Wave-soil-pipe coupling effect on the untrenched pipeline stability onsands is for the first time investigated experimentally. Tests are conducted in the U-shaped water tunnel, which generates an oscillatory flow, simulating the water particlemovements with periodically changing direction under the wave action. Characteristictimes and phases during the instability process are revealed. Linear relationshipbetween Froude number and non-dimensional pipe weight is obtained. Effects ofinitial embedment and loading history are observed. Test results between the wave-soil-pipe interaction and pipe-soil interaction under cyclic mechanical loading arecompared. The mechanism is briefly discussed. For applying in the practical design,more extensive and systematic investigations are needed.
