Mechanical Characterization Of Frozen Interface Between Saline Soil And Concrete Lining By Direct Shear Tests

Taking into account the factors of salt types,salt content,water content,freezing temperature and freezing time,direct shear tests for the frozen interface between foundation soil and concrete lining of irrigation canal are carried out in this study.The research contents can be divided into three parts:the shear strength test of rough frozen interface,the freezing strength test of smooth interface and the significant analysis of three factors of frozen strength of interface.The purpose of this paper is to study the effects of various factors on the mechanical properties of frozen interface,and to analyze the mechanism of these factors.The results are as follows:1.By conducting the test of shear strength of rough interface,the salt types,salt content and water content are considered.It can be found that the failure character of frozen interface is brittle,but the failure character can change to plastic with the increase of salt content.The shear deformation of the contact surface includes linear deformation and non-linear deformation.The linear section decreases with the increase of water content and salt content,while the non-linear section is mainly affected by salt content and increases with the increase of salt content.The shear modulus and shear strength increase with the increase of water content,but decreases with the increase of salt content.In this research,the concept of deformation energy is introduced to analyze shear failure,which is innovative in research methods2.The salt types,salt content and legal stress are considered in the test for frozen strength of smooth interface,which further prove that the failure character of frozen interface is related to salt types and salt content.A transition point from brittle failure to plastic failure in the shearing process is also found in the test.The initial frozen strength of the interface is mainly derived from the cementation of ice crystals on the interface,which is also related to the salt types and salt content.The initial freezing strength decreases with the increase of salt content.The effects of NaCl are more significant than that of Na₂SO₄.In addition,the effects of salt on cohesion and friction angle are summarized according to Coulomb’s formula.3.Considering water content,freezing temperature and freezing time,a comprehensive orthogonal analysis of the interface of frozen soil and concrete lining is carried out.The significant effects of various factors and their interaction on freezing strength are analyzed by F-test.It can be found that all factors can affect freezing strength,however,the effects of freezing temperature are most significant than others,and the interactions among factors are negligible.The relationship between the freezing strength and the factors are studied by the multivariate orthogonal polynomial regression analysis method.The regression equation of the freezing strength under three factors is established.The results show that the equation is basically used and could be applied to general engineering problems after misfit tests.Based on the experimental study,the effects of various factors on the mechanical properties of frozen interface are comprehensively analyzed.In the article,the effects of salinity on the mechanical properties of the interface are considered,and the mechanism of salt on freezing strength is revealed.Deformation energy is introduced to analyze the damage ability of the interface,and the freezing strength prediction model of interface is established by regression analysis.Therefore,the content and analysis methods of this research are innovative.The research results have some reference value for the study of interaction between special soil and structure in other projects,and fill in the blank of the research on freezing interface between saline soil and concrete lining in Shandong Province.