Cyclic smear strength of soft railroad subgrade

A laboratory study was conducted to investigate the behavior of a soft comp acted clayey soil subjected to repeated loading. The work was part of a com prehensive investigation of the Low Track Modulus section at the Facility f or Accelerated Service Testing, operated by the Association of American Rai lroads Transportation Technology Center in Pueblo, Colorado. The goal of th e study was to quantify the stress-strain behavior of the LTM subgrade soil subjected to physical and stress conditions existing under train traffic. To achieve this goal, cyclic triaxial tests were conducted on tube samples at their natural water content and on samples subjected to back-pressure sa turation. Results indicate that the normalized cyclic shear strength is sen sitive to drainage conditions and degree of saturation. Data trends indicat e that cyclic strength may decrease by approximately 80% as the initial deg ree of saturation is increased from 90 to 100%. Field observations of persi stently accumulating shear deformations in the the LTM subgrade are consist ent with the strength criteria developed in this study.