Nader Hataf

Due to the economic growth, the rapid process of industrialisation, and urban population increase, municipal solid wastes (MSWs) management problems are of great concern to the governments, especially in developing countries. Besides the environmental issues, several landfill failures have been reported in recent decades caused irreversible damages for human health and imposed financial burdens on the governments. To avoid such geotechnical failures, having a thorough understanding of the mechanical characteristics of MSW is crucial. To this end, we conduct standard compaction tests, direct shear tests, and consolidated undrained (CU) triaxial shear tests to obtain the mechanical properties of Shiraz MSW. Besides, using Slide 2D, we perform a back analysis to examine the geotechnical extents of the Shiraz landfill failure that occurred in 2013 during a firefighting operation. It was shown that the back analysis results have a better correlation with the data gathered from direct shear tests. Model results show that MSW water content increase due to the firefighting operation led to MSW shear strength decrease and slope failure. Considering the complex components of MSW, it is necessary to increase case study research on understanding MSW mechanical properties to design landfills more precisely and prevent such potential disasters in the future.

This study examines the behaviour of square footings located on unreinforced, single-, and double-layer geocell-reinforced sand slopes through a series of reduced-scale model tests. Contributing factors such as the distance between the footing and the edge of the slope, depth of burial of the first geocell layer, vertical span between successive layers of the geocell, length and width of the geocell mattresses, and the number of geocell layers were considered, and their effects are discussed in detail. The results indicate that geocell reinforcement plays a more effective role as the distance between the footing and the edge of the slope decreases. The optimum depth of placement of the first geocell layer for both single- and double-layer reinforced slopes was determined, and was found to be independent of the length of the geocell. In addition, the performance of the footing continued to decrease with greater vertical distance between the top and lower geocell layers. Only a marginal improvement in the behavior of the tested models was observed for a range of widths of the geocell.

Stone columns have attracted considerable attention as a ground improvement techniques recently. Performance of stone columns, however, depends on confining pressure offered by the surrounding soils. In the case of very soft soils, the lateral confining pressure may be insufficient and this may lead to column bulging failure. Encapsulating the individual stone column enhances the lateral resistance against bulging by additional confining pressure. In this study, the influences of the length of encasement and type of aggregate materials on the bearing capacity of a single stone column in both dry sand and clay bed were investigated. The results indicated a clear improvement by encasing the half-length of the column. The numerical study also showed the effect of reinforcement stiffness reduces with increase in the cohesion of the clay. Parametric study showed that the effect of encasement stiffness is insignificant for clay bed with high values of cohesion.