مطالعه ريزساختاري تثبيت خاك مارن جنوب با استفاده از آهك و نانوسيليس

Microstructural Study of Soil Stabilization of the Southern Marl Using Lime and Nano-SiO2

مارن­ها از خاك­هاي مساله ­دار هستند كه در صورت قرار گرفتن در معرض جريان آب به سهولت فرسايش مي­يابند و مشكلاتي را در پايداري بستر پروژه­هاي عمراني ايجاد مي­نمايند. يكي از روش­هاي اصلاح شيميايي خاك استفاده از مواد افزودني مانند آهك، سيمان و نانوذرات است. پژوهش حاضر به بررسي تاثير آهك و نانوسيليس بر ويژگي­هاي مهندسي خاك مارن و تشكيل تركيبات جديد ناشي از فرآيند تثبيت مي­پردازد. در اين راستا پس از تعيين خصوصيات ژئوتكنيكي خاك مارن، بهبود ويژگي­هاي مهندسي نمونه­هاي تثبيت شده با درصدهاي مختلف آهك شكفته و نانوسيليس بعد از پايان دوره عمل­آوري مورد ارزيابي قرار گرفته است. آزمايش پراش پرتو ايكس (XDR) براي شناسايي كاني­هاي موجود در خاك و بررسي تشكيل تركيبات هيدرات سيليكات كلسيم در واكنش خاك با آهك و نانوسيليس انجام شده است. نتايج نشان مي­دهد كه حضور نانوسيليس در سيستم خاك-آهك، منجر به توزيع يكنواخت تركيبات سيليكات كلسيم هيدراته (C-S-H) در خاك شده است. بر اساس نتايج، با افزايش زمان عمل­آوري، مشاركت آهك در انجام واكنش­هاي پوزولاني افزايش يافته، همچنين، نتايج بدست آمده از آزمايش حدود اتربرگ، كاهش در شاخص خميري نمونه مارن را با افزايش در مقادير آهك و نانوسيليس نشان داده است. بر اساس نتايج پژوهش حاضر، افزايش 6% آهك با 7/0% نانوسيليس در دوره عمل­آوري 28 روزه، موجب افزايش 67/92 درصدي مقاومت فشاري تك محوري نمونه مارن شده است.

Marl is a combination of clay and calcium carbonate which its carbonate content is between 35 to 65 %. Marl soils have variable characteristics and their engineering behavior may be highly different in dry and saturated conditions. Such soils suffer from falling, swelling, divergence, and loss of resistance when exposed to water and moisture. Marl deposits have higher erosionability than other deposits due to the structural nature such as the presence of destructive particles and chemicals (carbonate Calcium, Gypsum, Anhydrite and Salt). Palygorskite and sepiolite are clayey minerals forming the marl soil, which leads to instability, load capacity reduction and swelling in the soil. Microstructural study of soil stabilization of the Southern Marl using lime and Nano-SiO2. Using additives such as lime, cement and nanoparticles is one of the methods for soil chemical modification. The present study investigates the effect of lime and Nano-SiO2 on the engineering properties of marl soil and the formation of new compounds due to the stabilization process. The soil used in this study was the marl sample of the west of the Bandar Abbas l on the northern margin of the Persian Gulf. In this area, natural and artificial slopes are instable. Also, extensive failures in many of geotechnical projects such as failure in the foundations, tensile cracks and slopes on the roads have been reported. The structure and minerals of the marl soil can be considered as the main cause of such problems. Observations indicate that most of failures have occurred after rainfall. Based on the Unified Soil Classification System (USCS), Marl is a clay with low compressibility (CL) in which 95% passed through the No. 200 sieve. The hydrated lime used in this study was passed through the No. 100 sieve. The pH of lime is 12.81. In this regard, after determining the geotechnical properties of Marl soil, the improvement of engineering properties of the samples stabilized with different percentages of lime and Nano-SiO2 has been evaluated at the end of the treatment period. In order to identify present minerals in the soil and investigate the formation of calcium silicate hydrate compounds in the reaction of soil with lime and Nano-SiO2, the XDR test was conducted. Also, SEM was used to evaluate the impact of adding lime and Nano-SiO2 on the structure and morphology of the soil. The results showed that the presence of Nano-SiO2 in the limestone system led to the uniform distribution of cement (C-S-H) compounds in the soil. Based on the results, with increasing the treatment time, lime participation in pozzolanic reactions was increased, also the results obtained from the Atterberg limits test showed a diminution in the paste limit of the marl sample with increasing lime and Nano-SiO2 values. Based on the results of the Atterberg limits, compared to the outline of stabilization with increasing lime, the presence of Nano-SiO2 in the process of stabilizing with lime led to 4 units' reduction of the plastic limit. Based on the results of the present study, the stabilized marl soil showed best geotechnical properties in the presence of 6% of lime and 0.7 % of Nano-SiO2.