Study On Deformation And Strength As Well As Gas Permeability Of Unsaturated Intact Loess In Tianshui

With the unsaturated loess is special soil,engineering in loess area,different excavation and backfilling method will make the soil has different stress state,deformation and strength of soil and further affect the yield characteristics.Gas permeability is one of the parameters of consolidation analysis of unsaturated soil.It has been shown that gas permeability is affected by dry density,water content and void ratio.But in practical engineering,the stress path also has an influence on the soil permeability.It is of important theoretical and practical significance to study the deformation,strength,yield and gas permeability of unsaturated soil under different stress paths.First of all,isotropic compression,conventional triaxial compression and equal stress ratio compression test under suction control were carried out.Through to the compression test,study the deformation characteristics of intact loess and yield characteristics,analyzes the effect of suction on the deformation characteristics,namely the same net mean stress,the greater the suction deformation is small,the stress state of the initial yield point of loess.Through conventional triaxial compression tests of the three,research the stress strain and deformation strength and yield characteristics,research results show that the stress-strain relationship of a hardening type,total cohesion c with suction increases,the effective internal friction angle with suction changes basically unchanged,and the shear strength formula with conventional three axis compression should the initial stress path under the yield point.The stress ratio by compression test,the deformation and yield characteristics,research shows that the same suction conditions,the same axial deformation,the deviatoric stress increases with increasing stress ratio,and the initial stress path under the yield point.Based on the initial yield point under three stress paths,the yield line of K0 plane in Q-P plane is obtained,and the mathematical expression of the yield line is determined.Secondly,the air permeability test under isotropic compression and three axis shear stress path is carried out.Through to the compression gas permeability test under the stress conditions,the moisture content and net mean stress effect on gas permeability coefficient,namely the same moisture content,gas permeability coefficient increases with the net mean stress decreases,the same net mean stress,gas permeability coefficient increases with water content and reduced.Through the three axle shear gas permeability test under the stress conditions,the moisture content,void ratio,saturation,shear stress level factors on gas permeability coefficient,the results show that the moisture content,the same confining pressure,gas permeability coefficient increases the stress level decreases with shear stress with the water phase;the rate,the same confining pressure,gas permeability coefficient decreases with the increase of saturation;the same moisture content,gas permeability coefficient with void ratio decreases;and different moisture content,confining pressure when the Ka ~ e relation point distribution in a band.In order to predict the permeability coefficient of loess,a mathematical expression between the permeability coefficient and the corrected saturation is established.