ميرعبداله اميرحسين

Ballast, as a key component of railway track structures, plays a vital role in load transfer, lateral stability, an‎d controlling permanent deformations. Improving the mechanical behavior of ballast, especially its shear strength an‎d volumetric response, can greatly extend the service life of railway lines an‎d lower maintenance costs. This study examined the effect of using rubber strips as an environmentally friendly reinforcement method on the shear behavior of ballast. To achieve this, a series of large-scale direct shear tests was performed on unreinforced ballast specimens an‎d specimens reinforced with 6, 12, an‎d 18 rubber strips under three normal stress levels of 50, 100, an‎d 150 kPa. Shear strength parameters, including internal friction angle, apparent cohesion, an‎d dilation angle, were determined an‎d analyzed from the experimental results. The findings show that rubber strips generally improve the shear capacity of ballast an‎d help control volumetric deformations. At a normal stress of 50 kPa, the peak shear strength of specimens reinforced with 6, 12, an‎d 18 strips increased by roughly 31%, 47%, an‎d 67%, respectively, compared to unreinforced specimens. At 100 kPa, the corresponding increases were approximately 18%, 23%, an‎d 34%. When the normal stress reached 150 kPa, the greatest shear strength gain was observed in the specimen reinforced with 12 strips, with an increase of about 19%. Increasing the number of strips to 18 did not further improve shear strength. Meanwhile, the horizontal displacement at peak shear stress decreased in reinforced specimens, indicating increased stiffness an‎d quicker mobilization of shear resistance. From a volumetric perspective, results reveal that rubber strips effectively inhibit dilation an‎d promote internal confinement within ballast. The dilation angle at the first normal stress level decreased from about 17° in unreinforced specimens to around 12.6° with 12 strips (a 26% reduction), an‎d further to approximately 6.8° with 18 strips (a 60% reduction). Similar patterns were seen at higher stress levels, confirming the effectiveness of rubber strips in managing volumetric behavior. However, the sharp reduction in dilation angle for specimens with 18 strips suggests excessive confinement an‎d a tendency toward a critical state. Analysis of shear strength parameters showed that apparent cohesion increased with the number of rubber strips, becoming roughly two an‎d three times higher than in unreinforced specimens for the 12- an‎d 18-strip setups, respectively. Conversely, the internal friction angle slightly decreased, reducing by about 8% with 12 strips an‎d approximately 30% with 18 strips. This indicates that, although more strips boost apparent cohesion, the reduced friction component could negatively impact the overall shear performance when excessive reinforcement is used. Overall, this study demonstrates that the best results come from using 12 rubber strips, which balance improvements in shear strength, maintain internal friction, an‎d efficiently control dilation. Therefore, this reinforcement approach offers a promising an‎d sustainable solution for enhancing the mechanical performance of ballast in railway track systems.

بالاست راه‌آهن , نوار‌هاي لاستيكي بازيافتي , ، آزمايش برش مستقيم بزرگ‌مقياس , مقاومت برشي بالاست , رفتار حجمي بالاست , زاويه اصطكاك داخلي

Railway ballast , recycled rubber strips , large-scale direct shear test , ballast shear strength , ballast volumetric behavior , internal friction angle

Amirhossein Mirabdollah

Dr. Alireza Tolou Kian