The Research On Characteristics And Formation Mechanism Of Geological Disasters In Jin Zhai County

This thesis is based on the project of Detailed Survey on Geological Disasters in JinzhaiCounty. Through the field work and the indoor work, the author has comprehensivelymastered the general types and distribution characteristics of Jinzhai’s geologic hazard. Withan analysis on various types of geologic hazards’ development features and formationconditions, as well as the influencing factors affecting geologic hazards, a systematic andcomprehensive understanding of the general characteristics of Jinzhai’s geologic hazardsdevelopment have been mastered in this thesis, besides, the formation principles and inducingfactors of geologic hazards are also listed. According to different disaster types, the authorselects some typical cases and analyzes their distributions and also the developingcharacteristics chapter by chapter. Besides, the author also analyzes their transformations andthe activity characteristics, as well as the power and formation mechanism so as to giveinformation for the assessment of the stability and susceptibility reflected on the cases. In thethesis, the author applies the various methods as limit equilibrium, finite element analysis,discrete element analysis, stereographic projection as well as synthetic evaluation method.The results in this research shall give some hints for future’s geological disaster preventionplanning of Jinzhai. The main research results are as follows:(1) There are four types of geologic hazard in Jinzhai, namely landslide, collapse,unstable slope and debris flow, first three types of which are dominant ones. Geologic hazardin this county is primarily characterized by multipoint, wide range, small size and incredibleharm. Different types of geologic hazard have different distribution regularities anddevelopment characteristics.(2) One of the typical landslides in Jinzhai is miniature accumulated layer landslide,which is usually multiple failure based. It is mainly composed of residual soil and eluvial soil,with some amount of. The shallow layer assumes absolute superiority in soil thickness, therest of which is middle layers. Most landslides occur in the middle to lower part of slope anddebris deposits at the bottom of the steep slope. Collapses are mainly small-sized and thelithology is complete-strong weathered intrusive rocks and metamorphic rocks, which are mostly cause by man-excavated slopes. All the debris flows in Jinzhai are turbulent-gullying,and are in small and medium size. Unstable slopes are mostly man-made rock ones, lithologyof which are complete-strong weathered intrusive rocks and metamorphic rocks.（3）In the shaping process of geologic hazard, the main correlative factors are landform,geologic structure, formation lithology, and the inclination of slope. The most principalfactors are rainfall and human engineering activities; however, earthquake is a subordinatefactor.（4）Generally, rules of geologic hazard formation and activity in Jinzhai are as follows:surface water permeates into slip mass, which is caused by long-term and heavy rainfall, andincreases the capacity of slope’s rock mass, which enhances slide surface’s downslide strength;on the other hand, pore water decreases not only shear strength parameter c&φ, but alsoeffective stresses in soil-rock mass, which reduces sliding resistance. As a consequence ofjoint contributions of free face, slope slips without support. Toppling and fault are rock-fall’smain formation patterns, while the main formation pattern of soil-collapse is sliding. Underthe influence of joint segmentation, unstable rock masses are divided into blocks. With theexternal force, as earthquake, etc., blocks form into earth-rocks and rubbles in various sizes.Due to unstable slope toe excavation, unloading cracks are formed and they are destructive ifconnected. Most soil slopes develop into minor landslips, while most rock slopes eboulementsin various size. Together with the influence of short-term heavy rainfall, a lot of loosematerials and potential collapse bodies within watershed scale induce debris flow. Itscomponents are rock blocks, detritus and coarse sands and it is diluent.