Research On Characteristics Of Permanent Deformation Of Subgrade Sand Silt Soil In South Hot And Humid Areas

During road operation period,subgrade soils must continue to bear the traffic load from passing down the road.however,for a long time,we have an opinion of emphasizing pavement research and overlooking roadbed construction.This is due to the special characteristic of roadbed,and that is the reason why the study of roadbed is relatively backward.Under the repeated traffic loads,subgrade soils will have an accumulation of plastic deformation,it will eventually lead to the pavement rutting,cracking and other diseases.Although many scholars have done a lot of research works about the mechanical behavior of subgrade soils,however,we can not be able to come up with a reasonable way to define the critical stress of subgrade soils,as well as to establish a model to predict the permanent deformation.With regard to the hot and humid environment of south china,the subgrade soils of higher moisture content is easier to cause large amount of permanent deformation.Therefore,it is very necessary to do some research works on it.In the paper,the soil type of south china was conducted firstly,the typical soil:sand silt of low liquid limit was selected.In order to have a better comprehensive understanding of physical and mechanical properties of the selected soil,a series of basic tests:particle analysis,macrofunction measured,compaction test,CBR,etc.were carried out.And according to the results of compaction test,a moisture content-dry density model was developed.According to the research works about permanent deformation of subgrade soils of many scholars at home and abroad,the physical and mechanical properties of the selected soil was considered and through on-site investigation,the control contionds of specimen molding was developed,with moisture content:90%OMC,OMC,110%OMC,120%OMC and degree of compaction:91%,96%.The stress of subgrade work areas was calculated,deviatoric stress and confining pressure were determined,a repeated load triaxial test program which is suitable for sand silt subgrade soil in hot and humid region of south china was developed.Then,on account of the results of repeated load triaxial test,the plastic and shakedown behaviors of the subgrade soils under repeated loads were studied,the critical stress and shakedown stable area of the sand silt subgrade were proposed,plastic strain rate 10^-7 was determined.Also,the main influence factors:moisture content?the degree of compaction?deviator stress and confining pressure were discussed,the regular law of these factors do to permanent deformation of sand silt soil was analyzed.Finally,depending on the results of repeated load triaxial test,a prediction model of permanent deformation of south china was developed,and its reliability was verified.