| Helong city is a county-level city under the jurisdiction of Yanbian Korean Autonomous Prefecture,a border tourism city in the Changbai Mountain area,located on the north bank of the upper reaches of the Tumen River at the eastern foot of the Changbai Mountain and in the hinterland of the Northeast Asian economic circle.More than 90%area of this city is covered by mountains,with high mountains and deep valleys,well-developed river system,concentrated rainfall,and strong tectonic and volcanic seismic activities,so the geological environment in the area is relatively fragile.In addition,because of the continuous development of the forest resources and human activities increases dramatic,such as tourism,industrial and mining,the frequency of geological disasters is increasing year by year.The increasing geological disasters and the increasingly fragile geological environment led to the contradiction between the development of human economy and society and the sustainable development of geological environment in Helong city.Therefore,it is of great significance to carry out the geological hazards risk mapping and the geological environment carrying capacity evaluation to guide the prevention and mitigation work of geological disaster and to coordinate the contradiction between the production and living activities of human beings and the sustainable development of geological environment in Helong city.This study takes Helong city as the study area,and the typical geological disaster risk maps are conducted in the study area based on the results of the geological hazard mapping.Then,according to the geological,ecological and social environment factor,the mathematical statistical analysis method was used to build the geological environment bearing capacity evaluation model to study the bearing capacity of geological environment.The conclusions are as follows:(1)Through a combination of the remote sensing interpretation,filed investigation,geophysical exploration,drilling and mountain engineering,173 disasters which are unstable and 63 potential disasters which are all located on unstable slopes have been identified in Helong city.The potential geological disaster points contain two parts:one is the geological disasters that have happened and are not stable,and the other is the geological disasters that have not yet happened and have potential probability of occurrence.Therefore,it can be determined that there are 236 potential geological disaster points in the study area,including80 collapses,72 debris flows,63 unstable slopes,16 landslides,3 ground collapses and 2ground fissures.Based on the analysis of the development characteristics of various types of geological disasters points in the study area,it is found that the collapse,landslide and unstable slope are mostly controlled by slope structure and human engineering activities,and the debris flow is mainly affected by geomorphologic conditions,and the ground collapse and ground cracks are all caused by underground mining activities.(2)The typical geological collapse and landslide hazards mapping in the study area was conducted.Firstly,slope units which are mostly between regular triangle and circle in shape,with more uniform area and small change of slope angle and aspect based on the curvature watershed method are selected as the mapping units.According to the correlation between the geological environment characteristic and the collapse and landslide hazards,and the relative literature of the geological hazards mapping,the evaluation index system containing 13evaluation indicators in 8 categories,which consists of rock and soil mass,geological structure,topography and geomorphology,vegetation cover,meteorology and hydrology,human activities,triggering factors,and special geological environment was established.This study focused on the special geological environment conditions in the study area-the volcanic activity factor of Changbai Mountain.Then the correlation analysis was carried out on the evaluation index,the results show that the formation of Q and J,slope angle of18?24°and 24?30°,slope aspect of SE and S,elevation range of 255?860 m,land relief of103?180 m,252?339 m,339?595 m,convex slope,the closer distance fault,rivers,and roads,bare land and artificial vegetation,have the highest correlation with the landslide geological hazard.Then,the information content method,the analytic hierarchy process and the random forest were selected to build the collapse and landslide hazard evaluation model in the study area.The statistical parameters and the receiver operating characteristic curve were used to optimize the model.It can be seen from the results that the random forest model has the highest prediction accuracy.Finally based on the results of random forest model,the collapse and landslide hazard risk were analyzed,the results show that low,moderate,high,and very high risk area account for 40.28%,27.75%,19.09%and 12.88%of the total study area,respectively;the four hazard classes contains 0,2,31,126 happened landslides and unstable slopes,accounted for 0.00%,1.26%,19.50%,79.25%of the total happened landslides and unstable slopes,respectively.And the high and very high hazard area are mainly distributed around the towns in the study area,where human life and production activities are concentrated,so it will cause large loss of life and property in the case of landslide geological hazards happened.Therefore,it is recommended to increase disaster monitoring in these areas,realize the real-time monitoring and early warning of landslide and collapse disasters and pay attention to the deployment of the disaster prevention and mitigation work.(3)The debris flow hazard mapping was conducted in the study area.Firstly,the basin unit suitable was selected as mapping unit for debris flow hazard mapping.Then,an evaluation index system consisting of 11 evaluation indexes in 7 categories was established,including rock and soil mass,topography and geomorphology,geological structure,vegetation cover,meteorology and hydrology,the development stage of small watershed and special geological environment.The correlation between debris flow and each evaluation indexes was conducted.The results show that the strata of Q,K and J,slope angle of 6?11°,slope aspect of E,S and SW,area range of 2.55?7.77 km~2,relative height difference of 0?206 m,roundness range is 0.14?0.52,bare land,artificial vegetation and geomorphic information entropy range of 0.349?1.357,have the highest correlation with the debris flow hazard.And the closer the distance to the river,road and fault,the higher correlation with debris flow hazard.Then,the frequency ratio method,artificial neural network model and support vector machine model were selected to build the debris flow hazard evaluation model in the study area.The statistical parameters and the receiver operating characteristic curve were used to optimize the model.The results show that the support vector machine model has the highest prediction accuracy.Finally based on the mapping results of the support vector machine model for the debris flow hazard analysis,the results show that very high,high,moderate and low risk area were 44.61%,33.42%,11.77%,10.21%of the total area of the study area,respectively.And the low,moderate,high,and very high debris flow risk area contains 2,11,20,39 happened debris flow,respectively,accounted for 2.78%,15.28%,27.78%,54.16%of the total happened debris flows,respectively.In addition,the areas with high and very high risk class of debris flow hazard in the study area are mainly distributed in the northeast of Longcheng Town,Bajizi Town,the central part of Toudao Town and the northern part of Dongcheng Town.Therefore,it is suggested to increase the monitoring and early warning of debris flow hazards in these areas.(4)The geological hazard risk mapping in the study area was conducted.Firstly,the following five evaluation indexes:road density,building density,population density,per capita income of farmers,and cultivated land density were selected as the evaluation indexes.Analytic hierarchy process is applied to study the vulnerability of collapse,landslide and debris flow in the study area.The results show that the geological hazards vulnerability of the study area is mainly low vulnerability.Based on the results of the vulnerability mapping and the risk mapping,the geological hazard risk mapping in the study area is studied.The results show that the study area mainly belongs to the low-risk area of geological hazard.The areas with high and very high risk of geological hazards are mainly located in the northeast of the Longcheng Town which around the Dongcheng Town and along most of the border highway,accounting for 28.03%of the total area of the study area.The main threat objects of these hazards are the provincial highway S206,residential houses,farmland and border highway,etc.It is recommended to strengthen disaster prevention and mitigation work in this area.The moderate risk area of geological disaster accounts for 34.22%,and the management and monitoring of geological disaster should be carried out appropriately.The low geological hazard risk area has the most widely distributed area,with a ratio of 37.75%.(5)The carrying capacity of geological environment in the study area is synthetically evaluated.Combined with GIS technology,according to the characteristics of geological environment in the study area and the characteristics of human living and production activities,the evaluation index system consisting of 18 evaluation indexes in 3 categories in the study area are established to synthetically evaluated the carrying capacity of geological environment,include geological environment:evaluation difference,slope angle,geomorphologic type,fault distance,earthquake,formation lithology,landslide and collapse risk,debris flow risk;social environment:building density,population density,road density,cultivated land density;ecological environment:rainfall,land use type,river distance,per capita water resources,per capita food production and per capita mineral resources.Combined with the combination weighting method,the importance of each evaluation index was ranked,and it can be seen that the most important evaluation indexes for the geological environment carrying capacity of the study area are(top five):debris flow risk,lithology,landslide and collapse risk,earthquake,population density.Then the bearing capacity model of geological environment in the study area was built,the results show that the area of the low bearing capacity level was471.38 km~2,the area of the moderate bearing capacity level are1,097.24 km~2,the area of the high bearing capacity level are 1,416.67 km~2,the area of the very high bearing capacity level are 2,083.34 km~2,the bearing capacity of the four level area accounted for 9.30%,21.65%,27.95%,41.10%of the total study area respectively.It is recommended to control new mineral resources excavation,large human engineering construction in the area with the low geological environment bearing capacity,so as to avoid more serious damage.Transform the mining mode and utilization intensity of the existing resources such as land,mineral resources so as to gradually improve the geological environment conditions in the study area. |
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