Study On The Deterioration Characteristics Of Rock Mass On The Bank Of Flame Stone Reservoir In The Three Gorges Reservoir Area

The periodic rise and fall of the water level in the Three Gorges Reservoir Area leads to continuous damage and deterioration of the rock mass on the bank,affecting the stability of the bank slope,leading to geological disasters such as landslides,collapses,and dangerous rock masses,seriously endangering the life and property safety of the Yangtze River waterway and coastal residents.This article takes the Three Gorges Reservoir Area’s Flaming Stone Reservoir Bank as the research object,conducts on-site survey and investigation on its deterioration phenomenon,conducts in-situ and indoor tests,and uses a combination of macro and micro methods to analyze the deterioration phenomenon from the aspects of rock structure,structure,strength,mineral composition,pore structure,etc.,summarizes the deterioration law,explains the reasons for the formation of the deterioration phenomenon,and reveals the deterioration mechanism of the Flaming Stone Reservoir Bank’s rock mass.The main content is as follows:（1）Taking the bank of the Flamestone Reservoir as the research object,the field survey was carried out.The bank of the Flamestone Reservoir is inclined dip slope slope,and the formation lithology is mainly medium thick limestone and marl of Daye Formation（T₁d）of Lower Triassic System and chert bearing nodule limestone of the second member of Jialing River Formation（T₂j²）of Middle Triassic System.According to the deterioration phenomenon,it can be divided into three categories:bedding type deterioration,fault type deterioration,and dissolution type deterioration.（2）Water absorption tests,wave velocity tests,porosity tests,thin section identification,point load tests,and uniaxial compression tests were conducted on samples taken from the bank section of the Flame Stone Reservoir.Research was conducted on the basic physical properties,mineral composition,and mechanical properties of rocks.The results indicate that the shallow surface rocks on the bank of the Flame Stone Reservoir are strongly subjected to dry wet cycling;There is a good correspondence between rock porosity,water saturation rate,and wave velocity;The larger the porosity,the higher the saturation rate,and the lower the wave velocity.Thin section identification shows that the main mineral components of the igneous rock bank are calcite and dolomite,followed by clay minerals,chert and opaque minerals.Through thin section identification,the reservoir bank lithology can be divided into four types:chert nodule limestone,limestone,dolomite and marl;Among them,flint nodule limestone,limestone,and dolomite have slightly deteriorated in strength and still belong to hard rock;The strength of marl at the fault and interlayer has deteriorated to 47%,which has become weak interlayer.The calcite vein in the rock has a certain influence on the mechanical properties of the rock,and the rock mechanics strength of the calcite containing vein is lower than that of other rocks.Under uniaxial compression,the failure mode of the standard cylindrical rock sample in the dissipation zone of the Flame Stone Reservoir bank is splitting failure,and the failure feature is a vertical crack that runs through the sample;When there is calcite vein,fracture failure will be formed along the interface between calcite vein and rock or inside calcite vein;Calcite vein,as the weak structural plane of rock,affects the strength and failure characteristics of rock.（3）The internal deterioration of the rock mass was investigated using borehole imaging technology and borehole wave velocity technology.The results show that the shallow rock mass is relatively fragmented with low wave velocity,and the integrity of the deep rock mass is good.The wave velocity is close to the rock wave velocity,and the rock mass degradation mainly occurs in the shallow surface of the rock mass.The deep rock mass is less affected by the degradation,which is due to the surface rock mass being more strongly affected by temperature changes,weathering,mechanical erosion,and dry wet cycling.According to the distance between the interior of the rock mass and the surface of the rock mass,the interior of the rock mass can be divided into fractured zone,damaged zone,and original rock zone in sequence.（4）Based on nuclear magnetic resonance technology,the evolution law of pore structure of rocks under dry wet cycles was studied.The results showed that as the number of dry wet cycles increased,the porosity of rocks continued to increase,the total degradation degree continued to increase,but the stage degradation degree continued to decrease.Finally,the pore structure tended to stabilize.The evolution law of pore structure is that small pore size and small pore throat change to medium pore size and medium pore throat;Simultaneously accompanied by the formation of new secondary small pore sizes and small pore throats.Compared to intact rocks,joint fissures can exacerbate the influence of dry wet cycles on rocks,and the degradation amplitude of rocks containing joint fissures will be greater.（5）Based on on-site investigation and indoor and outdoor test results,the degradation mechanism of the rock mass on the bank of the Flame Stone Reservoir was studied.Under the periodic rise and fall of reservoir water level,the fabric,joint and fissure structural planes,lithology,and mineral composition of the rock mass control the different deterioration phenomena of the rock mass.For layered rock masses,the phenomenon of layer by layer erosion and deterioration along the bedding plane will be formed under dry wet cycles,mechanical erosion,and fracture cutting;If the lithology of the position where the bedding is developed is pure limestone,the groove type deterioration along the bedding plane will be formed due to the differential dissolution of calcite and dolomite.When the rock stratum is marl and the primary structural fissures are relatively developed,marl will significantly deteriorate the shear strength of the rock stratum after mechanical erosion,dissolution and weathering,and slip along the surface under the gravity load of the upper rock mass to form a deteriorated fault.When there are cracks in chert nodule limestone and limestone stratum due to tectonics,karst water will infiltrate and flow out along the cracks.Under the long-term dissolution of karst water,the calcareous part of the rock will be taken away by the flowing reservoir water after being partially dissolved,leaving insoluble siliceous part.The karst water will circulate in the cracks for a long time.The rock mass will be dissolved,so that the cracks will continue to expand and extend,forming corrosion type deterioration.