ICE PRESSURE

Greymouth Evening Star, 14 March 1936, Page 5

ICE PRESSURE

AMERICAN TESTS

Discovery of tremendous ice pressures, far greater than engineers have hitherto taken into account, may lead to large, savings in improved’ frost-resistant highways, according to investigations carried on at the Harvard Graduate School of Engineering by Prof. Arthur Casagrandle (says the “Christian Science Monitor”). Exhaustive tests disclosed that forces exerted by these ice pressures beneath highways causing heaving and cracking, far exceed 11 theoretical expectations. Professor Casagrande’s installation last year of one of the most complete “cold 1 room” laboratories for soil research in the world, made these studies possible. With such equipment he can reproduce and control natural ice formations at will.

Perhaps the most important discovery made, was that pressure exerted by crystallizing ice against the soil in which it is confirmed, is not the same for all freezing temperatures as was generally supposed. It was found that the pressure increases in proportion to the amount of temperature decrease below the freezing point. Thus at low temperatures such as are reached in the more northerly regions of the United States and Canada, exceptionally huge pressures are built un beneath highways. Furthermore, if the freezing progresses slowly enough, ice layers may continue to grow indefinitely. Professor Casagrande also discovered' that in sandy and silty soils, water for such “growing” ice layers is supplied from free ground water in the soil beneath.

Investigations carried on in New Hampshire in co-operation with the United States Bureau of Public Roads and the State Highway Department, in which heavings as high as six inches were found, led to the building of Harvard’s new cold room. Under extreme conditions, such heaving may reach more than a foot, said Professor Casagrande. “In clean sand and gravel wo have found no growth of ice lovers, either in field or laboratory observations. Such materials are therefore advised for use extensively in highway construction in places where the underlying soil would cause serious trouble if it were nenetrated by frost of any considerable dentin’’

Apparently, in certain soils, the water between soil particles not only freezes but such ice crystals as are formed continue to prow, forming layer after layer which ultimately reach considerable thicknesses.