بررسي آزمايشگاهي پارامترهاي موثر در مقاومت فشاري و خمشي مصالح خاك سيمان و بررسي عددي استفاده از اين مصالح براي فرازبند سد بختياري

Investigation into the Effective Parameters of Compressive and Flexural Strength of Soil Cement Materials using Numerical Modelling. Case Study: Coffer Dam of Bakhtiari Dam

خاك سيمان مخلوطي از سيمان پرتلند، خاك، و آب است، كه به‌واسطه‌ي عمل هيدراتاسيون سيمان و تراكم اجزا آن به هم چسبيده و تركيبي متراكم، با دوام، با نفوذپذيري كم، و مقاوم در برابر سايش ايجاد مي‌كند. پارامترهاي تاثيرگذار در مقاومت فشاري مصالح خاك سيمان مورد پژوهش پژوهشگران مختلفي قرار گرفته‌ و عواملي همچون نسبت آب به سيمان، ميزان سيمان و نوع آن از پارامترهاي موثر در مقاومت اين مصالح عنوان شده‌اند. هدف از اين مطالعه، بررسي پارامترهاي ديگري نظير: ارزش ماسه‌يي، شاخص خميري و نوع دانه‌بندي بر روي مقاومت فشاري و خمشي با استفاده از آزمايش تك‌محوري و خمشي روي اين مصالح است، كه بر روي 7 نوع دانه‌بندي مختلف مورد بررسي قرار گرفته‌اند. نتايج آزمايش‌ها حاكي از آن بوده است كه مقاومت فشاري و خمشي مصالح خاك سيمان با افزايش ارزش ماسه‌يي و كاهش انديس خميري متناسب بوده است. همچنين مدل‌سازي عددي بر روي سازه‌ي فرازبند سد بختياري حاكي از پايداري آن با استفاده از مصالح مذكور بوده است.

Soil cement is a mixture of Portland cement, soil and water, the constituents of which, due to the hydration of cement and compaction, bond together and make a dense and durable composition with low permeability and abrasion resistance. According to the definition of ACI 116R, soil cement is a mixture of soil and a certain amount of cement and water which has been compacted to a high density. A more comprehensive definition has been provided in ACI 230 IR, which defines soil cement as a hard material with specific engineering properties that is produced by the mixing, compaction and curing of soil, aggregate, Portland cement, additives and water. They are similar to roller compacted concrete; the main difference between them being, however, the type and size of aggregate particles. Soil cement is principally made of round natural fines, while roller compacted concrete is made of particles with a size of up to 19 mm. The soil cement mixture is usually used as protection for earth embankment slopes, while roller compacted concrete is mostly used in massive elements such as gravity dams. All types of soil can be used in soil cement construction, except organic and plastic soil and reactive sand. The most efficient soils are those containing 5 to 35% of fines, passing sieve 200. However, soil containing more than 2% organic material is strictly unacceptable. Soil cement application in dam and pavement construction has grown. Previous studies have investigated the effects of cement content, water to cement ratio, and compaction level, on the strength of soil cement mixtures. Some other factors affecting the strength of soil cement are pozzolans and chemical additives which are not usually economical for use in large civil projects. In this research, the effects of plasticity index and sand equivalent of soils on unconfined compressive and flexural strength have been investigated. The results show that the compressive and flexural strength of soil cement mixtures is dependent on the plasticity index and sand equivalent. Also, a numerical model developed for the coffer dam of the Bakhtiari dam, and results, show that its structure is stable with soil cement material.