Rosedale WWTP Shaft

Statement from Roger McRae, General Manager, McConnell Dowell Constructors Ltd, regarding LDD's performance at Rosedale......

"We cannot fault LDD on their performance on the Rosedale Outfall Riser Shaft drilling works. The planning and execution of their works was exemplary and produced an excellent result".

Large Diameter Drilling (LDD) has successfully deployed its Reverse Circulation Drilling (RCD) equipment and down-hole equipment install a 17m shaft at a diameter of 1950mm for the subsequent installation of a GRP liner for a discharge riser.

LDD were contacted by McConnell Dowell, the main contractor for North Shore District Council on the new Rosedale Waste Water Treatment works in Auckland, New Zealand. The initial contact was made mid August and after rapid negotiations a letter of Intent was presented to LDD early September. The majority of the equipment was prepared in LDD’s lay down yard in Cornwall prior to shipping in standard ISO containers early October. We also closely managed bespoke fabrication projects both in New Zealand and China to ensure all equipment arrived in a timely fashion, together on the quay in New Zealand to suit the Client’s desired programme.

LDD employed our PBA 408 pile top drill rig, which typically would be utilised for sockets up to 1300mm diameter, the restriction being the clearance through the base of the rig. It proved to be more than capable with dealing with the larger diameter of 1950mm. The LDD design team developed a novel solution which incorporated a false deck (cellar deck) flange bolted between the drilling conductor and drill rig. The large diameter items including the drill bit and bottom hole stabilisers were run inside the conductor and suspended from the false deck, before the drill rig was connected and the drill string run in the conventional fashion.

The main advantage for using the PBA 408 unit is the combination of reduced day rate and shipping space, fast mobilisation/demobilisation times and reduced handling weight particularly above the shaft centre.

Upon LDD equipment arrival the PBA 408 and down-hole equipment were loaded onto MacDow’s floating installation vessel SEATOW – 80 which was subsequently towed to site and held onto position using a 4 point anchor spread. LDD assisted Macdow in the installation of the sub sea frame, placement of concrete and the installation of the drilling conductor casing, during this phase LDD were able gain information regarding vessel movements and onsite weather conditions to ensure the safe and smooth installation of the drilling equipment.

The 1950mm drill-bit proved itself in the rock conditions encountered throughout the target depth of the shaft and out performed the client’s expectations by completing the shaft 1.5 days ahead of the project programme.

The environmentally sensitive surrounding area and close proximity to residential buildings caused concern both for our Client and local Council, all environmental impacts were accessed and working methods modified to suit the impact of noise and light. The PBA 408 demonstrated its minimal noise impact when an on site noise impact assessment was conducted, it fell well within the pre-specified limits.