SOIL NAILING DESIGN: THE ROLE OF BENDING STIFFNESS

Following a paper by R J Bridle in an earlier issue (see IRRD 824349) the authors suggest that a fundamental error of mechanics and a conceptual error in reinforced soil design theory have been perpetuated in the literature. The paper draws attention to an apparent error concerning the role of reinforcement bending stiffness. An analysis of the role of reinforcement bending stiffness is first described for circular bars made from an elastic, perfectly plastic material. Consideration is given to bars under combined loading, models for shear force in a soil nail, limiting combinations of shear force and moment and minimum shear width. The improvement to shearing resistance that a circular bar can provide in reinforced soils is then investigated at the two extremes of pure axial force and pure bending for limiting combinations of axial and shear force loading between the two extremes. The degree of improvement which can be achieved shows that reinforcement bending stiffness is not a significant parameter for soil nailing - the increased shearing resistance is small compared to that due to axial force only. The error in the literature is traced back to Schlosser (1983) and it is suggested this has led to the magnitude of shear force mobilised in a soil being overestimated by up to a factor of 20.