Andrew Lees, Geofem, Gavin MacDonald, Mouchel, and Andrew Sheerman-Chase, Cares Group. This paper was first published in GE’s September 2013 issue.
A curious slope movement pattern has been recorded during 10 years of monitoring at one unstable section of the downstream slope of Aldenham embankment dam, in Hertfordshire, UK. A slip plane in the upper slope was reactivated each summer, which was caused by shrinkage of the tree-covered toe of the embankment due to soil moisture deficit, leading to loss of support to and reactivation of the grassed upper slope slip mass. This led to a seasonal, ratcheting accumulation of crest settlement - a type of mechanism that presents a continual serviceability problem to infrastructure embankments as well as dams.
A soil nailing scheme was designed and installed to support the upper slope slip mass, and then grassed over. Inclinometer and wave wall settlement data in the seven years following nail installation showed the scheme to be successful, even resulting in some upslope recovery movements.