Failure patterns caused by localized rise in pore-fluid overpressure and effective strength of rocks

TL;DR

This study investigates how localized pore-fluid overpressure influences failure patterns in rocks, revealing five distinct failure modes through numerical simulations and analytical solutions, and providing a phase-diagram for failure prediction.

Contribution

It introduces a coupled numerical model for pore-fluid overpressure and rock failure, identifying failure patterns and deriving critical overpressure values with an analytical approach.

Findings

Five failure patterns identified, including shear banding and tensile fracturing.

Critical pore-fluid overpressure at failure onset derived analytically.

Phase-diagram constructed to predict failure modes based on conditions.

Abstract

In order to better understand the interaction between pore-fluid overpressure and failure patterns in rocks we consider a porous elasto-plastic medium in which a laterally localized overpressure line source is imposed at depth below the free surface. We solve numerically the fluid filtration equation coupled to the gravitational force balance and poro-elasto-plastic rheology equations. Systematic numerical simulations, varying initial stress, intrinsic material properties and geometry, show the existence of five distinct failure patterns caused by either shear banding or tensile fracturing. The value of the critical pore-fluid overpressure at the onset of failure is derived from an analytical solution that is in excellent agreement with numerical simulations. Finally, we construct a phase-diagram that predicts the domains of the different failure patterns and at the onset of failure.