Abstract
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.
Highlights
Civil engineering projects are often encountered with serious problems in soft soils
The additional confining stress can be calculated by considering the hoop tensile force in the geosynthetic encasement as follows: σr,g where Tg and d c are the hoop tensile force of the geosynthetic and column diameter respectively
The results of the testing program give some important insight into the performance of the encased stone columns
Summary
Civil engineering projects are often encountered with serious problems in soft soils. For very soft soils with undrained cohesion, Cu, lower than 15 kPa, encapsulating the stone column by geosynthetics as an alternative method is used [8]. With encasing the stone columns, confining pressure around columns increases leading to increasing in bearing capacity and reduction in settlement [1, 5, 18, 21]. Murugesan and Rajagopal [21] suggested the following relationships to estimate the ultimate bearing capacity of the single encased stone column in clay: qult,c = σr,0 + 4Cu + σr,g Kp (1) In which. Σr,g = additional confining stress by geosynthetic encasement. The additional confining stress can be calculated by considering the hoop tensile force in the geosynthetic encasement as follows: σr,g = (2). Where Tg and d c are the hoop tensile force of the geosynthetic and column diameter respectively. The hoop tensile force may be controlled by the geosynthetic elongation at failure (typically at 5%)
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