Grout pack restraining envelope

Abstract

A grout pack [ 1] restraining envelope is provided which includes a plurality of restraining rings [ 7, 8] shaped to extend circumferentially around a grout bag [ 2] in a vertically spaced arrangement up at least a part of the height of the grout bag to provide support against lateral deformation of an installed grout pack as it occurs under axial load. At least some of the restraining rings are of differing tensile strengths or are configured to yield at differing tensions. The grout pack may have a collapsible polymer or wire mesh [ 3] positioned on the inside of the restraining rings to which at least some of the restraining rings are fastened. Restraining rings [ 7] of relatively higher tensile strength are provided at vertical positions at which relatively greater lateral deformation of the grout bag is expected, and rings [ 8] of relatively lower tensile strength are provided at vertical positions at which relatively less lateral deformation of the grout bag is expected. The restraining rings may be of the yielding or non-yielding type.

1 . A grout pack restraining envelope which includes a plurality of restraining rings shaped to extend circumferentially around a grout bag in a vertically spaced arrangement up at least a part of the height of the grout bag to provide support against lateral deformation of an installed grout pack as it occurs under axial load, wherein at least some of the rings are of differing tensile strengths or are configured to yield at differing tensions. 
     
     
         2 . A grout pack restraining envelope as claimed in  claim 1  in which the restraining envelope includes a collapsible polymer or wire mesh positioned on the inside of the restraining rings to which at least some of the restraining rings are fastened. 
     
     
         3 . A grout pack restraining envelope as claimed in the  claim 1  in which restraining rings of relatively higher tensile strength are provided at vertical positions at which relatively greater lateral deformation of the grout bag is expected, and rings of relatively lower tensile strength are provided at vertical positions at which relatively less lateral deformation of the grout bag is expected. 
     
     
         4 . A grout pack restraining envelope as claimed in  claim 1  in which restraining rings at positions further up the height of the grout bag are of relatively greater tensile strength than restraining rings lower down the height of the grout pack. 
     
     
         5 . A grout pack restraining envelope as claimed in  claim 1  in which restraining rings of three different tensile strengths are used; an upper set of restraining rings of highest tensile strength, a middle set of restraining rings of intermediate tensile strength and a lower set of restraining rings of lowest tensile strength. 
     
     
         6 . A grout pack restraining envelope as claimed in  claim 1  in which the restraining rings are made from metal wire and may have differing tensile strengths by virtue of having differing cross-sectional areas. 
     
     
         7 . A grout pack restraining envelope as claimed in  claim 1  in which the restraining rings have differing tensile strengths by virtue of having different material properties. 
     
     
         8 . A grout pack restraining envelope as claimed in  claim 1  in which at least some of the restraining rings carry secondary outer restraining rings of greater diameter, the outer restraining rings being configured to provide restraint to the expansion of the grout pack prior to failure of the restraining rings of lesser diameter, thereby providing a progressive yield of the grout pack. 
     
     
         9 . A grout pack restraining envelope as claimed in  claim 1  in which any yielding restraining rings are formed by elongate elements that have first and second opposing ends connected to each other in an overlapping configuration to form an expansion zone so that the restraining rings yield by controlled extension of their length when tension applied to the restraining rings consequent on lateral deformation of the bag exceeds a predetermined tension force. 
     
     
         10 . A grout pack restraining envelope as claimed in  claim 9  in which the opposing ends of said yielding restraining rings are connected by means of at least one collar that provides a predetermined swaging force thereby creating a predetermined frictional or shear resistance to movement between the first and second opposing ends. 
     
     
         11 . Components in the form of restraining rings suitable for inclusion in a grout pack restraining envelope as claimed in  claim 1  wherein at least some restraining rings are adapted to yield at differing tensions.