Study On Mechanical Behavior Of Unsaturated Sulfate Saline Soil-Structural Interface Based On Freeze-Thaw Action

The saline soil is widely distributed in my country,especially in Northwest my country.The saline soil is widely distributed and the climate is complex and changeable.The freezing and thawing effect is obvious.As a weathering process,freezing and thawing constantly change the interaction between the soil and the structure.In order to study the influence of thawing on the mechanical behavior of saline soil-structure interface,the microstructure of unsaturated sulfate saline soil was studied by SEM observation and analysis.And through the indoor direct shear test,the unsaturated sulfate saline soil-concrete block and steel block contact surface were studied for the number of freeze-thaw cycles,salt content and other related factors.The main research content and conclusions includes the following points:(1)Scanning electron microscope observation and analysis on sulfated saline soils with different salt content found that the pore diameter of soil particles generally decreases first and then increases as the salt content increases.The sulfate saline soil with a salt content of 3% has the smallest pore diameter;As the salt content increases,the number of pores between grains generally increases first and then decreases.The sulfate saline soil with 3% salt content has the largest number of pores.(2)In the absence of salt,with the increase in the number of freeze-thaw cycles,the internal friction angle and the interfacial cohesive force of the sulfated saline soil-concrete and steel interface both firstly increase and then decrease.In the case of salt,with the increase in the number of freeze-thaw cycles,the internal friction angles at the two contact surfaces first increase,then decrease and then increase,while the interfacial cohesive force shows a downward trend.Under the effect of freezing and thawing,with the increase of salt content,the friction angle of the interface between the sulfate saline soil-concrete and the steel interface showed a law that first decreased,then increased and then decreased.Under the action of freezing and thawing,with the increase of the salt content,the cohesive force at the interface of sulfate saline soil-concrete and steel showed the law of first decreasing and then increasing.(3)During the entire direct shear test,the shear stress-shear displacement curve of the sulfated saline soil-concrete interface can be divided into four stages: linear elasticity,strengthening,softening and flow stages;The shear stress-shear displacement curve of the sulfate saline soil-steel block interface is roughly divided into three stages in order: linear elasticity,strengthening,and flow stage,and there is no softening stage.(4)For the sulfate saline soil-concrete interface,under the same freezing and thawing times,the shear strength of the contact surface generally shows a law that first decreases,then increases,and then remains basically unchanged with the increase of salt content.For the sulfate saline soil-steel interface,under the same freezing and thawing times,the shear strength of the contact surface generally de creases first,then increases and then decreases with the increase of salt content.Sulfate saline soil-concrete and steel interface,in the absence of salt,the shear strength of the contact surface increases first and then decreases with the increase in the number of freeze-thaw cycles;In the case of salt,as the number of freeze-thaw cycles increases,the shear strength of the contact surface first increases,then decreases and then increases.(5)Under different salt content,as the number of freeze-thaw cycles increases,the matrix suction at the interface of sulfate saline soil shows a gradual decrease.Under different freezing and thawing times,as the salt content of sulfated saline soil increased,the matrix suction at the contact surface of sulfat ed saline soil showed a law of first decreasing and then increasing.The shear strength of the sulfate saline soil-concrete and steel interface is directly proportional to the matrix suction area at the sulfate saline soil interface.(6)By citing different constitutive models,the applicability of the shear stress-shear displacement of the sulfate saline soil-concrete and steel interface was evaluated.It is found that the exponential curve model and the statistical damage model have a good fit for the shear stress-shear displacement of the sulfate saline soil-concrete interface;The exponential curve model,the statistical damage model and the gompaz model have a good fit for the shear stress-shear displacement of the sulfate saline soil-steel block interface.