Method of rock bolting and tube-formed expansion bolt

Method of rock bolting in a borehole for anchoring the strata of a rock formation, comprising:

• inserting in a borehole a first bolt (38) that is shorter than the borehole;
• expanding said first bolt against the walls of the borehole to clamp said first bolt against the walls of the borehole to thereby anchor said first bolt in the borehole;
• then inserting a second bolt (40) into the borehole until its inner end is adjacent to said expanded and anchored first bolt (38) and is axially overlapped by an element (39) of said expanded and anchored first bolt;
• and
• then expanding said second bolt against the walls of the borehole and against said element (39) of said first bolt such that it anchors in the borehole and clamps said element (39) between it and the borehole so that said two bolts (38, 40) each become anchored in the borehole and coupled to each other via said element (39).

A method of reinforcing rock comprising:

• providing a bolt that comprises an expansible elongated tube which has a deep continuous longitudinal depression which extends inwardly of the bolt toward the axis of the bolt, the tube having a major closed cross-sectional portion in the area of the deep longitudinal depression, and the tube being closed at one end thereof which is the bottom end thereof;
• drilling a hole in the rock of a diameter large enough to permit the unexpanded bolt to be freely inserted in the borehole;
• inserting the bolt in the borehole with said closed bottom end first;
• coupling the other end of said tube to an external source of hydraulic pressure fluid;
• plastically deforming said tube by temporarily applying said high pressure fluid to the interior of said tube to expand said tube against the borehole over substantially the entire length of the bolt by expanding said depression outwardly substantially without stretching the material of the tube so as to cause permanent gripping action of the tube against the inner surface of the borehole;
• and
• then relieving said tube of pressure and leaving the bolt anchored in the borehole.

A method of reinforcing rock comprising:

• plastically deforming a transverse cross-section of a circular tube so that its transverse size is reduced, at least a continuous portion of said tube in its longitudinal direction having said plastically deformed cross section to form a plastically deformed portion of the tube;
• drilling a hole in the rock, the hole having a diameter larger than the reduced transverse size of the plastically deformed tube so that the deformed tube can be freely inserted into the borehole;
• inserting the deformed tube in the borehole;
• and
• then further plastically deforming the deformed tube in the borehole substantially without stretching the material of the tube by temporarily applying an expansion medium to the interior of the tube so that it expands the deformed portion of the tube in the transverse direction of the tube and thereby clamps at least the non-deformed exterior of the tube frictionally against the inner surface of the borehole;
• and then
• removing the application of said expansion medium after expansion and clamping of the expanded portion of the tube against the inner surface of the borehole, the expanded portion of the tube remaining clamped against the inner surface of the borehole even after removal of application of said expansion medium.

A method of rock bolting comprising:

• providing a bolt that comprises a radially expansible elongated tube which, before being used, has a deep closed continuous longitudinal depression extending inwardly of the tube toward the axis of the tube, the tube being closed at one end therof which is the bottom end thereof, the tube having a major closed continuous cross-sectional portion at least over the longitudinally depressed portion thereof;
• drilling a hole in the rock of a diameter that is larger than the largest transverse dimension of the bolt before being used but smaller than the largest transverse dimension of the bolt if said longitudinal depression is fully expanded, so that the longitudinal depression cannot be fully expanded when the bolt is in the borehole;
• inserting the bolt in the borehole with said closed bottom end first;
• temporarily coupling the other end of said tube to an external source of hydraulic high pressure fluid to temporarily fill the interior of the tube with the high pressure fluid under substantially static conditions so that the tube is plastically deformed under the influence of said high pressure fluid to expand said depression outwardly of the tube so as to cause permanent gripping action of the tube against the inside surface of the borehole over substantially the entire length of the tube;
• and
• then relieving said tube of pressure by removing the external source of hydraulic high pressure fluid and leaving the bolt anchored in the borehole.