| Arch dam has such a long history of development that as early as the people of Old Roman have used the principle of arch to build dams. However, just after the Second World War there were many arch dams built. According to the statistics by International Dams Committee in the year of 1988, by the end of 1986, dams with a height of more than or equals 15m had reached 1608 of those had already been built, which was 4.4% of the total number of dams all over the world. Our country has the most arch dams in the world. By the statistics in 1992, dams higher than 15m which we had built was 753. With the development of water conservancy and hydroelectricity engineering constructed in our country, especially in the southwest, there are many arch dams appeared, the height, scale, rapid flood quantity of these dams is the biggest in the world, such as Xiaowan, Jinping, Xiluodu etc.The stability analysis of the rock masses at dam abutment is prior to its designs, constructions and operations. From related data both at home and abroad, we know that most of dam failures were caused by destabilization of rock masses at dam abutment. Under the appropriate engineering geology conditions, arch dam used by most people is economical and reasonable, safe and reliable. However, it is built on the basis of the stability of rock masses at dam abutment. Therefore, in the design of arch dams, the rock masses at dam abutment must be explored carefully and its stability must be analyzed thoroughly.The most popular form of rock masses destabilization at dam abutment is sliding destruction happens after the rock masses at dam abutment are subjected to forces. This situation generally happens on obvious slip crack surface of rock masses, such as faults, joints, fractures, weak interlayer and so on. Another case is that when there are big weak belts or faults in the downstream rock masses of dam, the engineering is dangerous because of adverse stresses in the dam produced by extra deformation, even if the stability against sliding of the rock masses at dam abutment can satisfy requirement. If necessary, appropriate reinforced measurements should be taken.At present, there are four methods which evaluate the stability of rock masses at dam abutment both at home and abroad, such as:â‘ deterministic analysis method,â‘¡uncertainty analysis method,â‘¢geology mechanics models,â‘£application of composite algorithm. During all these methods, the limiting equilibrium method of rigid body is the main method to analyze the stability of rock masses at dam abutment for many years. It is the method that engineers have become familiar with and accustom to, and defined by design codes in most countries. It has explicit concept and can be used simply. Besides, it has long term practice experience. However, it is somewhat rough in theory and need to be developed consistently at present. This paper improves the calculation accuracy through optimization of calculation methods on the deadweight and uplift pressure of slide blocks in order to develop the limiting equilibrium method of rigid body.With the development of computer technology, numeric method of stability analysis of dam abutment has developed quickly. Its calculation speed and accuracy have been improved enormously. The implementation of numeric method through procedures scheduled by computer is emphasized in the fourth part of this paper. Generally speaking, a good calculation should be easy to be made into procedures, and it will save the time and space. While a good calculation mode ought to analogue actual engineering situation accurately. During the sliding stability analysis of dam abutment of arch dams, relatively accurate calculation of various forces is the key to estimate the stability of rock mass at dam abutment. Under the current calculation theories and conditions, trying to improve calculation accuracy is theme of this paper. In the fifth chapter, the sliding stability analysis on the whole process of dam abutment is instructed briefly, and the main factors influencing calculation result or accuracy are analyzed combing with engineering of Gaixia Arch Dam. Besides, the method of improving calculation accuracy on the deadweight and uplift pressure of rock masses is provided, procedures are scheduled, and the stability of slide blocks is calculated on the both left and right bank of Gaixiaba Arch Dam.Through the stability analysis of slide blocks on both left and right bank and the flat stability analysis of Yunyang Gai-Xia-Ba Dam Abutment , the conditions of site on which Gaixia Arch Dam will be built on located in Yunyang county are described as following:(1)The drafted dam site locates in the gorge areas of Laoya gorge where the valley is narrow and terrain is intact. Thus, it is excellent dam site to build concrete dams.(2)The bedrock of the dam site is limestone of the fourth segment of Jialingjiang group of T1. It belongs to hard rock to medium-hard rock, and it has good integrity and equality. The effect of erosion to rocks is slight, the fault in the area of buildings is few and its scale is small. There is no low-angle fault at both banks of dam abutment and few low-angle joint. Therefore the anti-slide stability analysis of dam abutment is good. Through initial analysis, both the stress of dam body and the anti-slide stability satisfy the requirements in codes. In a word, the dam is safe, therefore, it is completely feasible to build the dam on the site.(3)Both thickness of rock mass in weathering zone and relief zone is not big, and the pervious ratio of dam base are generally weak to medium. Both the management of geology defect on dam base and the management of leakage control engineering on dam base are regular scheme.(4)The bedrock of dam site is hard, the rock mass has good completeness and equality, and both thickness of rock mass in weathering zone and relief zone are not big. The surface under which the dam is built on varies from weak weathering rock at middle and bottom to slight weathering rock on upper part. Relief zone in the scope of dam base has been excavated. So the dam base can satisfy the building requirements.
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