ABSTRACT
The concept of ‘arching’ of granular soil over an area where there is partial loss of support from an underlying strata has long been recognised in the study of soil mechanics (eg. Terzaghi, 1943). The ‘trapdoor’ approach has found some application in the analysis of piled embankments (Russell & Pierpoint, 1997), where the pile caps act as rigid supports, and the underlying soft subsoil as the ‘trapdoor’. Other approaches for the design of such structures include a semicircular arch in the granular fill, as initially proposed by Hewlett & Randolph (1988) (and developed by Low et al., 1994; and Kempfert et al., 2004), and analogy with backfill over a buried pipe (BS 8006, 1995). Notably there is not one generally accepted approach for design (Love & Milligan, 2003).
