English for hydraulic and hydroelectric engineering Earth and rock damSummaryEarth and rock dam, with another name as "local material dam",is mainly built with earth and rock materials near the site. It can be classified based on the materials it used, earth dam mainly with earth, sand, grit, and gravel, and rock dam mainly with rock ballast, gravel, and exploded rocks.Features of earth and rock damStrong pointsWith convenient supply of materials, many building materials such as steel, cement, and timbers can be saved.With granular structure more suitable to foundation deformation, it demands less on the foundation.Very flexible from simple artificial filling to highly mechanized construction, the procedure become simple, the construction become efficient, and the quality guarantee become easy.Simply structured, the cost is low, the operation is convenient, works is reliable, and maintenance and height adding is convient. Weak pointsOverflow not allowed, spillway has to be built.Diversion less convenient, cost increases.Section larger, earth to be filled is easy to be affected by climate. This kind of difficult means possible extention of time limit and cost increaseEarth and rock dam typesBased on constructing ways, earth and rock dams can be classified into rolled ones of earth & rock, thrown rock-filled ones, rock-filled ones with directional detonation, ones with earth thrown into the water, and ones filled by hydraulic forces. Among them, rolled ones are most popular.Based on the earth proportion and the location of anti-seepage parts, there are homogeneous (even-granular) dams, zoned earth dams, and dams with artificial anti-seepage materials. Strong points of homogeneous dams: one fold materials, simple process weak points: flat gradient, large section, weather-limited, strong water pressure in holes. Zoned dams are classified into ones with core anti-seepage and ones with front anti-seepage. Less amount of earth, less affect of season. interfering with the filling of the dam body. Less interference with the construction of the dam body. weaker anti-earthquake and uneven sinking. The anti-seepage parts of dams with artificial anti-seepage materials use asphalt concrete, reinforced concrete or other artifical materials. Sometimes, the anti-seepage parts are in the dam front facing the upstream, sometimes, they are at the core of the dam. Working conditionsTrapeziform sectionEarth-rock dam is a water retaining structure built with loose granules of earth and rocks filled and roller compacted. With weaker strength between these granules, both upsteam and downsteam slopes have to be kept at a certain degree to avoid landslide. So the dam section is usually trapeziform. It can be destablized in two ways, simple slope sliding and sametime sliding of slope and foundation caused by shear damage. It's a difference from other structuresSeepage effectsWith a large section, the dam is generally kept from entire sliding unless caused by weak interlayers. Effected by water levels at the upsteam and downsteam, seepage is easy to happen with streams passing the faying surfaces between the dam and foundation, and between dam earth and concrete buildings. The seeping streams form a free water surface inside the dam. Under the surface, all the earth body is saturated. Dipped in the water, the earth become lighter in effect. And its angle of internal friction is narrowed, and cohesive force weakened. With the hydrodynamic pressure from the seeping steams, more sliding of dam slopes is possible. When seeping steams move in soil, the dam body and foundation will be deformed from too steep hydraulic gradient. Sometimes the dam even crashes.Scour effectIts anti-scour ability is weak because the cohesive force between earth granules is small. On the one hand, the rain water enters the dam and lower the stability of the dam, and on the other hand, the rain scour the dam surface along the slope. At the same time, the waves inside the reservoir also wash out the dam surface, putting the surface in the risk of being damaged. Sometime, landslide even happens due to this. So effective protecting measures have to be taken for dam slopes both upstream and downstream.Sinking effectThe dam body and foundation will sink under their self weight and water load besides the space between earth granules. If it sinks too much, the elevation level will not be sufficient, and then the operation of the dam will be affected. And, too much uneven sinkage will cause fracture of the dam boday, and even a seepage passage, putting the dam at risk.Other effectsIn freezing regions, an ice-covered layer will be formed over the reservoir when the temperature is below 0 degree. Then the bank slope and dam slope will be frozen together with the ice. When the ice expands, slopes will be pressed. In this w。