Composite yieldable rock anchor with improved deformation range

The yieldable rock anchor according to any one of the preceding claims,

• wherein the tendon (12) includes at least one substantially non-yielding rigid further anchor portion (36) intermediate said proximal end and said at least one yielding portion (26).

The yieldable rock anchor according to any one of the preceding claims,

• wherein the non-yielding rigid first anchor portion (20) is provided with a plurality of anchoring members (22) protruding from an outer surface of the first anchor portion (20).

The yieldable rock anchor according to any one of the preceding claims,

• wherein each yielding portion (26) has a generally smooth outer surface.

The yieldable rock anchor according to any one of the preceding claims,

• wherein the at least one or at least one yielding portion (26) has an outer diameter that is smaller than an outer diameter of an adjacent rigid anchor portion.

The yieldable rock anchor according to any one of the preceding claims,

• wherein the first anchor portion (20) and any further anchor portion (36) has a higher strength than the at least one yielding portion (26).

The yieldable rock anchor according to any one of the preceding claims,

• wherein the at least one yielding portion (26), the first anchor portion (20) and any further anchor portion (36) are steel hollow bar members, the steel of the hollow bar members constituting the at least one yielding portion (26) being different from the steel of the hollow bar members constituting the first anchor portion (20) and any further anchor portion (36).

The yieldable rock anchor according to any one of the preceding claims,

• wherein the at least one yielding portion (26) has a deformation range of at least 100 mm/m, preferably of at least 120 mm/m, and most preferably of at least 150 mm/m.

The yieldable rock anchor according to any one of the preceding claims,

• wherein the tendon (12) includes an externally threaded portion (30) at or near said proximal end.