位移幅值对砾石-格栅界面循环剪切特性的影响

Effect of Shear Displacement Amplitude on the Cyclic Shear Properties of the Gravel-geogrid Interface

由于加筋土结构经常受到动荷载的作用,因此筋土界面的动力剪切性能也越来越受到重视;但目前筋土界面的动力剪切试验往往循环次数很少,一般只有10多次,不能充分反映筋土界面的动力相互作用。采用大型动态直剪仪,在剪切位移幅值分别为1、2、4、6 mm时,对砾石-格栅界面进行了2000次水平循环直剪试验,分析了剪切位移幅值对筋土界面剪切应力、竖向位移以及颗粒破碎的影响,揭示了筋土界面相互作用的机理。结果表明:在循环剪切过程中,界面平均峰值剪切应力先增加后减小;剪切位移幅值越大,达到界面峰值强度所需的循环次数越少,而达到界面残余强度所需的循环次数越多,较大的剪切位移幅值会使得砾石-格栅界面的剪切应力衰减现象更显著;随着剪切位移幅值的增大,试样最终剪缩量增大,但试样最终剪缩量增量逐渐减小;随着剪切位移幅值增大,界面剪切刚度逐渐减小,界面阻尼比却逐渐增大;通过对循环剪切试验后的砾石颗粒各粒组含量进行分析,发现剪切位移幅值越大,颗粒的相对破碎率也越大,相对颗粒破碎率与剪切位移幅值呈较好的对数关系,并与试验结果吻合较好。

The dynamic shear performance of the soil-geosynthetics interface is receiving increasing attention since reinforced soil structures are subjected to cyclic loads over a prolonged period of time.The current cyclic shear tests are usually performed over a limited number of cycles,generally ten,which fails to fully reflect the dynamic interaction at the interface of geosynthetics reinforced soil.In this study,horizontal cyclic shear tests with 2000 cycles were conducted on the gravel-geogrid interface with shear displacement amplitudes of 1 mm,2 mm,4 mm,and 6 mm.The effects of shear displacement amplitude on the shear stress,vertical displacement and particle fragmentation at the gravel-soil interface were analyzed,and the mechanism of interaction at the gravel-geogrid interface was proposed.The average peak shear stress at the interface was shown to increase and then decrease during the cyclic shear test.The results indicate that the larger the shear displacement amplitude,the fewer cycles are required to reach the peak strength of the interface,and more cycles are required to reach the residual strength of the interface.Larger shear displacement amplitude was shown to make the shear stress decay phenomenon at the gravel-geogrid interface more significant.Furthermore,as the shear displacement amplitude increases,the final shear shrinkage of the specimen increases,but the increment of the final shear shrinkage of the specimen gradually decreases.Moreover,as the shear displacement amplitude increases,the shear stiffness of the interface gradually decreases,but the damping ratio of the interface gradually increases.By analyzing the content of each particle group of gravel particles after the cyclic shear test,it was found that with the growing shear displacement amplitude,the relative particle fragmentation rate also increased.Further,the relative breakage ratio showed a good logarithmic relationship with the shear displacement amplitude and was in good agreement with the test results.