The Study On Strength In Unsaturated Fly Ash Soil Modified By Rubber Crumbs Based On The Soil-Water Characteristic Curve

At present,the study on unsaturated soil is still in the stage of development,it’s far from the study on saturated soil,especially the study on shear strength is very important for the research of unsaturated soil,it is not similar to saturated soil that has a mature theoretical system,and with the development of economy,many problems of unsaturated soil is discovered in practical engineering.The moisture content in subgrade soil will change under the influence of natural climate or human activities,it can result in the strength and deformation fall into an undesirable condition,which have a great influence on the bearing capacity and stability of subgrade,the influence of the subgrade humidity on the subgrade is great.After completion of the road,the subgrade is in an unsaturated state during the whole service life,subgrade humidity is mainly determined by matric suction.Shear strength is an index to evaluate the bearing capacity of subgrade,in other words,matric suction has an effect on shear strength.In this paper,fly ash soil modified by rubber crumbs is main research object,so matric suction test,shear strength tests have been done in different water content,dry density and freezing and thawing cycle times.And the shear strength model of fly ash soil modified by rubber crumbs is established,the reduction status of matric suction and strength under freezing and thawing cycle.The main research contents are presented as follows:1.The soil water characteristic curve of fly ash soil modified by rubber crumbs is measured by filter paper method.And VG model,FX3 moedel,FX4model are used to fit the SWCC.The fitting effect of three models have a great adaptability to fly ash soil modified by rubber crumbs,because the residual water content in the VG model and the FX4 model,there is no uniform test method to measure it currently,and it is also difficult to obtain,so FX3 model is chosen as the model of fitting.2.The shear strength and its parameters is measured by direct shear apparatus and the test results are analyzed,it’s show the water content and dry density have a certain influence on the shear strength parameters,cohesion has a peak value when water content gradually increases,and it will grow in linear trends with the dry density increases.The internal friction angle grows with the increasing of water content,but its rate of the growing is getting smaller,the internal friction angle also increases with dry density gradually increases,but no cohesion increases rapidly.3.Considering the effect of matric suction on shear strength,the shear strength formula of unsaturated fly ash soil modified by rubber crumbs was established.4.Study on the changes of the matric suction and shear strength under the action of freezing and thawing cycle,it shows that when increasing of freezing and thawing cycle times,the matric suction and cohesion decreases,and the internal friction angle increases,but all of them gradually become stable.The test results show that the relationship between the matric suction and the shear strength of fly ash soil modified by rubber crumbs has a power function under the effect of freezing and thawing cycle.