Correlation between seismic wave velocity, rock porosity and maximum principal stress based on the laboratory test data

Abstract

In order to determine the internal relationships among seismic wave velocity, axial pressure, and rock porosity, the rock samples taken from NRS170143 borehole of the Nickel Rim South mine are tested using a Hoek type triaxial cell equipped with axial linear variable differential transducers (LVDTs) and a data acquisition module. The empirical expression between seismic wave velocity and rock pressure is fitted based on the laboratory test data of rock samples. Then, P-V model P-φ model and φ-ε model are created to analyze the laboratory test data. The results show that: (1) the relationship between axial pressure and rock porosity can be represented by a new empirical equation φ=a*e-b*P-c. With an increase of axial pressure, the value of rock porosity gradually decreases below the straight line φ=1% and close to 0. The P-φ model can be a good judge if the pressure has reached the maximum compression pressure in the process of rock compression experiment; (2) The P wave velocity and S wave velocity exponentially increase with increasing axial pressure; Rock porosity and crack density parameter exponentially decrease with increasing axial pressure; (3) there is a linear positive correlation between the ratio of rock porosity to crack density parameter and the ratio of crack thickness to crack length. (4) the relationship between Vp and Vs in each compression test can be fitted to the linear equation Vp=a*Vs+b; for all different samples of NR170143, the ratios (M) of Vp to Vs ranges from 1.35 to 1.85. In summary, the P-V model, P-φ model, φ-ε model and Vp-Vs-φ model can intuitively reflect the relationship among seismic wave velocity, axial pressure and rock porosity.