Reinforced soil technology has been extensively used during the last decades in the construction of embankments and retaining walls. The similitude requirements between the reduced-scale model and the actual prototype were found to be difficult to formulate and practically impossible to verify. Therefore, the results of the laboratory model study cannot be extrapolated to provide a data base for empirical relationships between design parameters and system performance of actual structures. However, these reduced-scale models provided a very efficient, rapid and economical research tool to investigate the failure mechanisms of the reinforced soil slopes. Some laboratory experiments were performed to observe the behavior of steeped reinforced soil slopes in small scale laboratory model under the plane strain conditions. Reinforcements were made by a low strength paper strips and the loading on the soil surface was done by step-wised increments of dead weights. By this small model, effect of shear resistance of soil, number and width of reinforcement strips and width of loading surface are some subjects which have been studied. A computational program has also compiled in Matlab, in order to check the analytical interpretations of the Results. The effect of the external loading and the tensile strength of the reinforcement strips have been added to the well known formula of Fellenius and Bishop by which the stability and the relevant amounts of safety factor were analyzed. Based on the present study, the following remarks could be concluded: Failure conditions (i.e. the geometric parameters of failure surface and the maximum tolerable load) obtained from the tests show very well compatibility between the test results and logical expectable behavior. The results indicated that the cross section of the failure surface is quite and close to a circular arc in the cases corresponding to the external loads for all of the models. Increasing the number or width of reinforcement strips, width of loading surface, distance of loading from the edge and soil shear resistance, all are on the side of increasing the amounts of tolerable external loads and reducing the radius of failure surface arc. The effect of sidewall friction can be evaluated almost correctly for for considering in stability computations. Simplified Fellenius's limit equilibrium formula is the most reliable equation for the analyses regarding the failure conditions and factor of safety. The modification for considering the effect of tensile strength of reinforcement and the sidewall friction in model tests results in excellent compatible and acceptable results. It is very reliable to accept that the peak friction angle of soil is mobilized during the the failure rather than the residual.
