Liquefaction Of Seabed Silt Under Storm Waves

Silt is widely spread in estuaries of our country. Silt is easily liquefied. The liquefaction of seabed silt easily lead to interruption of submarine cable and instability of sea platform and pipeline, which causes great damage to ocean engineering. The Chengdao sea area where marine geological hazards happen frequently is selected as the study area. The research of silt liquefaction is carried out based on the previous research work.The disturbed silt is easily found through the high resolution acoustic sub-bottom profile by the previous, and liquefaction during storm time is believed to be the controlling factor. The data of hydrodynamic, topographic, sub-bottom profile and engineering geological is collected.The disturbed silt is characterised as disorder reflection, and quite different of the around undisturbed silt which has obvious bedding. Research of the character and liquefaction evaluation of disturbed silt and undisturbed silt would be carried out separately.By the statistic of the physical parameters of 42 cores, it is found that the disturbed silt has larger median diameter, lower clay content, higher water content,larger density, lower void ratio and higher SPT blow count compared to the undisturbed silt. The data of cone penetration test and the scanning electron microscope picture both prove that disturbed silt is more dense and harder than undisturbed silt.The numerical calculation of transient liquefaction shows that the limit depth of transient liquefaction is 1.69 m under the action of 50 years return period wave in the seabed of which the water depth is 8m. Under the action of 25,10,5 years returnperiod wave, the liquefaction depth is reached the maximum value on the seabed of7 m water depth..The numerical calculation of residual liquefaction shows that the residual liquefaction depth of disturbed silt is less than the residual liquefaction depth of undisturbed silt under the the action of same wind wave. Under the action of wave caused by 10 level of wind, the depth of residual liquefaction reach the maximum value of 5.25 m on the seabed of 8m water depth. This liquefaction depth is verified by the sub-bottom profile which is provide in the dissertation.