| China has broad karst regions, various types of karst developed, thus involving extensive and complex karst-related engineering and environmental problems. Controlled by the regional structure, groundwater, ancient geography and ancient climate environment, corrosion phenomena was well developed, formed different scales of dissolution space in Jurassic continental red beds clastic rock formation in Guanyinyan Hydropower distribution area, Jinsha River. This dissolution phenomenon different with the carbonate karst erosion in traditional sense, also different with the rock salt, gypsum rock dissolution effect in groundwater. As a special karst phenomena, this kind of karst developed in the red beds of the continental red clastic is due to conglomerate dissolution and calcium loss of the sandstone, formed huge corrosion hole that affects the stability and deformation of the dam foundation as well as the seepage project significantly.Based on the study of the regional geological background, the palaeogeographic evolution history of rock after the Jurassic, the stratigraphic features, and the evolution history of the valley near the dam of the Jinsha River, combined with the description of the rock dissolution type, the spatial distribution characteristics, the properties of rocks and the characteristics of dissolution of calcareous sand (gravel), summarized the karst development pattern, the mechanism of karst erosion of calcareous sand (gravel), take the rock mass classification and the permeability classification of the calcareous sand (gravel) as the main work, analysis the seepage deformation of the dam foundation rock and its influence to the project. This paper proposed some new understandings in the red beds karst formation mechanism analysis, characteristics and research methods as follows:(1) Based on the investigation, described the corrosion morphology of the calcareous sand (conglomerate), corrosion types, spatial distribution characteristics, properties of rocks and characterization of micro-corrosion, calculated erosion capacity and carried out corrosion contrast testing research, analyses the solubility of the calcareous sand (gravel) rock quantitatively of Guanyinyan hydropower dam, orientated the calcium dissolution phenomena developed so deep underground (maximum depth of 150m), with such scale (the largest-diameter 7.91m) that : different from other leaching dissolved effect in red beds formation in the salt rock, gypsum rock in the grounwater, the semi-karst phenomena developed in the Jurassic Panxi Shedian formation is between red beds clastic rocks and carbonate rocks - the dissolution strength is less than carbonate rocks while strong than clastic rocks, the dissolution behavior is similar to limestone.(2) Based on the analysis of the groundwater circulation system under the control of structural, combined with the water chemistry, isotope, water chemical thermodynamics and ESR dating methods, restorated the groundwater circulation and the calcium dissolution history, combined with the valley landscape and valley evolution history of the dam area, Jinsha River, analysis formation mechanism of its dissolution systematically, and deduced the calcareous sand (gravel) rock dissolution process, concluded that: after Jinsha River valley into the modern era, under the control of regional groundwater circulation system, and by the shallow groundwater circulation near the surface and the role of water impact, the erosion time of calcareous sand(gravel)is during 5.8~12.5×104a in study area, corresponding to the historical development of the Jinsha River valley, between the development period of the terraceⅡand terraceⅢ. At last calculated the corrosion potential.(3) Combination with the individual indicators data of the adit, drilling velocity, RQD and other comprehensive index, according to hydroelectric project adjacent geological classification, rock mass classification and RMR classification methods, conducted a comprehensive classification of the dissolution rock under the dam foundation, compared the control role and the weaken effect of the dissolution of the rock mass quality, presented the discount rate of velocity values of corrosion damage for different degrees of calcareous sand (conglomerate).(4) According to the dissolution type, the spatial distribution characteristics and dissolution characteristics of the calcareous sand (gravel) rock, combined with various lithological association of calcareous conglomerate, sandstone, siltstone and mudstone rock, analysis the rock permeability test and field pressure test for four grades erosion degree, the paper proposed the permeability for difference lithologic association under the effect of dissolution of Guanyinyan power project area for the first time, and put up predictive evaluation of the spatial distribution of permeability for the calcareous sand (conglomerate).(5) Study the seepage stability of the rock mass under of dam foundation. Simulation and contrast the groundwater seepage field of project area under natural conditions and under the construction, prediction and evaluation the seepage control measures. On this basis, identified the infiltration deformation of the dam foundation rock mass, analyzed the penetration failure mode under high head pressure. Summarized the domestic and international experience of red beds hydropower project that exist large number of corrosion phenomena and strong dissolution of calcareous sand (gravel) rock foundation, proposed seepage system and the drainage system, the drainage facilities is essential to improve the penetration stability of soft rock foundation.
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