Correlation between mechanical strength and microstructural parameters of dolomites and limestones in the Judea Group-Israel

The relationship between elastic modulus, mean grain size, bulk porosity, and mechanical strength of the brittle Aminadav dolomites and Bina limestones is reported. The selected lithologies are considered here as good representatives of the dolomite and limestone members of the Judea Group in central Israel. Elastic modulus represents intergranular and matrix stiffness, whereas mean grain size and bulk porosity scale the availability of initial flaws, or stress concentrators, in the rock. It is found that the three microstructural parameters affect the studied rock formations differently. In Bina limestone the role of individual grain size is insignificant and uniaxial compressive strength depends primarily on initial porosity and elastic modulus. It is concluded that in Bina limestones pores and open fissures, rather than grain boundaries, function as stress concentrators and fracture nucleation sites. The mechanical strength of Aminadav dolomites, however, is clearly related to mean grain size, in addition to porosity and elastic modulus. It is therefore suggested that in dolomites both initial voids (pores, fissures) and grain boundaries function as stress concentrators, and that the influence of rock stiffness on overall strength is less important. The interaction between microstructrural parameters in the two lithologies is believed to be different, and therefore a single failure model cannot be applied to both lithologies. We present here an adequate failure criterion for each lithology that is based on measurable microstructrural parameters. These two failure criteria can be used, with caution, to predict the ultimate strength of these lithologies, using simple physical and mechanical parameters.