The middle-isolation piers is one of the key structures of permanent shiplock of Three Gorges Project on Yangtze River. China. This paper deals with the study on forecast deformation of middle-isolation piers of the second shiplock chamber. The time series analysis and grey system theory are used to predict the tendency of rock displacement. The comprehensive results are obtained and presented in the paper.
The Three Gorges Project (TGP) is one of the most important water conservancy projects in the middle stream of Yangtze River, China. The dam site is located in the middle sector of Xiling Gorges of the river near Yichang City. The concrete gravity dam, with the width of 175m and length of 2335m, is being built on hard and intact granite, 40km upstream from the Gezhouba dam. The reservoir with total capacity of 39.3 billion m3 will cover an area of 1084km2. The power station will be equipped with 26 sets of machine units with the total capacity installed of 18.20MW. The permanent shiplock for navigation, as one of dominant structures of the project, is constructed at the left bank in an excavated granite rock mass across the ridge of Tanziling Hill. The structure consists of a double-line continuous 5 stage shiplock. After excavation, the middle-isolation piers (MIP) with width of 60m is kept between two shiplock chambers. After excavation, the cutting of rock mass arranged from top to depth forming a high and steep slope with the maximal height of 170m and average angle of 63°. Especially for MIP, the sidewall of chamber is vertical up to 60m. Therefore, the stability and deformation law of MIP after excavation and during operation will be of vital importance the safely of shiplock, so as far the whole project in operation. In order to research these problems connecting with shiplock, many relevant researches based on different methods, such as field investigation, evaluation of rock quality, in-situ tests, physical and numerical simulations etc were carried out one after another, and a number of considerable important achievements are obtained (Chen D.. 1999: Chen Changyan, Wu Xingchun et aI., 1996; Wu Xingchun & Wang Sijing, 1996.) Formability of rock mass of' the dam foundation and high slopes. The stability and deformation law of rock mass of the MIP are seldom taken into account in these achievements. The present researches in this aspect are limited in the quantitative analyses such as geological investigation, rock mass structure and cause analysis etc. (Chen D., 1999: Yang Qigui & Wang Dongzhen, 1999). All these achievements are of considerably Significance, and play an important role in the construction of TGP. In the course of excavation, the cracks were found on the top of concrete surface of the MIP, especially in the part of the second shiplock chamber. In order to analyze the rock deformation, the time series analysis and grey system theory were performed to predict the tendency of rock displacement. In this paper, the second shiplock chamber is taken.