The mechanism of strong seismic cracking of concrete dams under the coupled action of salt immersion, dry-wet cycle, and freeze-thaw cycle
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Abstract:
In recent years, China's hydropower resource development has been steadily progressing to high altitude and cold areas. Alpine areas have more complex conditions than mild climate areas, such as large temperature differences, extremely low temperatures, strong radiation, strong wind, and dryness. These complex conditions run throughout the dam's entire life cycle of construction, water storage, and operation, directly affecting the dam's safety and durability, introducing many safety risks such as cracking to the concrete dam and putting the dam's long-term operation safety to the test. Therefore, it is necessary to explore the law of strong seismic failure of concrete dams in the whole life cycle under complex cold conditions.The dynamic response analysis of dam is carried out by material deterioration test and numerical simulation method. Salt erosion, dry-wet cycle, and freeze-thaw cycle deterioration tests were carried out for different positions of the dam body. Through checking the environmental impact report of Yalong River hydropower station, content of each ion in the water can be obtained to configure the salt solution. To shorten the failure time of the specimen, a 10-fold concentration of complex salt solution is configured in the laboratory. The concrete specimens were successively put into the sulfate resistance cycle testing machine and freeze-thaw testing machine for salt immersion-dry and wet-freeze-thaw cycle test, first 4 salt immersion + dry and wet cycles (soaking for 15 h, drying at 80 ℃± 5 ℃ for 9 hours, which is a salt immersion-dry and wet cycle), taking 4 days, and then 25 freeze-thaw cycles (freezing at ?18℃±2 ℃ for 2 h, melting at 5 ℃±2 ℃ for 2 h, for one freeze-thaw cycle), taking 4 days. A full salt-dip-wet-freeze-thaw cycle, or large cycle, takes 8 days, and the compressive strength, mass loss, and kinetic elastic modulus of concrete are measured after each large cycle. Based on the material test results, the numerical model of gravity dam was established by ABAQUS finite element software, and the element type adopted 4-node bilinear plane stress quadrilateral reduced integral element (CPS4R), with a total of 23,189 elements in the model, and the hydrodynamic pressure was applied in the form of additional mass and artificially excited. The occurrence, development, and collapse failure of concrete dams under strong seismic stimulation before and after the deterioration of salt-immersion-wet-freeze-thaw cycles of concrete materials is simulated.The research showed that: (1) The three factors of salt leaching erosion, dry and wet cycle, and freeze-thaw cycle all lead to concrete deterioration and reduce mechanical properties to varying degrees. The combination of three factors causes the most serious deterioration of concrete, followed by the impact of the freeze-thaw cycle. (2) In the vicinity of the normal water storage level upstream, due to the coupling of three factors, the deterioration of concrete here is significant, and its strength, the elastic modulus and the mass loss decrease. (3) The deterioration of concrete reduces the seismic bearing capacity of the dam structure, and the cracking acceleration decreases by 19.53%. (4) The deterioration of concrete materials has changed the stress distribution pattern of the dam body and even caused collapse.When designing gravity dams in alpine regions, the durability of concrete requires special consideration. During the life cycle of a dam, it is necessary to take timely and appropriate maintenance measures for the vulnerable location of concrete.
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