Structure Stiffness Method. The Structure Stiffness Method was developed by
Christopher, et al. (1990) based on instrumentation of full scale test walls and review
of data reported in the literature from instrumented in-service walls. The Structure
Stiffness Method is similar to the Tieback Wedge Method, however a bilinear
envelope of maximum reinforcement tension is assumed for inextensible (steel) 11
reinforcements and a Rankine failure plane angled at 45+ φ/2 from the horizontal is
assumed for extensible (geosynthetic) reinforcements. The lateral earth pressure
coefficient, Kr, is based on a complex formula that takes into account the global
stiffness of the reinforcement, where the global stiffness is directly related to the area
of tensile reinforcement times the reinforcement modulus of elasticity. Therefore, as
the reinforcement density increases, both the global stiffness and the resulting
coefficient of earth pressure, Kr increase. This method was not adopted by state DOTs
and, therefore, does not appear in any AASHTO specifications. However, the method
did lead to development of the earth pressure ratio Kr/Ka which is now used in the
Simplified Method