The size of the concrete area is usually: the minimum thickness of the external (I, II, III) concrete area is 2-3m, and the thickness of the upstream face is greater than that of the downstream face. The thickness of foundation concrete (VI) area is generally 0.1L (L is the side length of the dam bottom), not less than 3.0m. There should be a good contact area between different grades of concrete. During construction, vibration shall be adequately enhanced by mixing, or pool joints shall be used. At the same time, the grade difference between adjacent concrete grades shall not be greater than two grades. Otherwise, due to the great difference between the two kinds of concrete, the hydration heat temperature rise and volume shrinkage deformation are different, and cracks are easy to occur on the contact surface