What is meant by the term Griffith cracks, and how do they affect rock strength and fracture propagation?
What will be an ideal response?
Answer: The term stems from A. Griffith, who considered natural rocks to be flawed by the presence of microcracks. He modeled such microcracks as elliptically shaped features with very large aspect ratios, and they have since been referred to as Griffith cracks. The presence of Griffith cracks weakens a rock and helps explain why the theoretical strength of an unflawed rock is much higher than the strength estimated from experiments. Favorably oriented Griffith cracks (those with high shear stress) are expected to grow faster than others and to link up to form a through-going mesoscopic fracture in the rock.
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a. Columnar joints b. Caldera c. Pillow lava d. Lava tubes
The precautionary principle is guided by the idea that we must make decisions that prevent a problem from occurring or worsening.
Answer the following statement true (T) or false (F)
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A. wealthy upper class B. wild animals C. middle class D. minorities E. politicians
What was Apartheid in South Africa? How was it resisted and what brought about its end? What are its enduring legacies?
What will be an ideal response?