Monument MPM2037 - Limestone and timber structures, Dry Dock No.3, Portsmouth Historic Dockyard

Substantial limestone and timber elements of the structure of Dry Dock No.3 revealed by boreholes during geotechnical investigations in 2008. The most substantial limestone and timber structures were present in boreholes positioned at the north-east and south-west corners of the dock.

Boreholes drilled during geotechnical investigations in 2008 revealed substantial limestone and timber elements of the structure of Dry Dock No.3 at each corner of the dock. The most substantial limestone and timber structures were present in boreholes positioned at the north-east and south-west corners. A brick structure was also found in the borehole in the north-west corner. Locations recorded for boreholes are estimated from report.

BH01 (north-west corner)
A limestone wall was encountered at a depth of 2.91mOD. Excavation was stopped and the location of the borehole was moved further north due to the presence of the wall. This second borehole was given the reference BH01A.

BH01A (north-west corner)
Timber was encountered at a depth of 9.80m to 10.30m below ground level. This overlaid a deposit of limestone at 10.50m. Another layer of timber beneath the limestone sealed the natural clay at a depth of 11m below ground level.

Above the timber, at a depth of 5.25m was a 0.35m layer of limestone capping and a brick feature recorded to a depth of 7.20m.

BH02 (south-east corner)
Limestone blocks were encountered at a depth of 2.13m below ground and continued to 5.70m. Beneath the blocks was a 0.70m layer of gravels which overlay natural sands at a depth of 6.40m. Overlying the blocks were layers of made ground and the modern tarmac ground surface.

BH03 (south-west corner)
The borehole recorded a 0.55m layer of concrete and 0.15m layer of brick stone rubble beneath which limestone blocks were encountered to a depth of 10.30m. Beneath the blocks, timbers were recorded to a depth of 10.75m. Further limestone blocks were then recorded to a depth of 11.20m which overlay natural clay and sand deposits.

BH04 (north-east corner)
A series of made ground was recorded to a depth of 5m beneath which limestone was present to 11.30m. Natural clay and sands were recorded beneath the limestone.

Sayer, Kathelen, 2009, Archaeological Monitoring of Geotechnical Works at the Portsmouth Historic Dockyard, Portsmouth, Hampshire (Unpublished document). SPM612.