Study On Structure Damage And Evolution Of Loess

Loess region is the key area of infrastructure constuction during western development. Stabilization and settlement of loess body after constructing is one of the main problems confronted during the engineering construction of trafic engineering, railway engineering, hydraulic engineering, construction engineering, energy engineering and so on. The special microstructure leads to the special engineering properties of loess, a reduction in strength and deflection in augment inavitably affect the normal use of construction as a result of coupling of load and water content. Under the load of constrution and water increasing of loess, the deformation development process is the process which original struture loses and the secondary structure develops gradually, that is the microstructure flaw that results in the whole mechanical property degradution gradrually, the phenomena of which is named structre damage. Therefore, structure damage variable of loess determined reasonably is the foudation of forming a ture estimation of structure damage extent, and which have an important meaning for construction engineering in loess area.Based on the consolidated undrained tiaxial shear test(CU) of Yangling loess, it is proved that consolidation pressure, water content and shear strain rate have important effect on structural property of loess, and main research results can be gained as follows:(1) Shear stain rate has abvious effect on behavious of stress-strain curves of unsaturated loess, and high shear strain rate can lead to the phenomena of strain rate sftening; the shear strength, cohesion, damage stress shreshold and initial tangent moudulus of loess increase at first then decrease with the increase of shear strain rate, the critial value of shear rate is 0.18 millimeter per minute, all these change regulations show that the loss of loess structure becomes slow at first then becomes qiuk gradually; the angel of internal friction basically appears to decrease sligtly in linear pattern with the increase of shear rate. The change laws of loess strength are relative to whether the cohesion and internal friction bring into play synchronously or not with the shear rate.(2) Given the other same factor condations, two critical values of water content impacting on the structure of loess exist, separately 18 persent and 26 persent, the fomer can be thougth as keeping the structure of loess better, the latter can be regarded as the structure of loess beginning to disappear entirely, which is the terminate water content of structural strength.(3) The relationship of angel internal friction and initial water content is comparatively complex, it decreases at first then increases with the water increase when the water content is 18 persent, and it appears to be the peak when the water content is 26 persent, and later it decreases again with the water content increase.(4) The structure of loess is affected remarkbly by the change of initial water content, when the consolidation pressure and water content are all below 200kPa and 18 persent respetively, whereas, the structure of loess is affected sligtly by the change of initial water content.(5) Under different water content, consolidation pressure and shear rate conditions, not only the initial tangent moudulus are different, but the gross moudulus(that is the secant moudulus) during the shear process are also different, the resluts show that the change of moudulus during shear process also reflects the damage change of loess structure. And the structure damage variable of loess which is represented by secant moudulus can refect the extent of loess structure damage change better. The structure damage variable can be described as a compoud function which is influenced by main stain, consolidation pressure, water content and shear rate during the shear deformation process.