A custom-built automated raining system is used to prepare sand specimens of specific relative density Dr maintaining repeatability. This is achieved by raining the sand from a specific height (ranging from 65 cm to 130 cm) with controllable mass flow rate (adjusted through the raining velocity and the aperture of the soil hopper). The system has a maximum raining capacity of 0.3 m3/h and is capable of producing sand specimens with Dr ranging from 25% to 95%.