Analysis Of The Characters Of Shallow Soil In The Chengdao Sea Area And The Adaptability Of Pile Foundation

Chengdao oilfield located on the northern of modern Yellow River Delta,which is a delta lobes abandoned at1976, prominently with serious seabed washing and instability geological disasters. We utilized the survey data of wellsite over the years and the drilling platform plug pile engineering feedback data on the Shengli Offshore Oilfield for this research. The regional stratigraphic structure information obtained through on-site of engineering geophysical and surface sampling, and combined with environmental of the foundation soil of the alluvial plain on the Yellow River Delta to analyze the actual intensity distribution of the different layers of foundation soil under a variety of environmental and density conditions, as well as the engineering activities on the destruction and the strength recovery mechanism to fix geotextile experimental results establish of the foundation soil.The results have conducive to the promotion, including the development of engineering geology, marine engineering, marine geology and other disciplines cross, to guide marine engineering surveys and engineering practice, to prevent and reduce drilling platform the legs pierced instability, oil production jacket set less than a predetermined soil layer depth, break oil and gas pipelines, oil and gas leak, pollution of the marine environment marine engineering disasters.(1) According to the109wellsite survey data collected on the Chengdao sea, we analysis the wellsite side scan sonar, water depth terrain, shallow stratigraphic section the micro seabed landform types were analyzed and summarized in the study area, including the smooth seabed topography, rough seabed topography, residual mesa topography, erosion hollow landform, erosion the residual grooves and gentle slope, collapse pit landform, Goukan landforms and porphyritic topography. A variety of micro-landform types are alternative distribution in the seabed. The Seafloor microrelief of vast majority well location is the smooth seabed topography, erosion landforms and porphyritic geomorphology are just appear in the local waters. Chengdao sea submarine have entered a stable stage-gradual transition of porphyritic seabed topography to the smooth seabed or rough seabed topography. There are4types of the Chengdao sea submarine surface sediment, that are silt, silty clay, silty clay and silt, among that is given priority to with silt and silty clay. Silt main distribution in3-14m water depth, silt, silty clay and silty clay distribution in the eastern part of the study area where is more than14m in water depth and southwest side greater than14m water depth. Typical drilling of geotechnical experimental data based on the study area, a statistical analysis of the physical and mechanical properties of the surface sediments of the study area, including moisture content, void ratio, specific gravity, plasticity index, liquid, cohesive strength, angle of internal friction, compression coefficient, compression modulus, saturation, and standard penetration number.(2) Chengdao Island sea area shallow strata was quickly stacked to form a delta sedimentary facies (seabed between T1), in less than150years after1855the Yellow River the seizes Daqinghe river inflow into the sea by the Bohai, mainly with gray-brown silty clay, silty clay and silt. The sediments of seafloor is mainly silt and silty clay, concentrated in the3～14m water depth with the thickness of2～6m thickest of up to10m, and are good engineering geological bearing stratum. Gray silty clay layer below the silt layer and silty clay, soft plastic-plastic state, the intensity is low, the risk of piercing have occurred when the drilling platform, the silt layer as the waters of the bearing stratum job. The thickness of the layer becomes gradually smaller with increase of the depth. The rest of the sea surface is the gray silty clay, silt,is the weak layer of engineering geology. On the eastern side of the Chengdao sea area under the delta sedimentary facies, mainly yellowish brown silt and silt, slightly dense-dense state, high strength, bearing layer for better engineering geology.(3) The shallow stratigraphic of the the Chengdao island is complex in engineering conditions, according to the water depth, topography, stratigraphic distribution characteristics and engineering geological nature, the study area can be divided into the region Ⅰ,Ⅱ area, Ⅲ and Ⅳ area.