After several years to jumbolter research, the hard rocks always present in the soft ones in the wall rock procedure using jumbolter, which results in changing the boring tool during the procedure.

经过几年对锚杆钻机的跟踪研究，发现锚杆钻机在围岩作业中常遇到软岩中有硬岩夹层的现象，造成施工过程经常更换钻具的问题。

youdao

The beds were hard as rocks.

这里的床铺硬得跟石头一样。

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I had to find a way to grind the corn into flour, but the rocks on the island were not hard enough.

我必须想办法把玉米磨成面粉，但岛上的岩石不够坚硬。

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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

The committee is caught between assorted rocks and hard places most weeks, now.

BBC: MPs' demand for backbench debating time exceeds supply