Hydraulic Fracturing in Deep Underground Mining and the Role of Inflatable Packers
Hydraulic fracturing (HF) has emerged as a crucial technique in deep underground mining, particularly in hard-rock metal mines. In these environments, elevated in-situ stresses, brittle rock masses, and extensive excavations increase the risk of geotechnical hazards such as rock bursts, violent spalling, and unstable caving. Drawing from the foundational principles of fluid-driven fracture propagation, modern mining employs HF to achieve several engineering objectives. These include preconditioning the rock mass, redistributing stresses, increasing permeability, facilitating gas or water drainage, and characterising in-situ stress conditions.
In the context of deep block caving and other large-scale mining methods, hydraulic fracturing is primarily used to weaken stiff, high-stress rock volumes in advance of excavations. This process helps to manage the accumulation of controlled damage and mitigate the stress concentrations responsible for seismic activity and rock bursts. A key enabling technology for these applications is the inflatable packer, which ensures reliable hydraulic isolation of chosen borehole intervals and maintains pressure integrity at depth. This capability allows for the safe and repeatable initiation, control, and monitoring of fractures, as highlighted by Hamed Shirazi.
This discussion, based on work by Shirazi, PhD, on behalf of IPI Packers, synthesises the main applications of hydraulic fracturing within underground mining, with a focus on block caving, and places particular emphasis on the functional role played by inflatable packers.
Applications of Hydraulic Fracturing in Underground Mining
Hydraulic fracturing in underground mining serves five closely related purposes:
- Rock mass preconditioning and destressing
- Mitigation of rock burst and seismic hazards
- Facilitation of cave initiation and propagation
- Enhancement of permeability for drainage or gas management
- Measurement and characterisation of in-situ stress
Within deep hard-rock metal mines, hydraulic fracturing is frequently conducted around development headings, production drifts, and undercut levels. The aim is to decrease rock mass stiffness, encourage controlled yielding, and redistribute stresses away from critical excavations. For applications such as destressing and rock burst mitigation, inflatable packers are vital. They ensure that high injection pressures are delivered directly into intact rock, rather than being lost along the borehole or into zones already damaged by excavation.
In block caving, hydraulic fracturing is a central part of preconditioning strategies that support cave initiation and stable cave propagation. In solid rock masses with low fracture density, problems such as delayed cave initiation and uneven cave growth often arise, accompanied by increased seismic hazard. Inducing fractures through HF weakens the rock mass above and around the undercut, enhances fracture connectivity, and promotes more distributed failure. This reduces the risk of large, high-energy seismic events. Inflatable double-packer systems are used to generate fractures at specific depths and spacings, enabling a systematic approach to preconditioning instead of relying on uncontrolled breakage.
Hydraulic fracturing is also applied in coal and mixed-lithology mines to increase permeability for gas drainage or water control, as well as to weaken stiff roof strata. In these cases, inflatable packers provide interval isolation, ensuring that injection is concentrated within the target seam or layer, and preventing uncontrolled fluid migration into roadways or neighbouring workings.
Additionally, hydraulic fracturing is used for in-situ stress estimation. In this process, fracture initiation or reopening pressures in isolated borehole intervals are analysed to estimate principal stress magnitudes. This involves sealing a section of the borehole with two inflatable rubber packers, which are pressurised to adhere to the borehole wall. Hydraulic fluid, typically water, is pumped at a constant flow rate into the isolated section. Pressure gradually increases until a fracture is initiated in the rock, with the peak pressure at this point known as the fracture or breakdown pressure. The process is repeated several times, with the highest pressure from the first cycle recorded as the breakdown pressure (Pb). Accurate stress estimation depends on the packers’ ability to maintain isolation throughout pressurisation and shut-in stages.
