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Effects of Lower Tire Pressure on Frost Weakened Roads.
WASHINGTON UNIV SEATTLE
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Every year, thousands of miles of roads are closed or severely restricted to heavy traffic due to structural weakness during spring thaw. Spring thaw, as the period is known, varies in length depending on the severity of the winter. As thawing occurs, pavements become weak due to the high moisture content in the underlying base course and subgrade. In extreme cases, the base course and subgrade can become completely saturated and so weak that less than a hundred passes of an 18,000 pound axle will cause the pavement to fail. Most pavements with high traffic volumes in areas where roads are subject to freezing are designed to resist the effects of spring thaw. This type of construction can be expensive when it is considered that the depth of freeze can be over five 5 feet. Other methods used to resist the weakening caused by spring thaw usually increase construction costs. In this paper the results of a theoretical investigation of lower tire pressure on roads in a severely weakened condition such as is found in spring thaw are demonstrated. With the recent technological development of Central Tire Inflation CTI in the trucking industry, trucks may be able to operate on roads subject to load restrictions. CTI would allow trucks to operate at lower tire pressures on load restricted roads. The second chapter reviews the results of previous studies about the effects of tire pressure, axle loads, and tire type on pavement structures. In Chapter 3, the failure criterion used in this study are discussed. A computer software program designed to calculate strain in multi-layer systems called ELY8M6 was used to determine strains at the bottom of of the asphalt layer and top of subgrade.
APPROVED FOR PUBLIC RELEASE