The comfort and safety of a moving train is largely determined by the dynamic response of the railway track and its foundation (i.e., subgrade). To study the dynamic stability of a silt subgrade subjected to train traffic loading with increasing speed, cyclic triaxial tests were conducted for compacted silt specimens with varying dry density, water content, dynamic stress, and load frequency. The laboratory test results and field measurements of the subgrade dynamic stress under train loading indicate that with increasing train speed, an increase in dynamic stress and load frequency does not impair the stability of the silt subgrade, provided the subgrade is in sound physical condition (i.e., its natural water content approximates the optimal water content) and the relative compaction is at least 90%. However, if the relative compaction is 85%, the subgrade is stable only at a dynamic stress level that is below 70 kPa, and the subgrade may suffer shear failure at a higher dynamic stress level. The elastic...

Understanding effect of freezing phenomenon in a fiber-reinforced soil structure is essential to foundation technology, road construction and earthwork application in cold region. This research aims to present the results of experimental investigation relative to the unconsolidated-undrained triaxial compression behavior of fine-grained soil as a function of freeze-thaw cycles and fiber volume fractions. All measurements were carried out for 3 selected glass and basalt fiber fractions (0%, 0.5%, and 1%) and 5 selected freeze-thaw cycles (0, 2, 5, 10, and 15). It has been observed that for the studied soil, strength of unreinforced soil reduced with increasing number of the freeze-thaw cycles while fiber-reinforced soil shows greater effect and the strength reduction amount reduces from 40% to 18%. Moreover, the reduction trend for cohesion of the fiber-reinforced soil decreased, this was seen more prevalent on 1% glass fiber-reinforced soil. The resilient modulus of all specimens reduced with increasing number of the freezethaw cycles. The experimental results demonstrated that different fiber fractions and their mixtures could be employed as supplement additive to improve the freeze-thaw performance of cohesive soils for road construction and earthworks.