جستجوی مقالات مرتبط با کلیدواژه « plasticity index » در نشریات گروه « عمران »

Soil tensile strength is important in different geotechnical structures such as earth dams, roads, airports, landfills, and retaining walls. There are several experiments to study the tensile behavior of soils with different advantages and disadvantages. One of the methods used to investigate soil tensile behavior is tensile hollow cylinder apparatus, which has seldom been used. In this research, a hollow cylindrical device to measure the tensile properties of soil was built and operated. This device can apply tensile stress evenly to the entire soil sample so that stress concentration does not occur at any point in the sample.  After designing, manufacturing, and assembling the apparatus, validation tests were performed to ensure the device was operating well. The results of the repeatability tests show the accurate performance of the device. Also, in this study, the effect of plasticity index (PI) on the tensile behavior of kaolinite clay was investigated. Clayey soils with plasticity indices of 10 and 24% were selected. The results show that for clays with a similar mineral, the tensile strength increases and the tensile failure strain decreases with increasing the plasticity index.

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 de nition 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 de nition has been provided in ACI 230 IR, which de nes soil cement as a hard material with speci c engineering properties that is produced by the mixing, compaction and curing of soil, aggregate, Portland cement, additives and wa- ter. They are similar to roller compacted concrete; the main di erence between them being, however, the type and size of aggregate particles. Soil cement is principally made of round natural nes, while roller compacted con- crete 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 con- crete is mostly used in massive elements such as gravity dams. All types of soil can be used in soil cement con- struction, except organic and plastic soil and reactive sand. The most ecient soils are those containing 5 to 35% of nes, passing sieve 200. However, soil containing more than 2% organic material is strictly unacceptable. Soil cement application in dam and pavement construc- tion has grown. Previous studies have investigated the e ects of cement content, water to cement ratio, and compaction level, on the strength of soil cement mix- tures. Some other factors a ecting 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 e ects of plasticity index and sand equivalent of soils on uncon ned compressive and ex- ural strength have been investigated. The results show that the compressive and exural strength of soil cement mixtures is dependent on the plasticity index and sand equivalent. Also, a numerical model developed for the co er dam of the Bakhtiari dam, and results, show that its structure is stable with soil cement material.

A major problem in highway construction is the provision of materials to be used in pavement layers. In many regions, the materials with required specifications are not available or need to be transported in long distances. Therefore, improving the inappropriate materials available in the construction sites to make them usable in pavement layers is a measure for reducing the costs. In this research, a nano polymer stabilizer, called CBR PLUS, has been used for improving the physical and mechanical properties of three combinations of clay, sand and gravel, neither of which have the required properties defined by the specifications. Each combination is mixed with different contents of the additive and the properties of compaction, Atterberg limits, uniaxial compressive strength, California Bearing Ratio and permeability are evaluated. It is found that the stabilizer decreases the plasticity index and permeability and increases the compressive strength and CBR of the combinations. The combination of 50% gravel, 30%sand and 20% of clay is found to attain the highest strength with the stabilizer.

Organic soil is one of the important problematic soils in construction industry. The effect of organic materials on engineering features of soils is variable depending on the type and content of organic matter. The main purpose of this study is to investigate the effects of organic matter on the strength and physical properties of organic soils and its improvement. One of common improvement methods in this type of soils is chemical stabilization with lime, cement, etc. For this purpose, organic matter (peat) was added to inorganic clayey soil at three levels (3%, 6%, 9% by weight). The physical properties of the mixtures were determined by conducting a series of laboratory tests including Atterberg limits, compaction, unconfined compressive strength, and swell characteristics tests. The results showed that with increasing organic matter content, the percentage of lime required to modify the soil, changed too dramatically. Also results indicate that by increasing three percent in organic matter, the amount of required lime increases by two percent. The study of plasticity and swelling in each three soil types shows that these parameters are decreased after stabilization, but with increasing amount of organic matter, the rate of reduction can be reduced. To evaluate the mechanical properties of these soils, unconfined compression strength (UCS) test was carried out on lime treated samples. The results show that in all samples after 28 days of curing, the UCS has been increased noticeably. This growth in strength decreases with increasing organic matter content. pH of all samples has been reduced after 28 days of curing and the amount of reduction has been increased with higher organic matter. Considering the results, with increasing organic matter content from 0 to 9%, only soil with organic matter of 3% suitably stabilized.