How to write the reason for replacement and filling of retaining wall gravel?

According to the query, Baba official website shows.

1. Reasons for replacement of retaining wall foundation In the description of retaining wall in the original design, "The back fill of retaining wall should be made of sand and other materials with good water permeability and water stability.

2. The internal friction angle of the filler is not less than 35 degrees, and the friction coefficient of the base is considered as 0.4.