Cliff-top stabilisation of the Military Road, Isle of Wight

This paper describes the development of the design for an innovative retaining structure built to support an existing highway on the Isle of Wight. At Afton Down on the south-west coast of the island the A3055 Military Road passes above high chalk cliffs. Continuing erosion at the toe of the cliffs led to the cliff edge receding to within 15 m of the highway. As a result options to maintain the road were investigated. A public inquiry ruled out realignment inland onto the adjacent downland, whilst measures to prevent erosion at the toe of the cliffs were unacceptable for environmental whilstcoastal management reasons. Consequently the road was kept open, with instrumentation installed to warn against failure of the cliff, and work began on the design of a scheme to maintain the road along its existing alignment. An environmental assessment was carried out to address the potential impacts of schemes on the adjacent downland, with the resulting arrangement of a tied retaining wall aiming to minimise these. Furthermore, outline methods for decommissioning the structure when it reaches the end of its serviceable life were identified. Planning permission was granted in 2002, and following a series of trials the scheme was constructed in 2003 and the road reopened to the public.