Effect of bio-cementation on the strength behaviour of clay soils using egg shell as calcium source

Improving the mechanical properties of low-strength soils (e.g., high plasticity clays) is one of the main branches of geotechnical engineering. The adoption of stabilization techniques for ensuring that structures will be founded on an adequately strong soil base is a common practice. Stabilization techniques for clay soils may include inert materials (cohesionless soils), chemical substances (cement, lime, or industrial additives), or the use of randomly distributed fibers. While all of these additives are added to low-strength soils by mixing, the question remains whether an optimal combination of stabilization techniques can be achieved for maximizing soil strength. Besides, each one of these additives contributes to an increase in soil strength in a different manner (soil replacement, chemical bonding of soil particles, and soil reinforcement respectively), while, according to the literature, each technique has its limitations. The latter refers to a limited effect on strength improvement and a maximum possible percentage, beyond which an additive has an adverse effect on strength; it also refers to other factors, such as brittleness failure, material availability, overall cost, and environment-related issues. Hence, in the present study, the efficiency of improving the basic geotechnical properties of a very high plasticity clay (liquid limit ωl = 86%) with a coupled effect between dune sand, lime, and polypropylene (PP) fibers has been investigated. The samples prepared by combining the three aforementioned soil improvement techniques were compared in terms of plasticity, compaction characteristics, unconfined compressive strength (UCS), and California Bearing Ratio (CBR) index. The experimental results show that the combination of these additives may lead to a considerable improvement in the strength and ductility of soils, even with a small amount of lime additive. Also, it was observed that 20% of sand, 3.4% of lime and 0.9% of fibers (by wt%) offers the best performance in terms of strength improvement for the clay tested (i.e., 12.75 times improvement compared to the untreated clay).

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Improving Very High Plastic Clays with the Combined Effect of Sand, Lime, and Polypropylene Fibers

Strength Enhancement of Clay Soil Stabilized with Ordinary Portland Cement, Sodium Silicate and Sodium Hydroxide

Abstract Nano soil-improvement is an innovative idea in geotechnical engineering. Nanomaterials are among the newest additives that improve soil properties. Herein, laboratory tests, such as unconfined compressive strength, direct shear test, and initial tests, were conducted to investigate the geotechnical properties of Kelachay clay with micro- and nanosized cement to evaluate its particles in untreated soil and observe changes in the behavioral properties of treated soil compared to those of untreated soil. Scanning electron microscopy and X-ray fluorescence images were analyzed before and after the grinding process to determine the nature of the studied particles. Furthermore, effects of time and nanocement content (0%, 1%, 3%, 5%, and 7%) on curing performance were evaluated. The optimum percentage of nano-cement was found to be 7%, which increased the unconfined compressive strength by up to 29 times and reduced the strain at rupture by 74% compared to the untreated soil. The results showed that nano-cement significantly improved the strength and stiffness of the soil–cement mixture by forming calcium silicate hydrate (C–S–H) gel that filled the pores and bonded the soil particles. Nano-cement also acted as a nucleation site for more C–S–H growth, enhancing the durability and strength of the mixture. 

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Nano soil improvement technique using cement

Stabilization of soils with nanoclay subjected to freeze-thaw cycles

The current study presents the laboratory investigation on the use of nano-silica (0.2, 0.4, 0.8 and 1.0%) and polypropylene fiber (0.25, 0.50, 0.75 and 1.0%) in problematic clayey soil to enhance the shear strength and compaction characteristics. From the Transmission electron microscopy (TEM) analysis, it is observed that the diameter of nano-particles used in this study was in the range of 10–20 nm. The nano-particles have a spherical shape and amorphous in nature. Extensive laboratory tests such as the standard Proctor compaction test and unconfined compressive strength test have been conducted on untreated and polypropylene fiber along with nano-silica treated clayey soil. The outcomes showed that the addition of polypropylene fiber in poor soil, increase the maximum dry density and reduce the optimum moisture content of the soil. Whereas, the addition of nano-silica to the clay soil results in reduced maximum dry density and increased optimum moisture content. Unconfined compressive strength of clay soil is increased with the addition of polypropylene fiber and nano-silica to the clay soil. The optimum dosage of polypropylene fiber and nano-silica added to the poor soil was 0.75% and 0.8%, respectively. The Young’s modulus of clay soil was increased with the addition of polypropylene fiber and nano-silica. The microscopic analysis confirmed that C–S–H gel was the main cementitious product, and the inclusion of nano-silica can contribute to a denser packing of soil particles.

V. S. Kayalvizhi

Papers

Combined effect of nano-silica and randomly distributed fibers on the strength behavior of clay soil