Experimental Study On Interface Friction Characteristics Between Pile And Calcareous Sand

As a special geotechnical engineering medium,calcareous sand has the problem of low pile side friction resistance in engineering properties.At present,domestic and foreign scholars focus on the low mold resistance of the calcium sand pile side,which is mainly concentrated on the particle breakage and dilatancy effect.The influence of cementation on the lateral friction of calcareous sand piles and its causes are still unclear.At the same time,since the original sample of calcareous sand is difficult to obtain,and the distribution and cementation of calcareous sand are unevenness,this made it difficult to obtain a certain amount and quality of cemented calcareous sand and to conduct research.Therefore,this paper selected the South China Sea calcareous sand as the research object,By using three kinds of cementing agents(cement,gypsum and heavy calcium powder)to incorporation and setting up two kinds of self-made pile-soil interface test instruments,the direct shearing test and interface friction test of different normal stress,different cementing substances and different degree of cementation were conducted.Finally,combined with the shear strength index,interface shear strength index and friction coefficient of the sample,the following main research results were obtained:(1)The cemented calcareous sand samples of different sizes were compared with two kinds of apparatus designed by ourselves.At the same time,the foot size sample is more representative.(2)By comparing the results of pulling tests under different normal stresses.The influence of different normal stresses on the shear strength and friction coefficient of calcareous sand interface is limited.Only limited growth and fluctuations were obtained,so the normalization method can be used to calculate the coefficient of friction.(3)Through the results of the pulling tests of different cements,it is found that the friction coefficient of the pile-soil interface obtained by using three different cements of calcareous sands shows a downward trend,but the decline amplitude shows a difference.The coefficient of friction after cementation,the cement dropped the fastest,and the final drop was 42.37%.Gypsum followed,basically consistent with heavy calcium powder.(4)Pulling tests with different degree of cementation,according to the results of the Mohr Coulomb strength envelope test,it showed that the peak shear stress and friction coefficient show a significant downward trend in the process of calcareous sand from uncementation to weak cementation and then gradually flattened.From 0% to 5%,the coefficient of friction decreased by 30.51%.It can be seen that cementation is an important reason for the decrease in side friction resistance of calcareous sand piles.(5)Compared with the quartz sand pulling test results,it is found that the peak shear stress and friction coefficient of the quartz sand pile-soil interface increase gradually with the degree of cementation,and the calcareous sand shows a downward trend.(6)A suitable damage statistical constitutive model was established to fit the pile-soil interface curve of cemented calcareous sand.