三峡库区瞿塘峡至巫峡段消落带灰岩质量劣化特征OA北大核心

The study area encompasses the section of the Three Gorges Reservoir area from Qutang Gorge to Wuxia Gorge,stretching from Baidicheng in Fengjie county,Chongqing City in the west to Guandukou of Badong county in the east.The lithology of this area is predominantly composed of Permian and Triassic carbonate rocks.Since the impoundment of the Three Gorges Reservoir in 2008,multiple geological disasters have occurred in the carbonate rock slopes.The periodic changes in reservoir water levels have exacerbated rock mass degradation,leading to the development of new geological hazards that pose a significant threat to the geological safety of the reservoir area.Rock mass degradation is primarily driven by water level fluctuations,dissolution,and stress changes,involving complex interactions of physical erosion and chemical dissolution.Existing research has focused on obtaining physical and mechanical parameters of rocks,with limited attention to the original structures,structural degradation,microscopic mechanisms,and prolonged evolution patterns.These geological factors are crucial in influencing the development of geological hazards in the Three Gorges Reservoir area.This study focused on limestone in the study area to reveal the patterns and mechanisms of rock mass degradation,aiming to provide technical support for the prevention and control of rock slope disasters in the Three Gorges Reservoir area.This study also employed in-situ testing methods such as rebound strength of rock masses and acoustic wave velocity,along with laboratory experiments including dry-wet cycling and CT scanning,to analyze the degradation of rock mass(rock)quality,changes in strength,and microscopic degradation patterns. The results show,(1)After 13 cycles of reservoir water level fluctuations(2008-2021),the rebound strength of rock mass surfaces in zones of water level fluctuations decreased by 11.15％-24.81％,with an annual average reduction rate of 1.01％-2.26％.(2)Acoustic wave velocity and borehole television images reveal that the rock mass is more fractured near the surface,with densely developed fissures.Overall,the shallower the rock mass is buried,the higher the rate of decrease in acoustic wave.(3)After each dry-wet cycle,the longitudinal and transverse acoustic wave velocities of the rock samples decreased by 0.08％-0.15％and 0.26％-0.65％,respectively.The uniaxial compressive strength decreased by approximately 0.94％,and the deformation modulus decreased by about 0.38％.(4)After 50 dry-wet cycles,the average reduction rates of longitudinal and transverse wave velocities were 5.74％and 0.52％,respectively,while the uniaxial compressive strength and deformation modulus decreased by 0.94％and 0.38％,respectively.(5)CT scans of the rocks showed that under water-rock interaction,the internal pores of the rock mass continuously increased,and the integrity of the rock mass declined significantly,indicating obvious degradation. Conclusions are drawn as follows,(1)The degradation of rock mass quality is closely related to the distribution of fissure surfaces and the depthes of the rock layers.Defects,such as fissure surfaces,are controlling factors for the degradation of rock mass quality.This degradation is not uniform;it occurs more rapidly near the surface and at a slower rate at greater depths.(2)Physical scouring erosion and chemical dissolution,both caused by reservoir water flow,are significant factors in the degradation of rock mass quality in the drawdown zone.Physical scouring erosion occurs more rapidly and is more pronounced than chemical dissolution.