黄土斜坡震害面波勘探调查及其动力稳定性分析——以甘肃岷县、漳县M_s6.6地震为例

Surface Wave Investigation and Dynamic Stability Analysis for Earthquake-Induced Loess Landslides

摘要:

2013年7月22日,甘肃省定西市岷县、漳县交界处发生6.6级地震,地震诱发了约600余处地质灾害(隐患点),其中规模最大的是岷县梅川镇永光村四社西的两个相邻滑坡。本文对永光村西侧滑坡进行了多种手段的现场勘测,特别是在坡顶及坡底开展了高密度面波勘探,分析了该黄土滑坡成因及滑坡附近的地形、地层等因素。采用动力有限元法和强度折减法结合的方法分析该滑坡在地震荷载作用下的动力响应、滑坡动力稳定性的影响因素以及地震荷载与滑坡失稳状态之间的关系。结果表明,由于地震前的强降雨导致表层黄土的抗剪强度降低,在地震荷载作用下黄土层之间存在拉应力效应并导致崩塌滑动。

Abstract:

The sliding and collapse of a slope during an earthquake are the main types of slope-related geological disasters,and the dynamic stability of slopes has been one of the most important topics in geotechnical engineering and seismic engineering.About 600 instances of landslides,collapses,and other geological disasters such as collapses,debris flow,and shattered mountains were induced by the Minxian and Zhangxian MS6.6 earthquake on July 22,2013,in Dingxi area in Gansu province; this earthquake damaged many towns and killed 95 people.Furthermore,it resulted in a very high death toll and economic loss in China.The largest and most serious and damaging landslides post this earthquake were the two neighboring landslides in Yongguang village in Meichuan town,Minxian.The western landslide had a length of 1 500 m,average width of 28 m,and area of about 42 000 m2.The landslide occurred from an elevation of 2 700 m to 2 545 m,i.e.,a distance of 155 m.It can be considered as being a crushed-debris flow,remote landslide,resulting in 12 deaths.The area of the eastern landslide was about 33 000 m2.A field survey on geological disasters is very helpful to gain a better understanding of mechanisms of earthquake-induced disasters,particularly of dynamic slope stability.Such geological disasters associated with earthquakes （e.g.,landslides,collapses,debris flow,and shattered mountain） can be subsequent potential geological hazards with long-term,hidden,and unexpected features.According to a variety of survey methods,especially Rayleigh-wave exploration conducted on both of the top and bottom of the landslide in detail,the status of the loess landslide and the topography,stratigraphy and other factors are investigated and the sliding mechanism is analyzed.Based on it,a dynamic numerical analysis method was used to evaluate the dynamic response of the slide,and the factors influencing the stability of the slide and the relationship between instability failure and earthquake motions were identified.The dynamic stability of the slide was analyzed by the dynamic finite element method and a strength reduction method.As a result,it was found that the shear strength of the loess on the slope surface reduced because of heavy rain before the earthquake,and tensile stress occurred,which led to the collapse of seabed slides.