25 years of monitoring of rock anchors installed for landslide stabilisation at Nantgarw, South Wales

Investigation and monitoring of cracks in the A470 trunk road at Nantgarw identified landslide movement of the hillside below the road as the primary cause. A scheme comprising a row of anchored pads was designed and constructed in 1980 to stabilise the landslide. Particular consideration was given in the design to ensure the durability of the anchorage system whilst allowing monitoring and inspection of the anchor heads.

The loads in the anchors have been regularly checked over the period 1981 to 2006 since installation and where necessary the anchors have been re-stressed. On each occasion, the total lift-off load of all the anchors has been found to be below the total notional design load with individual anchors having generally lost rather than gained load with time. It would appear therefore that the landslide has demanded less restoring force from the anchors than the design landslide stabilisation load. This confirms site observations that the landslide has been adequately stabilised by the anchor scheme.

This paper describes the installation and monitoring of the anchor system, discusses the results of the load measurement and re-stressing and comments on the effectiveness of the stabilisation scheme.

• Introduction

• Monitoring Regime

• Loss of Anchor Load

• Anchor Condition

• Conclusions

• Acknowledgements

• References