A method for stabilising a multi-walled structure, the structure comprising a first wall and a second wall and a filler layer sandwiched between the first and second walls, the first wall providing a first side of the structure and the second wall providing a second side of the structure, the method comprising: - providing at least one hole extending through the first wall and the second wall and said filler layer between said walls from the first side of the structure to the second side of the structure; - inserting a tube through said hole, the tube having a central bore, a first end of the tube extending from the first side of the structure and a second end of the tube extending from the second side of the structure; - inserting a peg through the bore of the tube, the peg having a head portion at a first end of the peg, at least a part of the head portion having an outer diameter greater than the diameter of the bore of the tube, and the head portion being located on the first side of the structure; - pulling the peg through the tube towards the second side of the structure so that the head portion causes the first end of the tube to deform radially outwards so that the first end of the tube expands beyond the diameter of the bore of the tube to bear against the first side of the structure; - securing a first securing means to a second end of the peg on the second side of the structure such that said first securing means bears against the second end of the tube in order to secure said expansion of the first end of the tube; and - securing a second securing means (84, 86) to the second end of the tube such that the second securing means bears against the second side of the structure; wherein, the deformed first end of the tube on the first side of the structure and the second securing means (84, 86) on the second side of the structure clamp together the first and second walls (46, 36) of the structure thereby applying a compressive force to the filler layer between said walls. - providing at least one hole extending through the first wall and the second wall and said filler layer between said walls from the first side of the structure to the second side of the structure; - inserting a tube through said hole, the tube having a central bore, a first end of the tube extending from the first side of the structure and a second end of the tube extending from the second side of the structure; - inserting a peg through the bore of the tube, the peg having a head portion at a first end of the peg, at least a part of the head portion having an outer diameter greater than the diameter of the bore of the tube, and the head portion being located on the first side of the structure; - pulling the peg through the tube towards the second side of the structure so that the head portion causes the first end of the tube to deform radially outwards so that the first end of the tube expands beyond the diameter of the bore of the tube to bear against the first side of the structure; - securing a first securing means to a second end of the peg on the second side of the structure such that said first securing means bears against the second end of the tube in order to secure said expansion of the first end of the tube; and - securing a second securing means (84, 86) to the second end of the tube such that the second securing means bears against the second side of the structure; wherein, the deformed first end of the tube on the first side of the structure and the second securing means (84, 86) on the second side of the structure clamp together the first and second walls (46, 36) of the structure thereby applying a compressive force to the filler layer between said walls.