Limited Water Supply Freeze-thaw Effects Of Compacted Loess In Winter Irrigation District

Southeast ningxia is part of the loess plateau,covered by a large amount of loess.Because of cold climate,lower underground water level,higher rising height of capillary water in the loess,high moisture content and strong frost heave,freezing damage is a very serious problem in the compacted loess slope of many engineering such as embankment,channel and reservoir projects in Ningxia area.By improving the internal factors of compacted loess and reducing the effect of freezing and thawing on compacted loess,it has become a hot spot for scholars to study.There are many researches on the structure and mechanical properties of water content and dry density in ningxia.However,there are few quantitative studies that affect the degree of saturation and compaction.And it is not clear that the change rule of different freeze-thaw cycle times.Therefore,researching on the frost damage problem of compacted loess slope in Ningxia,exploring the saturation and compaction effect of freezing thawing deformation and mechanical properties of compacted loess in Ningxia,revealing the damage mechanism,and putting forward countermeasures for prevention of frost damage,which are necessary and have high social value.In order to explore the saturation distribution of Ningxia compacted loess in the capillary water rising zone,the capillary water migration of loess with different compactness was studied by using standpipe method.Combined with the regional characteristics of the local climate and loess in Ningxia,orthogonal test scheme was designed with the factors such as compaction and saturation,and using one-dimensional unidirectional freezing thawing test method which saturation is kept the same,the frost heaving and thawing settlement characteristics of compacted loess were studied with limited water supply,The dominant factor and freezing damage mechanism of compacted loess slope will be further analyzed in combination with mechanical and collapsibility test.The distribution of saturation,frost heaving and thawing settlement and influences of the freeze-thaw cycling on the mechanical property and collapsibility of compacted loess will be discussed.The correlative models will be established.The results show that:(1)The steady water content and saturation of the loess in the rising area of capillary water decrease gradually along the height.The effect of compactness on steady water content is significant,but on steady saturation not significant.It is considered that the distribution of steady saturation has nothing to do with the compactness.(2)Under the condition of limited water supply,the frost heaving ratio and thawing settlement coefficient of compacted loess increase with the increase of freeze-thaw cycles.They have a hyperbolic relationship with the number of freeze-thaw cycles and tend to be stable about 12 times,and effects of freeze-thaw cycle improve with the increase of compaction or saturation.(3)The compressibility of the loess increases with freezing thawing,and the compressibility increases with the increase of the number of freezing and thawing cycles.The influence of degree of compaction and saturation on compacted deformation of compacted loess is very significant,and the influence of saturation is greater than that of compactness.The number of freeze-thaw cycles with the increment of the compression coefficient on stability is related to the degree of saturation and the degree of compaction.(4)Under the condition of limited water supply,the cohesion and internal friction angle of compacted loess decrease with the increase of freeze-thaw cycles.The absolute value of the two increment is hyperbolic with freeze-thaw cycles.The cohesion gradually increases with the increase of compaction,and gradually decreases with the increase of saturation.The absolute value of friction Angle increases with the increase of compactness and saturation.