Research On Strength Characteristics Of The Disturbed Loess By Earthquake Under The Effect Of Freeze-thaw Cycles

Loess in China has a wide distribution range,the mechanical properties of loess are influenced by porosity,disintegration and structure.Recently,with the development of the western region,the number and scale of Engineering in loess area is gradually expanding,and earthquakes and freeze-thaw disasters occur frequently in Northwest area,which makes the study on unsaturated loess more practical.Researching the influence of freeze-thaw cycles on mechanical properties of the disturbed loess by conducting the test indoor based on the ancestors' research achievement.The main research results of the article are as follows:(1)Firstly,the SWCC of the undisturbed loess is measured by the pressure-plate test,the results indicate that matrix suction of the undisturbed loess increase with the decrease of the water content,and by comparing with the matrix suction which is measured by unsaturated three-axis apparatus,verifying the accuracy of unsaturated three-axis apparatus in measurement of matrix suction of loess.(2)Secondly,by conducting the shaking table test,long-term freeze-thaw test and unsaturated three-axis test,the influence of freeze-thaw cycles on matrix suction,stress strain curve and strength of disturbed loess has been studied,the experimental results show that: ? With the increase of the number of freeze-thaw cycles,the matrix suction of undisturbed loess and disturbed loess will appear first decreased and then stabilized variation;the freezing temperature has little effect on matrix suction;with the increase of confining pressure,the matrix suction will continuously decreases.? When the confining pressure is 100 k Pa,as the freeze-thaw cycles increasing,stress strain curve of undisturbed loess and disturbed loess show strain softening,and stress strain curve of undisturbed loess are still strain softening type with the decrease of freezing temperature;when the confining pressure is 200 k Pa,as the freeze-thaw cycles increasing and freezing temperature decreasing,stress strain curve of disturbed loess curve will change from softening to hardening,but stress strain curve of undisturbed loess is strain hardening;when the confining pressure is 300 k Pa,as the freeze-thaw cycles increasing,stress strain curve of disturbed loess and undisturbed loess are strain hardening,and stress strain curve of undisturbed loess is still strain hardening with the decrease of freezing temperature.The stress strain curve of disturbed loess is fitted by Duncan-Zhang hyperbolic model,which has a high precision.? With the increase of freeze-thaw cycles,the static strength of disturbed loess and undisturbed loess will appear first decreased and then stabilized variation;cohesion first reduced and then increased after several freeze-thaw cycles;the internal friction angle increase after the first freeze-thaw cycles,but it is considered to keep invariable in long term freeze-thaw cycles because it fluctuates between 1° and 2° all the time.The freezing temperature has no significant effect on static strength,cohesion and angle of internal friction of disturbed loess and undisturbed loess.(3)Finally,the experimental data are analyzed.? The freeze-thaw damage variable of loess cohesion is defined.As the freeze-thaw cycles increasing,cohesion damage variable of disturbed loess and undisturbed loess first increased and then stabilized,but the amplification of cohesion damage variable of disturbed loess is lower than that of undisturbed loess;the influence of freezing temperature on cohesion damage variable of disturbed loess is not significant.? The model of cohesion deterioration of disturbed loess was established to reflect the relationship between cohesion of the unsaturated and disturbed loess and times of freeze-thaw cycles.