Journal of Engineering Geology

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The use of piles, helical anchors and, in general, helical foundations has considerably increased in the last 30 years. The adoption of this technology in the international and domestic codes of each country, as well as in research and studies, and, finally, the publication of numerous books and papers in this area, and the existence of manufacturers’ products, committees, and contractors of this technology has contributed to its expansion and development. However, such methods have progressed at a very slow pace in many countries, especially in developing countries. This paper attempts to assess the global advancement of the helical foundations by reviewing 292 papers from 1990 to 2020 and comparing the related research findings. This will help clarify the issue and determine the scope of technological progress. On the other hand, collecting valuable papers in this area will make it easier for researchers to make further research. Subsequently, the characteristics of this technology are highlighted and the reasons for its lack of progress in the developing countries are addressed. For this purpose, a questionnaire is sent to researchers, developers, designers, and contractors of the geotechnical projects. The purpose of this questionnaire is to specify the type of existing projects, the soil type of project site, the degree of familiarity with the helical foundation technology, the reasons for not using this method and the solutions available to expand and develop this method. Finally, there are suggestions to develop this approach and the issues that need further research.

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Clayey soils in terms of sharp reduction in strength and swelling ability as a results of water and moisture absorption, it is considered as one of the most problematic soils in civil engineering and construction works. Nowadays, Nano materials such as Nano clay are used to improve and stabilize of clay. On the other side, the increasing volume of municipal waste and residues materials especially debris of building destruction have caused many problems in mega cities such as environmental issues due to incorrect disposal of waste material. Main propose of this research is study of possibility in effecting Nano clay and limestone powder mixture for improve geotechnical properties of Kuye Nasr clayey soil in Tabriz City. In this study, Nano clay and limestone powder in both separate and combined conditions with 5 and 10 percentage are mixed with clay. Curing of stabilized specimens have been performed in 7, 14 and 28 days. For evaluating geotechnical behavior of mixture materials some tests were performed such as Atterberg limits, Compaction, uniaxial strength and direct shear (in 1, 2 and 3 kg/cm2 vertical stress). Results show that the simultaneous effects of 5% Nano clay with 10% limestone powder with 7 days curing period in ambient temperature conditions in clay reduced plasticity index by 72%, improved graining skeleton structure, reduced void ratio of inter grains and increased shear strength by 33%.

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In current paper the effects of surface unreinforced / reinforced sand layers coupled with and without single and group sand columns on the bearing capacity – settlement behavior of soft clays has been investigated. In this regard behavior of soft clay, clay + unreinforced / reinforced sand layer, clay + single / group sand piles and clay + unreinforced / reinforced sand layer + single / group piles samples has been assessed. Geogrid was adopted as the reinforcement, a circular plate 5cm in diameter as the loading surface and C.B.R. apparatus as the loading system. Results show that employing unreinforced / reinforced sand layers at a settlement ratio of 5% improves bearing capacity by 4 t0 7 times the soft clay. Coupling the surface unreinforced / reinforced sand layers with single / group sand piles further increases the bearing capacity by 7 to 9 times that of soft clay.

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