Dissertation > Astronomy,Earth Sciences > Geology > Hydrogeology and Engineering Geology > Engineering Geology > Soil science > Special soil > Loess

Experimental Study of Effects of Loess Strength on Moisture Content

Author ChengXiaoYong
Tutor XiangWei
School China University of Geosciences
Course Geological Engineering
Keywords Moisture Structural Shear Strength Macroscopic structural strength parameters Microstructure strength parameters
CLC P642.131
Type Master's thesis
Year 2009
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Loess is a typical structured soil, due to its unique historical environment and the presence of the build environment, the formation of columnar joints and large apparent pore structure, making loess with special structural and special sensitivity to water, these characteristics directly affect the loess engineering and mechanical properties, but also the mechanics of loess particularity lies. With the western development strategy, implementation of the plan, in the loess region widening project number and size, makes the characteristics of unsaturated loess becomes very meaningful. In this paper, Henan, and Shaanxi loess two complete different laboratory tests, through the undisturbed samples saturated samples and samples of compacted remodeling collapsible statics tests and microscopic analysis, the non-structural and strength characteristics of unsaturated loess-depth study. First, the structural and loess formation mechanism based on the analysis completed by changing the water content of undisturbed loess direct shear tests to investigate the water content and shear strength of the law, show that: with increasing water content, shear strength index undisturbed loess declining trend, cohesion exponential relationship between water content, water content in the friction angle and a linear relationship was found moisture content on cohesion friction angle greater than sensitivity. Undisturbed sample water content increases from 19% to 23%, the cohesion of a bigger drop, reaching 85%; increased from 23% to 27%, the cohesion of relatively small magnitude lower, with the water content gradually increased cohesion will tend to zero. Compaction remodeling like cohesion and water content relationship curve \Compaction shear strength index as remodeling like dry density decreases downward trend; friction angle increased with age and was first increased and then decreased stable state; cohesion increases with age showed an increasing trend. Triaxial shear test results through undisturbed loess, compaction remolded loess at different confining pressure, moisture structural strength to play the next process, show that: with the confining pressure increases, the structural strength of undisturbed loess stabilized, stress - strain relations hardening curve, in the case of the strain increases, soil structural strength meet Duncan - Chang (Duncan-Change) hyperbolic model. Secondly, through the interior structural tests to further explore water content, dry density, age and other factors and the structural strength of the law, on the basis of complete compaction test, relationship between matric suction and water content and consolidation compression research. In the same moisture content, different kind of dry density compaction remodeling stress - strain curves are different, indicating that the structural strength of loess play process is different, the maximum dry density of compacted samples remodeling stress - strain curve showing sclerosis or close to the ideal bomb modeling, compaction remolded loess cohesion, friction angle and dry density linear. To reshape the kind of compacted samples for TSE as a standard correction of structural parameters, as pressure increases, m p ' value decreased and stabilized, indicating As the soil in the process of being stress increases structural strength is constantly play, when m p ' with pressure exceeds 300kPa, the soil tends to be structured stable, the results indicate that the structural parameters can be adjusted on the TSE is reasonable, and that theoretically m p ' in the latter should return to 1. Collapsible through microscopic test, combined with GIS software and fractal theory, come in collapsible loess process variations pores and particles, the amount of quantitative research collapsible water immersion class rules. Qualitative analysis: collapsible water content is closely related with the water content increases, large pores are filled with particles and debris disappear, overhead pores and intergranular pores persists, compacting soil particle arrangement; contact between particles way from the point - point contact, the point - gradually to the surface contact surface - surface contact transformation; moderate kind of mild degree collapsible collapsible kind cementation obvious; generalized suction reduces large pores gradually close pores and intergranular pores overhead generalized suction , saturated soil porosity, soil particles no longer move restructuring process is completed collapsible soil, soil structure is stable, but the structural strength of the weak; structural deformation is collapsible to provide space for the collapsible suction between grains provide drivers force. Quantitative Analysis: loess micro pore structure was reduced with increasing moisture content, particle aggregation state. The pore size and grain size number is defined as the ratio of the number of k, w and k come flooding volume exponential relationship formula k = 0.5755e -0.0847w . On an experimental basis, combined with previous research on the structural parameters is proposed based on direct shear test macro structural strength parameters, expressed under different conditions of soil shear strength changes, the use of dynamic systems theory concept, combined with water content, porosity ratio and other factors change, describing quantitative indicators of soil, soil structure strength acting on the soil strength and vertical pressure on the relationship. Based on relative changes in particle size and pore microstructure strength parameters proposed by the quantitative research loess grain and pore size variations to study the structural changes of soil, water increased, micro ginseng gradually decreased in soil structural change adjustment, structural strength in the play of a process. With the gradual increase flooding, if the micro-reference changes slowly, indicating stable structural soil, pore size, and arrangement of such particles less affected by water immersion, which can show a higher structural strength of the soil. On the contrary, the rapid changes in water baptism micro parameters, indicating that easily collapsible soil, water soil mass structured and easy to change, then structural strength is small. Flooding volume has a strong sensitivity of micro parameters. Analysis of macro-and micro-structural strength parameters of structural strength parameters defined basis and feasibility of Bertalanffy general system theory as the basis for geotechnical engineering system theory as a guide, from the soil macro and micro aspects, combined with the existing structural Parameters research results, try to establish the structural parameters of the theoretical system of loess research framework for the study of the structural parameters of the soil to provide a new idea. Dynamic system theory concepts, so that expression of the structural strength parameters water content, porosity, grain variation and soil structural strength between the law and found that the water content of structural strength parameters on the macro-and micro-structural strength parameters have greater sensitivity. Finally, the combination of Henan Yanshan Reservoir spillway and natural gas sub-long segment of the phenomenon of geological disasters occur, the use of macro-and micro-ginseng ginseng and theoretical analysis of structural parameters and propose preventive measures, Henan Yanshan Reservoir spillway slope on both sides of the main slump caused by the precipitation, precipitation resulting slope water content increased, the macro-structural strength parameters are changed, soil structure strength decreases; followed by a slope stability than the design safety factor is too large to small. West-East sub-long segment of the surface precipitation, runoff and groundwater effects, causing soil collapsible, microstructure strength parameters drastically reduced, soil structure strength crash, there latent erosion, subsidence, and caves, and that leads exposed pipes, overhead and shift phenomenon.

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