Fabric Damage And Mechanical Degradation Of Coastal Saline Soil Reinforced With Fiber And Lime Under Freeze-thaw Cycling

Coastal saline soil is widely distributed in the west coast of Bohai Gulf,coastal area is in the climate conditions of freezing in Winter and thawing in Spring.The saline soil structure is damaged because of freeze-thaw cycle,and results in engineering properties degradation of saline soil and some engineering geological problems,such as the deformation,cracking,dissolution of the soil in road embankment,so saline soil should be stabilized in engineering construction.Polypropylene fiber-lime-soil enhances the strength and deformation resistance performance of the soil for struggling against the soil engineering properties degradation in the condition of freeze-thaw cycle by means of the fiber interaction and the spatial constraint on soil.In the special climate and environment geological conditions in the west coast of Bohai Gulf,mechanical properties of the stabilized soil still be deteriorated by freezethaw action.In this paper,the schemes of coastal saline soil reinforced with polypropylene fiber and lime were optimized.The unconfined compressive test,triaxial compression test and splitting tensile test were completed to evaluate the soil mechanical properties and its degradation law.The SEM,NMR and CT test were carried out to study the soil micro structure and its correlation with the mechanical index.With the comprehensive viewpoint of "point","section" and "soil mass",the variation law of porosity,pore distribution and spatial fissure rate were analyzed,and the fiber reinforcement effect in resisting freeze-thaw action was clarified.The results are as follows:1.Based on the unconfined compressive test results of fiber-soil and lime-soil,the appropriate fiber parameters and lime content were determined,that is,19 mm of length(1/3 of sample diameter),0.2% of mass rate,and 8% of lime content.2.The compressive strength,cohesion,internal friction angle and tensile strength of lime-soil and fiber-lime-soil decrease with the increase of freeze-thaw cycles,which can be divided into three variation stages,that is,the larger decreasing stage,the smaller decreasing stage and the stable stage.Under the same freeze-thaw cycle times,the compressive strength,cohesion,internal friction angle,tensile strength and failure strain of the fiber-lime-soil are higher than those of the lime-soil,it have been shown that the strength,deformation resistance and the freeze-thaw durability of soil are enhanced because of adding fiber to the soil.3.The porosity increases and the pore distribution varies by freeze thaw action.On less freeze-thaw cycle times,the pores are small.With the increase of freeze-thaw cycle times,the micro pores decrease gradually,and small pore,medium pore and large pore increase.After 10 freeze-thaw cycle times,the large pore proportion is basically stable.The increase ratio of the porosity and spatial fissure rate is decreased,and the extension and connection of pores is limited by adding fiber.The increase ratio of porosity,the proportion of medium pore and large pore,fissure length,fissure width and spatial fissure rate of fiber-lime-soil are less than those of lime-soil.The freezethaw degradation of soil is reduced due to adding fiber.4.The influence of freeze-thaw on the soil mechanical properties is evaluated by the degradation degree on soil mechanical parameters.The degradation degree of the fiber-lime-soil are less than those of lime-soil.The degradation degree of cohesion is the largest,and the degradation degree of tensile strength,compressive strength,failure strain and internal friction angle decreases in turn.The mechanical properties degradation is consistent with soil microstructure damage.The Area Fraction,Equivalent Diameter,Aspect Ratio from SEM test results were used to quantitatively analyze the soil microstructure variation before and after freezethaw action with the "point" viewpoint.Based on the NMR test results,the variation of porosity and pore distribution under freeze-thaw cycling was analyzed with the "soil mass" viewpoint.Based on the CT test results,the fissure development trend at the same scanning section and the variation of spatial fissure rate were analyzed before and after freeze-thaw action.The variation regulation of fissures are described with the "section" and "soil mass" viewpoint respectively.The comprehensive viewpoint of "point","section" and "soil mass" and microstructure evaluation is proposed.The relationship between the mechanical properties degradation and the microstructure damage of the fiber-lime-soil is established,which can predict the degradation law of mechanical properties and the microstructure damage trend of soil.