Laboratory Investigation of Geogrid Reinforced Railroad Ballast Performance on Particle Movement

Produced with a Trial Version of PDF Annotator - www.pdfannotator.com Laboratory Investigation of Geogrid Reinforced Railroad Ballast Performance on Particle Movement Shushu Liu Graduate Research Assistant The Pennsylvania State University 327 Research Dr Office 49 Phone: (84)8659669 Email: sxl45@psu.edu Hai Huang Associate Professor The Pennsylvania State University 26D Penn Building Altoona, PA 66 Phone: (84) 949-5346 Email: huh6@psu.edu Tong Qiu Associate Professor The Pennsylvania State University 226A Sackett Building University Park, PA 682 Phone: (84) 863-735 Email: tqiu@engr.psu.edu Word Count: 3347 Words + Figures (275 Words) = 697 Words AREMA 26 965

Abstract In railroads, ballast particle s movement including translation and rotation is one of the railway track maintenance issues. Ballast movement results in settlement of railway track. Geogrid, used as reinforcement in ballast layers, can create interlocking with ballast particles to confine the particle movement. In order to investigate the effect of geogrid on particle movement in ballast, a half section of railway structure, consisting of a rail, two crossties and a ballast layer, was constructed in a ballast box. A sheet of geogrid with triangular aperture were placed 25 cm below the top of the ballast. A wireless device SmartRock was embedded underneath the rail seat and the edge of the tie in the ballast layer, respectively, to record the particle rotation and translational accelerations under cyclic loading. Also, a ballast box test without geogrid was conducted as a control. According to compare the test results between the two types of ballast box tests, the results indicate that ) ballast particle had significant horizontal translational movement and rotation under cyclic loading; 2) ballast particle s movement were more consistent within the geogrid included in the ballast; 3) the vertical displacement at the top of the ballast layer were significantly reduced within the geogrid; 4) the stiffness of the ballast layer with and without geogrid were close under 5 cyclic load repetitions, but the stiffness of the ballast layer with geogrid reached a steady-state value much faster than that without geogrid. The laboratory investigation also demonstrates that the SmartRock is able to record the real-time particle translational and angular accelerations, hence can be used as a monitoring tool of railroad maintenance. 966 AREMA 26

INTRODUCTION Railroad track structure are susceptible to track geometry defects resulting from excessive movement and particle rearrangement within ballast layers. Under good condition of track geometry or alignment, track will have no need for frequent maintenance, and thus can significantly reduce maintenance cost. Ballast is an unbounded granular medium that move laterally under high frequency repeated loading (Indraratna et al. 23). In order to reduce lateral movement of ballast particles, geogrid reinforcement is widely used in ballast and subballast layers as it provides confinement through interlocking between geogrid aperture and individual particles. Especially in railroad applications, due to uniform distribution of the ballast/subballast particles, numerous research studies agreed that geogrids can effectively stabilize ballast/subballast layers (Bathurst and Raymond 987; Matharu 994; Raymond 22; Shin et al. 22). Consequently, the track maintenance cost is largely reduced and the maintenance interval is increased (Walls and Galbreath, 987; Brown et al. 26). On the other hand, research efforts have been documented and attempted to investigate the relationship between geogrid properties and ballast performance aiming at optimization of geogrid application. For example, laboratory pull-out tests were conducted to investigate the fundamental mechanics of ballast/geogrid interactions (Jewell 99; Brown et al. 27; Chen et al. 24); McDowell et al. used the discrete element method (DEM) to propose a ratio of.4 between geogrid aperture size and ballast particle diameter to achieve optimum performance; Qian et al (23) proposed a DEM model to optimize the position of geogrid in the ballast layer through large-scale triaxial shear strength testing. However, very little research has been completed to quantify the effect of geogrid on ballast particle movement. Knowledge based so far, although limited, has showed that ballast performance is highly dependent on individual particle movement (Raymond 22; Saussie et al. 26; Tutumluer et al. 26 and 27; Liu et al. 26) ballast settlement is a process of particle compaction and rearrangement as a means of translation and rotation. Under repeated loading, ballast particles can never get stabilized (Liu et al. 26). Therefore, an investigation of particle translational and angular movement pattern would help understanding ballast performance with geogrid at a level of individual ballast particle movement. This paper aims to investigate the effect of geogrid on particle movement inside railroad ballast. A ballast box was constructed to simulate a half section of railroad track structure. Two ballast box tests were conducted: one without geogrid as a control and one with geogrid. A wireless device SmartRock was embedded in the ballast box to monitor individual ballast particle movement under cyclic load. The measured particle movements in unreinforced and reinforced ballast are compared. Conclusions are reached on the effect of geogrid on ballast particle movement and the applicability of the SmartRock device as a potential monitoring tool in railroad ballast research. BALLAST BOX The constructed movable ballast box has a dimension of 244 cm (long) 83 cm (wide) 2 cm (high), as shown in Fig. and Fig. 2. The ballast box was composed of a steel frame, angle beams, a sheet of steel board and four sheets of plywood. The plywood was attached to the side walls; whereas the steel board was placed at the bottom of the ballast box to mimic a relatively rigid foundation. Angle beams with a spacing of 6 cm were welded to the side walls to reinforce the steel frame. AREMA 26 967

Fig.. Movable ballast box A A 83. B Vertical Loading 244. 2. 89. Cross Section A-A Vertical Loading 83. 2. 89. Cross Section B-B Rail Tie Ballast BALLAST AGGREGATE PROPERTIES Fig. 2. Geometry of ballast box (unit: cm) Clean angular limestone aggregates were used in this study. The gradation of the ballast, as shown in Fig. 2, conforms to the No. 4A gradation requirements of the American Railway Engineering and Maintenanceof-Way Association (AREMA). Morphological properties of aggregates are known to affect performance in terms of strength, modulus and permanent deformation. Current practices consider the effects of physical properties of aggregates, such as shape, texture and angularity on the strength, stability and performance of the railroad trackbed. To qualify those properties of aggregate materials, the image analysis device, University of Illinois Aggregate Image Analyzer (UIAIA), was utilized to analyze images and compute three morphological indices, i.e., angularity index (AI), flat and elongated (FE) ratio, and surface texture (ST). The UIAIA uses 3 orthogonally positioned cameras to capture 3-dimension shape properties of aggregates. These indices are determined based on the particle image outlines obtained from each of the top, side and front views. The lower bound of AI is, which represents a perfect sphere with no angularity, while the upper end could reach 7-8 degrees, indicating very high angularity. The ST index typically exhibits 968 AREMA 26

Passing Percentage (%) values up to for smooth gravel with higher values for increasing angularity, crushed faces, corners and jagged edges in the case of % crushed stone (AI-Rousan et al. 27). The results of the image analysis are shown in Table and Fig. 3. The shape of ballast aggregates was angular with a rough surface texture. 8 6 4 2 AREMA No. 4A Ballast aggregate 2 3 4 5 6 7 Particle Size (mm) Fig. 2. Gradation of limestone ballast material Table Particle Shape Characterization Physical Properties Angularity Surface Texture Average 47.3 2.2 Maximum Value 632.2 4.5 Minimum Value 293.9.3 Standard Deviation 89.7.7 GEOGRID PROPERTIES Fig. 3. Images of individual aggregate particles The principle function of geogrid in ballast stabilization is to laterally confine the ballast to minimize movement of the ballast particles, reduce downward dynamic ballast migration, and increase time between track maintenance operations. Table 2 lists the properties of the large aperture multiaxial geogrids used in the tests. The sheet of geogrid has a dimension of 24 cm (long) 8cm (wide) and was placed in a way that the machine manufactory direction of the geogrid was in the same direction as the length of the ballast box. AREMA 26 969

Table 2 Physical Properties for Geogrids Used in Track Stabilization Aperture Shape Triangular Aperture size (mm) 6*6 Radial stiffness @.5% strain (kn/m) 35 Flexural rigidity (Machine direction) (mg-cm) 2,, Junction efficiency (%) 93 INSTRUMENTATION SMARTROCK A proprietary wireless device SmartRock, as shown in Fig. 4, was utilized to monitor ballast particle movement under cyclic loading. The development of the SmartRock was explained in detail in Liu et al. (25b). The SmartRock is composed of a tri-axial gyroscope, a tri-axial accelerometer, and a tri-axial magnetometer, which can record rotation, translation, and orientation in 9 degrees of freedom, respectively. The SmartRock is capable of sending raw data to a base station for visualization and analysis via the Bluetooth. 3D printing technology was employed to form the shape of the SmartRock similar to a real ballast particle. It should be noted that the weight and size of SmartRock could potentially affect the measured particle accelerations. The nominal dimensions of the SmartRocks used in this study are 6 cm 6 cm 6 cm, as shown in Fig. 4, which are slightly larger than the nominal maximum size of AREMA No. 4A aggregate (see Fig. 2) and, hence, considered acceptable for the purpose of this study. TEST SETUP Fig. 4. A photo of SmartRock A half section of a typical railroad track structure that consists of a ballast layer, two crossties, and a rail (Ibeam) was constructed in the ballast box, as shown in Fig. 5. The ballast aggregates were poured into the ballast box in three layers. The aggregates were leveled on each layer. A 2H: V slope as typical in a railroad ballast layer was formed at the top. Two ties were placed on the top of the ballast layer with /3 of the depth buried into the ballast. 97 AREMA 26

Load actuator Rail (I-beam) Tie plate z y x Rail seat Edge of tie Fig. 5. A photo showing actuator, rail (I-beam), two ties, and ballast Two types of tests were conducted: one without geogrid as a control and one with a sheet of triangular aperture geogrid, as shown in Fig. 6. The geogrid was horizontally placed 25 cm below the top of the ballast. Two SmartRocks were placed at two critical locations 25 cm below the top of the ballast (right on the surface of the geogrid): one underneath the rail seat and the other underneath the edge of tie. For the test without geogrid, the same SmartRocks were placed at the same locations, respectively, inside the ballast layer. The ballast layer was removed and new clean ballast aggregates were replaced and releveled in the ballast box after each test. The sheet of the geogrid was reused during the tests since the geogrid was not damaged. (a) (b) Fig. 6. Installation of geogrid: (a) a sheet of triangular geogrid; (b) placing ballast particles over geogrid The ballast box was then placed under a reconfigurable loading frame, MTS 793, shown in Fig. 5. An actuator with a load capacity of 49 kn, was utilized to conduct the tests. Linear Variable Differential Transformer (LVDT) was equiped in the load actuator which can record the displacement of the load AREMA 26 97

Vertical Displacement (cm) actuator with time. A harmonic load 65sin 2 t 65 kn (i.e., 3 kn at a frequency of Hz) was used for repeated loading testing. The magnitude and frequency of the load are within the range of a typical train wheel load. In the case of railroad ballast, the shake down process in the first few hundred cycles is of most importance; therefore, a total of 5 load cycles were applied for each test to focus on the behavior of the ballast layer during the shake down process. RESULTS AND DISCUSSIONS Fig. 7 shows the vertical displacement at the top of the ballast layer versus load cycles as recorded by the LVDT in the actuator. The displacement data within the first 5 load cycles were removed in all the tests in order to eliminate variations in test results due to initial seating error (Raymond and Bathurst, 986). The displacement continued to increase as the loading cycle increased for all the tests. However, without geogrid reinforcement, the magnitude of the vertical displacement rapidly increased load cycles, likely due to particle rearrangement as the ballast re-densifies into a more compact state due to the initial compaction phase (Stark et al. 25); with geogrid reinforcement, the magnitude of the vertical displacement increased at a much slower rate and the accumulated vertical displacement in the end of the loading was reduced from approximately.3 cm to.4 cm corresponding to a 7% decrease. This is likely due to the geogrid locking ballast particles in place hence reducing the settlement from particle rearrangement..2 -.2 -.4 -.6 -.8.2.4 Without Geogrid With Geogrid 2 3 4 5 Fig. 7. Vertical displacement vs. load cycles Fig. 8 shows the changes in stiffness of ballast layer (i.e., vertical load divided by vertical displacement) with load cycles for the three tests. During the first cycles, the stiffness of ballast layer decreased rapidly. For the test without geogrid, the stiffness of ballast layer subsequently experienced steady increase with load cycles, which is likely due to the densification of loose-conditioned ballast particles under cyclic loading; for the test with geogrid, the stiffness of ballast layer quickly reached the steady-state value due to better interlocking of ballast particles by geogrid. 972 AREMA 26

Stiffnes(kN/cm) 22 2 8 6 4 2 Without Geogrid With Geogrid 8 2 3 4 5 6 Load Cycles Fig. 8. Stiffness of ballast layer vs. load cycles Real-time motions of the embedded SmartRocks can reflect motions of the surrounding ballast particles during cyclic loading. Fig. 9 shows the comparison of angular rotations of the SmartRocks without geogrid and with geogrid beneath the rail seat and the edge of the tie, respectively. The SmartRock had the greater angular rotations without geogrid; with geogrid, the accumulated SmartRock rotations had minor rotations. It also can be noted that without geogrid, the particle rotations were much higher beneath the edge of the tie than beneath the rail seat because the particles underneath the rail seat tended to be pushed to the edge of the tie due to lack of confinement along the edge. With geogrid, the particle rotations were significantly restrained by the confinement that the ribs of the geogrid aperture provided, especially beneath the edge of the tie; the geogrid had greater confining effect on particle angular rotations, and the accumulated SmartRock rotations were less than.2 at both locations, as shown in Fig.9(b) and 9(d). AREMA 26 973

Particle Rotation (degree) Particle Rotation (degree) Particle Rotation (degree) Particle Rotation (degree) 3 Beneath Rail Seat: Without Geogrid (a) 3 Beneath Rail Seat: With Geogrid (b) 2 2-2 Rotation_x Rotation_y Rotation_z -2 Rotation_x Rotation_y Rotation_z -3 2 3 4 5 3 Beneath Edge of Tie: Without Geogrid (c) 2-3 2 3 4 5 3 Beneath Edge of Tie: With Geogrid (d) 2-2 Rotation_x Rotation_y Rotation_z -2 Rotation_x Rotation_y Rotation_z -3 2 3 4 5-3 2 3 4 5 Fig.9. Particle rotation: (a) beneath rail seat: without geogrid; (b) beneath rail seat: with geogrid; (c) beneath edge of tie: without geogrid; (d) beneath edge of tie: with geogrid Figs. and show the comparison of recorded translational accelerations of the SmartRocks between without geogrid and with geogrid beneath the rail seat (Fig. ) and beneath the edge of tie (Fig. ), respectively. It also can be seen that without geogrid, the SmartRock had noticeable horizontal accelerations (x and y directions), which implied that under cyclic loading, the SmartRocks not only had vertical displacement, but also moved laterally; the acceleration magnitudes of the SmartRock had more fluctuations beneath the edge of the tie than those beneath the middle of the tie, which is likely due to ballast migration caused by lack of confinement at the shoulder. With geogrid, the particle accelerations were significantly reduced quantitatively under cyclic loading. Qualitatively, the trends of the accelerations were more consistent with geogrid than without geogrid. Especially beneath the edge of the tie, the confinement provided by the geogrid was significantly effective according to the SmartRock recordings of particle rotations and accelerations as shown in Figs. 9(c), 9(d) and. 974 AREMA 26

-.5 Without Geogrid: Acc_x With Geogrid: Acc_x 2 3 4 5.5 -.5 Without Geogrid: Acc_y With Geogrid: Acc_y.5 6 2 3 4 5 (c) Beneath Rail Seat (b) Beneath Rail Seat.5.5 (a) Beneath Rail Seat.5 -.5 Without Geogrid: Acc_z With Geogrid: Acc_z.5 6 2 3 4 5 6 Fig.. Particle translational acceleration 25 cm beneath rail seat: (a) x direction; (b) y direction; (c) z direction -.5 Without Geogrid: Acc_x With Geogrid: Acc_x.5.5 -.5 Without Geogrid: Acc_x With Geogrid: Acc_y.5 2 3 4 5 6 (c) Beneath Edge of Tie.5 (b) Beneath Edge of Tie (a) Beneath Edge of Tie.5 -.5 Without Geogrid: Acc_z With Geogrid: Acc_z.5 2 3 4 5 6 2 3 4 5 6 Fig.. Particle translational acceleration 25 cm beneath edge of tie: (a) x direction; (b) y direction; (c) z direction CONCLUSIONS Based on the results of the ballast box tests, the following conclusions specific to the test conditions (e.g., ballast particle size, geogrid type, loading configuration, etc.) can be summarized as follows: SmartRock is capable of recording real-time particle movement including translation and rotation; it can be possibly serving as a quantitatively monitoring tool as it investigates ballast performance at individual aggregate level. The accumulated vertical displacement under 5 load cycles was significantly reduced with the inclusion of a sheet of geogrid at 25 cm below the top of the ballast layer. The elastic deformations of the ballast layer with and without the geogrid were similar. However, the stiffness of the ballast layer with geogrid was able to reach a steady-state value slightly quicker than that without geogrid. Particle translational and rotational movement were higher beneath the edge of tie than beneath the rail seat. The particle movement were significantly reduced with geogrid reinforcement under cyclic loading. ACKNOWLEDGEMENTS The authors acknowledge the funding provided by Federal Railroad Administration (FRA) Broad Agency Announcement (BAA) for the SmartRock project under the direction of Hugh B. Thompson II and Theodore R. Sussmann, Jr. The authors also acknowledge Tensar International Corporation for providing the geogrid. Lastly, the authors thank The Pennsylvania State University Altoona undergraduate students Ryan Smith and Andy Fayerweather for help with laboratory test setup. AREMA 26 975

REFERENCES Al-Rousan, T., Nasadm E., and Pan, T. (27). Evaluation of image analysis techniques for quantifying aggregate shape characteristics. Journal of Construction and Building Materials, Vol. 2, pp. 978-99. Bathurst, R. J., and Raymond, G. P. (987). Geogrid reinforcement of ballasted track. Transportation Research Record 53, Transportation Research Board, Washington, DC. Brown, S.F., Kwan, J., Thom, N.H. (27). Identifying the key parameters that influence geogrid reinforcement of railway ballast. Geotextiles and Geomembranes. 25 (6), 326 335. Brown, S. F., Thom, N. H., and Kwan, J. (26). Optimising the geogrid reinforcement of rail track ballast. Railway Foundations: Proc., Rail found 6, Univ. of Birmingham, Birmingham, UK, 346 354. Chen, C., McDowell, G.R. and Thom, N.H. (23). Investigating geogrid-reinforced ballast: experimental pull-out tests and discrete element modeling. Soils and Foundations, 24;54():. Coleman, D.M. (99). Use of geogrids in railroad track: a literature review and synopsis. Miscellaneous Paper GL-9-4. US Army Engineer District, Amaha. Indraratna, B., Hussaini, S.K.K., and Winod, J.S. (23). The lateral displacement response of geogridreinforced ballast under cylic loading. Geotextiles and Geomembranes, Volume 39, August 23, Pages 2 29. Jewell, R.A. (99). Reinforcement bond capacity. Geotechnique, 4 (3), 53 58. Koerner, R.M. (998). Designing with Geosynthetics, Fourth edition, Prentice Hall, Upper Saddle River, NJ. Liu, S., Huang, H. and Qiu, T. (25). Comparison of laboratory test using SmartRock and discrete element modeling of ballast particle movement. Journal of Materials in Civil Engineering, ASCE, D66, -7. Liu, S., Qiu, T. and Huang, H. (25b). Laboratory development and testing of smartrock for railroad ballast using discrete element modeling. In Proceedings of the 25 Joint Rail Conference 25, San Jose, California. Matharu, M. (994). Geogrids cut ballast settlement rate on soft substructures, Railway Gazette International, March 994. McDowell, G.R., Harireche, O., Konietsky, H., Brown, S.F. and Thom, N.H. (26). Discrete element modeling of geogrid-reinforced aggrgeates. Proceedings, Institute of Civil Engineering Geotechnical Engineering, 59(GE):35-48. Network Rail, (25). Formation Treatments, Business Process Document NR/SP/TRK/939. Qian, Y., Lee, S., Tutumluer, E., Hashash, Y. M. A., Mishra, D. and Ghaboussi, J (23). Simulating ballast shear strength from large-scale triaxial tests: discrete element method. In Transportation Research Record: Journal of the Transportation Research Board, No. 2374, Transportation Research Board of the National Academies, Washington, D.C., 23, pp. 26 35. Raymond, G. P. (22). Reinforced ballast behavior subjected to repeated load. J. Geotextiles and Geomembranes. 2(), 39 6. Raymond, G.P. and Bathurst, R.J. (987). Performance of large-scale model single tie-ballast systems, Transportation Research Record 3, pp. 74, 987. 976 AREMA 26

Saussine, C., Cholet, C., Gautier, P.E., Dubois, F., Bohatier, C. and Moreau, J.J. (26). Modeling ballast behavior under dynamic loading. part : a 2d polygonl discrete element method approach. Computer Methods in Applied Mechanics and Engineering, 95(9-22), 284-2859. Shin, E. C., Kim, D. H., and Das, B. M. (22). Geogrid-reinforced railroad bed settlement due to cyclic load. Geotech. Geol. Eng., 2(3), 26 27. Stark, T.D., Wilk, S.T., Rose, J.G., and Moorhead, W. (25). Effect of hand tamping on transition zone behavior. In proceedings of the 25 Annual AREMA Annual Conference, Minneapolis, MN. Tensar, Product Specification TriAx TX9L Geogrid Tensar International Incorporation. Tutumluer, E., Huang, H., Hashash, Y., and Ghaboussi, J. (26). Aggregate shape effects on ballast tamping and railroad track lateral stability. In Proceedings of the 26 Annual AREMA Annual Conference, Louisville, Kentucky. Tutumluer, E., Huang, H., Hashash, Y.M.A. and Ghaboussi, J. (27). Discrete element modeling of railroad ballast settlement. In Proceedings of the 27 AREMA Annual Conference, Chicago, Illinois. Tutumluer, E., Huang, H., and Bian, X. (22). Geogrid-aggregate interlock mechanism investigated through aggregate imaging-based discrete element modeling approach. Int. J. Geomech., 2(4), 39 398. Walls, J. C., and Galbreath, L. L. (987). Railroad ballast reinforcement using geogrids. Geosynthetics '87 Conference Proceedings. New Orleans, LA. AREMA 26 977

Laboratory Investigation of Geogrid Reinforced Railroad Ballast Performance on Particle Movement 978 AREMA 26 Shushu Liu, Ph.D Student Tong Qiu, Ph.D, P.E. Hai Huang, Ph.D, P.E. The Pennsylvania State University AREMA 26 Annual Conference & Exposition

AREMA 26 979 Introduction Previous Research Studies Railroad Ballast Large sized angular aggregates; Horizontal and rotational movement. Number of cycles,,,,, 25 Geogrid Interlocking with particles; Application in railroad ballast. 5 75 25 5 CBR = 39% control CBR = 39% reinforced CBR = % control CBR = % reinforced AREMA 26 Annual Conference & Exposition AREMA 26 Annual Conference & Exposition Previous Research Studies Previous Research Studies Maximum vertical stresses at interface between base and subgrade. Vertical stress distributions at 2th load cycle. Qian et al. (2) Tutumluer et al. 2 AREMA 26 Annual Conference & Exposition AREMA 26 Annual Conference & Exposition SmartRock Ballast Aggregates Shape; Wireless device; Data storage; Sleep mode; Translation, rotation and orientation. Images of individual aggregate particles 8 Passing Percentage (%) 6 4 2 AREMA No. 4A Ballast aggregate AREMA 26 Annual Conference & Exposition 2 3 4 5 6 7 Particle Size (mm) AREMA 26 Annual Conference & Exposition

98 AREMA 26 Geogrid Properties SmartRock Initialization Physical Properties of Geogrids Used in Track Stabilization Property Test Method Units Geogrid Properties Aperture shape Observation Equilateral Triangular Aperture size (machine x cross machine direction) Flexural rigidity (Machine direction) Direct measurement mm 6 x 6 ASTM D77482 mg-cm 2,, Radial stiffness @.5% strain ASTM D6637 kn/m 35 Junction efficiency ASTM D7737 % 93 SmartRock reference system Ballast Box reference system Local coordinate system Global coordinate system Ballast box coordinate system AREMA 26 Annual Conference & Exposition AREMA 26 Annual Conference & Exposition Laboratory Testing WITHOU Geogrid Laboratory Testing WITH Geogrid z y x AREMA 26 Annual Conference & Exposition AREMA 26 Annual Conference & Exposition Displacement and Stiffness Particle Rotation beneath Rail Seat.2 22 Without Geogrid With Geogrid Vertical Displacement (cm) -.2 -.4 -.6 -.8.2 Without Geogrid With Geogrid.4 2 3 4 5 Stiffnes(kN/cm) 2 8 6 4 2 Without Geogrid With Geogrid 8 2 3 4 5 6 Load Cycles Particle Rotation (degree) 3 2-2 Beneath Rail Seat: Without Geogrid (a) Rotation_x Rotation_y Rotation_z Particle Rotation (degree) 3 2-2 Beneath Rail Seat: With Geogrid Rotation_x Rotation_y Rotation_z (b) Vertical displacement vs. load cycles Stiffness of ballast layer vs. load cycles -3 2 3 4 5-3 2 3 4 5 AREMA 26 Annual Conference & Exposition AREMA 26 Annual Conference & Exposition

AREMA 26 98 Particle Rotation beneath Edge of Tie (d) Rotation_x Rotation_y Rotation_z -2 Rotation_x Rotation_y Rotation_z -2 2 3 4 5-3.5 -.5 Without Geogrid: Acc_x With Geogrid: Acc_x.5 2 3 4 (a) X direction; 2 3 4 (a) Beneath Rail Seat 2 Particle Rotation (degree) Particle Rotation (degree) Beneath Edge of Tie: With Geogrid Beneath Edge of Tie: Without Geogrid (c) 2-3 () 3 5 6.5 -.5 Without Geogrid: Acc_y With Geogrid: Acc_y.5 2 3 4 (b) Beneath Rail Seat With Geogrid () Without Geogrid 3 Particle Acceleration beneath Rail Seat 5 6 (c) Beneath Rail Seat.5 -.5 Without Geogrid: Acc_z With Geogrid: Acc_z.5 (b) Y direction; 2 3 4 5 6 (c) Z direction 5 AREMA 26 Annual Conference & Exposition AREMA 26 Annual Conference & Exposition Visualization Particle Acceleration beneath Edge of Tie -.5 Without Geogrid: Acc_x With Geogrid: Acc_x 2 3 4 (a) X direction; 5 6.5 -.5 Without Geogrid: Acc_x With Geogrid: Acc_y.5 2 3 4 (b) Beneath Edge of Tie.5.5 (a) Beneath Edge of Tie 5 6 (c) Beneath Edge of Tie.5 -.5 Without Geogrid: Acc_z With Geogrid: Acc_z.5 (b) Y direction; 2 3 4 5 6 (c) Z direction AREMA 26 Annual Conference & Exposition Conclusions SmartRock is capable of recording and visualizing real-time particle movement including both translation and rotation. SmartRock can be possibly serving as a quantitatively monitoring tool as it investigates ballast performance at individual aggregate level. The movement of particles adjacent to the geogrid is effectively confined. More SmartRocks at different locations. Attempt to characterize ballast performance based on particle movement pattern. AREMA 26 Annual Conference & Exposition AREMA 26 Annual Conference & Exposition Acknowledgements Funding for the SmartRock project has been provided by -- FRA ( Federal Railroad Administration) BAA (Broad Agency Announcement) Program. Support from Mr. Cameron Stuart, Mr. Hugh Thompson and Dr. Ted Sussmann is greatly appreciated. For assistant with printing SmartRocks and laboratory testing -- Alex Ricci, Ryan Smith and Andy Fayereweather. AREMA 26 Annual Conference & Exposition

982 AREMA 26 Thank you for your attention! AREMA 26 Annual Conference & Exposition