HUGE DREDGE CRAWLS HILLS TO FRESH ORE
By PHIlIP HAMPSON
A story of an unusual engineering feat undertaken at below zero temperatures was brought to Chicago from Steep Rock lake, Ont., last week by Paul H. Blair, a naval architect employed by the Construction Aggregates corporation, widely known Chicago engineering firm.
The feat involved the moving of two huge dredges from one iron ore body on the lake to another two miles distant over steep and winding roads.
Steep Rock lake is the site of a vast iron ore deposit -- about 700 miles north of Chicago -- from which the mining of ore was started some years ago. Chicago's Inland Steel company has leased a large ore deposit area at the lake from which it expects to start moving high grade iron ore to Indiana Harbor in about 1960.
The dredge moving job is being done for Steep Rock Iron Mines Ltd., whose properties adjoin the Inland Steel leasehold. Iron ore is taken from ground below Steep Rock lake after some 250 feet of water and overburden of sand, mud, and rock have been removed by dredges.
When all the water and overburden were removed at one section of the lake the mining company sought a way to move the dredges to another point about two miles distant without going thru the painful work of tearing them down and rebuilding them at the new site.
Blair with the collaboration of the Manitowoc Engineering company developed an ingenious means for doing the job. All water was completely removed from a construction site in the lake and a number of cribs built.
Enough water was permitted to flow back into the lake to form a pool sufficiently deep to permit the dredges to be floated onto the cribs. After this was done the water was pumped out of the area again, leaving the dredges standing on the cribs.
Mounted on Tractors
Giant 20 ton crawler-
A block and tackle system using tractor power provided the motive power for moving the dredges. Other tractors pushed. The dredges weigh about 850 tons apiece. One has already arrived at its new site and the other is enroute there.
The Steep Rock country is wild and inhospitable, with temperatures in winter dropping to as low as 56 degrees below zero. When Blair left there last week it was 36 degrees below zero.
The road over which the dredges travel has grades at points of from 8 to 11 degrees. Each dredge is 140 feet long, 40 feet wide, and 10 feet deep. They are equipped with pumps powered by 6,000 horse power electric motors for getting rid of the water and overburden.
Lift 55 Million Yards
Blair said that these two dredges removed 55 million cubic yards of overburden from the lake before exposing the ore. More than a million tons of iron ore has been taken from the earth. Ore is moved by rail from Steep Rock lake to Port Arthur on Lake Superior from which it is moved to steel mills by lake ore boats.
Construction Aggregates has the contract for removing the water and overburden from Inland Steel's property. Powerful dredges equipped with pumps run by 10,000 horse electric motors will be used for getting rid of water and overburden.
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