Most research on backward erosion piping (BEP) focuses on the critical conditions leading to failure. This paper studies the development of piping over time once the critical conditions are exceeded, which is useful to estimate time to failure. A commonly used small scale rectangular box setup is modified in order to monitor pore pressures and pipe pressures with a high spatial and temporal resolution. The experimental program includes three different sand types to study the effects of grain size and compaction, and different degrees of hydraulic loading. The results indicate that the transport of particles in the pipe affects the progression rate, and that the progression rate is related to the bed shear stress in the pipe. @en