Risk Assessment And Control Of Debris Flow In Gunmaling

As a typical solid-liquid dual-phase mountain hazard, debris flow has the characteristics of rapid flow velocity, and a huge capacity for material content - as well as strong destructive forces. Debris flow causes huge economic losses and human casualties, and meanwhile, irreparably alters the regional ecological environment balance. Debris flow can intensify soil loss resulting in desertification trends and has a far-reaching impact on the region. With the acceleration of urbanization in China, economic construction is gradually spreading to mountain areas, raising alarm amongst residents as they gradually realize the harm which debris flow can cause. As a result, Debris flow has caused widespread concern from the academic and engineering fields.On August 5th 2001, a rare and extremely severe storm struck the area of Gunmaling river basin of Shijia Valley, Xiamatang Town, Nanfen District, Benxi City of Liaoning province, and caused a torrential flood, which also resulted in geological disasters like landslides and debris flow. The situation ranked as a major disaster with direct and indirect financial losses exceeding 45 million RMB; it endangered the local reservoir, causing traffic disruption and destroying huge amounts of farmland. Human casualties included 19 dead and more than 60 wounded; 94 houses destroyed with 24 families becoming homeless. Through on-site investigation afterwards, various geological environmental conditions were found to help the formation of debris flow, which hast the potential to cause future debris flow hazards if heavy rains arise. At present, the region is still considered a high risk area, a fact that looms ominously over its 174 citizens and has the potential to cause monetary losses of up to 1.7 million RMB. This seriously influences local economic development and social stability.Taking the debris flow in Gunmaling river basin as the study object and focusing on the risk ratio of debris flow in this area and debris flow control, this thesis is expected to evoke a significant discussion on the risk assessment method of debris flow in mountain areas - with the goal of ensuring the safety of lives and property in the downstream communities. This thesis is mainly formed by five parts of introduction, the basic situation and formation conditions of Gunmaling debris flow, the fractal research of debris flow gully, the risk ratio assessment and the control of debris flow. The main contents include:(I)Introduction: mainly expounds the significance of geological disasters in debris flow; briefly explains the background and the basic situation of Gunmaling debris flow; analyses the current research trends in risk ratio assessment and control of debris flow; illustrates the research content and the technical route as well.(II)Basic situation and formation conditions of Gunmaling debris flow: respectively introduces the geological environment in the research area, formation conditions of Gunmaling debris flow and fundamental state on the investigation sites. The geological environment includes four parts of natural geographical conditions, layer lithologic characters, geological structure and seismic situation. The formation conditions of debris flow is expounded in detail from several aspects such as source conditions, topography conditions, climate hydrological conditions, vegetation cover and human engineering activities. In addition, the fundamental state on the investigation sites expounds quantitatively the locations, site properties, disaster history, scale, potential hazard and stability in a form.(III)Fractal research of debris flow gully: discusses the hazard level of Gunmaling debris flow by Fractal Theory. It also expounds briefly the definition of Fractal Theory, geometry fractal (regular and irregular geometric figures), calculation of irregular dimensions (to measure dimensions by Compasses method, studying Perimeter-area or Surface area-volume, Box-counting method, Sandbox fractal dimension measurement, Area-cyclotron radius, Converting method and Density method), and scale marking the unchanged intervals. In example calculation in the research area, the thesis makes fractal analysis of gullies (include major gully) by adopting 1:10000 topographic map, interpreting gully water system through electronic sand table function of Mapgis to form the 3D file of Gunmaling debris flow river basin gullies and the contour line nearby. Through calculation, the fractal dimension (namely slope absolute value) is 1.353, and the graphics in phase correlation coefficient is 0.98. The study results clearly show that Gunmaling debris flow gully is in the maturity period, and the debris flow gully with fractal dimension of 1.35 is of medium dangerous rate.(IV)Risk assessment of debris flow: on the basis of detailed field investigation and others'previous research work, this thesis calculate the risk ratio of debris flow by using Effect-measure grey correlation analysis and Extension method. In the first place, the selection of various specifications is analysed, which affect the risk ratio of debris flow, using grey correlation theory to compare selection sequence of the evaluation factors such as basin area S(km2), major gully length L(km), basin relative maximum altitude difference H(km), basin cutting density D(km/km2), basin bending coefficient B and maximum rainfall in 24 hrs R(mm). By the sequence of data dimensionless, correlation coefficient calculation and the calculation of correlation and effect degree, this thesis finds the effect degree of Gunmaling debris flow rk to be 0.4, which means the Gunmaling debris flow is in medium danger and major-medium scale debris outbreak is possible. Therefore, the control in recent period and close attention of the trend of debris flow are necessary. The extension assessment of debris risk is analyzed by selecting evaluation factors such as basin area S(km2), major gully length L(km), basin relative maximum altitude difference H(km), basin cutting density D(km/km2), basin bending coefficient B and maximum rainfall in 24 hrs R(mm) as the specification for evaluating the risk ratio. On basis of engineering practice and previous research work, this thesis hierarchies the risk ratio with single factor method and determine classical domain and field. By classifying the risk ratio as Super Risk N1, Major Risk N2, Medium Risk N3 and Light Risk N4, this research makes the correlation function values of the debris flow to assess the risk of the debris flow through calculation of the factors. The result of quality rank correlation calculation shows that the risk ratio of Gunmaling debris flow is Medium Risk. Hence, by using Effect-measure grey correlation analysis and Extension analysis to calculate the risk ratio of Gunmaling debris flow, both of the results are at the same level - medium risk, which also meets the conclusion from outdoor field investigation.(V)Control of debris flow: According to the basic situation and risk assessment of Gunmaling debris flow, this research suggests the adoption of check dam to block the debris flow. The location of check dam is selected by comprehensive analysis and investigation. Additionally, the dam's geometry size is determined on the base of geological profile. All the calculation results of the anti-sliding stability, anti-inclining stability and inner force meet the requirement of stability, and the reasonable construction suggestions are proposed. At the same time, other relevant methods are also put forward for the comprehensive control of debris flow.The research illustrates that by adopting the Fractal Theory, Effect-measure grey correlation analysis and Extension method, the risk assessments of the Gunmaling debris flow have the same result with the outdoor filed investigation. The gully formed under the non-linear dynamic role must possess some non-linear characteristics. For the revelation of the non-linear characteristics, the non-linear characteristic of the dynamic control can also be studied during the forming of debris flow gully. By statistical analysis of the debris flow and the non-linear relationship of forming measurement, the research studies the quantitative relationship among the factors for evaluation to get their respective fractal values by box counting method, which is of great meaning for the further study of the debris flow in this area. The study of risk ratio by Effect-measure grey correlation analysis and Extension method from multi-dimension and multi-factor with selected parameters of unlimited varieties and quantities can be suitable for different rock and soil engineering characteristics and take advantage of survey results of engineering to the maximum limit reasonably, which overcomes the previous shortcoming of the previous study of fixed factors classification, so as to get more practical assessment. The successful application of Effect-measure grey correlation analysis and Extension method has a significant meaning to the study of debris flow.At the same time, it is proved through study and engineering practice that check dam control engineering has a great many advantages such as the use of local materials, simple structure, convenient construction, and good economic effect. It can surely prevent the hazard of debris flow to save people's lives and property with the utility of other assisting methods.