Mechanical Properties Test And Microstructure Analysis Of Artificially Frozen Silty Clay

The artificial freezing method has been widely used in mine construction,subway tunnels,and cross-river cross-sea tunnel construction.With the continuous development of China's economy and the acceleration of urbanization,the artificial freezing method will be more applied to urban underground construction.The unconfined compressive strength of artificial frozen soil is an important parameter of the freezing method.It plays an important role in ensuring the safety during the construction of the freezing method.The factors affecting the unconfined compressive strength of artificial frozen soil:freezing temperature,time effect,water content will also affect the safety and stability of surrounding buildings after the freezing method is completed.In this paper,the freezing time,water content,freezing temperature,freezing and thawing cycles are taken as variables,and silty clay is taken as the research object.The influence of above variables on the mechanical properties of the frozen silty clay and melted soil was studied,and try to explain the changes in macroscopic mechanical properties based on the changes in the microstructure of melted soil.Firstly,the unconfined compressive strength test was carried out on frozen silty clay with different independent variables which include water content,temperature,and freezing time.The mechanical properties of freezing time,water content,and freezing temperature during the freezing process of the artificial freezing method were discussed.The influence of stress-strain relationship and strength of frozen silty clay was analyzed.The results show that with the increase of freezing time and decrease of water content and negative temperature,the unconfined compressive strength of frozen soil increases,and freeze brittleness which is dependent on the freezing time and freezing temperature.Secondly,taking the water content,the number of time of freeze-thaw cycles and the freezing time as test variables,direct shear tests were carried out on unfrozen silty clay and frozen-thawed soil after primary and secondary freeze-thaw cycles.Through the experiment,the mechanical properties of the unfrozen soil and the frozen-thawed soil were quantified and compared,and the freeze-thaw effect of the artificial freezing method was applied to analyze the influence law of the shear strength,cohesion,and internal friction angle of silty clay.The results show that under different conditions,the shear strength of silty clay after freezing and thawing is lower than that of silty clay without freezing and melting under the same conditions.Thirdly,in order to explore the changes of the soil microstructure under different freezing conditions,and try to reveal the inherent reasons for the change of the mechanical properties of the soil from the standpoint of microstructure.The experiment of scanning electron microscopy of the silty clay which was jrozen firstly and then melted under different conditions of the freezing temperature,freezing time and number of freeze-thaw cycles was carried out.The results show that the freezing of the soil is equivalent to exert different sizes and directions of force on soil skeleton.Concurrently,the liquid water becomes solid ice to fill micro-pores inside the skeleton of soil,the melting is equivalent to the action of removing the force acting on the skeleton of the soil,and the original connection of the soil will be destroyed after freezing and melting cycles.The increasing porosity leads to the reduction of strength.Figure 42 table 10 references 74...