If the sides of the excavation are completely covered with timbering , it is know as close timbering whereas any form of partial covering is called open timbering.
Whichever system of timbering is used , there should be as few struts , that is horizontol members , fixed accross the width of the trench as possible as these obstructs ease of working in the trench.
structs should be cut to fit tightly between poling or walling biards and secured in position so that they are not easily knocked out of place
the type and amount of timbering required will depend upon the depth and anture of the subsoil . Over a short period , many soil may not require any timbering , but wheather condition and duration of the operations must all be taken into account .
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