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Test drilling precedes Liverpool dock deepening

The Port of Liverpool has always had to develop and reinvent itself to meet the changing needs of the world economy.

So port owner Peel Ports wanted to deepen the berths in the Alexandra Dock to accommodate larger vessels, the condition of the walls and base of the dock had to be assessed.

Geotechnics Limited was appointed to carry out investigation works. This involved inserting four water boreholes to measure the depth of silt and sediment which would have to be removed from the bed and to prove the depth and condition of the underlying sandstone strata.

Spudded pontoon barge

Cable percussion boring and rotary drilling work was carried out from a spudded pontoon barge using a standard Pilcon Wayfarer boring rig and a Mobile Drill B24 rotary rig.

The condition of the dock walls, their depth and foundations were critical to the scheme designer RG Parkins & Partners. Quayside level is 12.2m above chart datum, the base of the wall was expected to be at about 3m below chart datum, and the proposed dredged level is 2.9m below chart datum, so there were serious concerns that the walls would lose frontal lateral support.

The investigation called for rotary core holes to be drilled from coping stone level, through the Victorian mass concrete wall and into the foundation materials. Geotechnics Limited used a Comacchio 205 track mounted rig, working as close as 1m from the water’s edge and chose a T6/116 water flush, coreline set, drill barrel, and Series NF drill bits supplied by JKS Boyles UK. The wall structure proved to be variable but intact and the drilling equipment successfully cored granite coping stones, mass concrete and sandstone blocks.

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