Rock failure is often controlled by fracture initiation, propagation and coalescence. Prediction of the explicit fracturing process is necessary for many industries such as mining, geothermal energy, nuclear waste disposal and CO2 geosequestration. Since 2007, CSIRO has been leading an international collaboration to develop FRACOD, a unique numerical code for modelling coupled rock fracturing processes.

Unique features of FRACOD:

  • Uses Displacement Discontinuity Method (DDM)
  • Predicts both tensile and shear fracture propagation
  • Predicts complex fracture propagations in jointed rock mass
  • Simulates fully coupled mechanical-thermal-hydraulic process
  • Predicts time-dependent subcritical crack growth
  • Models rock strength and anisotropy
  • Simulates ice swelling mechanism
  • Incorporates strain failure criterion
  • Predicts two- and three-dimensional fracture propagation

Interaction between rock fracturing, fluid flow and rock temperature changes.

Example Application 1 – Tunnel Stability: Tunnel instabilities are often caused by explicit fracture development due to high stress concentration in the tunnel wall. FRACOD gives realistic predictions of the failure patterns of tunnels in fractured rock masses.

Failure pattern of an overstressed tunnel and the fracturing pattern predicted by FRACOD

Example Application 2 – Hydraulic Fracturing: Hydraulic fracturing is commonly used in the petroleum and geothermal industry for permeability enhancement and in the mining industry for caving control. FRACOD has been applied to investigate the hydraulic fracturing process with and without interaction with natural fractures. The results compared favourably with analytical and laboratory results.

Fracture propagation pattern and displacement distribution during a hydraulic fracturing process (left); and comparison of the predicted injection pressure between FRACOD and theoretical results (right).

Example Application 3 – Stability of nuclear waste repository: Deep geological disposal of high level nuclear waste requires an understanding of the risk of rock fracturing due to thermal heating, glaciation and swelling pressure from bentonite. FRACOD has been adopted by Posiva Oy (Finland) as a key numerical tool to predict the stability of their nuclear waste repository.

Conceptual configuration of a nuclear repository (left); and Predicted fracturing pattern around the deposition hole after 40 years heating (right).