The advantage of this system is it ensures that the extent and location of all core losses are obvious. This is considered to be essential since core losses generally represent the most important features in the core. Other systems of boxing core, where the pieces of core which have been recovered are simply pushed together, usually insufficiently compacted and with no visual indication of losses, are quite unsatisfactory since the core losses are hidden and at the same time the better rock is overemphasised. It is then no longer possible to obtain a realistic impression of the true quality of the rock mass sampled by the drilling.

Core removed from the box for laboratory testing is replaced by square section timber painted white.

The cores are not removed from the site until logged by the geologist, after which they are taken into storage. They are then kept at least until completion of the project. During this time they may be examined repeatedly by geologists and various engineers as the project develops and by contractors, particularly during the tendering stage.

The cores from each hole are photographed as soon as possible after completion of the hole. Usually this is done from a specially built tripod or platform. Care is taken to have the axis of the camera at right angles to the plane of the core boxes to minimise distortion. The photographs are enlarged to a uniform scale of l in. = 1 ft. They are an extremely useful record, especially where used in conjunction with the geological log.

Results of Drilling.

Useful information is derived from three sources—the drilling process, geological examination of the core, and tests in the drill hole.

Information from the Drilling Process:

The driller is required to fill in a shift report at the drill site and to keep it up to date lift by lift. He is encouraged to record any observations which might be of value. Useful observations include the percentage of drilling water returning to the surface, the nature of the drill cuttings, and any indications of instability of the walls of the hole such as caving. Changes of drill bits are recorded

Geological Examination of the Core :

The geologist logs the freshly drilled core on site as often as practicable. He inspects the driller shift reports and seeks explanations from the driller about possible causes of core losses and about any unusual features in the core. Checks are made to see that the core is correctly labeled and properly boxed. A common error made by inexperienced or careless drillers is to place all or part of a lift upside down in the box.

Logs are made in the field on blank paper prints of the standard log sheet and are later transferred to transparent linen sheets. The scale mostly used is l in. = l0 ft. which means that each sheet covers 100 ft. of drilling.

The present log sheet, an example of which is shown in Fig. l, has evolved through many editions. It is designed to be a compact self-contained record of significant information not only about the core but also about tests on the drill hole.

Detailed headings on the form serve during logging as a check list of items to be recorded. An attempt is made to display the most important features graphically so that the type and quality of the rock can be recognized at a glance. The graphical part of the record is supported by concise written descriptions.