| As the "Western Development" is carried out in depth,the "One Belt and One Road" has emerged in the new era.The scale of construction projects in the northwest region is even larger and the working conditions are more complex,and the study of slope loess is also increasingly of practical significance.Wet and dry cycles not only affect the properties of shallow soils in loess slopes,but also affect deeper soils due to fractures caused by earthquakes.This paper takes the undisturbed loess in Xi'an as an example to study the properties of the slope loess when considering the dry-wet cycle.First,this paper uses high-pressure consolidation instrument to carry out compression deformation test research.The results show that the void ratio of loess before and after wet-dry cycle decreases with increasing pressure and water content,but pressurization in different pressure ranges and humidification in different water content ranges have different contributions to increase the compression deformation.Wet and wet cycles increase the coefficient of collapsibility.Samples with different dry densities,different wet-dry cycles,and different water contents have the same trend of compression rebound curves.Most of the compressive deformations occurring during the first pressurization are plastic deformations,and the repressurization still causes less plastic deformation;under repeated loading,the void ratio fluctuates up and down at different levels,and the amplitude becomes smaller and tends to be stable.The elastic deformation and plastic deformation of saturated specimens are all greater than those of dry specimens.The smaller the dry density of the saturated sample,the faster the void ratio decreases.Dry and wet cycles make it harder to compact the loess when it is dry,and easier to compact when saturated.Second,this paper uses the GDS permeameter to carry out saturation penetration test.The results showed that the loess before and after the dry-wet cycle under a low confining pressure(P<36 k Pa): the small head difference(<3 k Pa)is insufficient to penetrate,after the head difference exceeds a certain value(3k Pa),however,the permeability coefficient suddenly increases;confining pressure has little effect on the permeability of loess;under the condition of smaller head and lower confining pressure,the dry-wet cycle slightly increases the initial head difference and the permeability coefficient.At higher confining pressure(50<P<300k Pa): When the confining pressure increases beyond the initial collapse pressure,the loess sample will collapse during the infiltration process,the void ratio and the permeability coefficient will decrease,and the greater the confining pressure,the slower the deceleration.The total void ratio e includes the pore ratio e1 related to the permeation and the pore ratio e2 independent of the permeation,and the pore ratio e1 related to the permeation is the intermediate function of the confining pressure P and the permeability coefficient k;The total void ratio e of the sample with larger dry density can reflect the quantity,size and patency of the water passage more accurately and lower;In the condition of larger head(30k Pa)and lower confining pressure(<100k Pa),wetting and wetting cycles increase the permeability coefficient.In the condition of large head(30k Pa)and high confining pressure(>150k Pa),the wet-dry cycle reduces the permeability coefficient;Gradually apply higher confining pressure,plastic deformation occurs in the water passage;The pore ratio e1 associated with the infiltration mainly consists of voids related to elastic deformation.Third,the use of pressure plate and non-saturated triaxial apparatus to carry out the experimental study of matrix suction.The results showed that the matric suction increased with decreasing water content,and the smaller the water content,the faster the increase.The axis translation technique requires the application of air pressure,so the measurement curve usually increases first and then slowly decreases.The lower the water content,the longer the suction reaches stability.The sample with low water content(w=10%)has higher suction and continues to increase when sheared;The sample with high water content(w=30%)has lower suction and continues to decrease when sheared;The suction of a sample with a water content close to the plastic limit wp(w=22%)decreased at the start of shearing and then slowly increased.Wet and dry cycles reduce initial suction;"Directional" wet-dry cycles reduce suction even lower.The normal wet-dry cycle shortens the time for the initial suction force measurement to stabilize,and the "directional" wet-dry cycle makes the stabilization time longer.In the whole shearing process,the suction of dry and wet cycle loess is lower than that of the original loess.Fourth,this paper uses non-saturated triaxial apparatus to develop the shear test.The results show that the loess elastically deforms within 2% of the axial strain and then plastically deforms.As the confining pressure increases,the bearing capacity gradually increases,and the failure mode gradually changes from the weak softening type to the stable type.With the increase of water content,the cohesion force,internal friction angle and strength all decreased,and the damage morphology gradually changed from the weak softening type to the stable one.If the water content varies from 10% to 22%,the intensity will change drastically.Wet and dry cycles reduce the cohesion and internal friction angle,especially the reduction of cohesion.Compared with ordinary dry and wet cycle loess,the “directional” wet-dry cycle results in less cohesion and a slightly larger internal friction angle.Under the higher confining pressure(30-50 k Pa),the wet-dry cycle makes the sample gradually change from the weak softening type to the stable type,and even the hardening type appears.The higher the water content is,the greater the confining pressure is,and the loess samples are more prone to shearing during the shearing process.Wet and dry cycles make the loess more susceptible to shrinkage. |
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