强震作用下含软弱夹层顺层岩质斜坡 动力响应规律试验研究

Experimental study of dynamic response law of bedding rock slope with weak interlayer under strong earthquake

青藏高原东南三江流域沿江分布着数以万计的古滑坡和潜在滑坡,对在建的川藏铁路构成严重的威胁。通过振动台模型试验研究了强震作用下含软弱夹层顺层岩质斜坡的动力响应规律。分析不同地震动参数、输入波类型和软弱结构面对斜坡动力响应规律的影响。试验结果表明:斜坡的自振频率随着输入地震波次数的增加而逐渐降低,振动强度为0.3g和0.6g是斜坡启裂和失稳的临界动力条件。斜坡具有明显的高程效应,加速度放大系数沿坡表呈现先增加、后减小、再增加的趋势,在1/4坡高和坡顶处较大。坡内竖直向加速度放大系数随高程增加呈现线性增加的趋势。频率对斜坡动力放大响应影响较大。斜坡对低频地震波的放大效应不明显,甚至有抑制作用。随着频率的增加,斜坡的动力放大效应越来越明显。随着幅值的增加,斜坡加速度放大系数呈现先增大后减小的趋势,在振动强度为0.3g~0.4g时达到最大值。不同类型地震波作用下,斜坡对天然波的放大作用高于人工合成波。软弱夹层的存在使输入的地震波出现了明显的放大,并通过快速傅里叶变换(fast Fourier transform,简称FFT)发现,软弱夹层的位置对输入地震波的频段的敏感程度不同。该试验揭示了含软弱夹层顺层岩质斜坡在强震作用下的动力响应规律,为进一步研究此类斜坡的失稳破坏机制和防治提供了依据。

Tens of thousands of ancient landslides and potential landslides are distributed along the Three-rivers basin in the southeast of Qinghai-Tibet Plateau,posing a severe threat to the Sichuan-Tibet railway under construction.A shaking table model test was performed to study the dynamic response of bedding rock slope with weak interlayer under strong earthquake.The influences of different ground motion parameters,input wave types,and weak interlayer on slope dynamic response were analysed.The test results show that the natural frequency of the slope decreases gradually with the increase of the number of input seismic waves,and the vibration intensities of 0.3g and 0.6g are the critical dynamic conditions for crack initiation and instability of the slope.There is an obvious elevation effect on the slope,and the acceleration amplification factor increases first,then decreases,finally increases along the slope surface,and is larger at 1/4 of the slope height and the top of the slope.The vertical acceleration amplification factor inside the slope increases linearly with elevation.The frequency has a great impact on the dynamic amplification response of the slope.The slope does not significantly amplify low-frequency seismic waves,and even inhibit them.With the increase of frequency,the dynamic amplification effect of slope becomes more and more prominent.As the amplitude increases,the acceleration amplification factor firstly increases and then decreases,finally reaches the maximum value at the vibration intensities of 0.3g–0.4g.Under the excitation of different types of seismic waves,the amplifying effect of slope on natural waves is higher than that on synthetic waves.The existence of a weak interlayer amplifies the input seismic wave markedly,and the fast Fourier transform(FFT)shows that the sensitivity of positions of the weak interlayer to frequency bands of input seismic waves differs.This experiment reveals the dynamic response law of bedding rock slope with weak interlayer under strong earthquake action and provides a basis for further study on the failure mechanism and prevention of slope.