地震长期效应对黄土力学性质的影响

Influence of long-term seismic effect on mechanical properties of loess

黄土高原地区,具有大孔隙、弱胶结特征的黄土遭遇地震荷载影响后,其内部结构受到扰动,微结构的变化会在后期物理力学性质中集中反映出来。通过动三轴试验对原状黄土试样进行模拟历史地震预处理,对处理试样依次进行饱和、固结、不排水剪切试验。结果表明:黄土试样的初始含水率为10%时,经历历史地震扰动的黄土较未扰动黄土相比,其偏应力明显增加,孔隙水压力降低,抗剪强度指标值增大3.42 kPa和2.67°;当初始含水率增加至15%时,历史地震产生的长期效应将引起后期黄土强度持续增大,增幅远远超过10%的黄土试样,黏聚力和内摩擦角达到3.98 kPa和3.02°。通过扫描电镜试验和压汞试验,从微观角度分析地震长期效应对黄土力学性质影响的内在机制,结果发现历史地震引起黄土内部颗粒移动、孔隙结构变化是黄土强度增加的重要因素。

Since earthquake occurs frequently in the loess plateau,the internal structure of loess with large pores and weak cementation structure will be disturbed by the influence of dynamic loading,while the change of microstructure will be reflected by physical and mechanical properties in later stage.To study the change of loess mechanical properties under the long-term influence of frequent earthquakes,dynamic triaxial tests and consolidation undrained shear tests were conducted on the loess samples.The results showed that when the initial water content of loess samples is 10%,compared to undisturbed loess samples,the deviatoric stress of disturbed samples is significantly increased,and the shear strength index value is increased by 3.42 kPa and 2.67°,but the pore water pressure is reduced.When the initial water content increases to 15%,the long-term effect of historical earthquakes would cause the strength of loess to continue increase in later period.The increment is far more than 10%of the loess samples,and the cohesion and internal friction angle are up to 3.98 kPa and 3.02°.Results of SEM and MIT revealed that the inter particles movement and the pore structure change caused by historical earthquakes are key factors for the increment of loess strength.