Research On Mechanical And Deformation Characteristics Of Solidified Soil In Full Suction Range

Unsaturated soils are commonly found in nature and practical engineering,and suction has an important influence on the water retention,mechanics and deformation characteristics of unsaturated soils.Solidified soils such as solidified clay are mostly unsaturated when be used as artificial fill or road base materials,and its water content often varies periodically due to rainfall-evaporation,groundwater level fluctuation,etc.In recent years,the increase in greenhouse gas content has driven global climate change.The frequent occurrence of extreme weather and climate events prompts the soil-atmosphere interaction more intense,increasing the magnitude of the change in soil suction.Therefore,the study of soil-water characteristics,mechanical and deformation properties of solidified soils in the full suction range can provide relevant theoretical guidance for the application of solidified soils in practical engineering.In this paper,the soil-water characteristic curves of solidified soil with different cement contents are systematically investigated in the full suction range,and the general rules and mechanisms are summarized by performing microscopic tests.On this basis,a series of tests on unconfined compressive strength,triaxial shear,one-dimensional consolidation and wetting-induced deformation tests were conducted on solidified soils with different cement contents under low and high suction conditions.The main research results of this paper are as follows:（1）Combined with the pressure plate method,filter paper method and vapor equilibrium method,the soil-water characteristic curves of solidified soils with different cement contents were measured in the full suction range.Through the analysis of the soil-water characteristic curves,it was found that with the increase of cement contents,the more hydration products occupy the pores in the solidified soils,resulting in the smaller water content of the solidified soils under saturated condition.The VG equation can fit the SWCC of solidified soils with different cement contents well.At low matrix suction,the dominant factor which controls the water content change in solidified soil is large pores,so the lower the cement content of solidified soil,the greater the drainage rate in the drying process.While the small pores dominantly control the drainage rate in the high suction section,and the drainage rate increases with the increase of cement content.The SWCC of solidified soil with different cement contents tends to be the same when the residual water content is reached.SEM and MIP tests show that the pore distribution of the solidified soil becomes more uniform with increasing cement content.The large pores gradually decrease,the small pores gradually increase and the pore volume becomes smaller.With the increase in cement content,the macropores were converted to small inter-aggregate pores,the pore spaces were distributed more uniformly,and the particle surface became rougher,resulting in the higher water retention capacity and significant hysteresis of SWCC.（2）Combined with the unconfined compressive strength test and triaxial shear test to analyze the mechanical properties of solidified soil in the wide suction range.It was found that the unconfined compressive strengthen of solidified soil increased with the increase of cement content.With the increase of net confining pressure,the contribution of matric suction to the strength gradually decreases.The stress-strain curves at low matric suction as well as high suction conditions showed strain softening,and the higher the net confining pressure and suction,the higher the shear strength of the solidified soil.The contribution of suction to strength gradually decreases with the increase of cement content.The increase of net confining pressure in the test range has a significant effect on the increase of peak strength in the wide suction range,especially in the high suction range.The solidified soil showed ductile behavior under low matric suction range,while it shows brittle behavior under high suction range.The larger the suction,the smaller the strain of that occurs when the solidified soil reaches the peak strength.There is a good correlation between the failure strainε_f,deformation modulus E₅₀ and the unconfined compressive strength.The effective cohesion c′and total cohesion c of solidified soil with three different cement contents increased with the increase of suction.The contribution of suctionin the low suction range mainly controls by the capillary menisci,while adsorption is the main factor under high suction conditions,resulting that the effective internal friction angle φ’does not varied in the low suction range but gradually increases under the high suction range.The suction friction angle φ^b decreases as the suction increases and its effect on the shear strength is almost small when the suction increases to a certain magnitude.（3）One-dimensional consolidation tests and wetting deformation tests were conducted on the solidified soil under low and high suction conditions,and the deformation characteristics of the solidified soil in the wide suction range were analyzed and discussed.The void ratio decreased with increasing vertical stress in the wide suction range for all the soils with three cement contents.As the amount of cement is increased,the effect of suction on the deformation resistance gradually decreases.The yield stress of solidified soil increases with the increase of cement content and suction.The degree of saturation of the solidified soil during loading gradually increases as the soil skeleton is compressed.As the cement content increases,the inter-particle bonding of the solidified soil increases,the initial void ratio gradually decreases,and the pore structure inside the cured soil is more compact,leading to the decrease of water absorption rate.The time for wetting deformation increases with the increase of cement content.The wetting deformation rapid increase and then tend to stable with the wetting time.The wetting deformation of solidified soil does not increase with the decrease of matric suction in the whole process of wetting,but increases first and then tends to be stable.