Experimental Study On Dynamic Properties Of Silt Sub Grade Under Cyclic Load

Silt exists widely in Beijing-jiulong Railway.Confined with the design theory and construction technology,in addition excessive loads,many and quite serious diseases have been found out in the roadbed of Beijing-jiulong Railway.Along with the implementation of railway raising speed strategy,more and more roadbed diseases will be found out.The project nature of silt is analyzed in this paper based on a mass of related technical information through triaxial tests,cyclic triaxial tests and multi-stage cyclic triaxial pre-load tests in laboratory.The thesis studies properties of unsaturated soil by cyclic triaxial tests.Based on the situation of research in cyclic properties of unsaturated silt,the article chiefly studies the following influencing factors:compaction degree,moisture content,stress history of soil,stress level and frequency of repeated load.The article lists critical dynamic stress of different samples.At the same time,this article studies the change of dynamic modulus and damping ratio as the change of compaction degree,moisture content,dynamic strain,confining pressure and frequency of repeated loading.The paper studies the critical dynamic stress,stress-strain relation of silt under the train repeated load and relevant factors of permanent deformation.The research shows that the critical dynamic stress varies strongly as the change of the compaction degree of subgrade soil,when the compaction degree of subgrade soil is not less than 0.90,the dynamic stress of silt subgrade will be smaller than critical dynamic stress; with increase of degree of saturation,subgrade soil's critical cyclic stress significantly decreases.It also shows that the dynamic stress-strain relation of silt under the train repeated load can be described as R.L.Kondner hyperbola;the results reveal that plastic cumulative deformation of railway subgrade has direct relation with saturation degree of railway subgrade.With the improvement of saturation degree of railway subgrade,the plastic cumulative deformation enhances and strength of surface layer soil lowers.The change of dynamic modulus and damping ratio varies as the change of moisture content,dynamic strata,confining pressure.