中文摘要：

通过在三轴试样的轴向和径向同时施加循环荷载,并以试样45°面上的应力来模拟地震拉压动荷载和剪切动荷载的作用,分析双向循环荷载耦合下黄土的动剪切模量和动变形特性。试验结果表明：相位差对黄土的动剪切模量有一定影响,其动剪切模量随相位差的增大以φ=180°为转折点呈现先减小后增大的趋势,在φ=180°时达到最低水平。φ〈180°时相位差的增大加速了黄土动剪应变的发展,φ〉180°时黄土的动剪切变形的发展速度随相位差的增大而减缓。同时径向动荷载幅值的增大明显降低黄土的初始动剪切模量。通过计算转化,分析拉压动荷载和剪切动荷载变化对黄土动剪切变形发展的影响规律,发现拉压动荷载的施加能加快黄土动剪切变形的发展,而当拉压和剪切动荷载同时变化时,剪切动荷载变化对黄土动剪切变形发展的影响更明显,作用更显著。

英文摘要：

When an earthquake occurs,seismic waves propagating from the earthquake source to the ground include transverse waves（S-waves）and longitudinal waves（P-waves）.Transverse waves produce dynamic shear loads whereas longitudinal waves produces dynamic tension and compression loads.Consequently,under the effects of these two dynamic loads,horizontal shear vibration and vertical tension and compression vibration occur simultaneously in loess.By simultaneously applying axial and radial dynamic loads on a triaxial specimen and using stress on the surface of the specimen at an angle of 45°,the effects of seismic tension and compression and shear dynamic loads are simulated and the characteristics of the dynamic shear modulus and dynamic strain of loess are analyzed under bidirectional cyclic load coupling.The test results indicate that phase difference has certain effects on the dynamic shear modulus of loess.Withφ=180°as the turning point,the dynamic shear modulus of loess decreases first and then increases with increase in the phase difference,and when the phase difference is 180°,the loess dynamic shear modulus decreases to its lowest level.Analysis of the initial dynamic shear modulus of loess under the bidirectional cyclic loads shows that with increase in the phase difference,the initial dynamic shear modulus of loess follows the same development law as that of the dynamic shear modulus.When the phase difference is in the range of 0°to 90°,the initial dynamic shear modulus of loess decreases quickly,but when it is in the range of 90°to 180°,the decline velocity slows down.Correspondingly,the initial dynamic shear modulus increases slowly when the phase difference is in the range of 180°to 270°;however,the increase in the velocity of the initial dynamic shear modulus becomes higher when the phase difference is in the range of 270°to 360°.When the value of the confining pressure is 200 kPa and the radial vibration amplitude is 20 kPa,the initial dynamic shear modulus of loess under the phase differe