Study On Equivalent Strength Of Crack Director And Fracture Of Layer Surfaces In RCC Dam

The construction technique of RCC (Roller Compacted Concrete) dam combines advantages of concrete dam and earth-rock dam and has been widely used in hydraulic engineering. However, there are still many problems to be deeply studied in the design and construction of RCC arch dams and RCC gravity dams. For RCC arch dams, the thermal crack is one of the most dangerous problems. In order to avoid the disorder temperature cracks in RCC dams, crack directors are usually adopted in most RCC arch dams domestically and abroad. The right understanding of the equivalent strength, fracture properties of crack directors and the rational design of their sizes and location in arch dams is the precondition of thermal stress analysis of RCC arch dams. However, there are still some problems in the research of equivalent strength of crack directors at present. For RCC gravity dams, the number of RCC layer surfaces continuously increases with the height of dams. At present, there are many studies on strength properties of RCC layer surfaces but few studies on fracture problem of RCC layer surfaces. With the support of National Natural Science Foundation of China-Study on equivalent strength of crack directors of RCC arch dam, this paper focuses on researches as follows:(1) Fracture properties of RCC are initially studied by using three-point bending tests and axial tension tests. Upon the analysis of three-point bending tests results of RCC, it is found that fracture toughness of RCC has size effect rule, which is similar to that of common concrete. Upon the comparison of fracture toughnesses for different types of RCC specimens, it is concluded that nominal fracture toughness of three-point bending specimen is equaled to that of axial tension specimen, the heightof which is twice as that of the three-point bending specimen. The size effect formula suited to RCC nominal fracture toughness is obtained on the basis of fracture test results of RCC.Different induced planes are embedded into the RCC tension specimen to simulate all kinds of crack directors, and then axial tension tests are performed. The variation of the equivalent strengthes of all kinds of crack director specimens with dimension and area reduction rate are analyzed. Some conclusions are drawn as follows: For specimens with the same sizes, the equivalent strength increases with the decrease of area reduction rate. For specimens with the same area reduction rate, the equivalent strength decreases with the increase of specimen dimension. It has obvious effect on the reduction of equivalent strength that the specimen with one crack director is replaced by the one with two or more crack directors. the equivalent strength of notched penetrating crack director specimen is smaller than that of center penetrating crack director specimen.(2) Many engineering situations are adopted to simulate layer surface before initial setting time, middle layer surface, layer surface after final setting time and body formations. Wedge splitting specimen and double notch pressure specimen are employed to perform modeI fracture test and mode II fracture test. The variation of fracture toughness of all kinds of layer surface are summarized on the analysis of tests results, the reason of which is analyzed from microstructure. The effect of treatment and interval time of the RCC layer surface on fracture properties of that are compared, and then relative merits of the RCC layer surfaces are judged from several aspects.(3) The nominal fracture toughness size effect formula of RCC is applied into equivalent strength model of crack director, and the equivalent strength model of RCC crack director is built. Then the formula of surplus rate of crack director section's strength is obtained on the basis of the equivalent strength model. Then the variation of equivalent strength model and surplus rate of crack director section's strength with length of crack director and ratio of fracture toughness to strength are presented. Relative merits of unilateral interval crack directors and bilateral interval crack directors are compared.(4) The built equivalent strength model of RCC crack director is adopted to calculate the equivalent strengthes of crack directors in ShaPai RCC arch dam, which is selected as strength parameters of crack director elements in the dam construction simulation analysis program. Stress fields of ShaPai RCC arch dam during the constructing and operating period are analyzed. The open state of crack directors in ShaPai RCC arch dam during the constructing period is analyzed. Upon the comparison with the measured results, the validity of equivalent strength model of RCC crack director is verified. Whilst the stress distribution and damage state of dam during the constructing and operatinging period are analyzed on the basis of the analysis of simulation results.