lesson 15 soil mechanical(土木工程专业英语)

Lesson 15,Text: Soil Mechanics,教学要求:1、掌握有关Soil Mechanics的专业术语；2、 熟悉一些常见的表达方式；3、 延伸了解一些土力学历史和名人；4、 能正确、流畅地翻译,Soil mechanics is concerned with the use of the laws of mechanics and hydraulics in engineering problems related to soil. Soil is a natural aggregate of mineral grains, with or without organic constituents, formed by the chemical and mechanical weathering of rock. It consists of three phases: solid mineral matter, water, and air or other gas. Soils are extremely variable composition, and it was this heterogeneity that long discouraged scientific studies of these deposits.,hydraulics haidr:liks 水力学 aggregate grigeit 集合体phase feiz 阶段,相heterogeneity .hetrudini:iti 异质性,多相性,土力学研究的是在工程问题中与土相关的力学和水力学定律的应用。土是矿物粒的天然集合物，这些矿物粒是岩石经过化学或物理风化而形成，含或者不含有机成分。土包含有三个相：固态的矿物质，水，空气或其他气体。土的组成极其复杂，正是这种异质性，长期以来阻碍了对这个堆积物的研究。,(生物体,有机体),Gradually, the investigation of failures of retaining walls, foundations, embankments, pavement, and other structures resulted in a body of knowledge concerning the nature of soils and their behavior sufficient to give rise to soil mechanics as branch of engineering science.,retaining wall :挡土墙 embankments imbkmnt 堤防, 筑堤pavement peivmnt 路面,逐渐地，通过对那些失败的挡土墙、基础、堤坝、路面及其他结构的调查研究，人们积累了大量的有关土的类型及其性质的知识，从而形成了工程学科的分支土力学。,History. Little progress was made in dealing with soil problems on a scientific basis until the latter half of the 18th century, when the French physicist Charles-Augustin de Coulomb published his theory of pressure (1773). In 1857 the Scottish engineer William Rankine developed theory of equilibrium of earth masses and applied it to some elementary problems of foundation engineering. These two classical theories still form the basis of current methods of estimating earth pressure, even though they were based on the misconception that all soils lack cohesion, as does dry sand. Twentieth-century advances have been in the direction of taking cohesion into account; understanding the basic physical properties of soils in general and of a the plasticity of clay in particular; and systematically studying the shearing characteristics of soilthat is, their performance under conditions of sliding.,cohesion kuhi:n 内聚力,粘聚力 ;plasticity plstisiti 塑性;,历史。18世纪后叶之前，人们在研究有关土的科学理论方面进展很小，直到法国物理学家查里.奥古斯丁.库仑（Charles-Augustin de coulomb）在1773年出版了他的土压力学说。1857年，苏格兰工程师朗肯（William Rankine）发展了土的平衡理论，并将其用于基础工程的基本问题中。尽管这两个经典理论是建立错误的假设上，即认为土和干燥的沙子一样是缺乏粘聚力的，但仍然形成了当前估算土压力方法的理论基础。这方面的研究，在21世纪有了突破，粘聚力计入计算，了解了一般情况土的物理性质和特殊情况下土的塑性，还系统地研究了土的剪切性质也就是土滑动时的性能。,Charles Augustin de Coulomb (17361806) was a French physicist. He is best known as the discoverer of Coulombs law, which defines the force of electrostatic attraction and repulsion. The SI unit of charge, the coulomb, was so named in his honour.,William John Macquorn Rankine (1820-1872) was a Scottish engineer and physicist. Rankine 被后人誉为那个时代的天才，他在热力学、流体力学及土力学等领域均有杰出的贡献。,Both Coulombs and Rankines theories assumed that the surface of rupture of soil subjected to a shearing force is a plane. While this is a reasonable approximation for sand, cohesive soils tend to slip along a curved surface. In the early 20th century, Swedish engineers proposed a circular arc as the surface of slip. During the last half century considerable progress has been made in the scientific study of soil and in the application of theory and experimental data to engineering design.,rupture rpt(r) 断裂approximation 接近、近似值cohesive kuhi:siv 粘性的(有结合性的,有粘聚性的),A significant advance was made by the German engineer Karl Terzaghi, who in 1925 published a mathematical investigation of the rate of consolidation of clays under applied pressure. His analysis, which was confirmed experimentally, explained the time lag of settlements on fully waterlogged clay deposits. Terzaghi coined the term soil mechanics in 1925 when he published the book Erdbaumenchanik (“Earth-. Building,Karl Terzaghi （ 1883 1963 ）卡尔特扎吉 consolidation kn.slidein 固结waterlogged w:tlgd 浸满水的,mechanics”),Karl Terzaghi,The Father of Soil Mechanics.,Born: October 2, 1883 in Prague Died: October 25, 1963 in Winchester, Massachusetts He was married to Ruth D. Terzaghi, a geologist. He won the Norman Medal of ASCE four times (1930, 1943, 1946, and 1955). He was given nine honorary doctorate degrees from universities in eight different countries. He started modern soil mechanics with his theories of consolidation, lateral earth pressures, bearing capacity, and stability.,nutshell:,Researching on subgrade materials, the natural foundation under pavements, was begun about 1920 by the U.S. Bureau of Public Roads. Several simple tests were correlated with the properties of natural soils in relation to pavement design. In England, the Road Research Board was set up in 1993. In 1936 the first international conference on soils was held at,subgrade 路基 U.S. Bureau of Public Roads 美国公路局 Road Research Board 公路研究部,Harvard University.,Today, the civil engineer relies heavily on the numerical results of tests to reinforce experience and correlate new problems with established solutions. Obtaining truly representative samples of soils for such tests, however, is extremely difficult; hence there is a trend toward testing on the site instead of in the laboratory, and many important properties are now evaluated in this way.,.,今天，土木工程师都会借重于试验的数据来加强经验，把新问题和已确定的解决方法联系起来。但是，要获得具有代表性的土样做测试，是非常困难的，因此，现在倾向于用在现场做测试来取代实验室的试验。现在，大多数重要的土特性采用这种方法来评定。,Engineering properties of soils. The properties of soil that determine their suitability for engineering use include internal friction, cohesion, compressibility, elasticity, permeability, and,internal friction 内摩擦力cohesion kuhi:n 粘聚力compressibility km.presibiliti 压缩性permeability .p:mibiliti 渗透性capillarity kpilriti 毛细性,Capillarity.,Internal friction is the resistance to sliding offered by the soil mass. Sand and gravel have higher internal friction than clays; in the latter an increase in moisture lowers the intern friction. The tendency of a soil to slide under the weight of a structure may be translated into shear; that is , a movement of a mass of soil in plans, either horizontal, vertical, or other. Such a shearing movement involves a danger of,内摩擦力土体是抵抗滑动的力。沙子和沙砾比粘土的内摩擦力大，后者的内摩擦力随着湿气的增加而降低。土在结构的重力下，其滑动的趋势可能会转换成剪切，也就是土的平面的，水平的、竖向的或者其他方向的运动。这种剪切运动会造成危险的建筑事故。,building failure.,Also resisting the danger of shear is the property of cohesion, which is the mutual attraction of soil particles due to molecular forces and the existence of moisture between them. Cohesion is generally very high in clays but almost nonexistent in sands or silts. Cohesion values range from zero for dry sand to 2,000 pounds per square foot for very stiff clay.,mutual mju:tjul共同的,相互的 particle p:tikl 粒子,点,极小量 molecular mulekjul 分子的silt silt 淤泥,Compressibility is an important soil characteristic because of the possibility of compacting the soil by rolling, tamping, vibration, or other means, thus increasing its density and load-bearing strength.,An elastic soil tends to resume its original condition after compaction. Elastic (expansible) soil are unsuitable as subgrades for flexible pavements since they compact and expand as a vehicle passes over them, causing failure of the pavement.,rolling r:uli碾压 tampingtmpi 夯实vibration vaibrein 振动flexible pavements 柔性路面,Cross sections of modern pavement,Permeability is the property of a soil that permits the flow of the water through it. Freezing-thawing cycles in winter and wetting-drying cycles in summer alter the packing density of soil grains. Permeability,Capillarity causes water to rise through the soil above the normal horizontal plane of free water. In most soil numerous channels for capillary action exist; in clays, moisture may be raised as much as,thawing :i 融化 packing density 堆积密度numerous nju:mrs 许多,can be reduced by compaction.,30 feet by capillarity.,Density can be determined by weight and volume measurements or by special measuring devices. Stability of soils is measured by an instrument called a stabilometer, which specifically measures the horizontal pressure transmitted by a vertical load. Consolidation is the compaction or pressing together of soil that occurs under a specific load condition; that,stability stbiliti 稳定性 stabilometer .steibilmit 稳定仪,稳定性量测仪,密度可以通过测定重量和体积得到，或者用特殊的测量仪器测得。土的稳定性可用一种稳定仪测得，稳定仪可明确测出竖向荷载带来的水平压力。固结是土在一种特殊荷载下的发生的压实或者挤压，同样也可以测试出来。,property is also tested.,Site Investigation. Soil surveys are conducted to gather data on the nature and extent of the soil expected to be encountered on a project. The amount of effort spent on site investigation depends on the size and importance of the project; it may range from visual inspection to elaborate subsurface exploration by boring and laboratory testing. Collection of representative sample is essential for proper identification and classification of soils.,survey s:vei 测量 elaborate ilbrt 精细的,详尽的 boring b:ri 钻孔identification ai.dentifikein 鉴定,确认,The number of samples taken depends on previously available data, variation in soil types, and the size of the project. Generally, in the natural profile at a location, there is more variation in soil characteristics with depth than horizontal distance. It is not good practice to collect composite samples for any given horizon (layer),since this does not truly represent any one location and could prove misleading. Even slight variation in soil characteristics in a horizon should be duly noted. Classification of the soil in terms of grain size and the liquid and plastic limits are particularly,profile prufail 剖面，侧面plastic limit限,important steps.,An understanding of the eventual use of the data obtained during site investigation is important. Advance information on the site conditions is helpful in planning any survey program. Information on topography, geological features (outcrops, road and stream cuts, lake beds, weathered remnants, etc.), paleontological maps, aerial photographs, well logs, and excavations can prove invaluable. Geophysical exploration methods yield useful corroboratory data. Measurement of the electrical resistivity of soils provides an insight into several soil,topography tpgrfi 地形学,地势geological dildikl 地质学的，地质的outcrops autkrp 露头paleontological古生物学的； geophysical地球物理学的；electrical resistivity ：电阻,characteristics.,Seismic techniques often are used to determine the characteristics of various subsurface strata by measuring the velocity of propagation of explosively generated shock waves through the strata. The propagation velocity varies widely for different types of soils. Shock waves also are utilized to determine the depth of bedrock by measuring the time required for the shock wave to travel to he bedrock and return,Seismic saizmik 地震的 strata streit pl层(地层,阶层,薄片) stratum: streitm velocity vilsiti 速度propagation .prpgein 传播,地震学技术通过测定激震波穿过地层的传播速度来确定不同地层的性质