This section is from the book "A Treatise On Architecture And Building Construction Vol2: Masonry. Carpentry. Joinery", by The Colliery Engineer Co. Also available from Amazon: A Treatise On Architecture And Building Construction.
142. Shoring is a method of temporarily supporting the walls of a building by means of posts or struts set at an angle, to keep the wall from tipping or bulging while the 2-6 foundations are being carried down, or during the needling and removal of the lower portion of the wall.
When columns or girders are to be used in place of brickwork, the method of shoring the wall for the purposes above mentioned is shown in Fig. 5G. Grooves, or sockets, are first cut in the wall, as shown at a, and in these the angle braces, or shores, b, b are inserted. These are also called spur braces, and when tightened up by means of screw jacks, instead of the wedges d, they are known as pumps. The lower ends of the shoring timbers rest on a timber crib c, supported on the ground. At least two sets of braces are usually put in, one to support the wall, as low down as possible, and the other placed higher up, to keep it from bulging. The platform must be made large enough to distribute the pressure brought upon it over the ground, and the shores should be well wedged with iron or oak wedges, as shown at d. The timbers carrying the ends of the braces should be adjusted, to the proper inclination by means of wedges, as shown at e. It is customary to allow a space of about 5 feet between braces, and all piers and chimneys should be separately shored.
The foundations should be removed in small portions at a time. When three sets of braces, or shores, are in place the wall should be underpinned, as hereafter described, after which the shores over it may be moved along; two sets, however, must always be kept in place.
143. Shoring is often resorted to when it is necessary to hold up the corner of a building, to build a pier, or set a column under it. When a girder is placed under the upper part of a wall, needling is necessary, as being-attended with less risk.