爆破震动作用下斜坡体的地震动分布及其动应力响应特征

DISTRIBUTION CHARACTERISTICS OF GROUND MOTION AND DYNAMIC STRESS RESPONSE OF VALLEY SLOPES UNDER BLASTING LOADING

利用爆破震动作为震源,观测、分析兰州市皋兰县城附近一黄土沟谷斜坡体的地震动分布情况及其动应力响应特征,为斜坡地震地质灾害的易发性研究提供科学依据。试验分析表明:(1)斜坡体上的地震动最大幅值变化明显受地形条件控制,斜坡中上部强震观测点QZH14所处部位地势内凹,对地震波有汇聚作用,其水平分量PGA明显大于周边其他测点。(2)爆破地震动作用下河谷底部反应谱以单峰型为主,斜坡体上为双峰型,反映河谷底部与斜坡体不同结构地质体的地震动特征。(3)爆破试验场地同一位置处的地震动与其动应力响应具有很好的对应关系,地震动幅值大的部位土体的动力响应也较大;斜坡体不同埋深部位的土体动力响应并不一定表现出一致增大或减小的规律,受地形和岩土结构等影响可能存在显著差异。研究认为地震动幅值、频率特征、地震波的入射角度等因素通过影响斜坡体的地震动参数变化,进而影响地震地质灾害的发育程度。

According to the seismic records,ground motion parameters are significant difference on various parts of alpine and gorge region,where earthquake damage investigation shows the damage is more serious than wide flat terrain and secondary disaster occurs frequently. In order to reveal the mechanisms of action,characteristics of blasting ground motion and the corresponding dynamic stress response,the blasting ground motion test for a loess valley slope located in Gaolan County,Lanzhou is carried. The testing analysis shows that：（1） Ground motion on the slope is obviously controlled by topography,especially in the cove（QZH14） on upper part of slope,where the PGA is higher than nearby observation points due to the wave superposition.（2） The response spectrum of blasting shows two attributes of ground motion on the slope and the foot of valley-bimodal pattern the former and unimodal pattern the latter. On the slope,long period component attenuates slowly with the hypocentral distance increasing.（3） There is a apparent correspondence between ground motion and its dynamic stress response,higher amplitude of ground motion,larger dynamic stress response. Due to the topographic effect and the geotechnical structure,inner stress response of the slope emerges significant variation in different depths rather than increasing or reducing trend with the distance of macro-epicenter increase. It suggests that the development degree of earthquake induced geological disasters are affected by the parameter variation of strong ground motion on the slope,which is usually determined by various factors,amplitude,frequency characteristics and incidence angle of seismic wave etc.