Numerical Modeling of Hydromechanically Coupled Responses (HMC)

Open pit mining is a dynamic process that continuously induces changes to the hydromechanical conditions within the rock slope. Over the past decade, extensive studies were performed to understand and evaluate the stability of mine slopes, however, the incorporation of changing hydromechanical conditions has been challenging due to uncertainty associated with mechanical stresses and corresponding water pressures. This project focused on understanding the dependent interaction of water and rock, or hydromechanical coupling (HMC). Two-dimensional numerical modeling was completed using a Fast Lagrangian Analysis of Continua (FLAC) coupled (undrained-drained) analysis to recreate HMC responses observed for a monitoring case study at a mine in Nevada, USA. Modeling efforts considered factors that impact HMC responses by varying governing parameters such as porosity, rock stiffness (elastic modulus), and permeability and evaluate their impact on pore pressure changes and recovery. The case study data suggest two concepts that have not previously been well documented; firstly, that HMC processes can occur in permeable materials, provided they are confined both vertically and laterally; and secondly that, where such conditions exist, pore pressure changes due to unloading can occur remotely from the point of stress change.

Project Highlights

• Numerical modeling demonstrated the concept of hydromechanical coupling on an open-pit mine site where rock-water interactions due to slope excavation are observed in a piezometer monitoring sensor.
• The case study data suggest that HMC responses can be observed remotely at a lateral distance from the point of stress relief in confined environments with high permeability.
• The model highlighted that the pore pressure is reduced in correlation to slope excavations and the magnitude of the response is influenced by the porosity and elasticity of the rock mass.
• The model shows that pore pressure recovery time is sensitive to the permeability and porosity of the formation, with anisotropy of hydraulic conductivity a factor, and that the response is controlled by flow-related boundary conditions.
   

Numerical Investigation of Mining-induced, Hydromechanically-coupled Responses for a Nevada Mine Site. 
Noonan, G., Lorig, L., Beale, G., Ferré, P.A. (2023, June). Numerical investigation of mining-induced, hydromechanically-coupled responses for a Nevada mine site [Paper presentation]. 57th US Rock Mechanics/Geomechanics Symposium 2023, Atlanta, Georgia, USA.