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Engineering Geology

Engineering Geology - geomuseu

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E n g i n e e r i n g G e o l o g y<br />

Figure 7.5<br />

Piston sampler of hydraulically operated type. (a) Lowered to bottom of borehole, boring rod clamped in fixed position at the<br />

ground surface, (b) Sampling tube after being forced into the soil through water supplied through boring rod.<br />

in the rock. Full-face bits, which produce an open hole, are used. These are usually of<br />

the studded, cruciform or tricone roller bit type (Fig. 7.9). The technique is most effective in brittle<br />

materials since it relies on chipping the rock. The rate at which drilling proceeds depends upon<br />

the type of rock, particularly on its strength, hardness and fracture index; the type of drill and drill<br />

bit; the flushing medium and the pressures used; as well as the experience of the drilling crew.<br />

Compressed air, water or mud may be used as the flush. If the drilling operation is standardized,<br />

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