Deformational behavior of fouled railway ballast

Abstract

Plastic strain of railway ballast subjected to various fouling conditions was determined under simulated traffic loading through testing with large-scale cyclic triaxial equipment. Mechanisms by which fouling material affects the plastic strain of railway ballast were investigated. Fouling content (% by weight of particles <12 mm) increased the plastic strain of ballast by contaminating the contact points of ballast particles. Increasing moisture (>3%) resulted in larger accumulation of plastic strain in fouled ballast under traffic loading. Soil-suction tests showed that plastic strain of fouled ballast with suction >2000 kPa is similar to that of clean ballast, regardless of fouling and moisture content. For noncohesive fouling material (mineral and coal fouling), plastic strain is affected by fouling and moisture; therefore, a noncohesive fouling index (NFI) is proposed. In cohesive (clay) fouling, plastic strain is controlled by moisture and fouling content, as well as compositional characteristics of the cohesive fouling material, primarily represented by Atterberg limits and % mass <0.075 mm. A cohesive fouling index (CFI) is proposed to characterize the deformation of cohesive fouled ballast.