Fracture Performance Of Baihetan Dam Concrete

The stability of a dam is one of the most important factors to ensure the normal operation of a hydropower station.Cracks will occur during the construction and service of the dam.As time goes by,the existence and expansion of cracks will have a greater impact on the stability of the structure.Therefore,the research on the fracture performance of dam concrete has important engineering significance for dam construction and later maintenance,operation and prevention.Based on this,this article mainly conducts research from the following aspects,and draws the following conclusions:1.The specimen height from 750 mm to 2250 mm full grade wedge split tensile specimen and The specimen height from 200 mm to 600 mm wet sieve wedge split tensile specimen at the age of 18d,28d,90d and 180d in winter batch W and spring batch S casting on site at Baihetan were selected to conduct fracture tests.The initiation toughness,unstable toughness,and fracture energy of the specimens are calculated through experiments,so as to explore the size effect of the concrete fracture parameters of the Baihetan Dam and the change trend of the fracture performance during the observation age.The results show that there is no size effect on the fracture toughness for the full grade specimen when the specimen height is greater than 1.5 m.When the initial fracture height ratio of the specimen is within the range of 0.1-0.5,the fracture toughness and instability fracture toughness of the specimen are not size effect.For the wet screen specimen,when the specimen height is greater than 0.4m,the fracture parameters are constant and there is no size effect;when the specimen’s initial seam height ratio is in the range of 0.1-0.4,the instability fracture toughness and fracture energy have no size effect.When the initial seam height ratio of the part is in the interval of 0.1-0.5,the fracture toughness of the initiation has no size effect.When it exceeds the limit range,as the initial seam height ratio increases,the fracture parameters also decrease.During the observation period,the fracture parameters of the fully-graded and wet-screened concrete gradually increased,and the growth rate was the largest during the 18d to 28d age period.As the age increased,the growth rate of the fracture parameters gradually decreased.2.The digital image correlation method is used to observe the fracture process area and the crack propagation trajectory of the full grade dam concrete.The high-precision camera is used to capture the relative displacement changes of the speckle on the surface of the specimen,and the displacement field is extracted for processing and analysis.The crack opening displacement and crack propagation trajectory curve at one observation time.From the final output curve,it can be seen that due to the existence of large aggregates,the opening displacement and crack propagation length are not linear at the initial stage of crack propagation,and the relationship between the two is linear in the end as the cracks gradually propagate;at the moment of peak load,the subcritical propagation length of the cracks Aac to the ratio of the initial ligament length(H—a0)has a certain relationship with the size of the specimen.When the height of the specimen reaches 1500 mm and above,the value ofΔac/(H—a0)is stable at about 0.19,and the slit height ratio has no effect on Δac/(H—a0).The Δac/(H—a0)of the 750 mm specimen is stable at 0.325.3.The finite element program is used to perform numerical simulation on all specimens in this experiment based on the Type Ⅰ crack propagation criterion.The simulation results fit well with the experimental results,which can reflect the actual crack propagation situation.The relative error between the peak load calculation results and the test results of the full-graded specimens is about 7%;the wet screen specimens are more susceptible to external factors,and the relative difference between the peak load calculation results and the test results is about 20%.At the same time,in order to describe the change of concrete resistance during the crack propagation process,the KR resistance curve is calculated based on the simulation results of this number of times.The results show that when Δa/(h—a0)of the Baihetan dam concrete is less than about 0.75,the KR resistance curve increases as the height of the specimen increases.When Δa/(h—a0)is greater than about 0.75,the KR resistance curve decreases as the height of the specimen increases;when Δa/(h—a0)is less than about 0.75,the KR resistance curve increases.At about 0.835,the KR resistance curve decreases as the seam height ratio of the test piece increases.When Δa/(h—a0)is greater than about 0.835,the KR resistance curve rises with the increase of the initial seam height ratio of the test piece.