Secondary Reinforcement for Slopes

Secondary reinforcement in slopes is typically designed without any stability considerations. A rational stability analysis is attempted in this paper, based on shallow collapse mechanisms confined to the neighborhood of the slope face. The kinematic theorem of limit analysis is used to arrive at the necessary spacing of the secondary reinforcement and its strength and length. Analysis of a collapse limited to the soil between the layers of reinforcement is used to determine the required soil cohesion necessary to maintain stability. Since this cohesion depends on the size of the mechanism, the spacing of the secondary geosynthetic can be determined from this analysis. Some cohesion is usually present in the zone close to the slope face because of moisture in the soil, cementation due to a small amount of fine particles, or vegetation. Even a small amount of cohesion may have a significant effect on the stability. The strength and length of secondary reinforcement are determined from shallow collapse mechanisms engaging secondary reinforcement in tension. The slope face becomes most susceptible to failure when the soil becomes saturated, because of the seepage and buoyancy forces, and because of the loss of apparent cohesion. A more approximate analysis based on an infinite slope model is also shown. Its description is limited to the presentation of the concept. This method relies heavily on the cohesion distribution in the zone close to the slope face. Because an estimation of this distribution is difficult, the infinite slope model may be difficult to apply in practice.