Volume 2, Issue 2 (February 2005)
Spatial Variations in Material Properties of Segmental Retaining Wall (SRW) Units, Part II: Sampling Considerations for Absorption Tests
Part I (Observed Variations) of this article summarized observed spatial variations in material properties that could exist in Segmental Retaining Wall (SRW) units. As a continuation of Part I, Part II of this article examines in more detail the statistical significance of these observed variations and the implications of such variations on sampling and test result interpretation. It was demonstrated that the observed spatial variations were statistically significant along the casting direction (parabolic distribution) and in a direction away from the split face (linear distribution). As a result of these variations, an analysis involving test simulations showed that, depending on how specimens are sampled, a technician could interpret the SRW unit as being either very uniform or marginally uniform. The effect of increasing the quantity of specimens per test was only to modestly improve the expected value of the perceived test variation, though the range of possible values of perceived variation was substantially narrowed. This analysis also showed that variations in test results decreased with increasing soak time. Finally, an alternate method of specimen sampling (stratified random sampling) was explored and shown to yield slightly more consistent test results by reducing the overall variability in test results.