Experimental Study On The Flow Of Liquefied Silty Soil Under Wave Action

Many rivers of the world carry a large number of sediment into the sea, thesediment formed estuarine delta under the marine dynamic conditions. Estuarine deltagenerally stockpile plenty of silty soil, such as the Yellow River Delta. Since theinstability of sediment and the role of ocean dynamics, estuarine seabed is unstableand easy liquefied. The liquefaction easily lead to geological disasters, such as slide,silt flow, pits, etc. This will directly affect a large number of development activities inthis area, for example oil exploration, subsea pipeline construction other marineconstruction. Therefore the study on the flow characteristics of liquefied silty soil wasimportant under wave action.In this paper, starting from the process of development of disaster, and the siltysoil in Yellow River delta was the main research object. Conduct research on themovement characteristics of each region, the change of physical properties and overallmovement depositional model of liquefied silty soil under wave action through flumeexperiment simulation and theoretical analysis.Uniform initial bed was composed of smooth and gentle slope area in flumeexperiment, which had a height difference of25cm. Liquefied test bed had the fluidcharacteristics and along with the wave motion under wave action, which providedthe initial liquefied silt flows. Flowing whole test bed could be divided into fourregions (liquefied flow area, side wall area, slope area, and the original fixed seabedarea). By observing and recording the process (outflow from the liquefied area, flowin the slope area, deposition became the side wall area at last), summarizing themovement patterns. In order to discuss the impact on the flow of liquefied silty soilthrough measuring the change value of clay content, moisture content, median grainsize and the density of test bed in the process of motion. After the motion stops, thedepositional bed possessed pits and layer phenomenon, so summarizing thecharacteristics and the reasons of the pits and bedding. The soil cycle transformation of liquefied flow area, side wall area and slope areadrive the entire liquefied bed forward with layer stacking in the process of liquefiedsilty soil motion under wave action. The liquefied flow area was converted into in-situdeposition model after the advance. Fine grained soil (mainly clay) migrated with thepore water, and large particles relatively sink in the process of liquefied silty soilmotion under wave action. The clay content and water content lowered, the densityand median particle size were relatively large at the same time. Resistance which theparticle fluid motion needed to overcome had increased and the liquidity of test bedhad decreased. The above factors changed the flow condition of silty soil fluid.The slope of surface was very small (less than1) after liquefied silty soildeposition. Bed appeared sedimentary textures similar with storm deposit and pits invertical depth direction. The bedding in liquefied flow area from down to uprespectively were: the original fixed bed, erosion contacts bedding, horizontal bedding,current lamination smaller climb bedding, swinging ripple (sand ripples) and floatingsludge. The bedding in side wall area from down to up respectively were: the originalfixed bed, erosion contacts bedding, horizontal bedding, swinging ripple (sand ripples)and floating sludge. The formation mechanism of pits and in-situ liquefaction wassame. The contribution ratio of clay migration and density increase for subsidencevalue of pit was20.5:1through in-situ liquefaction data. Bed was most compact nearerosion contacts bedding, forming a hard layer. The clay content and water content ofthe hard layer were less than the original bed and overlying sedimentary soil, and theparticle size was bigger.