Sedimentary Characteristics And Properties Of Loess In The Xizhongdao Area Of Dalian

The Quaternary period saw a number of major changes in global climate,with multiple ice age and interglacial transitions,during which the climate experienced constant changes between warm and cold,wet and dry.Loess is the most dominant deposit in the Quaternary sedimentary environment and one of the three pillars of information carriers for the reduction of the paleoenvironment.Loess has physical and mechanical characteristics such as loose porosity and low compaction,which makes it prone to geological hazards such as landslides,debris flows and cave-ins under natural conditions.With the development of the economy and society,there are many large-scale engineering activities that need to be carried out in loess areas,and some engineering geological problems related to the special physical and mechanical properties of loess are encountered in the process of project implementation.In this thesis,the loess in the Xizhongdao area of Dalian City is used as the research object,and particle size analysis tests,geochemical element tests and physical mechanics tests are carried out on it,and the sedimentological data and physical mechanics data of the samples are correlated to explore the sedimentary characteristics and physical properties of the loess in this study area.The following conclusions were reached.From the particle size composition of the loess sediments in the Xizhongdao area of Dalian,the dominant grain size in the study area is chalk(0.004mm-0.063mm),with the content of fine chalk being higher than that of coarse chalk;clay(<0.004mm)is the next most abundant;and sand(0.063mm-2mm)is the least abundant.Through the calculation and analysis of the particle size parameters of the samples in the study area,it is concluded that the formation of loess sediments is shaped by a combination of wind-forming and hydrodynamic effects,and it is presumed that its earliest source of material comes from winddynamic transport and later by hydrodynamic transport,and that the formation process of loess sediments is more wind-dynamic and weaker hydrodynamic,with poorer sorting of particle size.From the geochemical elemental characteristics of the loess in the West Central Island area,the main elements are relatively enriched in Al,K,Ti and Fe,and relatively leached in Na,Mg,Si and Ca,compared to the elemental content of the upper continental crust(UCC);the trace elements are relatively enriched in Mn,Ba,Zr,Rb,Cr,Cu and Ni,and relatively leached in P and Sr.Combined with the A-CN-K triangle diagram,the minerals are dominated by montmorillonite,illite and plagioclase,indicating that the loess in the West Central Island area is in the early to middle weathering stage.Comparison of geochemical parameters with the upper crust(UCC)shows that the chemical weathering of the loess in the study area is strong and highly weathered,and the climatic conditions of the depositional environment show warm and wet conditions.In general,the loess in the West Central Island area was deposited under moderate weathering conditions with relatively warm and humid climatic conditions.From the physical and mechanical characteristics of the loess experiments,it can be seen that the physical and mechanical characteristics of the loess in the Xizhongdao area of Dalian City were analysed through six indoor geotechnical tests: water content test,density test,limiting water content test,specific gravity test,unidirectional consolidation test and triaxial compression test.The results show that the loess in the study area is a secondary loess and the loess in the study area has a high water content,medium porosity ratio,medium compressibility,high plasticity and high strength.The correlation between the sedimentological characteristics and the physical and mechanical properties of the loess in the West Central Island area shows that the three factors of the sedimentological characteristics of the loess,namely the chalk content,the mean grain size and the Si O2 content,have the highest degree of influence on the physical and mechanical properties of the loess.The mean particle size of the sample grain size class is positively correlated with the shear strength in a moderate way;the Si O2 content is positively correlated with the compressibility,and the compressibility of the loess is stronger as the Si O2 content increases,and the Si O2 content is negatively correlated with the shear strength,and the shear strength of the loess is stronger as the Si O2 content decreases.