One Dimensional Freeze-thaw Effect Of Clay Treated By Bentonite In Closed System

The reported studies have shown t hat Ningxia is a arid and water-shorted region,so it is particularly necessary to save water.As we all known,Farmland irrigation is essential in Ningxia,so canal seepage control is an important way of agricultural water saving in Ningxia.However,in some parts of Ningxia,the soil has high sand content and permeability,so it is difficult to achieve anti-seepage effect as anti-seepage material.In order to improve the impermeability of soil,bentonite is added into loess,sand and clay to improve the impermeability of soil.Clay modified by bentonite is widely used in Ningxia anti-seepage engineering.It is found that Ningxia is a seasonal frozen soil area,and repeated freezing and thawing will inevitably affect the impermeability and mechanical properties of the composite material,which determines the applicability of bentonite modified soil.Therefore,it is very necessary to study the freezing and thawing effect of bentonite modified clay.Based on the above problems,according to the actual situation of projects,the bentonite and clay are mixed according to a certain proportion,and the orthogonal test scheme is designed.The effects of freeze-thaw and other factors on the freeze-thaw and mechanical properties of bentonite modified clay mixed soil were studied under the condition of closed system.The results show that:(1)Under the condition of closed system,freeze-thaw cycles and various influencing factors have significant effects on the freeze-thaw deformation of bentonite modified clay.One of the most significant decisive factors is saturation.The larger it is,the more obvious the influence is.The number of freeze-thaw cycles can promote the freeze-thaw deformation of bentonite modified clay,and the relationship between them is hyperbolic.The number of freeze-thaw cycles required to achieve basic stability is small,about 7 times;The freeze-thaw deformation of soil increases with the increase of saturation,and decreases with the increase of dry density and bentonite content.(2)Under the condition of freeze-thaw in a closed system,the compressibility of bentonite modified clay increases due to freeze-thaw.For the compressibility of bentonite modified clay,the saturation of bentonite can obviously promote it,and the increase of dry density and bentonite content can inhibit the compressibility of bentonite modified clay;The saturation and dry density have significant influence on the compressibility of bentonite modified clay,but the content of bentonite has no significant influence;The effect of dry density on compressibility of unfrozen soil is greater than saturation,but the effect of two factors on frozen soil is opposite;The smaller the dry density and the greater the saturation,the greater the increment of compressibility after freezing(3)Under the condition of closed system,the strength of bentonite modified clay decreases due to the freeze-thaw effect.The influence of saturation and dry density on the strength index of the composite soil is obvious,while the influence of bentonite content strength index is not significant;When the dry density is a constant,the increase of the saturation of the modified soil will promote the decrease of the soil strength index.When the saturation is a constant,the increase of the dry density of the modified soil will promote the increase of the soil strength index.