Wave-induced Seabed Sediment Liquefaction And Its Automtic Monitoring Study

The dissertation is relied on the project of National Science Foundation Project"Formation and Failure of Hard Crust on the Subaqueous Delta of Yellow River"(Contract No.141720888), and objective to research wave-induced soils failure of Subaqueous Delta of Yellow River.The study work of this dissertation which is sponsored by the project of National Natural Science Foundation Project"Study on Consolidated Sediment Re-suspension and Transportion in the Yellow River Estuary"(Contract No.40876042) is mainly about the wave-introduced sediment liquefaction failure and the sediment strength change on the seabed of the Yellow River Estuary and automatically monitoring system designed beyond the result of the test .In order to study the wave-introduced sediment lquefaction failure and the sediment strength change, following work was done: waves of different height was simulated by a water flume. The pore pressure of the soil bed in different depth and penetration strength space-distribution of the soil bed was measured under different wave condition. Analyzing the experimental phenomena, some disciplines of the liquefactio -n failure and srength variation was obtained while processing the pore pressure and penetration data, the mechanism was reveal.In order to study the automatic monitoring system for the seabed sediment strength evolution process, following work was done: The basic fuction and stucture of the system were designed acording to the flume experiment phenomenon and the in-situ conditon. By some in-situ testing jobs, parts function of the monitoring system was verified and improved.Following conclusions and results was reached through the above study:(1)The soilbed was broken when the working force produced by the wave action was greater than the strength left by the soil liquefaction. The working force was growing along the increasing of the wave height while the accumulating pore pressure which can lead strength decline growing too. The boundary of the"failure body"was of circular arc shape and it always re-happened when a stronger wave occurred. The liquefaction coefficient which was defined as the ratio between the excess pore water pressure and the float density of overlying soil was consistency with the maximum liquefaction depth.(2)A shallow soil layer whose strength is bigger than the others was formed when a smaller wave was impact on the homogeneous silt seabed and the distribution of it is consistency with the liquefaction coefficient. The liquefaction failure existed when the soilbed was impacted on a bigger wave. This is a close relation between the non-uniformity of the soilbed strength which is formed by the consolidation and liquefaction induced by wave and the evolution of the oscillation soil. The flume simulating test can be a very effective way to study the dynamic response of seabed.(3)By the discipline of marine sediment liquefaction failure and strength variation got in sink experiment, we designed a monitoring system about marine sediment strength loss, which monitored the strength loss process by an automatic settlement system. It based on the principle of effective stress: by measuring the total stress and pore water pressure to calculating the real-time of automatic settlement system. The main part of the system was composed by automatic settlement equipment, float, data acquisition device, signaling device, power device and storage device, et al. It could realized the real-time automatic acquisition, transmission and storage of the data. In the laboratory validation test, the result could meet the practical requirement after appropriate treatment.