Large open stopes mined by vertical crater retreat or sublevel stoping are sometimes backfilled with uncemented sand tailings to support the stope walls and alleviate rock bursts. The failure of bulkheads in two different mines prompted a research project at the Bureau of Mines to prevent a recurrence of these failures. A series of laboratory tests with gravel drains and sand filters was conducted to measure the bulkhead pressures when adequate drainage was maintained. Results showed that bulkhead pressure was reduced to near zero while drains were in operation, as compared with full hydrostatic pressure when drains were blocked or drainage was restricted. A relatively simple, light, free-draining bulkhead was shown to be adequate.