N52 Cloghan to Billistown Phase 2, Turin to Billistown Geophysical Investigation

The main objectives of the geophysical investigation are to assess the depth to rock and the rock mass characteristics in cut sections with shallow rock, and to assess the potential for karstification in the limestone bedrock.

The geophysical investigation required us to:

• Produce continuous 2-D profiles of resistivity and seismic velocity against elevation along the centreline of the route (approximate length 4.917km) and at selected locations perpendicular to the centreline in cuts and alongside roads.
• Map lateral and vertical variations in overburden type and thickness along the route corridor.
• Assess overburden stiffness and density with particular reference to identifying local variations that may be attributed to karstification in the underlying bedrock.
• Locate any zones of backfilled or made ground.
• Establish the depth to rockhead and estimate the mass characteristics of the rock, particularly rock quality, excavatability/ripability, rock strength, and discontinuity / bedding spacing.
• Identify the extent and significance of limestone karst features such as collapsed sinkholes, infilled dissolution features with pockets of soft compressible material, open conduits or caves. Identify locations that require further investigation as part of the detailed ground investigation contract using boreholes, rotary cores or other alternative investigation techniques as maybe appropriate.