Granular piles, either ordinary or encased with geosynthetic materials are being extensively used as one of the ground improvement techniques, depending on the strength of the adjoining soil. The optimum granular pile (GP) length is still a matter of research, even though the approach is widely established in the literature. In the present study, a thorough and detailed parametric analysis has been carried out to ascertain the optimum length for ordinary and encased granular piles using a 2D axisymmetric finite element model. The soil behaviour has been modelled with the linearly elastic perfectly plastic Mohr-Coulomb failure criterion constitutive model. The parameters considered in this study are area replacement ratio, encasement stiffness, soil properties, infill material properties, and crust layer thickness. The findings revealed that the parameters with the greatest influence on the optimum length are the area replacement ratio, encasement stiffness, surrounding soil strength properties, and friction angle of the infill material. For encased granular piles, the optimum length was often found to be longer than ordinary granular piles. It was found that the optimum length for ordinary and encased GP ranges between 0.8-2.12 and 1-2.75 times of footing diameter (D), respectively. Through this study, an effort has also been made to investigate how the aforementioned parameters affect the radial bulging of the end-bearing GP. The upper of 0.5-1.5D showed excessive bulging in each case. Additionally, the optimum encasement length was determined, and it was found that increasing the encasement length beyond 1.5D results in minimal improvement. Furthermore, a multiple regression analysis was employed to establish the correlation between the optimum length of GP and potential influencing factors.

The usage of locally available soil for construction purposes is a wise choice for enhancing its engineering properties. Depending on the size of the particles, the silty and clayey soils possess voids at the nano level. Generally, clay soil is affected by increased settlement, decreased stability and altered soil structure due to the increased plasticity index. Hence, it is necessary to enhance the soil properties using various additives. In recent days, nanomaterials have been increasingly utilized for improving soil stability and strength in various geotechnical engineering applications. This paper deals with the effect of nano-clay on the various geotechnical properties of three different silty and three different clayey soil samples. The influence of the wet-dry cycles on the unconfined compressive strength (UCS), coefficient of permeability (k) and settlement were discussed. Furthermore, the UCS and California bearing ratio (CBR) of the nano-clay-treated soil were predicted by using multiple regression analysis based on the index properties. Test results revealed that the optimum dosage of nano-clay was found to be 0.4%, 0.35%, 0.35%, 0.25%, 0.25% and 0.2% for three different silty soil samples and three different clayey soil samples, respectively. The UCS and CBR values were enhanced significantly irrespective of the nano-clay content and the soil type, due to the formation of CSH gels that effectively bonds the soil particles and facilitates the improvement of UCS and CBR and thus reduces the 'k' and settlement of soil samples. The predicted UCS and CBR values by regression analysis are in line with the experimental results in both treated and untreated conditions. As a result, this amorphous nano-clay is recommended for stabilizing weak soils irrespective of the type of soil.