Centrifuge investigation of load transfer mechanisms in a granular mattress above a rigid inclusions network

Reinforcing compressible soils by rigid inclusions is a method to reduce and homogenize settlements under many types of structures. A granular mattress, set between the structure and the group of inclusions, transfers by arching effects a part of loadings to the piles embedded in rigid substrate. A geosynthetic can be added between the heads of the rigid inclusions and the granular mattress. In addition to the arching effect, a membrane effect happens caused by the stretching of the geosynthetic sheet. An experimental mobile tray device, especially designed to test this reinforcement technique in centrifuge at 20g, consists in simulating the settlement of the soft soil located between the inclusions. An initial pretension can be applied to the geosynthetic. A parametric study of the load transfer mechanisms in the mattress is conducted with three different thicknesses of granular mattress, two different rigid inclusions networks and different initial pretensions in the geosynthetic.The efficacy of the load transfer and the settlements at the surface of the granular mattress are studied and discussed. With and without geosynthetic reinforcement, load transfer mechanisms are better for thicker load transfer mattresses and for higher mesh densities. The improvement made by a geosynthetic reinforcement is clearly shown trough both load transfer and differential settlement reduction.