A pilot study investigating the rapid estimation of intact dry density of chalk using low impact energy hardness measurements taken with an Equotip Leeb hardness tester

Abstract

Intact dry density (IDD) is a key parameter for characterising the rock mass behaviour of chalk and is often the main classification property reported for engineering design. The role of IDD in coastal chalk settings has been discussed in literature as an important rock control for coastal cliff recession behaviour. This study demonstrates a tool that can reliably estimate the IDD of chalk samples. Originally developed for testing sheet steel materials, the Equotip has been shown to be adaptable for geological applications and the results of this study show that the Equotip can be used to derive a surface hardness value of dry chalk samples that has a positive correlation with IDD. Furthermore, the results show that the device is sensitive to the anisotropy of chalk and that testing undertaken in the diametral orientation give more accurate correlations. The results of this study also show that the Equotip is sensitive to environmental setting and the effects of weathering, giving a separate correlation for samples collected along the Sussex coastline to those obtained inland. A statistical assessment of the results shows that a characteristic hardness within an acceptable margin of error can be achieved from an optimal number of single impacts.