Do you need to build an inclined wall on a wall 20 cm thick and 40 cm long?

Need. The function of oblique masonry at the top is arching to prevent horizontal cracks from appearing at the bottom of the top beam on the wall. The advantage of oblique masonry at the top is that the slope can effectively resist external forces, strengthen the strength of masonry, and is not easy to cause cracks and deformation of the wall. Inclined wall is a term of water conservancy science and technology published by 1997, which is located in the inclined impervious body of earth-rock dam body near the upstream slope.