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A study on the stress-strain behavior of railroad ballast materials by use of parallel gradation technique

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2004
Kaya, Mustafa
The shear strength, elastic moduli and plastic strain characteristics of scaled-down ballast materials are investigated by use of the parallel gradation technique. Uniformly graded ballast materials chosen for the investigation are limestone, basalt and steel-slag. Steel-slag is a byproduct material of Eregli Iron and Steel Works, which is suitable to meet the durability test requirements as well as the electrical resistivity and the waste contaminants regulatory level. Conventional triaxial testing at a strain rate of 0.4 mm/min is used to obtain these characteristics for the scaled-down materials with a diameter of 100 mm specimen under a confining stress of 35 kPa, 70 kPa and 105 kPa; whereas that of only 35 kPa is used to characterize the accumulated plastic strain. The angle of internal friction, f, and the apparent cohesion, c, may be conservatively taken to be 42o and 35 kPa for all materials. The elastic moduli values for all materials may be predicted within an adequate estimate for the engineering purposes by using the power law parameters, K and n, determined for L-9.5 (D50 = 12.7 mm), the coarsest gradation tested for limestone. K with a reference pressure, pr = 1 kPa and n values for L-9.5, respectively, are 4365 and 0.636 for initial; 8511 and 0.419 for secant; 25704 and 0.430 for unloading-reloading elastic moduli. The unloading-reloading moduli increased, as the number of cycles increased. An increase in unloading-reloading modulus at N = 20 obtained was roughly 15% for scaled-down limestone; 10% for the basalt; and 5% for the steel-slag. The plastic strain after first cycle, e1, and the plastic strain coefficient, C can be represented as a function of mean particle size for each material type. For the limestone, basalt and steel-slag prototype size, D50 = 45 mm, e1 values of 0.59, 0.43 and 0.75 and C values of 0.54, 1.42 and 0.74 are predicted,