For hard rocks as granite, rock mass class is mostly associated with discontinuities.

花岗岩这样的硬质岩石，其岩体质量与结构面关系极为密切。

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The test results show that the permeability of hard rocks is obviously different from that of soft rocks not only in permeability-strain behavior but also in value of coefficient of permeability.

试验结果反映出在变形过程中不论是渗透性 -应变关系特点 ，还是渗透性量值 ，软岩和硬岩均表现出明显差异。

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Studying the variety laws of the plastic failure, distortion and stress of soft and hard rocks alternate-layered roof with the constant vertical stress only the horizontal stress changing.

在垂直应力不变，不断改变水平应力的条件下，分析各类软硬岩互层项板的应力、变形、破坏规律。

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Hydraulic fracturing, also known as fracking, involves drilling down and creating tiny explosions to crack the hard shale rocks to release the gas inside.

BBC: Drilling for gas

Hydraulic fracturing or "fracking" is a process of forcing water mixed with chemicals through deep wells to shatter and crack hard shale rocks to release the gas inside.

BBC: Hydraulic fracturing

That leaves Turkey trapped between rocks and hard places, belonging fully to neither.

FORBES: Turkey, Between Rocks and Hard Places