The Study On Mechanical Property And Microstructure Of Compactrd Cement-Loess

In China, the distribution area of loess is about 0.63million km2. In districts of loess, the natural foundation often can't meet the requirement of bearing capacity or settlement because of loess's special engineering property, so it requires foundation treatment. The composite foundation of compacted soil-cement pile, one of ground improvement methods developed in 1990's, is regarded as a promising foundation treatment method due to its many advantages. In order to explore the suitability and the reliability of compacted soil-cement pile in loess districts, pile material of compacted soil-cement pile when improve loess, compacted cement-loess, is studied in this paper.In this paper, change laws of shear strength, compressibility and microstructure of compacted cement-loess with different cement mixing ratio, different water content and different compactive effort are studied through direct shear test, compression test and microstructure test. The results indicate that cement mixing ratio, water content and compactive effort have important influence on shear strength, compressibility and microstructure of the compacted cement-loess. Contrasted with intact loess, the shear strength of compacted cement-loessimproves greatly while the compressibility reduces greatly. When other factorsare same, the shear strength and the cohesive of compacted cement-loess firstincrease then decrease as initial water content increasing and a summit existingnearby optimum moisture content increasing; Coefficient of compressibility firstdecreases then increases as initial water content and a minimum existingnearby optimum moisture content. When other factors are same, the shearstrength and cohesive of compacted cement-loess grow as cement mixing ratiorising and the growth rate are more when compactive effort are more;Coefficient of compressibility reduces as cement mix ing ratio rising. Whenother factors are same, the shear strength and cohesive of compactedcement-loess ascend as compactive effort rising while coefficient ofcompressibility descends as compactive efforts rising. When compactive effortis same, the shear strength and cohesive at optimum moisture content grow ascement mixing ratio increasing; Coefficient of compressibility declines ascement mixing ratio increasing. When cement mixing ratio is same, the shearstrength and cohesive at optimum moisture content grow as compactive effortincreasing; C oefficient of compressibility declines as compactive effortincreasing. But in this experiment no law is founded between angle of internalfriction and different influencing factors of compacted cement-loess.Analysis on SEM images confirms that the change of microstructure determines the macro mechanical property. The new microstructure in reinforced loess brings about mechanical property improving greatly. Additional, the influence of compactive effort, cement mixing ratio and initial water content on microstructure has the same reflection as on macro mechanical property. In those samples with better mechanical property, there are many hydrate materials between grains, voids are tiny and the distribution is discrete, the void ratio is small and there are rather dense soil grains or hydrate materials around the voids. The connection between particles is close bonded structure. In those samples with poor mechanical property there are bigger and aggregate voids, the connection between particles is loose bounded structure.