Page:Final Report - The Columbia River Interstate Bridge.pdf/46

 economies afforded by this method of erection have already been mentioned. The work was carried out under the personal direction of Mr. Gay Willard.

(3) The Tacoma Dredging Company moved its hydraulic dredge to the bridge site. installed pipes and pumped its ﬁrst sand on June 9, 1915. By November 20th of the same year all of the embankment of the Union Avenue approach south of Oregon Slough had been placed, so that the placing of this material, which had a total net volume of 821,000 cubic yards. occupied 160 days. or a net average of about 5,000 cubic yards a day.

The material was excavated from the Oregon Slough by means of a suction dredge with a cutting head and was transported to place by being pumped through a line of pipe 24 ins. in diameter. The operation was by electric power and the main pump on the dredge was operated by two 500-horsepower motors. The pump was of capacity to give a discharge through the 24-inch pipe at a velocity of 12 to 15 feet per second. Operation continued 24 hours per day during the time speciﬁed and the dredge was actually running about 14 hours per day. For