Timber pole retaining walls 1

[steelnz2003]

When building a retaining does any one knows exactly why we need to have about 100 mm of metal below posts
I say it is to protect the pole from direct contact with the soil ? but the pole is already treated so does anyone have idea ?

 

[hokie66]

The gravel is to help with drainage, thus decreasing the time the end of the pole is in contact with wet ground. No timber material, treated or naturally decay resistant, gives complete surety against rot. Another advantage is that the granular material can more readily be graded than the existing material to allow the poles to bear uniformly.