Simulating Ballast Shear Strength from Large-Scale Triaxial Tests

Abstract

The railroad ballast layer consists of discrete aggregate particles, and the discrete element method (DEM) is the most widely adopted numerical method to simulate the particulate nature of ballast materials and their particle interactions. Large-scale triaxial tests performed in the laboratory under controlled monotonic and repeated loading conditions are commonly considered the best means to measure macroscopic mechanical properties of ballast materials, such as strength, modulus, and deformation characteristics, directly related to load-carrying and drainage functions of the ballast layer in the field. A DEM modeling approach is described for railroad ballast with realistic particle shapes developed from image analysis to simulate large-scale triaxial compression tests on a limestone ballast material. The ballast DEM model captures the strength behavior from both the traditional slow and the rapid shear loading rate types of monotonic triaxial compression tests. The results of the experimental study indicated that the shearing rate had insignificant influence on the results of the triaxial compression tests. The results also showed that the incremental displacement approach captured the measured shearing response, yet could save significant computational resources and time. This study shows that the DEM simulation approach combined with image analysis has the potential to be a quantitative tool to predict ballast performance.

Effect of Particle Size Distribution and Packing Characteristics on Railroad Ballast Shear Strength: A Numerical Study Using the Discrete Element Method

“…For example, typical specimen sizes selected by researchers for direct shear testing of railroad ballast are 400 400 300 mm mm mm  (Dissanayake et al, 2016), 300 300 200 mm mm mm  (Indraratna et al, 2012;Ngo et al, 2014). Similarly, typical cylindrical specimen sizes used for triaxial monotonic shear strength testing of railroad ballast are, 610 height 305 diameter mm mm  (Qian et al, 2013(Qian et al, , 2015Mishra et al, 2014a), 600 height 300 diameter mm mm  (Indraratna et al, 2009(Indraratna et al, , 2012Lu and McDowell, 2010;Ngo et al 2016), 508 height 254 diameter mm mm  (Kashani et al, 5 2017, Rohrman et al, 2017, 300 height 150 diameter mm mm  (McDowell and Li, 2016).…”

“…Owing to the large particle-size (often as large as 63 mm ) of railroad ballast, significantly large specimens have to be tested in the laboratory for realistic estimation of the shear strength properties. For example, typical specimen sizes selected for triaxial monotonic shear strength tests are, 610 height 305 diameter mm mm  (Qian et al, 2013(Qian et al, , 2015Mishra et al, 2014a). A schematic of the stresses applied to the specimen in a triaxial test setup is shown in Figure 2.8.…”

“…Once a "primary" specimen is created and tested under simulated (Indraratna et al, 2012;Ngo et al, 2014Ngo et al, , 2015Wang et al, 2015); or (c) polyhedral particles Qian et al, 2013). Decisions regarding the particular approach to use are primarily dependent on (1) capabilities of the modeling software used, and (2) nature of the granular assemblies being modeled.…”

“…The triaxial shear strength test is traditionally performed in the laboratory to evaluate the effects of monotonic and repeated loading on ballast behavior (Indraratna et al, , 2009Suiker et al, 2005;Aursudkij et al, 2009;Lu and McDowell, 2010;Qian et al, 2013Qian et al, , 2014Qian et al, , 2015Mishra et al, 2014a;McDowell and Li, 2016;Ngo et al, 2016).…”

“…The simulated model was calibrated using laboratory data extracted from research study conducted by Qian et al (2013). The ballast material tested by Qian et al (2013) …”