Study On Strength Characteristics Of Unsaturated Loess Under Different Compaction Work

Subgrade is an important structure in highway engineering,and the compaction degree of its fill has an important impact on the strength and stability of subgrade.Unsaturated loess is widely used as a filling material in subgrade filling,and its engineering characteristics after compaction are the focus of attention in current engineering.With the development of construction machinery and compaction technology,the compaction work in highway subgrade construction is often greater than the heavy compaction test standard specified in the specification.Under different compaction work,the corresponding maximum dry density and optimum moisture content will also have corresponding changes,which will further affect the shear strength of compacted loess.In this paper,the unsaturated loess in Xi’an area was selected as the research object,and the compaction characteristics and strength characteristics of unsaturated loess after compaction under four different compaction work(589.2,2692.1,3589.4,5683.3 k J·m^-3)with wide water content（2%～22%）were studied by means of laboratory test.The main research work are as follows:（1）Through the compaction test,the complete compaction curves of loess under four kinds of compaction work were analyzed,and the applicability of the four parameter equation in the complete compaction curve obtained after the compaction work exceeds the heavy compaction work was verified;The process of predicting the complete compaction curves of overweight type I(3589.4 k J·m^-3)and overweight type II(5683.3 k J·m^-3)by using the complete compaction curve obtained under light or heavy compaction work was realized.（2）The influence of compaction work and compaction moisture content on the parameters of Fredlund formula for unsaturated shear strength was analyzed by direct shear fast shear test and filter paper method;Combined with the four parameter equation of complete compaction curve,the parameter equation of the relationship between shear strength and moisture content of loess was established;The shear strength water content curve of two kinds of compaction work can be used to predict the strength curve of the same soil sample under other compaction work.（3）Based on the unsaturated triaxial unconsolidated exhaust undrained test,the variation of unsaturated shear strength parameters with compaction work and dry density obtained by direct shear test and triaxial test was compsared and analyzed.The results show that the parameters obtained by the two methods have similar rules,and the shear strength parameters obtained by the triaxial method are larger.It is pointed out that the parameter equation of loess shear strength and moisture content curve obtained by direct shear fast shear test combined with filter paper method is feasible and safe.