Two-dimensional Freeze-thaw Effect Of Compacted Tongxin Loess Under Non-hydrating Condition

The concentric area of Ningxia is located in the northern part of the Loess Plateau in China.The loess is widely distributed.In addition,the concentric area has low winter temperatures and strong seasonal freeze-thaw effects.Under the strong seasonal freeze-thaw action of loess slopes,ditches,etc.,frost damage such as cracking,uplifting,and slipping of linings often occurs.How to prevent the problem of frost damage on the loess bank slope works in this area and reducing the impact of freeze-thaw on the loess Key research directions.Most of the existing researches on freeze-thaw effects of loess are unidirectional freeze-thaw,and the two-dimensional freeze-thaw of loess bank slope engineering is often affected by two-dimensional temperature source.At present,there are few researches on two-dimensional freeze-thaw of compacted loess.Aiming at the serious problem of frost damage on the loess bank slope,the loess in the concentric area of Ningxia was taken as the object,and the two-dimensional freeze-thaw characteristics of the compacted loess under non-hydraulic conditions were studied.Frost damage prevention provides technical support.The closed-system two-dimensional freeze-thaw test method was used to design a test plan based on local climate and hydrological conditions in Ningxia’s Tongxin area,taking compaction and saturation as the influencing factors.The freeze-thaw deformation,collapsibility,and compressibility of the loess were studied.And shear strength,establish a model of the relationship between the influencing factors and two-dimensional freeze-thaw deformation,and study the impact and significance of compaction and saturation on the collapsibility,compressibility,and shear strength of the loess,analyze the mechanism and law of action,and specifically draw the following conclusions:(1)Under the action of freeze-thaw cycles,the loess sample will undergo frost upset and thawing deformation in the vertical direction and frost heave and thawing deformation in the horizontal direction.The overall volume of the sample will become larger,and the horizontal frost heave rate and thawing coefficient will be vertical.The frost heave rate,thawing coefficient,and volume change rate increase gradually with the number of freeze-thaw cycles,and stabilize after 20 freeze-thaw cycles;compaction and saturation have a significant effect on two-dimensional freeze-thaw deformation of loess.There is a hyperbolic relationship between the two-dimensional freeze-thaw deformation of the loess and the degree of compaction and saturation.The freeze-thaw deformation of the sample gradually decreases with the increase of the compaction degree,and gradually increases with the increase of the saturation.(2)When the degree of saturation is constant,the sample with a larger degree of compaction has a larger cohesive force and a higher internal friction angle;when the degree of compaction is constant,the sample with a larger degree of saturation has a cohesive force,The lower the friction angle;after the freeze-thaw cycle of the loess sample,the increase in cohesion and internal friction angle is negative,the cohesion and internal friction angle decrease,the strength of the sample decreases,and the cohesion and internal friction angle increase.The absolute value of the quantity decreases with increasing compaction,and gradually increases with increasing saturation.(3)The concentric loess has greater compressibility.Under the non-hydraulic condition of the closed system,the compression coefficient of the sample gradually increases with the number of freeze-thaw cycles.There is a certain correlation between the compaction,saturation and the compression coefficient of the sample.The compression coefficient and the increase of compression coefficient of the loess gradually decrease with the increase of the compaction degree,and gradually increase with the increase of the saturation degree.(4)The collapsibility of the concentric loess increases after the freeze-thaw cycle,and some of the loess that does not have collapsibility are transformed into weak collapsible loess or medium collapsible loess after the freeze-thaw cycle.The collapsible coefficient of the concentric loess follows the freeze-thaw cycle.The increase of the number of times gradually increased,and the increase of the subsidence coefficient decreased with the increase of compaction and saturation under the freeze-thaw cycle.