Geotextile Encased Columns (GEC): Load Capacity & Geotextile Selection
This paper summarises the analytical procedures used in the design of a new foundation system 'Geotextile Encased Columns' (GEC). Variations in the modulus and the tensile strength of the geotextile are presented to investigate their effect on the load capacity of the columns and overall settlement predictions. In addition, the selection of appropriate polymers and long-term design parameters for the geotextiles, compatible with the design life and performance of the columns, is discussed.
GEC have already proved a practical foundation system for embankments constructed on very poor soils (cu < 2 kN/m2).
A series of design calculations were performed for dimensioning of Geotextile Encased Columns (GEC) beneath an embankment on soft soil. Two recent analytical procedures were used, which are believed to be precise enough. A "standard" case was analyzed, varying some important parameters in a typical practice-related range.
The results are presented as graphs which can be used in a simple way for rough pre-design calculation of settlements and/or required "percentage" of columns for determining the required tensile module in ring direction of the geotextile encasements (Ringtrac).
The load bearing capacity of the columns can be optimized by the geotechnical engineer by varying the ring-tensile module and percentage area of columns in the embankment base. Additionally by selection of appropriate polymers with low creep propensity the post construction creep strain related settlements can be reduced to negligible levels.
The range of tensile moduli (from 1000 to 4000 kN/m) corresponds to the range of short and long-term moduli offered by the current Ringtrac family of products.