Event/Activity EPM184 - Archaeological Watching Brief on land at HMS Nelson, Queen Street, Portsea, Portsmouth

Southampton Archaeology Unit carried out a watching brief on groundworks for a new five-storey building to provide 240 Y scale bed spaces and 30 Z scale bed spaces for Junior Rates on land at HMS Nelson in 2013. The condition for a watching brief was imposed as the site lay on the line of the former 18th century Portsea town defences, which protected the Dockyard and were demolished during the 1870s. A complex of air raid shelters made up of concrete box-section tunnels was known to exist beneath the development site, car park to the west, and Vanguard Building. The top of the tunnels was situated approximately 300mm-400mm below the present ground surface. The east-west tunnels were generally 2.5m high and 1.0m wide, the north-south tunnels 2.5m-2.0m wide. The air raid shelters were removed by the contractor, and much of the site excavated to a level of 4m and backfilled prior to the commencement of the watching brief. Geotechnical investigations consisting of three boreholes and six test pits were carried out on the site in 2012, followed by cone penetrometer tests. These investigations had suggested that the levelling of the ramparts and backfilling of the moat was uneven, between 0.90m and 1.70m below the modern ground level. Observations were carried out on ground works comprising the drilling of 166 augured piles and the excavation of five trenches. The augured piles measured 450m in diameter and were approximately 18m deep. The dimensions of the trenches were as follows: Trench One measured 14m long, 0.7m wide and 1.7m deep; Trench Two measured 15m long, 1.7m wide and over 1.7m deep; Trench Three was an extension of Trench One and measured 17m long, 0.65m wide and 1.4-1.7m deep; Trench Four was dug to remove an obstacle encountered by the pilling rig and measured approximately 2m long, 0.4m wide and 5-6m deep; Trench Five was a general level reduction to remove parts of the large complex of Second World War air raid shelters located beneath 80% of the site. It measured approximately 85m long, 26m wide and 0.6-4m deep. Most of this trench had been excavated and backfilled with mixed soil and rubble up to 4m thick before the watching brief commenced. The watching brief established and recorded the approximate location, preservation, alignment, extent and nature of the surviving elements of the fortifications. It was possible to ascertain some details relating to the form and construction of the complex of air raid shelters. As parts of this complex still survive in other areas of the HMS Nelson site, it might be possible for a more detailed record to be made in the future. Accession No: 2013/898