Definition - What does Lagging mean?
Lagging is the structural material (most often wood) that spans the distance between spars at an excavation site. Lagging, and the steel spars they connect to, provides temporary ground support as a safety measure during tunneling. The lagging is installed horizontally between vertically installed spars. In trenchless construction, ground support is an important aspect of any drilling or tunneling project.
Trenchlesspedia explains Lagging
Lag spacing can be installed by wedging-driving a wooden block between the earth and the spars, the stops which is completed by welding small angles onto the ribs' outer flange or with clamps applied to wood or steel lags. The lagging spacing and thickness is determined by geotechnical analysis. As lagging is designed to be a temporary component of the trenchless construction process, all existing materials used in the lagging process will be removed when no longer required.