Journal of Engineering Geology

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Introduction
Loess soil is one of the problematic soils that should be improved its geotechnical properties before the project is implemented. Lack of attention to this issue has caused in many problems for civil projects in Golestan province. This has been more evident in some of the rural areas built on this type of soil. Moreover there are many reports regarding different geological hazard such as subsidence, divergence, erosion and landslide in Golestan loess soil. Among the different types of loess soils found in Golestan province, silty loess should be given more attention due to their large extent and being the bed soil of many villages, and many reports of its hazards.
One of the methods for improving soil mechanical behavior and its geotechnical properties is to use additives to reduce geological hazards. Due to the fine-grained structure of loess soils, the application of nanoparticles is more efficient and could result in solving many of the related problems. Nanotechnology is new scientific field which affects many aspects of engineering and in recent years, many efforts have been made to use this new technology in various geotechnical branches.
So far, research has been carried out on the improvement of various soil types with additives such as cement, bitumen, ash, lime and various types of nanoparticles. Nowadays, the use of nanoparticle additives due to reduction of environmental pollution than other additives has a wider application in improving the physical and chemical properties of problematic soils.
In the present study, the effect of nano-kaolinite on strength properties including uniaxial compressive strength, elasticity modulus, cohesion, and internal friction angle of silty Loess in Kalaleh city of Golestan province have been investigated.
Material and methods
In order to carry out the present research, sample of the silty loess soil from Kaleh city of Golestan province was collected and prepared. Then, 0.5, 1, 1.5, 2, 3 and 4 weight percent of nano-kaolinite were added to soil samples. The soil samples were prepared in a natural state (without additives) and with the additive for uniaxial compressive strength and direct shear tests. Strength properties of soil specimens including uniaxial compressive strength, elastic modulus (based on uniaxial compressive strength test), cohesion and internal friction angle (based on direct shear testing) were determined for native soil and its mixture with different percentage of nano-kaolinite. The data were analyzed and the effect of nano-kaolinite on the strength properties of the silty loess soil sample was investigated.
Results and discussion
Uniaxial compressive strength and modulus of elasticity have been increased with increasing amount of nano-kaolinite, and after 2% nano-kaolinite, increase in nano-kaolinite did not have any significant effect on uniaxial compressive strength and modulus of elasticity. The uniaxial compressive strength and the modulus of soil elasticity in the natural state (without nano-kaolinite) are 1.12 and 15.89 kg/cm² respectively, and when 2% of the nano-kaolinite is added to the soil, the values ​​of these properties are maximal and reached to 1.19 and 18.10 kg/cm², respectively.
For native soil (without nano-kaolinite), the cohesion value is equal to 0.09 kg/cm², and with increasing nano-kaolinite from 0.5 to 2%, the cohesion shows an incremental trend and reached to 0.16 kg/cm². With increasing the additive percent from 2 to 4% the amount of cohesion were constant and equal to 0.16 kg/cm². The increasing of cohesion can be attributed to the fact that nanoparticles enhanced water absorption of soil particles which caused in better cohesion and also they affected chemical actions and surface electrical charge of soil particles.
Conclusion
The results of the uniaxial compressive strength tests show that adding up to 2 weight percent Nano-kaolinite to the dry soil increases the uniaxial compressive strength and modulus of elasticity of silty loess soil in the Golestan province, which can be due to proper locking between the nanoparticles and soil particles and increased cohesion.
The results of direct shear tests showed that adding up to 2% nano-kaolinite to dry soil increased the cohesion of the soil and consequently increased the shear strength of the soil.
On the other hand, adding the different amount of nano-kaolinite has not changed much in the internal friction angle of the silty loess soil in the Golestan province.
 
 

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