Study On Strength Characteristics And Mechanical Model Of Collapsible Loess In West Area Of Liaoning

Because of its unique collapsibility to water, loess has been the focus of the study of Chinese and foreign scholars from the past century. As a result of the regional differences of the distribution of loess in China, the scientists mainly concentrated to research loess in the northwest and North china. Fuxin and Chaoyang district in west area of Liaoning are firstly listed in the marginal zone of loess by the national standard Architecture Criterion in Collapsible Loess Area (GB50025-2004).With the development of economic construction in Liaoning, there are lots of engineering problems caused by special collapsibility of loess in engineering construction especially in expressway construction, so it is our duty to study how to avoid the engineering accidents and disasters that are caused by way of the unique collapsibility of loess. Due to the regional differences of loess, it is very practical significant to understand the engineering characteristics of loess in west of Liaoning by detailed and comprehensive. This paper analyses and researches the mechanical properties of Liaoxi loess by detailed from a large number of experimental data and data collection. This paper is divided into six parts:The first part of the paper describes the basic properties of loess, including the nature of loess structures,collapsibility,the research about loess at home and abroad,elaborating the purpose and significance of the research about loess in this paper and the major contents.The second part introduces the consolidated undrained triaxial shear tests and the specific processes of experimental operation,the basic physical properties of loess and how to prepare the test soil samples.The third part mainly researches the moistening and drying deformation characteristics of collapsible loess in west of Liaoning. From the moistening and drying stress - strain relationship curves, we can see that curves show strain-softening,weak strain hardening and strain hardening characteristics with different moisture content , the moisture content and confining pressure play a significant role for the stress-strain relationship . The stress - strain curves increase with the increase of confining pressure when in the same moisture content under different conditions of confining pressure, and the curves change from strain-softening or weak strain hardening to strain hardening, and the curves appear weak strain hardening at low confining pressure; appearing strain hardening at high confining pressure, which shows confining pressure is significant important to the loess structure properties. The stress - strain curves decrease with the increasing of the moisture content at the same confining pressure under different moisture content, and the influence to the stress - strain relationship imposed by confining pressure is greater than moisture content. Theε1 /(σ1?σ3)?ε1curve is in a straight line at low moisture content and is a cut in the rate for the line at high moisture content, which shows Duncan - Zhang model doesn't fit to describe the strain hardening curves. TheΔv ?ε1 curves show the trend of increasing with the increasing of confining pressure at low moisture content and the trend of decreasing at high moisture content when at the same moisture content under different confining pressure. Similarly, theΔv ?ε1 curves show the trend of increasing with the increasing of moisture content at lower confining and show the trend of decreasing with the increasing of the moisture content at high confining pressure when at the same confining pressure under different moisture content. Effective principal stress ratio increases with the increasing of the axial strain. At the same moisture content under different confining pressure or at the same confining pressure under different moisture content, theσ1 ' /σ3'?ε1curves all show the trend of decreasing. Meanwhile, there is the trend of the curves from scattered to focus with the increasing of the moisture content and confining pressure. There is a significant influence from confining pressure to effective stress path, while, there is little from the moisture content. The effective stress path curve also reflects the high strength of Liaoxi loess. In the consolidation process, the consolidation of pore pressure and consolidation of variable all show variable mutation, and in the initial stage of consolidation ,the changes about the variable and the pore pressure will have been generally made, there will be no longer changing after that process which is due to the under-voltage density and the macropore properties of loess.From the research about the shear strength characteristics of loess in the fourth part of paper, we can see that the ultimate strength of loess decreased with the increasing of the moisture content, and increase with the increasing of confining pressure, the (σ1 ?σ3)f ?σ3relationship curves and the (σ1 ?σ3)f?ωcurves will not pay to the same point ,which showing that the moisture content and confining pressure all have the influence to the structural strength of loess, and the structural strength of loess is the dual function about moisture content and confining pressure. From calculating, we know the indicators of the strength of loess c and ? decreases with the increasing of moisture content which is according to the law of the change of the shear strength of unsaturated loess when is under consolidation undrained shear. The impact to the structural strength of loess from moisture content is mainly seen in the indicators of the shear strength of loess c decreases with the increasing of moisture content. Because of the special characteristics of the material composition and structure, the impact to the indicators of the shear strength of loessc from moisture content is greater than the impact to indicators? .The fifth part first introduced that it is the main purpose of laboratory testing to establish models fitting the three-axis shear stress - strain curves and studying the relation in the area of researching the mechanics of the collapsible loess. And then analyzing and introducing the Duncan - Zhang model and the model proposed by LiuZu-dian can not reflect all the characteristics about the strain hardening and strain-softening of unsaturated collapsible loess in this test. This paper tells the mathematical model proposed by LiuZu-dian, Guo Zeng-yu and Chen Zheng-han is better to reflect the characteristics of strain hardening in this article. And Duncan - Zhang model is more realistic on the weak strain hardening properties of the loess. The paper established a more realistic model to reflect the strain-softening properties. From the comparison between the weak strain-hardening curves of loess under low moisture content and low confining pressure and the text of the model, we can see that the model established in the paper is better to fitting the experimental curves, and can better to reflect the characteristics of weak strain-hardening curve at low moisture content and low confining pressure. From the comparison between the high strain-hardening curves at high moisture content and high confining pressure and the model, we can see that the model established in line with the experimental curves, and are also better able to more accurately reflect the characteristics of the high strain-hardening curves. Through the comparison between empirical model and the strain-softening curves of loess at low moisture content, we can see that , at low confining pressure ,the model curve and experimental curve have a certain deviation before the peaks from the curve, after the peak in the curve, the model is in coincide with the experimental curve well; at high confining pressure, there is a deviation between the model curve and experimental curve, indicating that this model is essentially a reflection of strain-softening characteristics of loess, in the future application of the specific circumstances of the need ,the model need further improvementsThrough consolidation undrained triaxial shear test, this paper researches the Liaoxi collapsible loess, understanding of the mechanical properties of Liaoxi collapsible loess, the mechanical model to the specific stress - strain relations is also more in line with the actual, reached the purpose of researching about the loess in western of Liaoning, Establishes the foundation for further studying of loess in western of Liaoning.