Model tests on geosynthetic-reinforced stone columns: a comparative study

ABSTRACT: The use of stone columns is popular as a ground-reinforcing technique for supporting flexible structures on soft to very soft soils. When a very soft soil improved by stone columns is loaded, the stone columns undergo excessive bulging, because the very low lateral confinement provided by such a soil gives rise to a very low failure stress of the composite ground. The performance of stone columns in such conditions can be improved either by encasing them with geosynthetics or by placing horizontal strips of geosynthetics within the columns at regular intervals. In the present study, model tests have been carried out on short, floating and fully penetrating single columns with and without reinforcement to evaluate the relative improvement in the failure stress of the composite ground due to different types of reinforcement. A comparative evaluation of the column shape on exhumation reveals subtle differences in failure mode due to the different configurations and types of reinforcement. Whereas for the end-bearing stone columns encasement is clearly the best method, for the floating columns there is no significant difference between the performance of the horizontal strip reinforcement and that of the encasement. For end-bearing columns a geogrid is the best type of geosynthetic to use for both types of reinforcement, but for floating columns the best types of geosynthetic are geogrid as the horizontal strip and geotextile as the encasement.