Influence of moisture content on shear behavior of differently aged ballast mixture

Ballasted tracks are the most common railway tracks worldwide, consist of coarse aggregates (19-63 mm) that facilitate drainage. Over time, ballast particles degrade due to train-induced attrition and abrasion, generating fines that clog voids and reduce drainage efficiency. Increased moisture further leads to cyclic plastic deformation. This study examines the mechanical behavior of differently aged ballast mixture under monotonic triaxial compression tests in three moisture conditions viz. air-dried, saturated, and unsaturated (matric suction= 5 kPa) to study the mechanical behavior of in-situ railroad ballast. Field investigations on Indian Railways show that tracks typically contain 80-90% clean ballast (CB) and 10-20% aged ballast (AB). A test mixture (MIX 1) with 90% CB and 10% AB was used to analyse shear behavior. Results reveal that aging significantly weakens shear strength, especially in saturated and unsaturated conditions, highlighting that both aging and moisture negatively affect ballast performance, making drainage and stability are crucial for track integrity.