的动弹性模量随动应力幅值的增大非线性减小，且基于M-D模型的动弹性模量预测模型可较好地描述冻结粉质黏土动弹性模量随动应变幅值的非线性变化规律；在每级循环荷载作用下，动弹性模量随振次的增大有小幅波动；滞回曲线面积随动应变幅值的增大呈非线性增大的趋势，阻尼比随动应变幅值的增大呈现出先减小后增大的趋势。此外，在每级动荷载作用下，当加载级数较小时，阻尼比随振次的增大逐渐减小，随着加载级数的增大，阻尼比随振次增大而减小的趋势逐渐减弱；当加载级数较大时，阻尼比随振次的增大呈现出逐渐增大的趋势。

Dynamic Characteristics of Frozen Silty Clay Based on Martin-Darvidenkov Model

As a multi-component phase system, frozen soil consists of solid mineral particles, ice crystals, unfrozen water, and gaseous inclusions, with dynamic properties that are more complicated than those of unfrozen soil. To study the evolution of these dynamic characteristics and investigate the applicability of an equivalent linear visco-elastic model to frozen soils, a series of dynamic triaxial tests under multi-stage loading conditions was conducted for silty clay from the Qinghai-Tibet Plateau. The variation of dynamic modulus and damping ratio with dynamic strain amplitude, confining pressures, and cyclic numbers was analyzed. The results show that the initial slope of backbone curves decreases with an increase in the confining pressure, which reflects the strengthening effect of the confining pressure. The backbone curves were described using H-D and M-D models. The results show that compared with the H-D model, the M-D model is preferable for describing the strain softening phenomenon presented by the backbone curve under a high dynamic strain amplitude for the frozen silty clay. The dynamic elastic modulus decreases nonlinearly with an increase in the dynamic strain amplitude, and the prediction model of the dynamic elastic modulus based on the M-D model can reflect the change in the dynamic elastic modulus with the dynamic strain amplitude of the frozen silty clay. Under each cyclic loading, the dynamic elastic modulus fluctuate slightly as the cycle numbers increased. The area of the hysteretic curve increases nonlinearly with an increase in the dynamic strain amplitude, whereas the damping ratio first decreases and then increases with the dynamic strain amplitude. Furthermore, under each dynamic loading stage, the damping ratio decreases with an increase in the number of cycles when the loading stage is small; however, the decreasing tendency of the damping ratio reduces with an increase in the loading stages, and even the damping ratio gradually tends to increase with the number of cycles.