Full-scale pullout tests of rock anchors in a limestone quarry focusing on bond failure at the anchor-grout and grout-rock interfaces

Abstract

Rock anchors are a common safety measure for stabilising large-scale infrastructure, such as bridge towers, retaining walls, rock slopes and windmills. There are four principal failure modes for rock anchors: (a) tensile failure of the steel anchor, (b) anchor-grout interface failure, (c) grout-rock interface failure, and (d) rock mass uplift. Field tests were performed in a limestone quarry. These tests were designed to test failure modes B and C through pullout. In the tests of failure mode B, the shear stress on the anchor-grout interface is the largest at the top of the grout column and attenuates towards the distal end for small loads. The shear stress becomes uniformly distributed when the applied load is approximately 50% of the ultimate pullout load. The anchors designed to test failure mode C were installed with an endplate and had a higher toughness than the straight bar anchors. The shear stress on the grout-rock interface is the largest at the endplate and attenuates upward before slip starts along the interface. When the ultimate pullout load is reached, and the grout column starts to slip, the shear stress is approximately constant. The bond shear strength on the anchor-grout interface was approximately 20% of the uniaxial compressive strength of the grout, and the bond strength of the grout-rock interface was around 5% for that of the grout. The grout-rock interface is likely determined by whichever is weaker, the grout or the rock.