Study On The Property Of The Calcareous Concretion Clay In Downtown Of Xuzhou

The existence of calcareous concretion in clay makes the engineering property of soil different from cohesive soil and gravel soil.It is a special kind of soil,namely calcareous concretion clay.The calcareous concretion clay is Widely distributed in the Huaibei Plain and Xuzhou Plain,and is a kind of regional special soil.The paper takes the calcareous concretion clay in the downtown of Xuzhou as the research object,and comprehensively adopts various research methods.The main research work and achievements of the paper are as follows:(1)On the basis of collating and analyzing various regional geological surveys and geotechnical investigation surveys that have been conducted in the Xuzhou,comparing the results of stratigraphic dating and calcareous concretion dating,it was found that the age of the calcareous concretion and the Quaternary Upper Pleistocene strata in the study area are generally consistent,and then a brief analysis of the formation conditions and process of calcareous concretion is made.In the paper,the distribution of the calcareous concretion is summarized as a star-shaped distribution,nested or discoid distribution and layered distribution.At the same time,Arcgis and Sufer are used to draw the plane distribution and vertical distribution characteristics of calcareous concretion clay.(2)Through geotechnical tests,it was found that the void ratio,water content,specific gravity,natural gravity,and dry weight of the calcareous concretion clay are larger than or similar to the underlying hard plastic clay formation due to the existence of the calcareous concretion.The cohesion and internal friction angle of the calcareous concretion clay is of large range,on the whole,as the content of the calcareous concretion increases,the cohesion decreases and the internal friction angle increases.At the same time,the coefficient of compressibility of the calcareous concretion clay is much smaller than that of the overlying clay formation,but slightly smaller or similar to the underlying clay formation.(3)The calcareous concretion clay has a certain weak swelling property and does not have the conditions for forming an expansive soil foundation in a natural environment.Combined with pumping tests,it was found that the calcareous concretion clay will form a special “sand and gravel strata” when the calcareous concretion clay has a high content,large particle size and tight arrangement in a certain depth range through theoretical analysis and numerical calculation.If horizontal supply exists,the hydraulic conductivity and water yield property will change strongly,and the permeability coefficient will increase by 3~4 orders of magnitude compared with the conventional conditions,and can reach 2.58~8.51m/d,at the same time,the specific well yield can reach 0.20~0.68 L/(s·m),a medium-rich aquifer.(4)Through correlation analysis and regression analysis,it was found that the average cone tip resistance(qc)of the cone penetration test and the average content of calcareous concretion(w)well satisfy one-dimensional linear regression equation: qc=0.153w+1.419.At the same time,the sidewall friction resistance and the average content of calcareous concretion basically satisfy the one-dimensional linear regression equation: fs=5.629w+106.577.(5)Through regression analysis and neural network analysis,it was found that the foundation bearing capacity(fak)and the cone tip resistance(qc)satisfy the onedimensional linear relationship well: fak=22.849qc+138.805.At the same time,the neural network analysis comprehensively considers the cone tip resistance,the sidewall friction resistance,and the depth effect,as a result,the prediction effect is slightly better than the regression analysis,and can be further promoted in the research area.The research results are of great significance for understanding properties of the calcareous concretion clay in downtown of Xuzhou,and directly serving and guiding the engineering practice.