Burnett, W. R.

2018-03-29T12:21:36Z

2018-03-29T12:21:36Z

1953

The main conclusions and findings of this investigation may be summarised as follows:-

(1) The Geophysical Megger Earth Tester is an admirable machine for resistivity work. The only trouble experienced was the entry of water into the generator during very wet weather.

(2) With very thin vertical sheets the longitudinal traverse gives a more positive and more easily recognised anomalous resistivity curve.

(3) With thin vertical sheets the transverse traverse gives a better idea of the likely direction of the sheet.

(4) W- shaped resistivity curve is obtained from longitudinal traverse over both conductors and insulators, but with the former, the centre of the anomaly never rises above the country resistivity.

(5) The problem of traversing over vertical sheets may be solved by the theory of images. The resulting equations, although complicated looking, may be solved by various short cut methods.

(6) The types of curves obtained from longitudinal traverses vary greatly according to the thickness of the sheet, there being a typical curve for widths of sheet between integral multiples of the electrode interval until the sheet becomes wider than the whole electrode spread. These curves should be valuable in the interpretation of vertical bodies with wide extension along the strike such as dykes, fault planes or zones and highly dipping strata.

(7) Transverse traverses over thin insulating sheets yield a double peaked apparent resistivity curve. This soon gives way to a single peak as the sheet width increases. The converse, i.e. double and single troughs, is found over conductors.

(8) The problem of traverses over inclined sheets cannot be solved by the theory of images, but type curves can be obtained from laboratory experiments.

(9) Buried sheets yield similar but more rounded and less evident curves as the depth of cover increases.

(10) The method of traversing can often prove valuable in the field in the location and exploration of faults, dykes and buried channels. Shallow underground fires may also be within its scope.

(11) Two -layer problems are best_-solved by Tagg's method. Moore's method of cumulative resistivity curves cannot be held as satisfactory.

(12) The effect of lateral variations in resistivity on depth probes can be investigated by the theory of images, and can often be recognised in the field curves. Expanding probes crossing an interposed sheet of different resistivity will yield resistivity -depth curves with recognisable discontinuities. Depth probes parallel to the strike of such a sheet yield curves similar to those of two or three horizontal layers and great care will be required in their interpretation and recognition.

http://hdl.handle.net/1842/29483

The University of Edinburgh

Annexe Thesis Digitisation Project 2018 Block 17

The earth-resistivity method of geophysical surveying

Thesis or Dissertation

Doctoral

PhD Doctor of Philosophy