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地震发生时,尤其是直下型地震发生时,P波对场地土体的作用不可忽略。通过变围压动三轴设备施加的特殊应力路径,模拟了P波和S波耦合对饱和软黏土动力特性的影响,即循环剪应力和循环正应力耦合对饱和软黏土动力特性的影响。试验结果表明:变围压动三轴试验得到的包括循环剪应力和循环正应力的应力路径可以较好地模拟P波和S波的耦合作用;循环剪应力和循环正应力的相位差对饱和软黏土的动强度有较大的影响,当相位差为180°时,土体的动强度最低,当相位差为0°时,动强度最高;随着循环正应力幅值的增大,土体的动应变发展速度与常规恒定围压动三轴试验下的动应变发展速度相比,差距逐渐增大。这些发现一方面表明强震过程中P波的作用不可忽略,另一方面表明,在某些情况下,常规恒定围压动三轴试验高估了饱和软黏土的动强度,对抗震设计不利。
When an earthquake occurs, especially when a direct type earthquake occurs, the effect of P wave on the site soil can not be neglected. The effect of P-wave and S-wave coupling on the dynamic characteristics of saturated soft clay was simulated by changing the stress path of the three-axis equipment. The effect of coupling of cyclic shear stress and cyclic normal stress on the dynamic characteristics of saturated soft clay was simulated. The experimental results show that the stress path including cyclic shear stress and cyclic normal stress obtained by the triaxial compression-in-triaxial test can well simulate the coupling of P-wave and S-wave. The phase difference between cyclic shear stress and cyclic normal stress has a good effect on the saturation The dynamic strength of soft clay has a greater impact. When the phase difference is 180 °, the dynamic strength of the soil is the lowest. When the phase difference is 0 °, the dynamic strength is the highest. With the increase of cyclic positive stress amplitude, The dynamic strain rate of the body increases with the development of dynamic strain under the constant constant pressure and triaxial test. These findings, on the one hand, show that the effect of P wave during strong earthquakes can not be neglected. On the other hand, the conventional constant confining pressure dynamic triaxial test overestimates the dynamic strength of saturated soft clay in some cases, which is detrimental to the seismic design.