روش اختلاط عمیق جهت بهبود خواص مقاومتی زمین های ماسه‌ای ساختگاه پروژه زیتون 2 در بندرعباس

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Abstract

In deep mixing method lime or cement and or a combination of the two are mixed with in-situ soils by means of an auger to improve the strength properties of the soils. Strength of the improved soils may be evaluated in different ways, so that, the uniaxial compressive strength assessment is one of the most commonly used methods. The project site is located at Zaytoon 2 in Bandar Abbas City. In order to make the excavation of the sandy soils feasible and to mitigate the liquefaction potential hazard, deep mixing method was employed. In an attempt to establish a relation between strength properties of cement grout (cement + water) and the soil-cement mixed (cement grout + soils) two types of grouts; "A" and "B" with different admixtures were used. Type "A" with a water/cement ratio (w/c) = 0.8, where no bentonite was added, whilst in grout Type "B" the ratio w/c = 1.0, with 3% (by cement weight) and bentonite was added. In order to evaluate the strength properties of the grout and soil-cement, some representative samples were obtained. The 7 and 14 days cured samples were tested under uniaxial compressive loading condition. Several in-situ samples were also taken for reliability and quality control purposes. Comparative study of the results revealed that the rate of strength increase in grout type "B", due to using bentonite, is low as compared with the grout type "A". The relationship of uniaxial compressive strength and modulus of elasticity with both density and with the final strain of soil-cement mixed were investigated. Finally, based on the results of uniaxial compressive strength of cement grout, an empirical equation to predict the uniaxial compressive strength of soil-cement mixed has been suggested. The predicted strength was compared with the strength of in-situ samples. It has proven that the prediction method can be used as a reliable approach for determination of the uniaxial compressive strength of soil-cement mixed.

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