تاثیر سرباره کوره‌های ذوب فلزات و آهک بر واگرایی، مقاومت برشی و خواص خمیری خاک رس استان گلستان

خاک‌های واگرا از جمله خاک‌های مشکل آفرین است و در سازه‌های آبی نظیر سدهای خاکی و کانال‌های آبیاری باعث ایجاد صدمات و تخریب‌های موضعی بسیاری می‌شوند. از روش‌های تثبیت خاک‌های واگرا افزودن سرباره کوره‌های ذوب فلزات و آهک است. در این پژوهش، خاک رس با خمیری کم برای بهبود واگرایی، مقاومت برشی و خواص خمیری با 1 و 2 درصد آهک و سرباره با مقادیر 0.5، 1، 3 و 5 درصد وزنی ترکیب شده ‌است. نمونه‌ها به‌مدت 1 روز در دما و رطوبت ثابت نگه داشته شده و سپس روی آن آزمایش برش مستقیم، مقاومت تک‌محوری و پین هول انجام شده است. از نتایج حاصل از این آزمایش ها مشاهده شد که با وجود واگرایی نمونه اولیه خاک با نشانه d1 در آزمایش پین هول، نمونه حاوی 2 درصد وزنی آهک و 5 درصد وزنی سرباره غیرواگرا با نشانه nd2 طبقه‌بندی شده ‌است. نتایج آزمایش برش مستقیم نشان داد که میزان چسبندگی برای نمونه‌های تثبیت شده با %1 آهک از 0.238 کیلوگرم بر سانتی‌مترمربع برای نمونه بدون سرباره، به‌ترتیب به 0.251، 0.373، 0.41 و 0.48 کیلوگرم بر سانتی‌مترمربع به‌ازای افزودن 0.5، 1، 3 و 5 درصد سرباره افزایش یافته است. هم‌چنین میزان مقاومت تک محوری برای نمونه‌های تثبیت شده با %1 آهک از 1.0014 کیلوگرم بر سانتی‌مترمربع برای نمونه بدون سرباره، به‌ترتیب به 1.0616، 1.0782، 1.2127 و 1.2246 کیلوگرم بر سانتی‌مترمربع به‌ازای افزودن 0.5، 1، 3 و 5 درصد سرباره افزایش یافت. نتایج آزمایش‌های تعیین حدود اتربرگ بیان‌گر آن است که با افزایش سرباره و آهک، حد روانی و نشانه خمیری کاهش می‌یابد و موجب بهبود خصوصیات خمیری خاک می‌‌شود. با توجه به نتایج مشاهده شده می‌توان گفت که استفاده از سرباره به‌عنوان محصول فرعی صنایع ذوب آهن به‌صورت جای‌گزین درصدی از آهک مصرفی به‌منظور کاهش پتانسیل واگرایی خاک رسی موثر است.

The Effect of Melting Furnaces’ Slag and Lime on the Divergence, Shear Strength and Plasticity Index of Clayey Soil Located in Golestan Province

IntroductionDispersive soils are problematic and they cause a great many of local damages and destructions in hydraulic structures such as dikes and irrigation channels. The correct identification and recognition of divergence are fundamental measures taken in line with preventing the early destruction of the hydraulic structures. The soil improvement using lime, especially in clayey soils (CL), brings about an increase in the optimum moisture percentage, reduction of the maximum dry unit weight, reduction of swelling potential, increase in the strength and elasticity module. The effect of lime on soil can be classified into two groups, namely short and longterm stabilization. Raise of the soil rsquo;s workability is counted amongst the shortterm modification measures and it is the most important factor in the early improvement stages. The increase in the strength and stability can be considered as the lime utilization on longterm results occurring during curing and afterwards. Also, according to the reports, swelling and damages occur in the limestabilized soil containing sulfate. The effective role of the iron furnace slag has been well recognized in increasing the strength against sulfates and corrosive environment conditions of the mortar containing lime and sulfates.Material and methodsAdding the slag products of the melting furnaces and lime is a method used to stabilize dispersive soils. The present study makes use of a mixture of clay featuring low plasticity with 1% and 2% lime and slag, for 0.5%, 1%, 3% and 5% of the weight, to improve dispersivity, shear strength and plasticity. The samples were kept in constant temperature and humidity for a day and then were subjected to direct shear, uniaxial strength and pinhole tests.Results and discussionIt was observed based on pinhole experiment of the initial dispersive soil sample, denoted as D1, that the sample, shown by ND2, containing lime, for 2% of the weight, and slag, for 5% of the weight, turned out to have become nondivergent. The results of the direct shear test showed that the adhesion coefficient of the slagfree samples stabilized using 1% lime has been increased from 0.238 kg/cm2 to, respectively, 0.251 kg/cm2, 0.373 kg/cm2, 0.41 kg/cm2 and 0.48 kg/cm2 per every 0.5%, 1%, 3% and 5% slag added. The adhesion of the samples stabilized using 2% lime as determined in the direct shear experiment were 0.615 kg/cm2, 0.671 kg/cm2, 0.724kg/cm2 and 0.757kg/cm2 per every 0.5%, 1%, 3% and 5% slag added. Also, the internal friction angle of the samples stabilized using 1% lime was found an increase from 14.3 ° for slagfree samples to 18.11 °, 21.3 °, 21.86 ° and 21.92 ° per every 0.5%, 1%, 3% and 5% added slag. As for the samples stabilized using 2% lime, the internal friction angles were found in direct shear test equal to 23.15 °, 23.53 °, 23.76 ° and 24.12 ° per every 0.5%, 1%, 3% and 5% slag added. The uniaxial strength of the slagfree samples stabilized using 1% lime was found an increase from 1.0014 kg/cm2 to, respectively, 1.0616 kg/cm2, 1.0782 kg/cm2, 1.2127 kg/cm2 and 1.2246 kg/cm2 per every 0.5%, 1%, 3% and 5% slag added. The uniaxial strength rates has been determined in the direct shear test of the samples stabilized using 2% lime were 1.1367 kg/cm2, 1.1885 kg/cm2, 1.2322 kg/cm2 and 1.2872 kg/cm2 per every 0.5%, 1%, 3% and 5% slag added. The amount of axial strain of the slag free samples stabilized using 1% lime was found decreased from 9.6842% to, respectively, 9.3333%, 9.2683%, 9.6364% and 8.4444% per every 0.5%, 1%, 3% and 5% slag added. Moreover, the axial strain amounts obtained for the samples stabilized using 2% lime were 7.7333 kg/cm2, 7.6316 kg/cm2, 7.1517 kg/cm2 and 4.7619 kg/cm2 per every 0.5%, 1%, 3% and 5% slag added.The study results indicate that slag and lime have the capacity of improving the studied soil rsquo;s dispersivity. Furthermore, it was figured out that adding slag to the soil causes an increase in the soil strength and improves the shear strength parameters. It can be stated according to the observed results that the use of slag, a byproduct of iron smelting industry, as a substitute for a given percentage of lime is effective on the reduction of the clay soil rsquo;s divergence potential. The results of the experiments carried out to determine Atterberg limits are suggestive of the idea that the increase in the slag and lime fractions brings about a decrease in the liquid limit and plasticity and improves the plasticity properties of the soil. The reason why the soil plasticity has been reduced after being mixed with lime and slag is the cationic exchange and coarsening of the soil texture. Addition of lime to the soil causes an increase in the plasticity limit and a reduction in the liquid limit. Therefore, the plasticity index is decreased and the plasticity characteristics of the soil are improved. Adding 1% lime to the dispersive soil leads to small reduction of the liquid limit from 32.43% to 31.73%, a small increase in the plasticity limit from 13.42% to 14.66% and a insignificant decrease in the plasticity index from 19.01% to 17.07%.