Aprocedure that uses wood or metal braces to reinforce trench walls is called:

Answer;
            A procedure that uses wood or metal braces to reinforce trench walls is called SHORING or TIMBERING.

Explanation:
                   Unstable Trenches and excavations for pipeline, tunneling or underpass purposes is very dangerous for the workers. The trench can collapse injuring or killing workers. This collapse can occur due to ground vibrations, moisture in earth, rainfalls or due to depth of Trench.
                   So, in order to protect Trenches from collapse, a shoring process is done. In this method the walls of trenches are supported by using wood or metal braces, Hydraulic Shoring e.t.c.

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