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Sevenoaks bypass

Stability problems on shallow slope cuttings hindered construction of the A21 Sevenoaks bypass in Kent in the late 1960s, baffling engineers and making headlines in the tabloids as 'the road that can't be built'.

Subsequent research by Weeks & Skempton showed that shear surfaces associated with ancient landslides could occur in clay soils in south east England where the slope inclination was as low as 3degrees, and that movement on these surfaces could be triggered by construction earthworks. It was suggested that a periglacial climate was necessary (to generate high pore pressure) to get landslide movement on such shallow slopes. Weeks & Skempton described this process by the geomorphological term solifluction.

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