Page:Final Report - The Columbia River Interstate Bridge.pdf/49

 was constructed in a similar manner by an electrically operated suction dredge with 20-inch diameter pipe equipment. The maximum distance the material was carried was about 6,500 feet.

Looking toward Portland along the completed Union Avenue approach embankment. Width between fences 40 ft., pavement 30 ft. Height of embankment above surrounding ground about 25 ft.

There were several slips or subsidences of the supporting land caused by placing the great weight of the embankment on it, but they were less in number or in aggregate amount than had been anticipated or suggested by the speciﬁcations. The subsidences of the land probably average less than one foot over the whole area of the embankments. but in three locations there were considerable subsidences. of which two instances required merely the reconstruction of some bulkheads and the placing of additional material. The third and most serious was a subsidence combined with a slide at the south side of the Columbia Slough, which, although causing only comparatively small loss of embankment, destroyed the practically finished pier No. 27 in the slough. The weight of the wet sand embankment on the soft, oozy bottom of the slough and on the somewhat slippery bank was too much for the stability of the supporting material, and a part of the bank and the new sand just placed slid out into the slough, causing the damage to the substructure. The buried pier "F" on the land side of the slip was not disturbed by the move-