Behaviour of geocell–geogrid reinforced foundations on clay subgrades of varying strengths

This paper reports a laboratory model investigation performed on circular footing rested on geocell–geogrid reinforced foundations of different configurations. The model foundations comprised of geocell–sand mattresses (with an additional planer geogrid at the bottom) of varying thicknesses (H = 0·63–2·19D; where D is the footing diameter) placed on clay subgrades of different undrained shear strengths, ranged over very soft (c_u = 7 kPa) to stiff (c_u = 60 kPa). Responses of model tests have indicated significant influences of base-geogrid on the performance of geocell reinforced foundations, in terms of bearing pressure and surface deformation variations. An enhanced bearing capacity and uniform deformations at the foundation surfaces were noticed due to the inclusion of base geogrid. However, the beneficial effects were limited to shorter geocells (h ≤ 1·05D) and softer clay subgrades (c_u ≤ 15 kPa); while, adverse effects were noticed for thicker geocells (h ≥ 1·57D) and foundations on comparatively stiff clay (c_u ≥ 30 kPa). In general, improvements in bearing pressure were observed with an increase in footing settlement; about 40–70% enhancements in bearing pressures compared with geocell-alone systems, and maximum about 12-fold overall improvement (compared with corresponding homogeneous clay bed) were obtained in the experimental programme.