TAKING SHAPE

Rotorua Morning Post, Volume 3, Issue 659, 11 October 1933, Page 7

TAKING SHAPE

GREAT AMERICAN DAM NOW NEARING COMPLETION. ELABORATE TESTS Behmd the announctment that the Boulder Dam Conerete Engineering Council has met and ihat actual pouring of the worlds' largest block of conerete is partially under way, lies one of the romantic tales of modcrn natural science, says the Christian Science Monitor. Engineers, and espeeially those at the Reclamation Bureau in Denvtr, are not usually given to regard their business with romance. "Oh, you haven't seen anything yet," they will say when you question them about Boulder Dam. "Comb back in a few years and we will show you a dam ten times larger than that." But in the matter of the conerete for Boulder Dam, it is a differ.nt story, for if ever anything in this world was really tested, from an engineering viewpoint, it has heen the conerete which is to go into that dam. When completed, Boulder Dam will be a solid block of conerete 750 feet high, 650 feet thick at the base, and composed of some 4,400,000 cubic yards of conerete — enough to pave a standard-width highway from Chicago to San Francisco. But this concreto must be more than conerete has ever been before. First, it must withstand the enormous pressure of 30 tons a square foot. Second, it must be able to withstand the wear of water rushing over its surface — in flood time a quantity of water about equal to the Mississippi at St. Louis. Third, it must cool slowly — engineers estimate that if artificial cooling is not installed, it would take Boulder Dam a full hundred years to "cool." In Wyoming, and in south-westeern Colorado, tests were conducted on small mountain streams, with velocity conditions similar to those in Black Canyon, upon many samples of cem--ent to test water wear. Miniature dams were built and spillways, so now the engineers know just what to expect from conerete at the giant dam. Spectacular Test. But the most- spectacular tests were conducted in th'e basement of the new United States Customs House in Dcnver, where the Reclamation Bureau is quartered, ahd where the Boulder Dam was largely planned. A powerful testing machine, made for the Bureau hy the Baldwin Locomotive Works, was erected. In this machine conerete cylinders 36 inches in diameter, six feet high, and weighing some 6000 pounds apieee, were tested for diametrical expansion and compression strain. Then the conerete columns were set in the testing machine. The pressure was exerted, slowly at first, then in jumps — it was just about the nearest imaginable approach to the ancient physicists' dream of an immovablfe object struck by an irresistible force. Upward went the pressure until the maximum compression of 4,000,000 pounds had almost been reached, and then with ;a crack and; shock that jarred the block-long building, the big, solid conerete column crumbled. Day after day, month' after month, for two years ,the tests went on, and then the Conerete Coucil met, heard ;the evidence of rushing mountan streams, of almost inconceivable pres- ■ sures, and judged. Actual pouring ' followed. In the matter of cooling, it was decided to embed more than 160 miles of steel piping- in the conerete mass. Gold water will be pumped through this two-inch piping, and the "cooling" of the conerete effected in a relatively shor't time.