The Elements of economic geology

Bibliographic data

Monograph

Identifikator:: 1773832379

URN:: urn:nbn:de:zbw-retromon-172798

Document type:: Monograph

Author:: Gregory, John W. http://d-nb.info/gnd/11683014X

Title:: The Elements of economic geology

Place of publication:: London

Publisher:: Methuen

Year of publication:: 1928

Scope:: XIV, 312 S.; graph. Darst.

Digitisation:: 2021

Collection:: Economics Books

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Chapter

Document type:: Monograph

Structure type:: Chapter

Title:: Part IV. Engineering geology

Collection:: Economics Books

lg 7 (Y sd ly 2 it ‘h ig he 15 i, ve d .n nt COASTAL WORKS 24; measures to maintain and deepen the new channel of the Thames. The chief difficulties of an estuarine port are the silting of its channel and shoaling at the entrance. The channel may be maintained by dredging or by the automatic scour of the tidal current. On an open coast the only available method of harbour construction may be a costly breakwater, which, if ill-designed, is ineffective. Thus the breakwater at Ceara in Brazil (Fig. 62) was connected with the shore by a viaduct, in the hope that the stream under it would scour the harbour ; but in 20 years sand had filled the basin and carried the foreshore almost to the end of the breakwater. Sga-Warrs—Masonry may be weakened by the chemical action of sea-water on concrete. for the sulphate and chloride 1e or ad 7) st as al 28 10 se al :h te nt er he 1€ as ad 3) Fic, 62.—THE CEARA BREAKWATER, BRAZIL. Shoaling of the Ceara Breakwater, Brazil, built 1884. The four dots at the lower end of the Breakwater represent the piers of the viaduct. S.L. 1884, and S.L. 1903 represent the shore-lines in 1884 and 1go3. LW. 1884 and L.W. 1003, low water at the same dates. of magnesia alter any unstable form of lime into calcium sulphate and chloride, which are removed in solution. These reactions happen if the concrete contains an excess of lime, and ‘the trouble can be avoided by preventing the entrance of sea-water, or by the addition of material such as trass or brickdust or ground slag, which will combine with the free lime (D. B. Butler, Portland Cement, 3rd edition, 1913, p. 374). Sea-walls, if perpendicular, are struck with the full force of an advancing wave and may be undercut. If the foot projects in a curve the wave is checked gradually ; a slope of one vertical in ten horizontal is often adopted as it is usual in shingle banks. A projection along the top of a sea-wall is sometimes used to throw back the spray; but as this coping is subject to heavy upward blows it is liable to crack rhe wall.

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