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

Usage license:: Get license information via the feedback formular.

Chapter

Document type:: Monograph

Structure type:: Chapter

Title:: Part IV. Engineering geology

Collection:: Economics Books

236 ECONOMIC GEOLOGY wave traversing a plateau causes the particles to oscillate about their original position; but at the end of the plateau the ground is flung forward, just as a tap on one end of a row of billiard balls sends a wave through them but only moves the last, which is jerked forward. Structures should be light to reduce both inertia and momentum ; for on a sudden shock inertia tends to jerk the lower part from under the slower upper part; while momentum causes the upper part to continue the forward swing after the base has begun to move back. Hence factory chimneys are built with a broad strong base, which tapers upward, and the upper part is composed of sheet iron, to reduce the weight. A chimney built as a uniform cylinder would be fractured at the base. The danger of top-heavy chimneys was shown at the Warnambool earthquakes in Victoria of 1903; they are built of a dune limestone which is used in thick slabs and the weight of those at the cap rendered the chimneys as unstable as an inverted pendulum and many were overthrown. The strength of a wall is reduced by the doors and windows, for they serve like the perforations in a sheet of stamps, and the cracks run from one to the next. A medium angle of emergence is accompanied by cracks that radiate from the window corners, while a horizontal emergence is marked by vertical cracks. Vertical rows of windows are weaker than a diagonal or quincuncial arrangement. The arch is a dangerous structure in earthquake areas unless embedded underground ; for during horizontal move- ments the two sides may move in opposite directions at the same time, and the arch be torn asunder. The Kiso Sawa railway bridge in Japan rested on piers of masonry 26 feet long by 10 feet thick, each supported by two circular drum curbs, 12 feet in diameter. The bridge was destroyed by an earthquake, as the differential movement of the two drums tore each pier in twain; they were replaced by single drums 30 feet by 12 feet. The reduction of the stresses due to momentum and inertia specially concerns the design of roofs. When a building is jerked forward the roof tends to remain behind, and the side left unsupported may fall into the room. In Japanese temples the roof timbers were knit together by many joints

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