Study Of Triaxial Test On Shear Strength Of Unsaturated Soils Of Shijiazhuang

With the development of society and economy, construction industry has got rapid development.Tall buildings rising straight up from the ground like mushrooms, deep foundation pit engineering and high slope engineering emerging in an endless stream,which set higher requirements for the design and construction of ground foundation engineering.Meanwhile, with the progress and development of science and technology, people have more profound understanding and higher demands on the economy and the rationality of engineering, especially,the security and economy of engineering has become a hot topic in engineering. In many engineerings,the proportion of foundation in the investment is very high. A large number of theoretical research and engineering practice shows that application of saturated soil mechanics on unsaturated soil mechanics engineering problem is not accurate, and even may lead to engineering accident. This is detrimental to the cost and security aspects of Engineering.Therefore, the study of the mechanical properties of unsaturated soil and make full use of strength and engineering characteristics of unsaturated soil itself under the premise of ensuring engineering safety, has become one of the effective ways to increase saving cost of engineering economy.Because the research on unsaturated soil started relatively late, the research achievements are less, therefore, the current understanding of the unsaturated soil both foreign and domestic are far from the need of engineering degree. For the area of Shijiazhuang in Hebei province is more so on unsaturated soil. So the study of the mechanical properties of unsaturated soils especially on shear strength, both for the development of soil mechanics theory or engineering practice, is very necessary and meaningful.This paper uses TFB-1 type triaxial instrument for unsaturated soil to study unsaturated silty clay of a engineering in Shijiazhuang area through triaxial test.The test obtained the soil water characteristic curve of different initial moisture content through the test and has carried on the analysis.With matric suction increasing,in the consolidation process in the consolidated drained triaxial shear tests,the displacement increases.Consolidation time is associated with the ratio of air e ntr y val ue a n d c onfining pr e s s u r e. Wh e n c o n fi n i n g p r e s s u r e r e ma i n s unchanged,deviator stress decreases marginally with the increase of matric suction,but effective major principal stress has a more substantially increasing trend.In shearing process of soil the stress and strain curves are almost nonlinear and become strain hardening and failure mode is "drum-shaped deformation".When confining pressure is kept constant,air entry value vary within a certain range,effective principal stress ratio σ1 ’/σ3’ approaches a constant in destruction process of the soil.The three axle shear tests show that the values of cohesion(c) of unsaturated silty clay increases with the increasing of air entry value, while the intake value(matric suction) effect on the internal friction angle is very small. This law applied to the slope stability calculation, calculation of bearing capacity of foundation and retaining wall design example, we can see that the full use of the properties of unsaturated soil has a great decrease in the cost of project. At the same time we can see that water has a very big impact on unsaturated soil shear strength,and that we should pay great attention to the effect of water on slope stability and bearing capacity of foundation and the stress of retaining wall and other aspects in geotechnical engineering.