Abstract: Pre-drilled geotextile-encased granular columns were installed in silty clay. The reinforcement effect was evaluated through ultra-heavy dynamic penetration tests and plate loading tests, and the vertical bearing capacity of single geotextile-encased granular column was examined. The influence of geotextile-encased length on the vertical bearing capacity of single geotextile-encased granular column was investigated by building a finite element model of single column. Results unveiled that the characteristic value of vertical bearing capacity of single geotextile-encased granular column is about 2.4 times that of single ordinary granular column. Scale effect was found in the lateral constraint and contribution of bearing capacity to the column: the improvement to lateral constraint and bearing capacity weakens and the granular stone works as main component when the diameter of column is 1 200 mm with geotextile type of HP470. The compactness of granular stone exerts a remarkable influence on vertical bearing capacity in the depth ranging from (2-3)d (d represents diameter of column). Through dynamic compaction (3 000 kN·m) on granular stones in the depth range from column top to 3d, the vertical bearing capacity of the column increased by about 4.1 times. Under the requisite of guaranteeing bearing capacity and deformation, we suggest 6d as the minimum encased length (geotextile type of HP470) when vertical load is 200-250 kPa.

Key words: marine silty clay, geotextile-encased granular columns, vertical bearing capacity, scale effect, encased length