Trafficability tests with two vehicles with 9- to 10-ton wheel loads

Abstract

SOIL trafficability studies have been in progress at the U.S. Army Engineer Waterways Experiment Station (WES) since 1946. The results of these studies have been reported in Technical Memorandum No. 3-240, Trafficability of Soils, and 17 supplements thereto, and in other technical reports and miscellaneous papers. The early phases of the work were primarily studies of fine-grained soils. In 1955 the methods and techniques of measuring the trafficability of fine-grained soils were considered to be essentially complete, and a summary report was published[ 1 ]. This repoa contained formulas for computing mobility indexes and determining the soil strength requirements for all military vehicles in existence at that time (1955). Since 1955 there has been a trend toward extra-large, high-flotation tires on small vehicles and extra-heavy wheel loads on large vehicles, in contrast to the more familiar military designs of 21⁄2and 5-ton 6+6 trucks with standard military NDCC tires. Examples of the use of extra-large, high-flotation tires on small vehicles are terra tires used as replacements for conventional tires on 1/4and 3/4-ton trucks. Examples of extra-heavy wheel loads are the 25to 50-ton wheel loads of the B A R C and approximately 10-ton wheel loads of the 16-ton GOER vehicles. Limited data from tests conducted with vehicles mounted with constructionequipment-type tires--a Tournadozert, a 5-ton GOER [2], and a 5-ton Jumbo truck [3 ]--and results of test programs conducted by other agencies, such as Project Wheeltrack [4] and Swamp Fox II [5], indicated that heavy vehicles were immobilized on soil strengths that should have been adequate according to the published formulas. To determine if revisions were needed in the existing mobility index formulas for self-propelled wheeled vehicles, tests were conducted with small, lightweight vehicles mounted with high-flotation tires and with heavy vehicles mounted with construction-equipment-type tires. This paper deals only with the tests conducted with two of the heaviest vehicles. The specific objectives of the tests reported herein were to (a) determine experimentally the minimum soil strength requirements for go (on a 50-pass basis) of two vehicles with 9to 10-ton wheel loads, (b) compare the experimentally determined strength requirements with predicted strength requirements, and (c) investigate the interrelations of repetitive traffic of vehicles with heavy wheel loads and soil strength.