The unstable rock zone was developed at the rear of Guo Dashan Mount,on the middle hillside immediately behind Guo Da Street of Kangding City,posing great threats to lives and properties of nearly 2000 people in the vicinity.It was imperative to initiate field work on its stability.In this research,it started with an analytical survey of the unstable rock zone in the engineering geological conditions and evolutionary history.Result confirmed that the unstable rock zone of Guo Dashan Mount could be divided into three rockfall sections,Ⅰ,Ⅱ and Ⅲ.Typical unstable rock mass was selected at each section for qualitative categorization with reference to stability analysis and definite rockfall type.RMR method was referred to for determination of rock mass classification and it concluded that the unstable rock zone was in the poor quality,Ⅳ level,indicating that the whole rock mass was suffering from collapse;By stereographic projection analysis,it suggested that spalls,which consist of rock wedges enveloped by strata,joint 1 and joint3,was very prone to drop off from the rockfall section Ⅰ,Ⅱ in case of favorite conditions,such as weathering,rainfall,earthquakes and other external forces.Kinematics analysis exhibited that falling rocks in the rolling-sliding model would arrived at a rate of 33.05 m/s,52.15 m/s,57.41 m/s,in the rockfall section Ⅰ,Ⅱ and Ⅲ respectively,before it hit the collision mass;Restitution coefficient method was used to calculate the bouncing height of a falling rock in the numerical model of rockfall bounce and collision,with an estimated number 16.46m in height,In the end,the unstable rock zone of Guo Dashan Mount were zoning for risk division and accordingly geohazard division map was produced in terms of three levels,high risk,medium risk and low risk.This research provides some scientific basis and technical support for geohazard prevention and mitigation on a local basis.%郭达山后山危岩带位于康定县城郭达街后山山腰,直接威胁康定县城近2000人的生命财产安全,开展相应研究工作具有紧迫性和必要性.对郭达山后山危岩带的工程地质条件和演化历史进行了分析描述;将危岩带分为崩塌Ⅰ区、崩塌Ⅱ区、崩塌Ⅲ区,分析其基本特征,并对每个区内的典型危岩体进行了崩塌类型及稳定性定性分析;采用RMR岩体分类与质量评价法对崩塌岩体进行岩体分级,属Ⅳ级,岩体质量属差岩体,表明郭达山后山危岩带岩体整体稳定性较差;采用赤平投影分析得出崩塌Ⅰ区、Ⅱ区内由层面与裂隙1裂隙3切割成的楔形体在风化、降雨、地震等外力条件下极易发生崩塌;采用运动学原理分析运动特征,计算落石滚动滑动模式下落石与受灾体碰撞前的速度,分别为崩塌Ⅰ区33.05 m/s、崩塌Ⅱ区52.15 m/s、崩塌Ⅲ区57.41 m/s;采用恢复系数法计算落石坠落碰撞弹跳模式下的弹跳高度落为16.46 m,最后对郭达山后山危岩带进行了危险性评价,分高危险性、中危险性、低危险性三个等级制作了危险性区划图.为地方的防灾减灾提供了一定的科学依据和技术支撑.
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