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Engineering Geology

Engineering Geology - geomuseu

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Chapter 9<br />

<strong>Geology</strong> and Construction<br />

<strong>Geology</strong> is one of the most important factors in construction since construction takes<br />

place either at or below the ground surface. Hence, geology has an influence on<br />

most construction operations because it helps determine their nature, form and cost.<br />

Open Excavation<br />

Open excavation refers to the removal of material, within certain specified limits, for construction<br />

purposes. In order to accomplish this economically and without hazard, the character of the<br />

rocks and soils involved and their geological setting must be investigated. Indeed, the method<br />

of excavation and the rate of progress are influenced very much by the geology on site (Kentli<br />

and Topal, 2004). Furthermore, the stability of the sides of an excavation and the position<br />

of the water table in relation to the base level of an excavation are of importance, as are<br />

any possible effects of construction operations on the surrounding ground and/or buildings<br />

(Finno et al., 2005).<br />

A Note on Slope Stability<br />

The stability of slopes is a critical factor in open excavation. This is particularly the case<br />

in cuttings, as for instance, for roads, canals and railways, where slopes should be designed<br />

to resist disturbing forces over long periods. In other words, a stability analysis should determine<br />

under what conditions a proposed slope will remain stable. For a further note on slope stability,<br />

see Chapter 3.<br />

Instability in a soil mass occurs when slip surfaces develop and movements are initiated<br />

within it. Undesirable properties in a soil, such as low shearing strength, development of<br />

fissures and high pore water pressure, tend to encourage instability and are likely to lead<br />

to deterioration in slopes. In the case of open excavation, removal of material can give rise<br />

to the dissipation of residual stress that can aid instability.<br />

There are several methods available for analysis of the stability of slopes in soils<br />

(Morgenstern, 1995). Most of these may be classed as limit equilibrium methods, in which the<br />

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