Model Testing of Two-Layer Railway Track Ballast

Railway track ballast requires regular attention to maintain line and level. A recently developed maintenance method, known as pneumatic ballast injection (PBI) or stoneblowing, re-levels and realigns the track by lifting the sleepers and track and blowing smaller size gravel between the ballast and the base of the sleeper. This creates a two-layer ballast bed. Series of large-scale model tests have been carried out to gain a better understanding of the behavior of such a bed under repeated loading. The results confirm that stoneblowing is a better form of track maintenance than the commonly used ballast tamping method, but the size and type of stone and the thickness of the injected layer are of critical importance in determining the postmaintenance behavior.