Question

When tunneling through deep-level rock prone to squeezing, what is the primary physical change in the rock mass that necessitates a transition from rigid to yielding support systems?

Accepted Answer

The primary physical change necessitating a transition from rigid to yielding support is the shift from brittle failure to ductile deformation, or plastic flow, within the rock mass. In deep-level tunneling, the immense overburden pressure exceeds the rock&#x27;s strength, causing the rock to behave like a viscous fluid that continuously moves toward the tunnel opening rather than simply cracking or breaking apart. A rigid support system, such as thick unyielding concrete, would be crushed by this relentless movement because it cannot accommodate the rock&#x27;s ongoing deformation. By contrast, a yielding support system includes structural elements like sliding steel sets or compressible spacers that allow the rock to undergo a controlled amount of inward displacement. This controlled movement is essential because it allows the rock to mobilize its internal strength through a process called stress redistribution, where the rock arches itself to carry the load; if you block this movement entirely with rigid supports, the full, crushing force of the rock mass is concentrated directly onto the tunnel liner, inevitably leading to structural failure.

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When tunneling through deep-level rock prone to squeezing, what is the primary physical change in the rock mass that necessitates a transition from rigid to yielding support systems?

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