LABORATORY EVALUATION OF FOULED BALLAST UNDER HEAVY-AXLE LOAD AND HIGH TRAFFIC CONDITIONS

摘要

Excessively fouled ballast can result a high amount of plastic settlement and reduction of vertical and lateral resistance of the track. A significant portion of railroad maintenance costs is associated with degraded fouled ballast. Therefore, it is important to understand the effects of ballast fouling at different moisture levels on the behavior of ballast under repeated loading conditions. Development of the testing equipment and procedure to better simulate and evaluate the performance of ballast under heavy loading and high traffic conditions can help the railroad industry to better understand the track risk factors. In this study a modified railroad ballast box test apparatus has been used to evaluate the effect of fouling on the plastic deformation of ballast in different moisture conditions up to 2,500,000 cycles, or the equivalent of 300MGT of heavy axle load traffic. The tests have been conducted under equivalent Heavy-Axle Load (HAL) loading conditions and for ballasts with ＜5%, 15% and 30% fouling. The tests simulate the gradual elastic and plastic deformation of fouled ballast by increase in repetitive cycles of load from dry condition to saturated condition. This paper presents the design and construction of the ballast box device with initial results of the tests. The results show a clear effect of water content and fouling percentage on the amount and rate of both plastic and elastic deformation in cyclic loading. Also, the factor of safety against track failure has been evaluated in highly fouled ballast at saturated conditions.