The Elements of economic geology

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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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Document type:: Monograph

Structure type:: Chapter

Title:: Part IV. Engineering geology

Collection:: Economics Books

226 ECONOMIC GEOLOGY The height to which water rises in rocks may be illustrated by a series of ‘* piezometers™ or pressure meters, as in Fig. 58. If a horizontal pipe from the lower part of a water tank is closed at the outer end by the tap T and bears a row of vertical tubes (P1, P2, P3, P4), the water will rise in each of them to its height in the tank, and that level is the hydro- static surface (HsS). If the tap be opened the water in the vertical tubes falls to a surface sloping from the water- level in the tank to the outlet. As the water is flowing, the conditions are hydraulic, and the inclined surface, HI Si, is the hydraulic slope or gradient. This gradient depends ba) -Hs S ase. ~ F16. 58.— WATER-LEVEL, Water-level in a series of piezometers P,-P,. HsS = Hydrostatic Surface. HI SI = Hydraulic Gradient. on the velocity of the water along the pipe; the greater its velocity, the lower the water-level in the vertical pipes. The height of the water in each of them is the pressure-head ; the difference of pressure-head between flowing and stagnant water is the ‘‘velocity-head’; the pressure-head and velocity-head together equal the hydrostatic-head. If the horizontal pipe be constricted (Fig. 58 B) so that the flow of water along it be reduced, or if part of it be filled with sand so that the friction is increased, then the pressure-head is raised. The hydraulic gradient therefore varies with the conditions in the outlet channel, and may be an irregular slope. If the pipes and the side of the tank were replaced by a block of porous sandstone the water would soak into the stone and flow through it to an outlet at the free end under

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