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any rocks lying chiefly in the weathering zone (including soil) and used by man for engineering and construction purposes. Ground can be used as the foundation of buildings and of various engineering projects, as material for construction (roads, embankments, dams), and as a medium for the placement of underground structures (tunnels, pipelines, storage facilities). Ground is subdivided into rocky ground and loose ground (nonrocky ground according to the classification adopted in the Construction Standards and Rules).
Rocky ground includes igneous, metamorphic, and sedimentary rocks with the grains rigidly bound together. These rocks occur in the form of a monolithic or fractured mass.
Loose (nonrocky) ground may be coarsely fragmental (noncemented), with more than half by mass of the rock fragments more than 2 mm in size, for example, debris (pebbles if rounded particles predominate). Or it may be finer ground, or gruss (gravel if rounded particles are dominant). There is also sandy ground, free-flowing when dry, lacking in plasticity, and with more than 80 percent by mass of the particles 2 mm to 0.05 mm (according to the classification adopted in Construction Standards and Rules, with less than 50 percent by mass of the particles larger than 2 mm).
Ground may be sandy, loessial. or clayey. Sandy ground may be further subdivided into gravelly, coarse, medium, fine, and silty ground. Loessial ground, in which silty particles from 0.001 to 0.05 mm predominate, often has the capacity to settle, that is, it can become more compact when wetted without change in the stress applied to it. Clayey ground, may be subdivided according to the amount of clay particles (less than 0.001 mm) into sandy loam, loam, and clay (according to the Construction Standards and Rules, the division of clay ground into sandy loam, loam, and clay is based on plastic properties). Clayey ground swells and becomes plastic when moistened. In its initial stage of formation clay ground, which originates as structured sediment in water in the presence of microbiological processes and which possesses a high moisture content and porosity, is called ooze. The various types of ground are studied in soil mechanics both as specific natural and historical formations whose properties depend on their genesis, on subsequent epigenetic processes, and on their recent modes of occurrence and as multiphase systems that change with time. Investigation of the properties of ground also includes the study of its composition, structure, texture, and physical environmental conditions (temperature, pressure, and so forth). The quality of ground is determined by its composition, structure, and texture. The structure may be defined as the regular arrangement of mineral particles and aggregates, differing in size and shape, into which ground may disintegrate; this arrangement is determined by the nature of the internal bonds. The texture of ground is the sum of the features characterizing the heterogeneity of the structure of the ground mass in a stratum. Among the most important properties of ground are its physical properties (specific mass and volumetric mass, porosity, plasticity, shrinkage, water permeability, electric conductivity) its physicochemical properties (adsorbing capacity, thixotropy), and its physicomechanical properties (shearing strength, capacity for deformation). From the practical standpoint, the most important properties of ground are the deformation and stability characteristics of its behavior under external stress. Thermal properties are important for frozen, freezing, or thawing ground. The petrographic characteristics of ground and their properties are studied under laboratory and field conditions both in samples and as a mass. The terms “properties of ground” and the “engineering and geological properties of rocks” are analogous.
In order to determine the location and thickness of strata and the groundwater level, which greatly influence the condition and properties of the ground, the latter is tested at a construction site by drilling, pitting, sounding, and geophysical methods. The properties of ground may be improved by adding cementing and binding agents, mechanical packing, draining, firing, freezing, and so forth.
REFERENCESGruntovedenie, 3rd ed. Edited by E. M. Sergeev. Moscow, 1971.
Sergeev, E. M. Gruntovedenie. 2nd ed. Moscow, 1959.
Tsytovich, N.A. Mekhanika gruntov. Moscow, 1963.
Larionov, A. K. Inzhenerno-geologicheskoe izuchenie struktury rykhlykh osadochnykh porod. Moscow, 1966. “Stroitel’nye normy i pravila.” part 2, section B, chapter I. Osnovaniia zdanii i sooruzhenii. Moscow, 1962.
Metodicheskoe posobie po inzhenerno-geologicheskomu izucheniu gornykh porod, vols. 1–2. Moscow, 1968.
E. M. SERGEEV and M. V. MALYSHEV
in painting), the intermediate layer that is applied to the support, that is, the surface of a wall, wooden panel, canvas, or paperboard in order to ensure that the paint layer will adhere to the surface and also to create the desired color background (white, brown, gray) and texture (smooth, grainy) in a painting. The main component of ground is a powdery substance, such as chalk, gypsum, lime, white lead, or zinc white, combined with glue, oil, or oil emulsions.
Depending on their main component, grounds may be divided into chalk, gypsum, lime grounds, and so forth. Classified according to their base, grounds may be glue, oil, or emulsion grounds. In mural painting, clay, gypsum, and lime grounds (of one or many layers) have been used since ancient times, and cement ground has also been employed since the ninth century. In ancient and medieval easel and miniature painting, chalk and gypsum grounds with animal-glue bases were used. With the development of oil painting in the 15th century emulsion and oil grounds (of one or many layers) came into use along with clay ground. In Russian medieval mural and icon painting, as well as in painted and gilded wood carving, the ground used was called levkas.
Ground in graphic art is the acid-resistant coating applied to the metal plate in some types of engraving (such as etching or aquatint) in order to render certain areas impervious to the biting action of the acid.
REFERENCESTiutiunnik, V. V. Gruntovannyi kholst tilia maslianoi zhivopisi. Moscow, 1949.
Kiplik, D. I. Tekhnika zhivopisi, 6th ed. Moscow-Leningrad. 1950.
Slansky. B. Tekhnika Zhivopisi: Zhivoposnye materialy. Moscow, 1962. (Translated from Czech.)
V. V. FILATOV and A. S. ZAITSEV
an installation used in connecting apparatus, machinery, and instruments to the earth. It consists of metal electrodes buried in the earth (ground electrodes) and the conductors connecting these ground electrodes to the grounded parts of the equipment.
Ground electrodes may be in the form of steel pipes driven vertically into the ground (for high-voltage electrical installations there may be dozens of pipes), rails, or horizontally laid steel or copper strips or wires. To reduce earth resistance, the ground electrodes should be placed at the level of the ground water. In broadcasting stations with mast antennas, the ground is built as a net consisting of 100–120 sections of wire extending radially from the foundation of the mast. The sections have a length equal to 0.35–0.50 wavelengths of the transmitter and are buried 15–20 cm deep in the earth. A steel cable or chain is sometimes used as a ground electrode—for example, in removing an induced static charge from gasoline tank trucks. In electrical systems a distinction is made among operating grounds (for example, the neutral of a transformer), protective grounds (for example, grounding of machine and apparatus housings), and lightning-protection grounds (for example, lightning rods and arresters).
In protective grounding installations it is imperative to keep to the lowest possible value the voltages to which operating personnel could be exposed if a short circuit occurred in electrical installation (contact and step voltages). This is achieved by lowering the resistance of the grounding electrodes and by equalizing the potential distribution in the area of the grounded equipment. Lightning-protection ground is intended to protect electrical equipment from the effects of lightning current; such ground is designed for currents up to 200 kiloamperes and for pulse durations of a fraction of a second.
REFERENCESOllendorf, F. Toki v zemle: Teoriia zazemlenii. Moscow-Leningrad, 1932. (Translated from German.)
Tekhnika vysokikh napriazhenii. Edited by D. V. Razevig. Moscow-Leningrad, 1963.
Oslon, A. B. “Zazemliaiushdiie ustroistva na liniiakh elektroperedachi i podstantsiiakh vysokogo napriazheniia.” In Elektricheskie stantsii, seti i sistemy. Moscow, 1966.
D. V. RAZEVIG
groundA reference voltage level of "zero potential" for electric and electronic circuits. For most equipment plugged into an AC outlet, the word ground generally refers to the earth, and the metal parts are grounded ("chassis ground") to the earth for safety. In the case of a short circuit, the current flows through the green wire and third prong in the power cord (U.S. and Canada), which causes the circuit breaker to trip.
Power supplies, circuit boards and signal pathways in most electronic equipment are also connected to the same earth ground as the chassis for reference voltage and safety. There are exceptions; for example, medical equipment that is attached to a patient is generally isolated from earth ground even when plugged in, because the time between a short circuit and the breaker tripping could prove fatal. Ethernet adapters and other networking equipment are also isolated from earth ground in order to prevent unbalanced ground loops from causing interference (see ground loop).
Every portable, battery-operated device, such as a laptop and iPod, as well as the electrical systems in every vehicle, have their own zero reference voltage. Naturally, these systems are not connected to earth ground, but the reference voltage is still called ground.
At the electric panel in U.S. and Canadian buildings, the ground lines are wired to the neutral line of the electric service, to the earth via a ground rod and to the metal plumbing pipes. In large datacenters, a separate ground system may connect every server via heavy-duty cable to the metal structure of the building to ensure that the voltage reference between all equipment is the same. See ground loop.