The seasonal ratcheting of clay cut slopes in response to seasonal weather cycles

Many cut slopes in the UK are in the later stages of their operational life but continue to support road and rail transportation networks. Some of these slopes experienced delayed, deep-seated, first-time failures between 10 and 50 years after construction. However, some continue to seasonally deform and then fail at shallow depth due to the process of seasonal, downslope ratcheting. This paper reviews the evidence for seasonally-induced, downslope ratcheting movements in clay cut slopes, gathered from physical model tests, in-situ monitoring and numerical simulations. The evidence shows that seasonal ratcheting is an increasingly dominant mechanism of slope deformation and ultimate failure for some high-plasticity clay cut slopes as they are exposed to many seasonal weather cycles. The rate of downslope ratcheting depends on the slope age (i.e., number of seasonal weather cycles since construction), the slope geometry (i.e., slope height and angle) and the strain-softening behaviour of the slope material (e.g., as observed in stiff, high-plasticity clays). This rate, when measured, can be used to inform monitoring and management strategies for old, clay cut slopes (e.g., ageing railway and highway cuttings) by identifying the slopes that are prone to seasonally-induced, downslope ratcheting towards the end of their operational life.