Evaluation of depth-dependent porosity and bulk modulus of a shear using permeability–depth trends

Both porosity and deformation properties of porous media are dependent on stress. For geological media, the stress-dependent porosity and deformation properties can be shown to be depth related. Unfortunately, both in situ porosity and in situ deformation properties are difficult to measure. In the current study, a method is developed to evaluate the changes in porosity and bulk modulus with depth by using in situ measurements of permeability, which can be easily obtained by employing packer tests. In the case study, the change in permeability of a shear in the Baihetan hydropower station in Southwest China is estimated. Then, the permeability–depth correlation is utilized to calculate the porosity and the bulk modulus at different depths. The results clearly show that the porosity decreases with depth while the bulk modulus increases with depth. Based on the proposed model, the bulk modulus is calculated to increase from 4–6 MPa on the ground surface to 18–30 MPa at the depth of 160 m. The Young's modulus of the shear estimated with this depth-dependent bulk modulus is consistent with in situ measurement.