G S Littlejohn, BSc, PhD, CEng, MICE, FGS, and C Truman Davies. This paper was first published in GE’s November 1974 edition.
The first stage of the construction of the Nuclear Submarine Complex at Devonport has resulted in one of the largest and most interesting anchoring contracts ever undertaken in this country. Two dry docks, separated by a central promontory housing workshops, offices and other support facilities, are to be constructed in an existing basin approximately 140m square, situated in HM Dockyard.
The site is immediately underlain by a series of geosynclinal sediments of Upper Devonian age, dominated locally by hard grey-blue banded slate, known as “shillet”. Numerous thin quartzitic greywacke layers occur, together with the occasional thin igneous intrusion. The rock surface dips at 3.5 deg on average from north east to south west across the site, and the uppermost 0.5-1.2m of bedrock are weathered and extremely fissile. The rock is tightly and strongly folded, due to its participation in the American orogenic period.