Selection Of Red Sandstone Chemical Reinforcement Materials And Optimization Of Proportionin Drawdown Area During The Course Of Three Gorges Reservoir Operation

The main reason for the deterioration of the strength of the rock and soil after the periodic "wet and dry" alternating action in the fading zone during the operation period of the Three Gorges Reservoir is the physical and chemical reaction that occurs when the reservoir water enters the rock and soil under the action of osmotic pressure.In this paper,the existing "Triaxial Test System for Soft Rocks in Water-loss Zone" has been modified by the research team.The modified system can make the alternation of osmotic pressure,bank stress and periodic "wet and dry" alternate before and after the reinforcement of the red sandstone in the water-loss zone.Under the action of "wet and dry" alternating environment simulation and strength and water absorption test test research;optimization of the chemical reinforcement materials of the red sandstone in the fading zone of the reservoir during operation and optimization of its composition ratio,coMParative analysis of the strength and strength of the red sandstone before and after reinforcement The improvement effect of water barrier performance verifies the rationality of chemical reinforcement materials and their optimal ratio.The specific research content and research results are summarized as follows.(1)Through the "Triaxial Test System for Soft Rocks in the Riparian Zone"already owned by the research group(this system can simulate the environment where the rock stress on the bank slope and the periodic "wet and dry" alternation in the reservoir run-off period are combined)The water flow channel has been modified to resist chemical corrosion,adding a chemical osmotic pressurization device that provides osmotic pressure,which becomes a set of osmotic pressure,bank slope stress and periodic "wet and dry" alternation that can simulate the rock in the sinking zone of the reservoir during operation The multi-functional test and test system that works together-"Testing system for rock macro-mechanical strength of the reservoir bank slope sink zone".The system was used to carry out alternating environmental simulation test of "wet and dry" red sandstone in the fading zone,and to determine the indoor "wetting"time of 1 hour and "7.5 hours" of medium weathering red sandstone in a reservoir operation period,strong weathering The "wetting" time in the red sandstone room is 0.7 hours and the "drying" time is 6 hours.(2)Under the conditions of 0.15MPa osmotic pressure and different confining pressures,the peak compressive strength,cohesive force,internal friction angle,point load strength and water absorption rate of natural red sandstone are presented with the increase of the number of wet-dry cycles The trend is that the decline rate is larger first,and then the decline rate gradually slows down to a stable trend;After 8 "wet-dry"alternations,the cohesiveness,internal friction angle,and water absorption rate of medium-weathered red sandstone deteriorated by 62.67%,16.15%,and 256.60%,respectively,and the point load strength and water absorption rate of strongly weathered red sandstone deteriorated,respectively36.48%,134.70%.(3)Determine the modified polyurethane-nanocomposite material as the most suitable chemical strengthening material for the red sandstone in the sinking zone.The optimized ratio is 4.27%of sodium silicate,4.16%of triethylamine,and 4.94 of dibutyl phthalate.diisocyanate 42.12%,polypropylene glycol 25.15%,silane coupling agent 7.61%,nano-TiO212.56%.(4)After the modified polyurethane-nanocomposite material is used to optimize the distribution ratio of the weathered red sandstone in the sinking zone,its peak compressive strength,cohesion,The internal friction angle,point load strength and water absorption rate all gradually decrease with the increase of the number of wet and dry alternations,but the decrease is very small coMPared with before the reinforcement.After undergoing 8 "wet-dry" alternations,the cohesiveness,internal friction angle,and water absorption of the weathered red sandstone deteriorated by 13.06%,6.58%,and 27.16%,respectively,and the degradation amplitude was reduced by 79.16%,61.13%,89.41%;the load strength and water absorption of strongly weathered red sandstone points were degraded by 12.17%and 41.58%,respectively,and their degradation ranges were reduced by 66.63%and 69.13%,respectively.It shows that the modified polyurethane has a good effect of improving the strength and water barrier performance of the red sandstone in the fading zone.(5)After the modified polyurethane nano-material is applied on the surface of red sandstone,the siloxane molecules generated in it form a water-repellent film on the surface of the red sandstone to prevent the reservoir water from entering the red sandstone body under the action of osmotic pressure;Polyurea makes the film have certain corrosion resistance and toughness,preventing the micro-shrinkage and expansion of the clay minerals in the red sandstone under the action of periodic wet-dry alternating damage to the surface film;a large number of sodium carbonate crystals combined with siloxane molecules make the internal structure of the film Dense,with a certain strength.