In the context of excavations this is called timbering irrespective of the actual materials used. if the sides of the excavation are completely covered with timbering it is known as close timbering whereas any form of partial covering is called open timbering.

An adequate supply of timber or other suitable material must be available and used to prevent danger to any person employed in an excavation from a fall or dislodgement of materials forming the sides of an excavation

A suitable barrier or fence must be provided to the sides of all excavations or alternatively they must be securely covered.

Materials must not be placed near to the edge of any excavation, nor must plant be placed or moved near to any excavation so that persons employed in the excavation are endangered.

Poling boards: a form of temporary support which is placed in position against the sides of excavation after the excavation work has been carried out. poling boards are placed at centres according to the stability of the subsoils encountered.

Runners: a form of temporary support which is driven into position ahead of the excavation work either to the full depth or by a drive and dig technique where the depth of the runner is always lower than that of the excavation.

Trench sheeting:form of runner made from sheet steel with a trough profile--can be obtained with a lapped joint or an interlocking joint

Water: if present or enters an excavation a pit or sump should be excavated below the formation level to act as collection point from which the water can be pumped away

Cofferdam: these are temporary enclosures installed in soil or water to prevent the ingress of soil and/or water into the working area with the cofferdam, they are usually constructed from interlocking steel sheet piles which are suitably braced or tied back with ground anchors. alternatively a cofferdam can be installed using any structural material which will fulfil the required function

Steel sheet piling: apart from cofferdam work steel sheet can be used as a conventional timbering material in excavations and to form permanent retaining walls. three common formats of steel sheet piles with interlocking joints are available with a range of section sizes and strengths up to a usual maximum length of 18000

Caissons: these are box-like structures which are similar in concept to cofferdams but they usually form an integral part of the finished structure. they can be economically constructed and installed in water or soil where the depth exceeds 18000.there are 4 basic types of caisson namely: Box caisson,open caissons, monolithic caissons: usually of precast concrete and used in water being towed or floated into position and sunk---land caissons are of the open type and constructed insitu; pneumatic caissons: used in water  :sometimes called compressed air caissons and are similar in concept to open caissons. they can be used in difficult subsoil conditions below water level and have a pressurised lower working chaber to provide a safe dry working area. pneumatic caissons can be made of concrete whereby they sink under their own weight or they can be constructed from steel with hollow walls which can be filled with water to act as ballast. these caissons are usually designed to form part of the finished structure.