To consider the adequacy of surface water drainage and identify the occurrence of perched groundwater
Within the glacial deposits there are permeable shallow zones of sand and gravel forming perched groundwater
that respond to short term rainfall fluctuations and there are indeed localised problems encountered, particularly after a wet season like last summer.
The open-face shield method of tunnel construction, incorporating a part-face tunnel machine, encountered variable conditions, including perched groundwater
, formational materials, and running/flowing soils.