Common methods of bracing the sides when the depth of
excavation does not exceed about 3 m are shown in Figs 20.26(a) and (b).
The practice is to drive vertical timber planks known as
sheeting along the sides of the excavation. The sheeting is held in place
by means of horizontal beams called wales that in turn are commonly
supported by horizontal struts extending from side to side of the
excavation. The struts are usually of timber for widths not exceeding
about 2 m. For greater widths metal pipes called trench braces are
commonly used.