Experimental Study On Dynamic Characteristics Of Expansive Soil In Cixian County,Hebei Province

Expansive soil is unsaturated cohesive soil,the clay fraction mainly strong hydrophilic mineral illite and montmorillonite,with fissures and over consolidation,water absorption expansion softening,water loss shrinkage cracking and repeated deformation characteristics.Despite the expansive soil geotechnical engineering disasters and geological disasters have been realized,but the under dynamic loading will show the hazard and vulnerability is the lack of comprehensive and in-depth understanding of.Expansive soil due to its remarkable swelling shrinkage performance very poor engineering properties,so it is not difficult to imagine in expansive soil under dynamic load will easily cause soil instantaneous instability or soil fatigue damage of abnormal deformation even engineering disease,underground engineering and the surface structure of the damage,that leads to loss of property and safety of people's lives and the threat.So the research on expansive soil dynamics is extremely necessary,it has very important scientific significance and practical value.This paper uses the GDS resonant column system,free swelling rate,water content,dry density and confining pressure ratio on dynamic shear modulus and damping of expansive soil of different free expansion,and obtained some conclusions.(1)The original soil and adding different proportion of bentonite,after comparing the test,it is found that the larger the free swelling ratio is,the greater the dynamic shear modulus is.The dynamic shear modulus of the sample with a free expansion ratio of 110% was significantly higher than that of the free expansion rate of 85% and 60% for the dynamic shear modulus of the specimens,respectively.The dynamic shear modulus of the sample increases with the increase of the free swelling ratio,and increases with the increase of the amplitude.But when the dynamic shear strain increases to a certain value,the increase of the amplitude becomes smaller.And the greater the free expansion rate,the greater the damping ratio of the specimen.The damping ratio of the specimen with a free expansion ratio of 110% was higher than that of the free expansion ratio of 85% and 60% for the damping ratio of the specimens.(2)Under the condition of strain 10-4-10-2,when the moisture content of sample is 20%,23% and 26%,with the increase of water content,the dynamic shear modulus of the sample decreases,and the amplitude increases obviously.At the same time,the larger the moisture content,the smaller the damping ratio.The damping ratio of the sample with water content of 26% was significantly smaller than that of the water cut of 23% and 20% specimens.With the increase of water content,the damping ratio decreases,and the trend of the reduction is increased.With the increase of water content,the effect of water content on the damping ratio of expansive soil is gradually increasing.(3)When the strain is small strain,in samples of dry density is 1.45 g / cm3,1.57 g / cm3,1.69 g / cm3,the dry density increases,the specimen of the dynamic shear modulus increases,and increasing trend is basically the same.When the dry density of the sample increases,the damping ratio increases.With the increase of dry density,the damping ratio of the sample increases,and the trend is basically the same.(4)Under small strain condition,the confining pressure is 50 kPa,100 kPa and 200 kPa,with the increase of confining pressure,the dynamic shear modulus of the sample increases,and the increasing trend is upward.But when the dynamic shear strain increases to a certain value,the trend is weakened.When the confining pressure increases,the damping ratio of the sample increases.(5)With the hyperbolic model for 1/G and ? fitting,after the results of the analysis,we can see that the different free expansion rate,water content,dry density and confining pressure,1/G and ? are good linear relationship.The test point and the straight line have better fitting and the discrete degree is smaller.It is showed that the hyperbolic model can describe the dynamic stress-strain relationship of expansive soil under different free expansion ratio,water content,dry density and confining pressure.