The cost of core drilling varies between much wider limits than almost any other kind of work. For large holes for wells or elevator foundations it may often be the case that the contractor has, from adjacent work, a quite accurate knowledge of the rock which will be encountered; further, the site is usually more convenient and accessible and the conditions are better, so that bids may be received at a reasonable price per foot. For strictly exploration purposes it is usually altogether more satisfactory for everybody concerned to arrange for such work on a basis of cost plus either a percentage or a fixed sum. Such holes are usually shallower, more scattered, at sites more expensive of access, may be in deep or running water requiring rafts, crib work or even suspended staging to support the drill; in fact, every condition is not only more expensive but more uncertain. A price per foot must include all the uncertainties, and nine times in ten it will much more than cover the cost.

In rock not too hard, free from seams and with all conditions exceptionally favorable, the cost per lineal foot might be as low as $1, or even slightly less. Several recent large holes in New York City cost not including plant and overhead charges as follows:


In Fordham, gneiss and granite conditions rather difficult.

2000 ft.,

10-in. diam. hole

cost per foot


14 ft.,

30-in. diam. hole

In trap-rock concrete con- taining steel I-beams.

cost per foot


775 ft.,

6-in. diam. hole

In mica schist and quartz

cost per foot


550 ft.,

8-in. diam. hole

In mica schist and quartz

cost per foot


50 ft.,

20-in. diam. hole

In mica schist and quartz, five holes each 50 ft. deep

cost per foot


On the other hand, the following extremely high cost is due to the most adverse conditions possible.

Conditions: remote Western river, borings made in the bed of a river 160 ft. wide; drill worked on suspended staging for which timbers and guys had to be imported; temperature below freezing and for much of the time below zero; one-half of the river 2 ft. to 4 ft. deep, remainder about 30 ft.; casing had to be put down to bed rock to keep running sand out of hole, though in only one case did casing have to be sunk through any loose material; some running logs and ice took out casing and broke core barrel several times; first machine was too light for the work and another was expressed to the job; some delay waiting for repair parts and on account of distance from repair shop; boiler on shore piped steam to engine operating drill, all holes tested at several depths by hydraulic pressure from hand pump; rock not very hard but tilted up to 15 deg. to 30 deg. from vertical and much distorted so that holes frequently choked.

The drill runner was skilful and industrious, and the contractor did all that was humanly possible to further the work. Eleven borings 12 ft. to 45 ft. in rock, were made for 329 total lineal feet. The hole was 3 in. in diameter and was made with a shot machine in January, February and March, 1913. The erection of staging and making borings cost as follows:

Labor pay roll...........................


Freight, express,cartage..................


Materials, including carload of coal.............


Rental, engine and boiler.....................


Plant 1968.43 minus salvage 1654.94.......


Railroad fares of crew.................


Traveling expenses of contractor..................


Provisions and camp outfit.......................


Insurance, telegraph, and miscellaneous.......



Equals $30.76 per lin. ft.

The above is cited only as showing what the cost might run to under extremely adverse conditions. For fairly accessible location, holes on land or from inexpensive supports in easy water, moderate weather conditions and good management, the cost should not be over $6 or $8 per lin. ft. and might often be much less. The cores, it need hardly be said, should be preserved strictly in the order that they came from the hole. The best way to keep them is in shallow trays with longitudinal partitions, the depth of tray and width between the partitions being just sufficient to include the diameter of the core. On the top of the partitions should be tacked thin strips such that none but the smallest fragments can drop out or be removed, while still permitting examination of the cores. (See Fig. 10.) With each withdrawal of the core barrel the pieces should be laid in their order and the depth marked on the partition; obviously the distance between two depth marks on the partition may be less than the distance indicated by subtracting one depth from the other; the relation will depend upon the percentage of core recovered.