Study On The Strength And Structure Of Malan Loess Under Dry And Wet Cycles

Loess is a special sediment formed in the Quaternary period,widely distributed in the Loess Plateau in northwestern China.Seasonal change and the influence of climate make the loess always in a state of alternating dry and wet,which makes the physical properties such as liquid limit,plastic limit and mechanical properties such as strength and collapsibility of the loess are affected.After the loess has undergone many cycles of drying and wetting in nature,the loess’ s shear strength will become lower,its ability to resist deformation will decrease,its deformation will increase,and the structure of the loess will be destroyed.The strength of roadbeds and the like has a great influence.The destruction of slopes in the loess area and the instability of the foundation are also related to the decrease of the strength of the loess due to the dry-wet cycle.Therefore,it is of practical significance to study the change law of the shear strength and structure of the loess under the dry-wet cycle.In this paper,the experimental soil was taken from Yonghe County,and the indoor routine triaxial test was used to study the attenuation law of loess shear strength and the change law of loess structure under dry-wet cycle.The main research contents of the paper are as follows:(1)First,based on the test results,the deformation characteristics of undisturbed loess and remodeled loess under different conditions(water content,confining pressure,and dry-wet cycle)were analyzed,and the relationship between the shear strength index of the loess and the water content was established.The law of the attenuation of the shear strength of the loess,it is believed that the attenuation of the shear strength of the loess is mainly due to the destruction of the cement of the loess by the dry-wet cycle.When the moisture content is low,the cementation is strong.Destruction,at high water content,cementation is weaker at lower water content,and after multiple dry and wet cycles,the extent of cementation damage becomes smaller,which also explains why loess is more sensitive to water at low water content.(2)The triaxial test results were collated to calculate the structural parameters of the undisturbed loess in different states.It is believed that the structural parameters of the undisturbed loess are divided into two parts: disturbed structural and immersed structural.For both strong structural soil and weak structural soil,the immersed structural structure is the dominant factor in the structural composition of the loess,and the strong structural The performance of the soil is particularly obvious.The weaker structure of the soil,due to the disturbance of the structural growth,the effect of the immersion structure becomes smaller,but it is still in a dominant position.(3)Analyze the changes of structural parameters with confining pressure,water content and dry-wet cycle under different conditions,and find that the structural release curves of the undisturbed loess are all softened.stage.It is believed that the structural parameters are affected by the confining pressure and the water content.When the confining pressure is low,the structural strength changes caused by the water content change dominate.As the confining pressure increases,the confining pressure and the water content together affect the structure.Confining pressure and structural parameters show a negative correlation.When the moisture content of the sample increases or the sample has undergone multiple dry and wet cycles,the weakening effect of the confining pressure and moisture content on the loess structure will decrease.After the dry-wet cycle of the sample,the structural parameters of the loess are significantly reduced,and the number of dry-wet cycles increases,the reduction will gradually become smaller.The different conditions of the sample(confining pressure and water content)also determine the degree of influence of the dry-wet cycle on the structural parameters.Under low water content and low confining pressure,the influence of the dry-wet cycle on the structure will be more obvious.Introducing structural parameters into the stress-strain curve of the undisturbed loess can correct the stress-strain curve to a hyperbola.(4)The structural parameter ratio,cohesive force ratio and internal friction angle ratio are used to relatively characterize the structural size of the undisturbed loess and the size of the loess shear strength index.It is concluded that the structural parameter ratio and cohesive force ratio and internal friction angle The ratio has a good positive correlation,that is,the structural parameters of loess have a good correlation with the shear strength of loess.The greater the structural loess,the greater the shear strength.