Experimental Study On Deformation Characteristics Of Loess Subgrade In Yuzhong Under Dry-wet Cycle

The wet-dry cycle is one of the important factors affecting the deformation of the loess subgrade.In actual use and operation,the subgrade is affected by repeated cycles of rainfall and evaporation in the atmosphere,causing subsidence,subsidence and slope erosion.Based on the actual roadbed engineering in Yuzhong area,this paper explores the physical and mechanical properties of loess in this area through laboratory tests on loess sampling in Yuzhong area,and improves the loess based on actual engineering.To lay the foundation for subsequent indoor model tests;The scale model is used to establish the subgrade model indoors for indoor model tests to study the influence of the dry-wet cycle on the deformation characteristics of the subgrade,and relevant conclusions are obtained.The main contents and conclusions of this article include:(1)The physical and mechanical properties of undisturbed loess and remolded loess in Yuzhong area are tested indoors,and the change laws of physical property indexes such as water content,density and liquid-plastic limit of loess in the area are obtained.Through routine triaxial shear tests,the mechanical properties of remolded soil samples under different conditions of compaction are obtained.The variation of cohesion and internal friction angle with the degree of compaction is analyzed,which provided a theoretical basis for subsequent model tests;(2)According to the actual engineering requirements,the loess is mixed with 5% lime to improve the loess,and the improved soil samples are tested in the laboratory to obtain the physical property index of the improved loess,and the compression characteristics and characteristics of the improved loess under different compaction conditions Analyze and summarize the change law of shear strength;(3)Based on the similarity theory,design and make indoor model tests,design the rain evaporation device according to the rainfall in Yuzhong area,and according to the requirements of mixing,filling and compacting subgrade soil,according to the similar scale,the inward layering of the model is different.Subgrade model under the condition of compactness.After the filling is completed,the standard maintenance is 28 d.After the maintenance is completed,the designed rain evaporation device is installed on the model to carry out the dry and wet cycle test of the subgrade model.After the test,observe and describe the structure of the subgrade.And the erosion amount of the subgrade structure under different compaction conditions under different dry and wet cycles is measured,and the density of the subgrade soil is measured,the compressibility and the mechanical properties are measured,and the analysis and test results are summarized;(4)Under the same compactness condition,with the increase of the number of dry and wet cycles,the erosion of the subgrade structure gradually increases,the density of the subgrade soil decreases,the compression modulus decreases,the compressibility increases,the shear strength index decreases,and the intensity drops.In the early stage of the dry-wet cycle,the changes in soil density,compression modulus and shear strength are large,and the changes are more obvious,and gradually stabilized in the later period.The reason is that the shrinkage and expansion of the subgrade structure soil.In the early stage of the dry-wet cycle,the pore structure of the soil changed,the soluble salt inside the soil gradually dissolved,the cementation of the soil decreased,the structure of the soil gradually decreased,and the roadbed structure cracked.With the increasing number of dry-wet cycles,The growing cracks provide space for the wet-dry shrinkage deformation inside the soil,and the corresponding soil deformation amplitude also slows down and gradually stabilizes;(5)Under the same number of dry and wet cycles,with the increase of the degree of compaction,the density,compression modulus,and shear strength of the subgrade soil all increase,and the amount of erosion decreases.The higher the degree of compaction,the lower the erosion amount,density,compression modulus and shear strength index of the subgrade soil body.This shows that the increase in the degree of compaction can increase the strength of the subgrade structure to a certain extent and reduce the Compressibility,minimize deformation of subgrade structure.Therefore,in actual engineering,improving the degree of compaction of the roadbed structure can reduce the roadbed settlement,collapse and other roadbed diseases to a certain extent.