Abstract: In a simple method of filling a wide crack in an exposed surface of an artificial or natural structures, a rigid plate is positioned on the surface, which plate has on the surface of the plate nearer the surface of the structure three enclosures each bounded by an upstanding wall of compressible material. Two of the enclosures (vacuum enclosures) each has an outlet port passing through the plate and one of the enclosures (the injection enclosure) positioned between the vacuum enclosures has two injection nipples passing through the plate. The plate is so positioned on the surface of the structure that the injection enclosure overlies the crack. Air is evacuated through the outlet ports from the vacuum enclosures to cause the rigid plate to be sucked tightly against the surface of the structure and hardenable material in a semi-liquid state is pressure injected through the injection nipples into the injection enclosure until the crack is filled.

Abstract: An inexpensive, readily handled receptacle for use in the bulk impregnation of timber by vacuum impregnation is made of flexible fluid-impermeable material and, over parts of its walls, is of double thickness to form closed pockets that can be inflated to form a container of rectangular shape hinged along one of its side faces to provide a sealable opening for loading and unloading. The pockets have a valve for inflating them with air; the receptacle has inlet and outlet ports for evacuating the receptacle and introducing impregnant. Preferably, the receptacle is supported in a two-part rectangular frame hinged along one side face.

Abstract: Corrections to be applied to the motion of a tunnelling shield to maintain or restore motion of the shield along a predetermined path are determined by directing a beam of collimated light in a direction parallel to or at a fixed angle with the axis of said predetermined path; focussing the beam on to the input end of an optical cable carried by the shield and comprising a plurality of optical fibres, the input ends of the fibres being arranged in an array in which the position of the input end of each guide relative to that of another is fixed; and displaying light transmitted through the optical cable or guides on to a screen at which the output ends of the guides are so arranged as to facilitate ready determination of any correction required to be applied to the motion of the shield. The method may be employed to indicate which propulsion rams of a tunnelling shield should be operated to apply the necessary correction to the motion of the shield.

Abstract: A wooden part of a structure or structural member, e.g. a telegraph pole, that is exposed to the atmosphere is impregnated with wood preservative by a vacuum impregnation process. The exposed wooden part of the pole is surrounded by a closely fitting, fluid-impermeable covering, e.g. a polythene shroud, and boundary edges of the covering are sealed to form a substantially fluid-tight enclosure. Air and any other fluid is evacuated from voids in the said wooden part of the pole and from within the fluid-tight enclosure and wood preservative in a flowable state is allowed to enter the enclosure and the voids in said wooden part of the pole until said wooden part is fully impregnated with wood preservative.

Abstract: Voids in at least a part of an artificial or natural structure adjacent an exposed surface of the structure are filled with hardenable material to strengthen the structure by closely fitting over the exposed surface a flexible fluid-impermeable covering having adjacent its boundary edges an endless hollow wall that surrounds and opens towards said covered surface and sealing boundary edges of the covering to the structure to form a substantially fluid-tight enclosure incorporating the hollow walls. Air and any other fluid is evacuated from the hollow wall and from voids adjacent said covered surface and hardenable material in a liquid or semi-liquid state is allowed to enter into the evacuated voids until the hardenable material appears at openings of voids in said covered surface. The hardenable material is then allowed to set.