Study On Strength Characteristics Of Freeze-thaw Cycle Loess Under Plane Strain Condition

Most of the loess regions in northern China are in the seasonal frozen soil area,which makes the loess affected by the water transfer during the freezing and thawing cycle,which results in the decrease of loess strength,in the slope and roadbed.In practical engineering,such as earth-rock dam,many engineering diseases are caused.In this paper,the undisturbed loess in Xianyang area is taken as the research object.In this paper,the undisturbed loess in Xianyang area is taken as the research object.The plane strain test under different consolidation confining pressures is carried out on the undisturbed loess samples under different water content and different freezing and thawing cycles.The moisture content ?,freeze-thaw cycle N and Influence of consolidation confining pressure ?3 on principal stress and axial strain curve,intermediate principal stress and axial strain curve,b and axial strain curve,and lateral strain and axial strain curve of undisturbed loess;moisture content ? and freeze-thaw cycle The effect of period N on the shear strength indicators c and cp of undisturbed loess.This research has certain theoretical value and guiding significance for the engineering disease problem under the plane strain condition of undisturbed loess in seasonal frozen soil area.Through the experimental research,the following results were obtained:(1)(?1-?3)-?1 curve shows that as the confining confining pressure increases,the slope of the curve increases continuously;and the curve increases continuously.The strength of the soil increases continuously;with the increase of water content and freeze-thaw cycle The slope of the curve decreases continuously,and the strength of the soil decreases continuously.The effect of the freeze-thaw cycle on the(?1-?3)-?1 curve is obvious with the increase of water content,and weakens with the increase of the confining confining pressure.(2)The variation of the ?2-?1 curve is similar to the change of the(?1-?3)-?1 curve,that is,the main stress-axial strain ?2-?1 curve moves downward as the water content and the freeze-thaw cycle increase.The main stress-axial strain ?2-?1 curve moves upward as the confining confining pressure increases.The b value in the b-?1 curve ranges from 0.12 to 0.35.There is no obvious regular change in the b-?1 curve for the increase of the confining confining pressure.As the water content increases,the b-?1 curve rises.The greater the contribution of stress to the strength of the soil,the curve decreases as the freeze-thaw cycle increases,and the contribution of the medium principal stress to the strength of the soil decreases.(3)The ?3-?1 curves are all hardened,and the effects of water content,freeze-thaw cycle and consolidation confining pressure on the lateral strain-axial strain ?3-?1 curve are obvious,and with the increase of the three The lateral strain-axial strain ?3-?1 curve gradually increases from a negative value to a positive value.In other words,as the freeze-thaw cycle,consolidation confining pressure and water content increase,the undisturbed loess test During the shearing process,it gradually changes from dilatancy to shearing.(4)According to the Mohr-Coulomb strength criterion,the influence of initial conditions on the shear strength index of undisturbed loess is studied.It is concluded that the cohesion and internal friction angles show a similar linear decrease with the increase of water content,and the cohesive force The increase of the freeze-thaw cycle shows an exponential decrease.The internal friction angle decreases slightly with the increase of the freeze-thaw cycle,but changes within the range of 3°.Therefore,the internal friction angle can be considered as the freeze-thaw cycle.There is no significant change in the increase.