پديد آورندگان :
شريفي اسدي، داريوش دانشگاه بين المللي امام خميني (ره) - دانشكده فني و مهندسي , اردكاني، عليرضا دانشگاه بين المللي امام خميني (ره) - دانشكده فني و مهندسي , گروسي، قاسمعلي دانشگاه بين المللي امام خميني (ره) - دانشكده كشاورزي و منابع طبيعي
كليدواژه :
بهسازي زيستي , رسوب ميكروبي كربنات كلسيم , مقاومت تك‌محوري , خاك ماسه‌اي , سيلت غيرخميري , روش بيولوژيكي در خاك‌هاي ماسه‌اي
چكيده فارسي :
يكي از روش هاي متداول بهسازي خاك، استفاده از افزودني ها به منظور بهبود خصوصيات مقاومتي و نفوذپذيري خاك است. اغلب از سيمان يا مواد شيميايي به عنوان عامل چسبنده ذرات خاك استفاده مي شود كه باعث افزايش مقاومت برشي خاك و كاهش هدايت هيدروليكي آن مي شود. در اين پژوهش با استفاده از آخرين فناوري زيستي ميكروبي، نوع جديدي از مصالح ساختماني، يعني سيمان زيستي، به عنوان جايگزيني براي سيمان و يا مواد شيميايي ايجاد شده است. سمنتاسيون زيستي يا فرآيند رسوب ميكروبي كربنات كلسيم (micp)، بهبود مقاومت و سختي خاك و سنگ با استفاده از فعاليت هاي ميكروبي و فرآورده هاي آن هاست. در اين پژوهش از خاك ماسه اي با درصد متفاوت سيلت %0، %5،%10، %15 و %20 و در دو حالت سست (dr=40%) و متراكم (dr=100%) و از باكتري sporosarcina pasteurii به دليل فعاليت اوره آزي بالا و غير بيماري زا بودن در فرآيند micp استفاده شد. به منظور در نظر گرفتن شرايط خاك بر عملكرد اين نوع روش بهسازي، پارامترهاي آزمايش تك محوري و ميزان رسوب كربنات كلسيم موردبررسي قرار گرفت. با توجه به نتايج، افزايش درصد ريزدانه از 0 تا 20 درصد منجر به كاهش %40 و %46 در ميزان رسوب كربنات كلسيم، افزايش %57 و %41 در مقاومت تك محوري و افزايش %79 و %71 در مدول الاستيسيته نمونه ها به ترتيب در دو حالت سست و متراكم گرديد. بنظر مي رسد اين تغييرات ناشي از كم شدن فضاي خالي و افزايش سطح تماس بين ذرات خاك بوده است.
چكيده لاتين :
One of the most common methods of soil improvement is to use additives in order to improve strength properties and permeability of the soil. Cements or chemicals are usually used as binders for soil particles, which lead to increase the soil shear strength and reduce its hydraulic conductivity (i.e. permeability). Nevertheless, these materials are not suitable for soil improvement in the long term because they require significant natural resources. The use of cement and chemicals for soil improvement is expensive and time-consuming. Management of renewable natural resources (microorganisms and their products) could lead to solve geotechnical and environmental problems and achieve great economic benefits in the building industry. In addition, the application of microbial biotechnology in the building industry make easier some of the existing methods of construction. Using the latest microbial biotechnology, a new type of building materials, namely biocement, has been produced as an alternative to cement or chemicals. Biocementation is the improvement of strength and stiffness of rock and soil by using microbial activity and their products. The process of the formation of precipitates or biocement in the presence of microorganisms is called microbialy induced calcium precipitation (MICP). Biocement can be used in solid and liquid states. In the liquid state, biogrout can flow like water with very low viscosity. Therefore, compared to cement and chemicals, it will be transmitted into the soil, more easily. Naturally, biocement is formed in the presence of microorganisms in ambient temperature and thus, it requires less energy. Because of the abundance of microorganisms in the nature and easy to reproduce with low cost, this type of cement is sustainable. The Microorganisms that are suitable for the production of biocement are usually non-pathogenic and environment friendly. In addition, unlike cement, soil can be improved without disturbance of ground and the environment; since microorganisms can penetrate into the soil and grow in it. This dissertation aims to realize the effect of ground condition on the MICP process in non-cohesive soils. Since this method is still in the laboratory stage, for being used in practical projects, it is required to carry out laboratory experiments, including relative density and particle size distribution, to evaluate the performance of this method in different ground conditions. For this purpose, it was used from Sandy soil with different silt contents of 0%, 5%, 10%, 15% and 20% in two states of Loose (Dr = 40%) and dense (Dr = 100%) conditions in this research. The high urease activity and non-pathogenic bacteria S. Pasteurii was also used in the MICP process. In order to consider the soil conditions on the efficiency of this type of improvement method, uniaxial compressive test parameters and precipitated calcium carbonate content were investigated. According to the results, increasing of silt content from 0% to 20%, leads to reductions of 40% and 46% in precipitated calcium carbonate content, increases of 57% and 41% in the uniaxial strength and increases of 79% and 71% in the elasticity modulus of the samples in two loose and dense conditions, respectively. It seems that these changes were resulted from shrinking of the empty space and increasing of the contact area between the soil particles.
