Evaluation of Critical Length of Encasement for Stone Column-Supported Embankment with Basal Geocell
Tóm tắt
Column-supported embankments are proven efficient in enhancing the bearing capacity of soft ground. The effect of geosynthetic encasement depends on the length and stiffness of the encasing material. With a basal geocell, the stress transferred to the subgrade is lowered, and the optimum encasement length can be reduced. Strain-controlled model tests were performed on soft clay reinforced with an encased stone column with basal geocell. Three different geotextiles were used to fabricate the encasement and geocell. Two dimensionless factors were introduced—improvement factor (IF) and successive improvement index (SII), to evaluate the independent effect of geocell and the effect of encasement length, respectively. The critical length of encasement lcr is evaluated at SII of 10% for the bearing capacity of clay and stress on the column. The test results indicate that basal geocell reduces a stone column's critical encasement length regardless of the material stiffness and stress-settlement levels. Geocell enhances bearing pressure and lowers stress on soft ground and stone columns. The lateral spreading enables the load to be distributed evenly on the stone column-reinforced ground, thus reducing the stress concentration ratio. The reduction in lcr arises from the fact that geocell dominates the action of the stone column, making the strain mobilized in the lower half of the column unutilized. Hence, the impact of geocell is unaffected by the increase in encasement length beyond 2/3rd of the column depth. For stiffer materials, the performance is enhanced at higher stress levels upon mobilization of adequate strain on the encasing sleeve and geocell walls. The numerical simulations carried out were validated with experimental observations.
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