The current design practice of geosynthetic reinforcements assume the backfill to be purely frictional irrespective of soil type. However, recent editions of AASHTO LRFD bridge design specifications allow for the inclusion of cohesion in the design of geo-reinforced slopes. Also recent studies have shown that accounting for the presence of even a modest amount of cohesion may allow using locally available cohesive backfills to a greater extent and less overall reinforcement.
Nevertheless, practitioners need to be aware that unlike purely frictional backfills, cohesive soils are subject to the formation of tension cracks. These cracks make the slope less stable and therefore need to be properly accounted for in any geo-reinforcement design relying on soil cohesion.
Abd and Utili (2017) derived a semi-analytical method for uniform c – phi slopes accounting for the formation of tension cracks that provides the amount of reinforcement needed as a function of soil cohesion, tensile strength, angle of shearing resistance and slope inclination by means of the kinematic approach of limit analysis.
In this paper first a summary of the main tenets of the theoretical formulation to design the reinforcement is laid out, then several example case studies are presented to illustrate the application of the new theory to various cohesive backfills representative of locally available soils in Brazil. Calculations of the required reinforcement strength are carried out for both uniform and linearly increasing reinforcement distributions. Also, the economic savings that can be achieved by accounting for the presence of cohesion are estimated.
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