عنوان مقاله [English]
In the present study utilizing large scale direct shear test, the effect of ballast encasing with geogrid has been investigated. In this mater two ballast grading of 1 and 4 have been considered in conjunction with three types of geogrids GP35/35, GP40/20 and GP60/20. All direct shear test have been carried out under the vertical surcharges of50, 100 and 150 kPa with shear deformation rate of 1mm/min. The outcomes of the results reveals that in absence of geogrid encasing, the shear strength of ballast depends on the maximum particle size, uniformity coefficient and the vertical surcharge value. In the case of geogrid encasing of the ballast has promoted the shear strength behavior whereas for the grade 1 gradation of the ballast, the maximum friction angle corresponding to 50 and 150 kPa surcharges have been 74.5 and 68.96 degrees while the maximum reduction percentage in dilation angle has been 32.22. On the other hand for ballast grading 4, the mentioned variations have been correspondingly obtained as 30.12, 14.67 and 27.86 percentages.