PELORUS SURVEYS was appointed by Mowlem to carry out geophysical surveys on the River Thames before scour protection works on the Westminster Bridge in central London.
Pelorus used its survey vessel to determine the state of underwater scour at several of the bridge piers. Sub-bottom geophysical surveys were also carried out to find potential obstacles to piling works.
Survey work included a bathymetric (echo sounder) survey to determine the river bed level to the required datum and aside scan sonar survey to map the sediment distribution across the site and identify any objects lying on the bed.
Further surveys included a seismic reflection test to profile the strata variations below the river bed and surrounding the bridge piers as well as identifying any objects buried in the silt and a magnetic gradiometer survey to identify any buried ferrous or ferric objects.
Data was collected by traversing the survey area on a regular grid - nominal spacing 2.5m.
Readings were taken continuously and the data logged and stored on computers onboard. The information was available on site immediately with further processing and imaging conducted in the office.