STUDY ON STRENGTH WEAKENING OF CARBONATE ROCKS WITH WATER LEVEL FLUCTUATING IN WUXIA OF THREE GORGES RESERVOIR AREA

Since the impoundment to the elevation 175 m above sea level in the Three Gorges reservoir area, the carbonate karst bank slopes of the Wuxia area have been deteriorating strongly under the periodic water level fluctuations, and a large number of geological disasters have been new-born or developed rapidly. This paper aims to study the law of strength weakening of carbonate bank slopes under cyclical water level fluctuations. It conducted researches from the physical structure, chemical properties, and mechanical properties of the rock(or rockmass). Six most representative reservoir banks in Wuxia area were selected, where in-situ rock rebound strength test, in-situ point loading test and indoor wet-dry cycle test, rock mineral composition analysis, rock apparent fissures scanning test were carried out. Through these tests, the strength weakening data of carbonate rocks(or rockmass) under the condition of fluctuating water were obtained. The results of in-situ rock rebound strength test show that the strength weakening rate of in-situ rockmass is 0.3% to 25.9% per year. The results of indoor dry-wet cycle test show that after 50 dry-wet cycles, the strength weakening rate of rock is 16.4% to 23.9%, and the deformation modulus weakening rate is 17.1% to 24.9%. The results of mineral composition analysis show that the dissolution loss of CaO is 0.5% to 5.6% after 100 cycles. Through the scanning results of rock apparent fissures, new signs of deformation were found on the rock surface, the water erosion marks were aggravated, the solution pores were enlarged and the cracks were extended. Based on the dry-wet cycle test data, the rock strength weakening function is established, and the exponential function weakening calculation model at each point is deduced. Then such functions can be used to predict the numerical relationship between rock strengths, deformation modulus and water level cycle times. Taking the Quzitan dangerous rock as an example, the catastrophic effect of rock strength weakening is discussed. The work methods and the data obtained from the research can provide data and technical supports for the prevention and control of the bank slope deterioration zone in the Three Gorges Reservoir area.