Study On Landslide Hazard Assessment In Gangu County Of Gansu Province

The Gangu County of Gansu Province is located at the transition region from the West Qin Ling rock mountain to the loess hills. Because of special landforms and topography, geological structure, the property of rock and soil, the geological environment near Gangu County is quite bad. Landslide、collapse、and debris flow hazards have frequently occurred and become principal geological environmental problems. They threaten the safety of lives and property of the inhabitants. The thesis is based on detailed investigation of geohazards in Gangu County of Tianshui City. On the foundation of extensively collecting geology data and investigation data in the region, establish geohazards database, analysis and study the features of development、mechanisms of formation and distributions of geohazards in the region. Through the method of combination of the AHP model with GIS software, we make zonation of the geological hazard susceptibility area and dangerous area. Through these studies, the major progress and conclusion are obtained in this thesis as follows:1) The background of the geology environment which controls the formation of the geohazards in Gangu County. The study area is placed in the transition region of the loess plateau in Long West region and Qin Ling mountain, which is in the composite area of many sets of structure. The geography is complicated, the strata and the rock property are diverse, the fold and fault are formed in large number. At the same time, the Gangu County is located in the join area of two seismic zones. Earthquake background is complicated, the activities of earthquake is intense and frequently; The geotectonic movement is active, discrepancy movement is obvious in the region; There are many rivers, which corrode the bank intensity. The degree level of vegetation cover is different in regions. Human activates have important effect on the nature environment. The combined actions of the factors above mentioned have provided a good environment for the development of the geohazards in Gangu County.2) The features of formation and distribution of the geohazards in Gangu County.The main four types of geohazards is landslide、collapse、debris flow and unsteady slope, the amount of landslides is the most. The geohzards distribute mostly at the both bank area of the Wei River、the loss hill in the north、the rock area of Qin Ling mountains, which are mostly in the secondary or third bayous of Wei River. To see from a macroscopic perspective, the geohazards distribute on the east-west fault belts alone the banks of the Wei River. The geohazards in Gangu County are formed main in the outcropped status of Quaternary loss、sand stone and clay stone of Neocene.3) The main control factors and the induce factors of the geohazarders in Gangu County. The main control factors of geohazards in Gangu County are landforms and topography, slope structure, the status and rock property, geological structure, hydrology, river system, the degree of cover vegetable, and so on. The main induce factors are rainfall、earthquake、human activities, especially the heavy rainstorm and continuous rain.4) Using strength reduction method, combined with study the finite element coefficient of safety, Comprehensive analysis the Maiduiping Landslide, which is of high risk and typical in Gangu. We research the stability of the landslide on nature condition and on saturated condition. The study is aim to provide reference data for studying formation mechanism and forecasting the harm of the landslides in Gangu County.5) Using the method of the AHP model, combined with GIS software, we make zonation of the geological hazard susceptibility area and dangerous area. Based on analysis the features and main factors of the geohazards, we build up the evaluation system of susceptibility, adopts the analytic hierarchy process method to determine the weight of each index. Based on the ArcGIS platform, we do statistic analyze the interrelation between each index and the intensity of geohazards (density of the geohazards), make classification and assign values, build up the index model of susceptibility at last. We calculate the values of each factor through GIS on computer, and make zonation of susceptibility. Based on the zonation of suspectivity, superposed the induce factor of rainfall and calculate, and obtain the danger zonation of geohazards, which is classified as four division. The four divisions are high danger division, moderate danger division, low danger division, extremely low danger division.