Study On Response Pattern And Chaotic Characteristics Of Xierguazi Landslide By Reservoir Level Fluctuation

With the fast development of hydroelectricity construction in southwest C hina, problems of large talus slide stability are becoming increasingly serious, reservoir filling and cyclic fluctuation of reservoir level are the main inducement to resurrection of old landslide. Therefore, the issues of old landslide resurrection mechanism, responses and monitoring data mining by reservoir level fluctuation have attracted the scholars' attention. Xierguazi landslide is located on the right bank of Heishui river and 3km away from Maoergai dam, it's a typical loose pieces of rubble mound Talus landslide of Maoergai reservoir area with the total volume of 13.41 million m3. The Beier tunnel which parallelly passes across the lower part of the landslide and the new Mawoji town next to the landslide become the most direct threat objects. After the Wenchuan earthquake, with the first water storage of power station dam, the front of the old landslide has obviously deformed. Therefore, studying the response regularity of the landslide by reservoir level fluctuation and excavating the evolution information of the landslide contained in monitoring data are significant to the disaster prevention and mitigation in reservoir area and the guarantee of normal operation of the reservoir.On the basis of the research on Xierguazi landslide, the geological engineering conditions of the landslide and the formation and resurrection mechanism of the landslide are analyzed. After fully grasping the geological model of the landslide, the displacement time series of thirteen monitoring points on three monitoring sections are taken as the study clue to analyze the deformation response regularity in every direction of the landslide by reservoir level fluctuation by using statistics, drawing and bivariate correlation analysis. Introducing the fuzzy pattern recognition and partitioning the sensitivity of the landslide by adopting the fuzzy pattern recognition model. The phase space of displacement time series is reconstructed, and the chaotic characteristic of the landslide is distinguished by multiple judgment. At last, based on the breach viewpoint, comprehensively considering landslide deformation response regularity, sensitivity partition and the research results of chaotic characteristic, the suggestions of monitoring optimization are put forward.The main conclusions got from the study of this thesis are as follows:(1) Starting from the engineering geological characteristics of the landslide, and analyzing the morphology characteristics, the change of the surface deformation phenomenon and the material composition, we conclude that the major influential factors of the formation of the landslide include rapid sapping of river, rock stratum with high dip toward river and soft and hard layer alternate, and the major influential factors of landslide resurrection are the steep rise of reservoir water level and “shook loose effect” by earthquake.(2) Based on analysis of monitoring results of the displacement monitoring points on the surface, we summarize the deformation response regularity in every direction of the landslide. With the bivariate correlation analysis, we arrive at that the deformation of the most monitoring points in area B is not remarkably related to reservoir level fluctuation except the monitoring point X04 which is close to area A. The deformation in area A is closely related to reservoir level fluctuation. The deformation on downstream side of area A is greater than upstream side in the process of the rising of the water level, b ut it doesn't appear to be much different in the process of the dropping of the water level.(3) Using the fuzzy pattern recognition to partition the sensibility of the change of the landslide displacement field with reservoir level fluctuation, the results indicate that the sensitivity of vertical displacement in area A(frontal part of the landslide) is from sensitive(area A1, area A3) to very sensitive(area A2) in the process of reservoir level fluctuation, and with the increase of slope elevation, the sensitivity in area B is from general to insensitivity except the area on the downstream side which is close to area A, with an obvious stepped distribution regularity.(4) Based on the reconstruction of the phase space of the landslide displacement time series, by calculating the correlation dimension(D2) and the largest lyapunov exponent(?max), we judge the chaos characteristics of the landslide by multiple judgment. The results show that all the four monitoring points in different sensitive areas have fractional D2 and ?max is larger than zero, indicating that the landslide enters the chaos state with long-term unpredictability. We can see from D2 and ?max of different sensitive points that D2 and ?max have risen with the development of the landslide deformation(sensitivity increases), meaning the chaotic degree become more and more obvious, which is related to that the landslide is acceleratingly slumping.(5) According to the breach viewpoint, and in accordance with the point that the area which has more sensitivity and higher chaos degree, contains more quantity of information outputted in the process of system development, optimization suggestions for the landslide monitoring system are put forward. Through the thinking of the question of monitoring optimization of Xierguazi landslide, the idea of landslide monitoring optimization which is based on the feedback of monitoring data by reservoir level fluctuation is put forward.