client, and the order to demobilise plant and equipment was given. In the following months, with the seepage barrier in place, mining operations were able to safely access the seawall hematite ore body and progress with drilling, blasting and excavation below sea level. Conclusions 1. The combination of grouting techniques and the ability to vary techniques along the alignment in response to the conditions found led to the success of the grouting. 2. The use of rapid gelling chemical grout combined with top hammer percussion drilling through the seawall rockfill proved to be an essential method of collaring the holes, which, in turn, would allow the passage of the jet grouting drill string. 3. Jet grouting was proven successful by the end result, and was an effective way to grout both the sediments underlying the seawall and the seawall fill itself, following the initial permeation grouting. 4. Tidal water movement was a constant factor and more pro- nounced during spring tide variations, so the use of rapid gelling grouts were an essential aspect of the success of the grouting works. 5. The grouted solution was a progressive and relatively adventurous proposal, but, with the excellent cooperation of all interested parties, the result was proven to sufficiently reduce and control the seepage through the seawall, which allowed the safe advancement of the Stage 4 pit below sea level. Acknowledgements The author would like to acknowledge the excellent cooperation, support and contribution throughout the project from Watpac Civil and Mining, Pluton Resources, Coffey Mining, and other Wagstaff Piling project team members. The comments and views in the paper are those of the authors and not necessarily those of other parties. Russell Denny, B.Eng (Civil), is a special projects manager at Wagstaff Piling Pty in Queensland, Australia. He has more than 27 years of experience with Wagstaff Piling operating throughout Australia and covering a broad range of deep foundation construction techniques including grouting, jet grouting, diaphragm walls, slurry trench cutoffs, soil mixing, cutter soil mixing, sheet piling, CFA piling, ground anchors, precast piling, driven piling, bored piling including under-slurry work, mass mixing, and platform stabilisation works. Chris Powell, M.Sc., FGS, is a senior geotechnical engineer at Pluton Resources. He is an experienced geotechnical design and construction engineer, specializing in soil and rock mechanics including ground reinforcement, slope stability, settlement, bearing capacity, piling, retaining walls, ground investigation, material characterization, instrumentation, construction works and quality control. DEEP FOUNDATIONS • MAR/APR 2017 • 19
