Effects Of Repeated Freeze-thaw On Silt In Winter Irrigation District

A large area of aeolian sand is distributed beneath the surface of Yinchuan area.In the cold winter,because of farmland irrigation,the groundwater is shallow.The capillary action of silt is more developed,the water content of shallow soil is higher,the frost heave of soil is large,and the frost damage is more serious.Buildings and structures on sandy soil,such as channels,lakes,constructed wetlands,etc.Frequent freezing and thawing results in lining heave,mslope slip and other potential bad geological phenomena such as ground liquefaction.The disease brings about many problems to the irrigation area of sand land base engineering.The effect of freezing and thawing soil has obvious regional.In order to ensure the study of freezing and thawing effect,the relationship between saturation and saturation time,compactness and composition of silt is involved.Based on the above problems,this paper combines the climate and hydrogeological characteristics of silt in Ningxia to test the soil mechanics of silt.Saturation characteristics,saturation time and dry density of soil sample are the main factors to study the saturation characteristics of silt.By analyzing the law and mechanism of the action,the relationship between saturation degree,saturation time and dry density of silt samples is established.The reasonable saturation method and saturation time of silt samples in Yinchuan are determined.The study of repeated freezing and thawing effect of silt is based on the degree of compaction,water content,the number of freeze-thaw cycles and the saturation conditions.Considering freeze-thaw conditions,one-dimensional freeze-thaw test method was used to study the freeze-thaw effect,the shear strength index and the freeze-thaw effect of the silt,and the correlation between freeze-thaw effect and freeze-thaw deformation is analyzed.The test results have important significance for the evaluation and prevention of Ningxia Irrigation District sand ground freezing engineering.The results show that:(1)Irrigation area of silt sample saturation is a hyperbolic relationship with saturated time.Irrigation area of silt sample saturation is a hyperbolic relationship with the saturation time,the saturation velocity of early,late and slow,and tends to be stable.Saturated by vacuum method,the saturated velocity of soil sample is fast and the degree is high,so the influence of dry density can not be considered.(2)When the water content(compaction)of unsaturated silt is definite,the freeze-thaw deformation increases with the increase of the degree of compaction(water content),and the number of freeze-thaw cycles is related to the degree of compaction(water content).Under the condition of non water supply,the freeze-thaw deformation of saturated silt increases with the increase of freeze-thaw cycles,and the number of freeze-thaw cycles reaching stability decreases with the increase of the degree of compaction.Under the condition of water supply,the frost heaving rate decreases with the increase of freeze-thaw cycles.Under the condition of water supply,with the increase of freeze-thaw cycles,the frost heaving rate decreases with the increase of the degree of compaction,and gradually increases with the increase of the degree of compaction.Compared with the non water filling conditions,the freeze-thaw deformation of saturated silt under the condition of water replenishment is obvious.(3)When the water content(compaction)of unsaturated silt is definite,the greater the degree of compaction(water)content of unsaturated silt,the greater the loss of cohesive force caused by freezing and thawing,and the degree of compaction has a greater impact on it.After repeated freeze-thaw cycles,the internal friction angle of silt has little change.Under the condition of non water supply,the strength index of saturated silt increases with the increase of freeze-thaw cycles,and the number of stable freeze-thaw cycles is related to the degree of compaction.Under the condition of water supply,with the increase of freeze-thaw cycles,the shear strength index decreases with the increase of the degree of compaction,and gradually increases with the increase of the degree of compaction.The compaction degree is small,the less stable freezing thawing cycles,and vice versa.Compared with non water filling conditions,the freeze-thaw effect of saturated silt under water replenishment condition is obvious.(4)When the water content(compaction)of unsaturated silt is definite,compression deformation increases with the number of freeze-thaw cycles increases,the stability of the freeze-thaw cycles increases with the increase of the degree of compaction(water content).The degree of compaction(water content)increase the freeze-thaw cycles,and the freeze-thaw cycles increase the degree of compaction(water content).Under the condition of non water supply,the compressive deformation of saturated silt increases with the increase of freeze-thaw cycles,and the stability of the freeze-thaw cycles increases with the increase of the degree of compaction.Under the condition of water supply,with the increase of freeze-thaw cycles,the compressive deformation decreases with the increase of the degree of compaction,and gradually increases with the increase of the degree of compaction.The increment of compression coefficient increases with the increase of freeze-thaw deformation rate,and there is a good linear correlation between the two factors.