Statistical insights arising from point load testing of Danian limestone

Abstract

"The characterisation of the mechanical properties of the rocks can be carried out with conventional strength testing (e.g. unconfined compressive strength tests, tensile strength tests and triaxial tests) or with ‘rapid’ tests such as the point load test (PLT). Compared to the conventional tests the rapid tests are economical, quick and can also be carried out in situ; on the other hand, the results tend to be more scattered, correlations with the strength parameters depend on the rock type and the experience in using them in the design stage can be limited. This paper presents the results of PLTs carried out on Danian limestone and Maastrichtian chalk specimens, either as irregular lumps or as cylinders/disks, from multiple sites on Zealand in Denmark. The Danian limestone formations are weak sedimentary rocks with highly variable properties in terms of their strength, stiffness and in mass permeability. Their mechanical properties are governed by genesis, induration and the large variability of the fissuring and distribution of fissuring. By statistically analysing the results of the PLTs, it is possible to appreciate the impact that the height to equivalent diameter ratio has on the coefficient of variation for each induration class, which can therefore be used as guidance for specimen selection and/or preparation on site or in the laboratory."