Experimental and Numerical Behavior of Railway Track Over Geogrid Reinforced Ballast Underlain by Soft Clay
In this paper, laboratory tests were conducted to investigate the effect of load amplitude, load frequency, on the behavior of reinforced and unreinforced ballast layer. A half full-scale railway was constructed for carrying out the tests, which consists of two rails 800 mm in length with three wooden sleepers (900 mm × 90 mm × 90 mm). The ballast was overlying 500 mm thickness clay. The tests were carried out with and without geogrid reinforcement; the tests were carried out in a well tied steel box of 1.5 m length × 1 m width × 1 m height. A series of laboratory tests were conducted to investigate the response of the ballast and the clay layers where the ballast was reinforced by a geogrid. Settlement in ballast and clay was measured in reinforced and unreinforced ballast cases.
In addition to the laboratory tests, the application of numerical analysis was made by using the finite element program PLAXIS 3D 2013 in order to verify the numerical model.
It was concluded that the amount of settlement increased with increasing the simulated train load amplitude, there is a sharp increase in settlement up to the cycle 500 and after that, there is a gradual increase to level out between, 2500 to 4500 cycles depending on the used frequency. There is a little increase in the induced settlement when the load amplitude increased from 0.5 to 1 ton but it is higher when the load amplitude increased to 2 ton, the increasing amount in settlement depends on the geogrid existence and the other studied parameters. Both experimental and numerical results have the same behavior. For unreinforced case, it was observed that the experimental results at the beginning show higher readings than the numerical ones, but after a number of cycles ranging from 750 to 2500 cycles the numerical results show higher readings.
It was also concluded that increasing the ballast layer thickness from 20 cm to 30 cm leads to decrease the settlement by about 50%. This ascertains the efficiency of ballast in spreading the waves induced by the track. The effect of load frequency on the settlement ratio is almost constant after 500 cycles.
KeywordsRailway track Geogrid reinforcement Finite elements Ballast Soft clay
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