Environmental Engineering Reference
In-Depth Information
Figure 2.10.
Crushed zone in Unit D (Interbedded siltstone and claystone) formed by overthrusting.
Photograph courtesy G. McNally.
Figure 2.11.
High stresses developed in valley floor and lower sides, and resulting hypothetical pattern
of sheet joints in strong rock without “tectonic” joints (model results from Alexander,
1960).
likely to occur in rock beneath the bottom of deep, youthful gorges, and so such destress-
ing effects, even if not visible, are likely to be present, as shown in Figure 2.11b.
2.5.5
Rock movements in excavations
Spalling, buckling upwards, and the formation of new sheet joints are relatively common
occurrences in near-surface excavations in very high strength rocks in North America,
Scandinavia and Australia. Emery (1964) reports that an anticlinal fold about 100 m long
with crest elevation of almost 5 m was formed overnight in a limestone quarry in Kingston,
Ontario. Lee et al. (1979) describe rock bursts in shallow excavations in granite and gneiss
in Maine, U.S.A. Ward (1972) describes a 30 m deep excavation in gneiss at New York City,
where inward movement of the walls caused rock bolt failures.
Bowling and Woodward (1979) describe “rockbursts” and the formation of new sheet
joints at Copeton Dam in New South Wales. Relatively minor spillway discharges of up
