This paper reviews the findings of the field studies undertaken by TRL and The Highways Agency (HA), over the last 20 years or so, on the degradation of metallic reinforcements. The measured rates of corrosion are compared to current requirements of HA in the UK and different methods of assessing the degree of corrosion of buried metallic reinforcements are discussed. Data are presented for coupons or reinforcements recovered from four sites.
At the time of the development of reinforced soil techniques by Vidal (1969) there was a paucity of data on the durability of metallic elements and on the long-term properties of polymeric materials suitable for use as soil reinforcements. An overly pessimistic view would have hindered the take-up of the techniques whereas an optimistic assessment could have led to the premature failure of structures. (Failures of in service structures due to the corrosion of metallic reinforcements have been reported by Ramaswamy and DiMillio (1986), Blight and Dane (1989), and Winter and Butler (1999)). Research was therefore initiated at the Transport Research Laboratory (TRL) to establish specifications for reinforced soil structures and also to determine the in situ rate of degradation of the materials used for reinforcements. This has included planned experiments and the opportune extraction and examination of reinforcements from in service structures. Brief details of these are provided in this paper, but a comprehensive presentation and discussion of the data has been completed by Greene and Brady (1999). This paper is limited to a discussion of metallic reinforcements.
In 1976, two 4 m × 4 m × 3 m deep pits were excavated in the natural soils at the test site located within the grounds of the Laboratory at Crowthorne and backfilled with either London Clay or Bramshill Sand.