Aging Characteristics Of Material, Structure Changes And Settlement Prediction Of Dredger Fill In The Consolidation Process Of Step Vacuum Preloading

With development of economic, it leads to an impending increase in the demandfor land resources for coastal countries and cities. Therefore, how to get more landresources becomes one of the focus problems. Combined with this status quo, manycoastal countries and cities use dredged mud and sand for sea reclamation to relievethe strain on land resources. In the reclamation process, sedimentary soil formed byhydraulic fill called dredger fill. When the dredger fill is used in the structuresfoundation, the commonly used reinforcement methods are: vacuum preloading, stackpreloading, replacement, dynamic compaction, etc.However, because of high moisture content, high void ratio, high compressibility,low permeability and low strength of dredger fill, it faces the following problems inthe process of reinforcement,(1) dredger fill would become hard shell commonly in2or3years, it will spend more time and money and limit the use of reinforcementmethods;(2) these methods still have big problems in reducing consolidationsettlement and uneven settlement;(3) when reinforce the dredger contain high claycontent, the powerful vacuum suction makes particles move with the water to rainpipes, form mud membrane and hinder its drainage consolidation.In allusion to the above mentioned problems of dredger fill encountered in theprocess of reinforcement, this paper will analyze the basic characteristics ofLianyungang dredger fill firstly, provide certain theoretical basis for later study; Andcombined with the existing reinforcement methods of dredger fill, propose forsolution of Step Vacuum Preloading (10kPa--20kPa--40kPa--60kPa--80kPa), thismethod uses the principle that the initial structure is formed in soft soil firstly, andthen to of drain and reinforce under low pressure, it can reduce the siltation of the tinyparticles in the soil, reinforce dredger fill step by step and form is the foundation with a certain strength finally. By analyzing the monitoring data in the simulation test ofreinforcement, aging characteristics of granularmetric and soluble salt composition,and its relationship with the depth and distance to drain, it can be known that: in thereinforcement process of Step Vacuum Preloading of dredger fill, smaller particlesmigrate to the certain directions, and the content of soluble salt reduce regularly.Secondly, combining with the “SEM Test” and “MIP Test”, carried on thequalitative and quantitative analysis to the microstructure of dredger fill. It can beknown that: in the reinforcement process of the dredger fill, it showed the agingcharacteristics of porosity lowering, bigger pores reducing and smaller poresincreasing; at the same time, the porosity, pore size distribution have a closerelationship with depth and the distance to the drain; In the reinforcement process, asthe growth of the time, pore and structure gradually get squashed, slender structureincrease, the directional property is not obvious, and the morphology change ofstructure is more complex than the pore. All of these reflect the soil consolidation.In addition to the analysis of granularmetric, soluble salt composition andmicrostructure, this paper also predicted the final settlement according to thesubsidence monitoring data. Based on the noise in the settlement data, introducedwavelet noise reduction method; and different from previous common method thatdetermine the weight of each single model in the portfolio model according to theminimum of settlement error square, considering multiple calculation result of anumber of prediction model evaluation index, introduced the coefficient of variationto determine the weight of each model, it made the combination model morereasonable. The optimized combination model has been proved by an example in useprocess, the calculation difficulty will not increase with the increase of the modelnumber, the fitting precision is high, and it can be applied in the engineering field.Finally, according to characteristics of composition and drainage andconsolidation of Lianyungang dredger fill, PFC3Dnumerical analysis software wasadopted to establish the Step Vacuum Preloading model, the aging characteristics ofthe particle movement, displacement and porosity distribution in the simulate processreflect the effect of different reinforcement stage, and based on the soil particle displacement monitoring in the reinforcement process to reflect the changes ofsettlement and realize the prediction of final settlement. Comparative analysis of theresults of numerical simulation and laboratory test, reflecting the feasibility of StepVacuum Preloading method, provide certain theoretical basis for the constructionmethods of dredger fill.