The (in?)Significance of Creep in a Prestressed Polyester Resin Grouted Rock Anchor

ABSTRACT: One of the major concerns regarding polyester resin grouted rock anchors is whether the resin creeps when loaded. The most extreme case would be that the resin behaves in a visco-elastic manner, exhibiting continuous movement or load decay. Examination of pull test results, however, indicates that polyester resin does not behave visco-elastically. The exact rheological behavior is unknown, however, time-dependent behavior is load-sensitive. When either the grout or rock-grout interface strength is exceeded, the excess load will transfer along the bolt. Should the anchor length "saturate" with load, the excess load will be shed onto the free length of the rock anchor, loading it in compression. The load distribution in the free length will require proportionately less transfer length than the equivalent load in the anchor zone due to the compressive loading of the free length. The added design length due to safety factors should prevent anchor failure by creep if the bond strength is adequately determined.