The apparatus consists essentially of a double pipe long enough to reach to the bottom of the test hole and provided at the upper end with a clamp, a pressure connection and a pressure gage, and at the lower end with a set of expansion washers which serve to provide adjustable packing or bushing between the pipe and the bore hole. (See Fig. 12).

The inside pipe 3/6 in. in diameter terminates at the upper end with a tee having the pressure gage on one branch and the pump valve on the other branch. Just below the tee the pipe has a smooth fit in a short vertical sleeve threaded outside and screwed into an adjustable collar. Set screws through the sleeves provide for fixing the pipe relative to the sleeve, and the screwing of the fixed outside collar raises or lowers the sleeve and the attached inner pipe. The lower edge of the outside collar takes indirect bearing on top of the 1-in. pipe which encloses the 3/8-in. pressure pipe and extends to within about 20 in. of the bottom of the latter.

The lower end of the pressure pipe is closed with a plug and has a shoulder or flange engaging a set of 1/4-in. pure-rubber washers that have a diameter just small enough to clear the diamond drill holes.

The washers enclose the pressure pipe and have on their upper surface a steel flange receiving the lower end of a perforated {-in. pipe 12 in. long, provided at the upper end with a flange and washer similar to those described for the lower end. The upper surface of the second set of washers engages a flange on the lower end of the 1-in. casing pipe.

Fig. 12. Apparatus for testing holes in foundation of Olive Bridge dam.

The full length of the test hole below the bottom of the pipe can be tested at one operation by removing the plug in the end of the pressure pipe. When testing near the surface of rock containing nearly horizontal seams it may be well to accompany the test with careful observations of the elevation of the adjacent rock surface for it is entirely conceivable that the pressure might open a seam and raise the rock.

Exploring The Site. Wachusett Dam

The Wachusett dam 1900-1906 is up to date the one whose site was most thoroughly explored and studied preliminary to construction. Nearly 900 wash drill borings and about thirty-five diamond drill borings were made, and the results published, with the specifications, for the information of bidders. A plan, showing the location of all the borings, and four out of the fourteen sections across the valley showing the nature of material and depths to rock, are given herewith. The interpretation of the borings was entirely substantiated later during the excavation. (See Figs. 13-14-15).