Relative density concept is not a reliable criterion

Abstract

Many years ago, a new concept called relative density was developed with the intention of appropriately defining the looseness and denseness of sand or sand-gravel soils in a meaningful way. Soon after, relative density found its way into ground improvement as an acceptance criterion by engineers who were more familiar with the construction of engineered backfilling rather than thick mass treatment. There are considerable amounts of research and publications that are able to well demonstrate the unreliability of relative density as an acceptance criterion. Relative density has no real influence on the soil's performance, its range of application does not span across all soil types, and it is subject to large inherent errors that make its use a technical risk. Here, the reasons why the concept of relative density is unreliable and should not be used for a ground improvement acceptance criterion are presented and discussed.

Engineering Properties of Tanjung Bin Bottom Ash

“…Where ρdmax is the reference dry density of a soil in the densest state of compactness that can be attained using a standard laboratory compaction procedure; ρdmin is the reference dry density of a soil in a standard state of compactness; and ρd is the dry density of a soil at the given void ratio. According to [20], relative density test is applicable only to soils that contains less than 15% of silt or clay and provided that it is free draining and cohesionless. For Tanjung Bin bottom ash samples, it was recorded that the silt or clay contents ranging from 1 -6%.…”

Relative density correlations are not reliable criteria

“…A fundamental question that crosses the mind is that, irrespective of the limitations and errors that are associated with relative density concept and formulation (Hamidi et al, 2013), would it be true to say that if two soils had the same relative density, then they would possess the same physical characteristics and will behave the same? It would have been very satisfying if the reply to this question was positive; however, this is not the case, and the use of relative density correlations based on average sand to predict soil behaviour without considering other parameters can result in poor or misleading predictions.…”

“…Introduction Hamidi et al (2013) have made a comprehensive review of current ASTM test methods (ASTM, 2006a(ASTM, , 2006b) and studies carried out by numerous researchers to demonstrate the limitations of relative density, and to show that although the objective of developing this parameter was to bring the behavioural characteristics of soils together on a common basis in consistent and practically useful relations and to provide a tool for communication between engineers, due to its formulation, relative density is prone to errors with magnitudes of tens of per cent (Hamidi et al, 2013). The amount of inaccuracy associated with relative density is so great that it makes this concept unreliable as a ground improvement acceptance criteria.…”

“…Although this amount of accuracy is by no means sufficient to reliably establish an acceptance criterion upon, in any case, here three parameters are involved, two (limit void ratios) of which are included in the original definition of relative density, and the third (the N value) is a function of the in situ density. It may be simply more appropriate to use the definition of relative density (ASTM, 2006a(ASTM, , 2006b to calculate a value which is prone to error (Hamidi et al, 2013) rather than going to the trouble of estimating a value which may be even more erroneous and misleading.…”

Editorial

“…In the second paper Hamidi et al (2013) discuss the reasons for the unreliability of the concept of relative density as an acceptance criterion for ground improvement. Relative density is considered to be a definition rather than an inherent soil property and with no real influence on the soil's performance, its range of application does not span across all soil types and is subject to large inherent errors that make its use a technical risk.…”