Theories and applications of FRACOD–a fracture mechanics approach to modern rock engineering problems
Baotang Shen*
Deep Resources Engineering. 2025, 2(3): 100210. 
doi.org10.1016j.deepre.2025.100210.pdf
Abstract: Rock failure is often governed by the initiation, propagation, and coalescence of fractures, particularly in hard rocks where fracturing, rather than plastic deformation, is the dominant failure mechanism. Therefore, predicting the explicit fracturing process is crucial when assessing rock mass stability for engineering applications. However, fracture mechanics are seldom employed in practical rock engineering design, primarily due to the limited understanding of complex fracturing processes in jointed rock masses and the absence of tools capable of accurately simulating these phenomena. Since the 1990s, a novel approach to modelling rock mass failure has emerged, utilizing a numerical code called FRACOD. This code, based on fracture mechanics principles, predicts the explicit fracturing processes in rocks. Over the past three decades, substantial progress has been made in advancing this method to the point where it can reliably predict rock mass stability at an engineering scale. FRACOD incorporates complex coupled processes, including thermal effects, rock mechanical response, and hydraulic flow, enabling it to address coupled problems commonly encountered in geothermal energy extraction, nuclear waste disposal, hydraulic fracturing, and underground LNG storage, etc. Numerous applications of FRACOD have been conducted over the last thirty years, including studies on borehole stability in deep geothermal reservoirs, pillar spalling under mechanical and thermal loading, and the prediction of tunnel and shaft stability, as well as the excavation disturbed zone (EDZ). This paper reviews the theoretical foundations of the fracture mechanics approach employed by FRACOD and highlights the most recent developments. It also presents several validation cases to demonstrate the accuracy of this approach. Additionally, a case study on geothermal energy development in the Cooper Basin, Australia, is included to illustrate the practical applications of this method.
Highlights:
• A new F-Criterion for mode I (tensile) and mode II (shear) fracture propagation is explained.
• Numerical fundamentals behind FRACOD are discussed.
• Theories and numerical processes for M-T-H coupling function in FRACOD are described in detail.
• Several validation examples for FRACOD applications to solving complex rock engineering problems are provided.
• A case study is given to use FRACOD to study borehole breakouts and in situ stresses at a deep geothermal well in Australia.
Keywords: Rock mass; Fracture; Propagation; Coupling, FRACOD; Thermal; Fluid flow; Geothermal
Cite: Shen, B.T., Theories and applications of FRACOD–a fracture mechanics approach to modern rock engineering problems. Deep Resources Engineering 2025, 2 (3): 100210. https://doi.org/10.1016/j.deepre.2025.100210
