DIAMOND DRILLING FOR FOUNDATION EXPLORATION-Moye
so widely that a triple tube core barrel was used to make a hole in a stiff mud. In the absence of "snorkel" equipment the ordinary core lifter adapter was used, complete with lifter, the marks of which were scored straight along the core. So in this instance (where orientation was immaterial) the inner tube evidently did not rotate.
(2) Core Boxes—(i) The best core boxes the writer has seen were made of dressed wood with hinged lids secured by hasps and staples with a nail or so for security in transit. Once opened the hasps and staples, pegged, were satisfactory for fixture handling. These boxes provided for core in 2 ft. 6 in. lengths and were very convenient in the office : as it happened they were only AM-AXT size.
(ii) By contrast the worst boxes were made for NX core in S ft. lengths. They were of undressed timber of too light a section for adequate strength and rigidity. The 5 ft. length was inconvenient when it was necessary to carry these boxes in the lift of the office building.
(iii) While it is very pleasant to be able to transfer a 5 ft. rim of core direct from barrel to box does such a run occur in the majority of cases. An extreme instance is where a new bit lost its face, thanks to some conglomerate, after a mere 5 in. If this had been followed by a good run of 5 ft. the end of that run would come at the start of the next section in the box.
In another instance the case lifter broke after 3 ft. of drilling and the barrel had to be pulled. Minor breakages of core occur so often that there seems to be no hardship involved in arranging core, properly marked of course, in shorter lengths than 5 ft.
The writers present feeling is that a 4 ft. box is considerably easier to make adequate without excessive weight and is more readily handled.
Reference.
D1. Lang, ]. G.—Some Measurements on the Performance of a Three–Inch Auger Core Soil Sampler. Civ. Engg. Trans. I.E.Aust., Vol. CE9, No. 1, April, 1967, pp. 71-76.
The Author in Reply :
To Mr. Stephenson: Hinged lids on core boxes are certainly convenient for secure transport. However, the lids prevent boxes of core being laid open side by side for inspection and photography, and from being inspected in place when stored in racks. Lids fixed on temporarily by nails or steel bands are preferred for security during transport. The lids are removed when the core is in permanent storage and used again.
During drilling, lifts are made as frequently as necessary to avoid grinding and obtain maximum core recovery. In the Snowy Mountains, where the rocks are characteristically closely jointed and often faulted, lifts are usually made at intervals of less than 5 ft., and often at two or three ft.—see for example the intervals shown on Fig. 1. However, it usually happens that the depth at the bottom of a lift is not a multiple of 5 ft. and therefore the core has to be deliberately broken to fit the 5 ft. long compartments which are pre-marked in intervals of 5 ft.
