Behavior of Calculated Nail Head Strength in Soil-Nailed Structures

Nail head strength is one of the parameters used in design of soil-nailed structures. It determines the stability of the nailed structure against failure involving the facing element. The nail head strength is a function of a number of factors, primarily the material strengths, vertical and horizontal nail spacing, and the nail head connection details. The variations in nail head strength as a result of changes in the vertical and horizontal soil-nail spacing and material strength properties are examined in this paper. Both temporary and permanent facing design is considered. For equal vertical to horizontal spacing, the nominal nail head strength for a temporary facing decreases continuously as the spacing is increased. The nominal nail head strength for permanent facing decreases initially and then remains nearly constant. For a fixed vertical spacing (Sv) the nail head strength for temporary facing decreases linearly as the horizontal spacing (Sh) increases. For permanent facing the nail head strength decreases very slowly for vertical to horizontal nail spacing ratio between 0.8 and 1.0 and then declines rapidly. The nail head strength increases most rapidly with increase in facing thickness. Higher strength reinforcement and concrete have a relatively smaller influence in raising the nail head strength. Charts are presented that can help in optimizing the design of soilnailed structures.