The Analysis Of Land Subsidence And Control Measures In Chengbei Area Of The Subaquatic Delta Of The Yellow River

Chengbei area,northeast of the subaquatic delta of the Yellow River, reserves affluent oil-gas resources and is the main exploitation of Shengli Oilfield. However,the failure of the ground bench mark was caused by the land subsidence,the water depth materials present mistake.thus the actual depth of water did not coincide with designed elevations of many platforms,which produced a huge economic losses but also triggered a series of secondary disasters.So researching the land subsidence in the Yellow River.subaquatic delta,forecasting the final settlement and settlement rate,preventing and reducing disaster geological phenomenon brought by settlement,aim to provide important parameters for marine engineering design,which are urgent problems for the marine geology and marine engineering to be solved.Through the collected reports of engineering geological prospecting,the well investigation,the submarinelines and cables routing investigation between platforms,this paper quantitatively and qualitatively analyses subsidence situations.Based on collected drill hole materials and predecessor publication's dates on seabed sediments physical and mechanical characters in the Yellow River subaquatic delta,the distribution and engineering geological nature of this area sediments are studied systematically;though the analysis geotechnical achievement tables and compression curves of those data,the layered summation was used to calculate the final subsidence quantity;Terzaghi consolidation theory was calculated and the Plaxis software was simulated subsidence with time changes;based on measured dates and other method,the quantitative analysis results were verified,Finally this study analyzes influencing factors and proposes control measures and proposals. According to the analysis result,the condition of the Chengbei Sea ground settlement were summarized:1) The stratum of the study area above 30m is Quaternary Holocene deltaic deposit and neritic facies deposit,and the geologic structure is silty soil,muddy-silty clay,silty clay and silt.The first layer is silty soil,which has been remodeled by after-oceanic hydrodynamic force,the topsoil is gradually coarsening and compacting,and its intensity is improved obviously,compressibility is reduced.The second,third layer is muddy-silty clay, silty clay,which is uneven distribution and phantom.Soil uniformity is bad,the soil layer is high-compression and the earlier consolidation pressure is greater than overlying effective deadweight pressure,which is under consolidation soil,in result that sediment consolidation still exist;2) the change scope of settlement quantity is 0.389～0.729m,which is not only associated with the compressibility of soil,but also the thickness of the layer.Sedimentation rate is 2.10～2.97 cm/a,which is consistent with the measured results,it indicates that land subsidence phenomenon exists;3)Analysis can be drawn by using the Plaxis software to simulate consolidation,with the increase of depth of embedment,the soil settlement shows linear reduction,moreover the trend of declining is quick;4) It can be seen that the physical and mechanical properties of the soil are internal causes,and the action of wave and tide is the external causes in the procession of subsidence.On these basis,influencing factors and the potential hazards brought by land subsidence were analyzed,which is important to provide instructions of theory and practice in the research of disasters prevention and mitigation,land use,river mouth and channel regulation and observation and monitoring in land subsidence.