. Journal of the New England Water Works Association . rock continued then until the rock outcrop at the noil h end of the damwas reached. The lengths of piles to be driven were at first determined by scalefrom the rock profile developed by the original borings, hut on account ofthe great unevenness of the rock it was later found to be better to make 460 THE DEEP CORE-WALL OF THE WANAQUE DAM. careful soundings, with the pile-driving rig and a steel rail, on the line ofpiling to determine the appropriate lengths of piles more accurately inadvance. After the sheeting had been extended to the nor
. Journal of the New England Water Works Association . rock continued then until the rock outcrop at the noil h end of the damwas reached. The lengths of piles to be driven were at first determined by scalefrom the rock profile developed by the original borings, hut on account ofthe great unevenness of the rock it was later found to be better to make 460 THE DEEP CORE-WALL OF THE WANAQUE DAM. careful soundings, with the pile-driving rig and a steel rail, on the line ofpiling to determine the appropriate lengths of piles more accurately inadvance. After the sheeting had been extended to the north end, the pile-driving rigs were moved to the other end of the walls of piling, the frame up and the same methods used to extend the sheeting to the south endof the dam. When possible, sets of three piles were driven at one time butwhen the penetration became difficult two piles were driven and finallyfor the deepest part only one pile was driven at a time. The maximumlength of penetration was 84 ft. and the slowest driving in that vicinity. > • Hi lT*iiiih i~ *? y Sheet Piling Rig, Guide Frame and Derrick. was some 90 blows to the inch. The vertical position of the piling as estab-lished by the first set driven was maintained throughout the job so thatno special wedge shaped pieces were required. A typical gang consisted of 1 foreman, 1 pile-driver operator and6 pile-driver men for each rig. Two rigs were run under one generalforeman and high pressure steam was supplied from a central plant so thata fireman was not usually employed with the driving rig. Pile-drivingprogress for two rigs is shown in Table 1. TABLE 1. — Progress of Driving of Steel Sheet-Piling. Month. Sq. Ft. Month. Sq. Ft. April, 1921 5 600 November 900 May 6 500 December 200 June 9 200 January, 1922 100 July 14,700 February 15 800 August 5 200 March 6 000 September 6 600 April 9 900 October 12 800 May 6 400 Total 99 900 PRATT. 461 Excavation. As soon as the driving was completed at the north
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