The works included installing vibrating wire piezometers in the boreholes to monitor pore water pressures.
Trenches were also excavated to examine the interface between the clay core, a later concrete extension to the core. Material in the shoulders of the dam will also be examined.
Ulley Reservoir, suffered scour when one of the spillways overtopped during a week of torrential rainfall in June this year. This lead to concerns about the stability of the dam (NCE 28 June).
Last week's ground investigation will assist Rotherham Metropolitan Borough Council's consultant Arup and the All Reservoirs Panel with their assessment of the dam and associated structures and will provide details which can be checked against historical construction records.
"The site investigation was a health check on the embankment," said Arup associate Rachel King."We were looking at stability, whether there were problems with seepage and gathering information for geotechnical analysis. The investigation works were successful.
"We have historical records of the dam which was built in the 1870s. We wanted to see if the dam was like the drawings and it is."
Rotherham Metropolitan Borough Council appointed Arup to oversee the site investigation and Chester-based ground engineer Geotechnics to undertake the site investigation.
Work started on site on the 26 November. Geotechnics' subcontractor Geotechnical Engineering carried out boreholes using a specialist slope-climbing rotary rig.
Initial results of the ground investigation are due this month and Arup expects to report its findings to RMBC in early 2008 to help them with the future management of the asset.