The prediction of geotechnical rock properties from sonic and neutron logs

Abstract

Sonic logs have been used successfully for estimating strength and static elastic moduli for coal measures strata at 18 sites in N.S.W. and Queensland, and empirical relationships between these geotechnical parameters and sonic log interval transit time are presented. Sonic logs are particularly sensitive to strength variations in weaker rocks, say less than 60 MPa compressive strength. Neutron log response is also proportional to strength, but the relationship is more qualitative. Sonic and neutron logs tend to overestimate porosity in clay-rich coal measures rock, counting the clay matrix with the air or water-filled voids.