Constructing CSM panels that the bagging procedure and sealing of the bags was inconsistent and that water was leaking into some of the bags during the voyage from Seattle, hydrating portions of the cement and requiring introduction of additional screening and significantly more manual labour effort at the “big-bag” station to remove the hydrated clumps of cement before they could enter the slurry mixing system and create a blockage. Due to the lag time generated by removing the hydrated clumps from the screens, it was also necessary to introduce a separate in-line cement silo, to facilitate uninterrupted CSM production by ensuring a ready supply of cement available to the mixing plant. Two CSM rigs were planned to operate simultaneously, with each rig scheduled to operate for 36 hours and then take a 12- hour break for maintenance. The reality was somewhat different. Wear and tear on the rigs, and in particular on the cutter head, was strongly influenced by geotechnical conditions across the site, with generally greater maintenance required in the zones where the CSM panels penetrated through compact to dense sand and gravel and cobble zones. 58 • DEEP FOUNDATIONS • JAN/FEB 2015 Extensive hard surfacing and cutter tooth replacement was required in these areas, with trialing of several tooth configurations necessary to develop an optimal mix of cutting productivity and tooth longevity. On average, it was necessary to replace 10 teeth per CSM panel, with instances where the entire tooth was sheared off by the aggressive ground conditions. The adoption, towards the end of the project, of Bauer’s recently developed “TungStud” wear reduction system, proved highly beneficial, particularly in the more aggressive conditions where gravels and cobbles were present, reducing the routine maintenance to about 50% of that previously required. Quality Control The management of the quality of the in- si tu product was of paramount importance to the project. Since the geometry of the installation was clearly defined and readily verifiable, the focus of the quality control program was on verification that the target strength, as defined by the design specifications, was consistently met or exceeded. Sampling of the in-situ mix at Kitimat involved both wet-grab sampling from within a newly completed panel and coring of suitably cured panels. Wet-grab sampling was completed using a custom sampling tool suspended from a 65T crawler crane that vibrated to the target depth in a panel using a hydraulic vibratory hammer with a 25T drive force. Typically, samples were retrieved from at least four depth intervals within a panel, the deepest sample being from about 22 m (72 ft) below grade. Initially, samples were tested at 7, 14, 28 and 56 days to assess strength gain with time and provide early warning of any issues with the mix design; however, as confidence in the mix increased, the 7- day test was omitted. In total, 230 panels (14%) were sampled using the wet-grab technique, within the order of 6,300 cylinders prepared, and a total of 4,125 Unconfined Compressive Strength (UCS) tests completed. The average 56-day strength observed in the wet-grab samples across the site was in the order of 3.8 MPa (551 psi), with over 90% of the samples exceeding the specified strength at or before 56 days. Large variations were noted
