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Sewer construction in New Haven, CT needed to avoid open trench methods because of near surface utilities and traffic congestion. The 0.73 km long alignment is in sands with the water table at the tunnel's springline. Designers considered that an EPB machine was ideal for the situation. However the winning contractor chose to excavate the tunnel by hand using an open face shield with breasting boards. The cost of the hand mining method was about half that of using TBMs. Excavations currently average 14 m/day with no excessive settlements., Sewer construction in New Haven, CT needed to avoid open trench methods because of near surface utilities and traffic congestion. The 0.73 km long alignment is in sands with the water table at the tunnel's springline. Designers considered that an EPB machine was ideal for the situation. However the winning contractor chose to excavate the tunnel by hand using an open face shield with breasting boards. The cost of the hand mining method was about half that of using TBMs. Excavations currently average 14 m/day with no excessive settlements.

Early mining at Manhattan demonstrated that blasthole assays alone were insufficient to control the disposition of material. A programme was begun using controlled blasting, intensive sampling and panning of crushed samples, fire assay checks, and geologic inspections to sort material in the pits. Statistical data confirms that the method provides effective control at minimal cost. The cost is easily offset by additional tonnage found in areas considered to be waste., Early mining at Manhattan demonstrated that blasthole assays alone were insufficient to control the disposition of material. A programme was begun using controlled blasting, intensive sampling and panning of crushed samples, fire assay checks, and geologic inspections to sort material in the pits. Statistical data confirms that the method provides effective control at minimal cost. The cost is easily offset by additional tonnage found in areas considered to be waste.

Grade control was formerly by panning assay of samples from 6m blastholes on 5m centres with the blasthole relocated by stadia survey after blasting. Holes assaying above the cut-off grade were flagged and mined as ore. Uneven distribution of gold made assay results unreliable, so an improved technique was introduced which, in some benches, has increased reserves by 50%. Blasthole drilling is now done on a 4m by 4m grid, with an assay sample every 3m. Holes are plotted on a level map together with their assays. The blasting technique used minimises disturbance to the rock enabling examination of its geological features. Mining is done in 3m lifts to minimise dilution; bench height is 6m. Although time-consuming and labour intensive, costs of improved grade control are offset by added tonnages discovered., Grade control was formerly by panning assay of samples from 6m blastholes on 5m centres with the blasthole relocated by stadia survey after blasting. Holes assaying above the cut-off grade were flagged and mined as ore. Uneven distribution of gold made assay results unreliable, so an improved technique was introduced which, in some benches, has increased reserves by 50%. Blasthole drilling is now done on a 4m by 4m grid, with an assay sample every 3m. Holes are plotted on a level map together with their assays. The blasting technique used minimises disturbance to the rock enabling examination of its geological features. Mining is done in 3m lifts to minimise dilution; bench height is 6m. Although time-consuming and labour intensive, costs of improved grade control are offset by added tonnages discovered.