What is the purposed of great walls?

Answer 1

It was to keep out the Barbarian Mongolian Invaders from the north. It was a physical barrier.

Answer 2

Taking into consideration that you are considering building a vinyl liner swimming pool I can tell you that: Steel panels do make a strong pool shell. It of course must be installed properly for your particular "ground conditions". It will last many years before you may have to change the liner due to damge from storms, accidents etc. that can damage the liner causing the need to replace it. When you replace it, you will find that your steel walls have built up corrosion and rust on them. This should be removed before replacing the new liner. The corrosion can be sanded off, then you need to paint the walls where they have been sanded (Rustoleum paint etc), re-tape the panel joints, clean the bottom from sanding debris etc. and drop the new liner. In case of severe rust where the panel is compromised, (thin, holes, etc) your pool company will probably need to replace the panel/brace/coping.) When you need to replace a liner in a polymer wall pool, you will need to retape the panel joints, clean the bottom if needed, drop the liner.