Optimisation of ground anchor head for non-destructive testing

Abstract

Ground anchorages and rock bolts are used widely in retaining walls, mines, dry docks, dams and prestressed structures to provide effective support for unstable rock strata. This paper offers a new design for ground anchor heads to maximise the quality of load estimation using the non-destructive ground anchorage integrity testing method. When using this method, the anchor head assembly needs to have a non-linear stiffness characteristic to permit changes in anchorage load to be detected. The initial estimate of the optimal stiffness characteristic is found using a lumped parameter dynamic model of the bolt assembly. Finite-element models of the proposed patented plate designs are then presented along with the corresponding load–displacement diagrams. The optimised bearing plate which was designed in this process was manufactured and tested experimentally, both statically and dynamically as part of a rock bolt assembly. The results from the experiments and the dynamic model are presented, and show good agreement. The resulting frequency shifts with a change of load prove the viability of building in the flexibility required to make non-destructive monitoring of load possible. The proposed design provides excellent load estimation.