Study On Reclamation And Soft Soil Characteristics In Dalian Coastal Zone

The economy in coastal cities has been growing fast in recent years,and cities are being modernized with each passing day which result in shortage of available building plot.It is an effective way to expand human activity space by exploiting coastal area especially in mountainous cities.However,the stability of foundation in practical is inevitably affected by various factors.And there are limited researches on foundation of sea reclamation.Therefore,it is important to study the Geotechnical properties of the foundation soil and the foundation treatment technology.The research is also benefit for the coastal cities'development and the rational use of Marine resources.In this paper,Dalian,China was selected as the research area.The methodologies include,but are not limited to field surveying,remote sensing interpretation,laboratory test,theoretical analysis and numerical simulation.First,the coastal evolution in Dalian were analyzed,and the area occupied by various reclamation areas is calculated.Second,Geotechnical properties were obtained from two sites in urban area by characterizing the mineral composition,particle composition,physical properties,mechanical properties and microstructure of the soft soil.Finally,a numerical simulation was conducted for the dynamic compaction in the reclamation area of Dalian,which provides guideline and advice for future foundation treatment in Dalian.In summary,the outcomes are followed:(1)Before 21st century,Dalian had very limited number of land reclamation projects.From 1998 to 2003,a total area of only 15.04km~2 was reclaimed.After 2008,the land reclamation area increased rapidly.In the following eight years,the new land reclamation area in Dalian had reached 181.08 km~2.However,it slowed down after 2016and up to 2019,the total land reclamation area is 255.56 km~2,and the unfinished area is 37.36 km~2.The area of salt pan is 491.45 km~2 and the area of mariculture is 185.01 km~2.(2)Dalian's special soil mainly includes silt and silty soil which mostly found along the coastline with width of tens to hundreds of meters.Special soil is also common in the narrow valley between two mountains and estuary of rivers and consists of silt,silty clay and silty silt.The area of soft soil in Dalian is about 602km~2,accounting for about 4.5%of the total area.The thickness of soft soil layer is mostly 3-10m with maximum of 17m.There is also significant difference in depth,which is mostly 4-8m below the ground,and both mono-and multi-layer structure were found for soft soil.The upper layer of soft soil is usually topsoil and the lower layer is silty clay or fine sand.Interbedding was found for soft soil and silt.(3)The soft soil in the research area consists of native element minerals e.g.quartz,clay mineral e.g.illite and montmorillonite.The soil is classified as silty clay with poor gradation and void ratio larger than 1.The natural moisture content outweighs liquid limit moisture content.It is also classified as high compressibility soil with low shear strength.(4)In Dalian,it is feasible and effective to conduct dynamic compaction when using stones from mountain for sea reclamation even if the lower layer was soft soil.The characteristic value of bearing capacity of foundation soil is no less than 250 kPa when conducting6000 kN·m dynamic compaction.As for silty soil in lower layer,more than 80 kPa increase in bearing capacity is realized which meets requirement in practical.It is found out that higher energy applied in dynamic compaction has better results.The model in this research is suitable for sea reclamation area with soft soil such as Pulandian Bay and Hulushan Bay.(5)It is feasible to analyze the mechanical properties of the gravel soil through reverse analysis on displacement when the parameters in neural network are properly set.In this research,accurate prediction was achieved by using 16 groups of data as training dataset shown the model adapts condition changes in practical.It has significant benefit for evaluation and prediction of soil sedimentation and displacement in sea reclamation area with similar soil layers.