The indications that suggest current design is conservative do not transitively imply that the remedy offered by the K-stiffness Method is correct. The issue of dormant reinforcement due to apparent cohesion is explicitly described in: Leshchinsky, D., “Geosynthetic reinforced walls and slopes: Is it magic?” Geosynthetics Magazine 28(3), 2010, 17-24. Indeed, apparent cohesion may render reinforcements dormant, but when the cohesion vanishes, the reinforcement will be activated and failure may occur. In fact, the K-stiffness method ignores the apparent cohesion in its statistics (the magnitude of this cohesion is impossible to determine in-situ) and, essentially, attributes the low ‘measured’ force in the reinforcement to what amounts to “magic.” That is, the method bypasses basic statics, ignoring simple global equilibrium in favor of uncritical acceptance of field data combined with statistics, and gives no scientific justification for the lower tensile forces.
Cohesion reduces or even eliminates the reinforcement load however, apparent cohesion is dependent on moisture content (or degree of saturation of soil) and should not be counted on in design as its value may periodically diminish over the life of the structure.
The field data that serves as a foundation for the K-Stiffness formula, deemed as a comprehensive basis for solutions, was very likely for situations where soil matrix suction rendered apparent cohesion. Seasoned engineers would and should be skeptical about the feasibility of such statistical shortcuts. Thus, the method ignores the vital inclusion of statics in design for the sake of rendering less conservative reinforcement tensile forces that are scientifically unsubstantiated over the long-term. The approach empirically links stiffness, spacing of the reinforcement layers, facing properties, batter, and shear strength of the soil using little more than statistical correlations. The formulation is not based in physics or statics, but in statistics, ignoring long term design stability essential to the safe function of a structure. The reasoning behind this conclusion is the formulation of the K-Stiffness method, which is a statistical analysis based on a compilation of field data of retaining walls from various, unrelated researchers. Although such implementation in the framework of MSEW is simple, we do not plan to perform the task since the current method appears to be invalid, very possibly rendering unsafe results. A few customers have requested implementation of the K-stiffness Method in program MSEW.