Reinforced concrete box
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A reinforced concrete box is a square or rectangular "pipe" made of concrete with rebar or wire mesh fabric strewn throughout for the addition of extra strength.
It is often used for sanitary sewer trunks, storm drain spillways, pedestrian subways, utility tunnels, catch basins, and other similar underground passage ways.
Available in many sizes, it is often ideal for use in sewers or tunnels that have little cover above them, and are subject to the stress of a road atop them. This is due to the enormous strength of reinforced concrete.