بررسي كارايي آهك بر بهسازي خاك هاي آلوده شده با مواد نفتي در محدوده پالايشگاه تبريز

The study of workability of lime on improvement of oil materials contaminated soils around the Tabriz oil refinery

در اين پژوهش تاثير آهك زنده بر رفتار مهندسي خاك هاي سطحي آلوده به مواد نفتي محدوده پالايشگاه نفت تبريز بررسي شده است. آلودگي خاك مورد مطالعه بيشتر از نوع هيدروكربن هاي آلكالي با بيش از 14 اتم كربن بوده و در دسته هيدروكربن هاي جامد قرار مي‌گيرند. آزمايش هاي آزمايشگاهي انجام شده در اين راستا شامل آزمايش هاي تعيين pH، تعيين حدود آتربرگ، تراكم استاندارد، مقاومت فشاري تك محوري و برش مستقيم است. آهك زنده در مقادير 1، 3، 5 و 7 درصد وزني به نمونه ها اضافه و نتايج آزمايش ها در دوره هاي عمل آوري 1، 3، 7، 14، 21 و 28 روز بررسي شده است. بر اساس نتايج به دست آمده از بهسازي نمونه هاي آلوده به مواد نفتي مشخص شد كه با افزودن آهك زنده، خواص خميري خاك كاهش يافته و پارامترهاي مقاومتي (چسبندگي و اصطكاك داخلي) افزايش مي يابد. در اين راستا، نمونه‌هاي خاك رسي محدوده پالايشگاه تبريز با بيش ازmg/kg 4/66 آلودگي با 3 درصد وزني آهك زنده و نمونه هاي با كمتر از mg/kg 4/66 با 5 درصد آهك زنده، بيشينه مقاومت فشاري را نشان مي‌دهند. مقدار آهك بهينه براي خاك‌هاي ماسه‌اي سيلتي تحت تاثير آلودگي قرار نداشته و به ميزان 3 درصد وزني رسيده است. به شكل كلي بررسي نتايج به دست آمده از اين پژوهش بيانگر كارايي آهك زنده بر بهسازي خاك‌هاي آلوده به مواد نفتي در محدوده پالايشگاه تبريز است.

This paper has investigated the affect of quicklime on engineering behaviour of contaminated soils from the Tabriz Oil Refinery. The type of contamination of studied soil was alkali hydrocarbons that had more than 14 carbon atoms (C14) and is classified in the solid phase. The laboratory tests that were undertaken are included the pH, Atterberg limits, standard compaction, uniaxial compressive strength and direct shear test. The quicklime is added to samples in 1%, 3%, 5%, and 7% of values based on weight percentages and the results of tests are investigated at curing time of 1, 3, 7, 14, 21 and 28 days. Base on the results of improvement process of contaminated soils using quicklime, the soil plasticity has been decreased. To assessment of accuracy of the affect of quicklime on contaminated soils, pH values are determined. Based on results, with addition of 5% of quicklime, the pH value was increased and then stabled that is showing the stopping of reaction between quicklime and soil. The pH values of improved contaminated clayey for 1%, 3% and 5% of added quicklime were 10.56, 11.87 and 12.52, respectively. Also, the pH values of improved silty sand for the same of added quicklime were 10.13, 11.63 and 12.17, respectively. According to the results of different researcher, the suitable pH for reaction between soil and quicklime is 12.4. Thus, adding of quicklime to the contaminated soils from Tabriz oil refinery is efficient for soil improvement. The results of compaction test indicated a decrease in maximum dry density and an increase in optimum water content for improved contamination soils. The results of compaction test are according to the results obtained by other researchers on uncontaminated soils. According to the values of UCS measured in the uniaxial compression strength tests on improved contaminated soils, there is a direct correlation between UCS and quicklime content. Base on the relationship of consistency and compression strength of soils, the CL and SM samples changes from soft consistency to hard consistency at the quicklime content of 5%. Regarding to results, the clayey soils with contamination of 66.4 mg/kg and the clayey soils with contamination more than 66.4 mg/kg, by 3% and 5% of added quicklime showed maximum strength, respectively. The optimum quicklime for contaminated silty sandy soil is not under the contamination effect and was 3% of values based on weight percentages. Comparing the uniaxial compressive strength of improved soil samples showed that the sample with low oil material contamination had high strength. Also, with increase of curing time, the uniaxial compressive strength has been increased. Direct shear test were carried out to find the effect of quicklime on strength parameters of contaminated soils from Tabriz oil refinery. The present results show a direct correlation between quicklime content and both internal friction angle and cohesion with increasing of quicklime content. The result indicate that oil material contaminated soils of Tabriz oil refinery can be stabilized satisfactory with addition of 3% and 5% quicklime. Totally, the results of laboratory tests on studied oil material contaminated soils from the Tabriz oil refinery could be used to estimate the optimum quicklime in order to improve the similar soils at the other sites