土木工程专业英语第二版(段兵延)Lesson15

Soil Mechanics

土力学

Soil mechanics is concerned with the use of the laws of mechanics and hydraulics in engineering problems related to soils 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 in composition，and it was this heterogeneity that long discouraged scientific studies of these deposits．Gradually，the investigation of failures of retaining walls，foundations，embankments ，pavements，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 a branch of engineering science．

土力学研究的是力学和水力学的法则在牵涉土的工程问题中的应用。土是一种天然矿物颗粒的聚集物，有的含有有的不含有机成分，它由岩石的风化或是机械作用形成。它包括三种成分：固体矿物质，水以及空气和其他气体。土质组成变化很大，正是这种不均质性大大地阻碍了科学家对这些沉积物的研究。渐渐地，对挡土墙，基础，护堤，人行道和其他结构的事故的调查发现其原因涉及到许多天然土的知识并且它们的工况充分提高了土力学作为工程科学的一个分支。

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－August in de Coulomb published his theory of earth pressure（1773）．In 1857 the Scottish engineer Willliam Rankine developed a theory of equilibrium of earth masses and a pplied it to some elementary problems of foundation engineering．These two classica l 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 cohesio n into account understanding the basic physical properties of soils in general and of the plasticity of clay in particular；and systematically studying the shearing characte ristics of soils—that is，their performance under conditions of sliding．

历史

直到18世纪后半期，法国物理学家查尔斯-奥斯丁库仑出版他的土压力理论（1773年）之前，以科学的基础处理土的问题几乎没有任何进展。1857年，苏格兰工程师威廉姆朗金发展了一种土体平衡理论并将其用于一些初步的基础工程问题。这两大理论仍然构成了当今计算土压力理论的基础，尽管他们建立在所有土都象干沙一样不考虑内聚力这一错误概念的基础上。二十世纪的进步在于：把内聚力引入计算；了解了通常情况下土的基本物理特性和特殊情况下粘土的特性；系统地研究了土的剪切特性，即——滑动剪切条件下的变形。

Both Coulomb’s and Rankine’s theories assumed that the surface of rupture of soil subjected to a shearing force is a plane．While this is a reasonable approximation f or sand，cohesive soils tend to slip along a curved surface．In the early 20th centur y，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 soils an d in the application of theory and experimental data to engineering design．

库仑和朗金土压力理论都假设土的剪切破坏面在一个平面内。然而对于砂土来说这是近似可信的，有内聚力土的滑动剪切面接近一个曲面。在二十世纪早期，瑞典工程师证明滑动剪切面是一个圆弧面。上个世纪后半段，在土的科研，理论的应用以及用于工程设计的经验数据方面都有了明显进步。

A significant advance was made by the German engineer Karl Terzaghi，who in 192

5 published a mathematical investigation of the rate of consolidation of clays under applied pressures．His analysis，which was confirmed experimentally, explained the t ime lag of settlements of fully waterlogged clay deposits．Terzaghi coined the term soil mechanics in 1925 when he published the book Erdbaumechanik（“Earth－Buildi ng Mechanics”）．

一个显著的进步是德国工程师卡尔泰沙基在1925年出版了一本关于粘土在许用应力下固结情况的力学调查。他的被工程经验证实的分析解释了在充分渗透的粘土上沉降随时间增长的问题。泰沙基在1925年出版了Erdbaumechanik(“土力学”)一书后开辟了土力学时代。

Research on subgrade materials，the natural foundation under pavements，was begu n about 1920 by the U．S．Bureau of Public Roads．Several simple tests were corre lated with the properties of natural soils in relation to pavement design．In England，the Road Research Board was set up in 1933．In 1936 the first international confer ence on soils was held at Harvard University．

关于地基材料，人行道下的天然基础的研究始于1920年美国公共道路局。他们做了一些关于人行道设计的和天然土有关的简单实验。在英格兰，道路研究司创建于1933年。1936

年第一个岩土方面的世界会议在哈佛举行。

Today，the civil engineer relies heavily on the numerical results of tests to reinfo rce experience and correlate new problems with established solutions．Obtaining tru ly representative sample of soils for such tests，however，is extremely difficult；henc e there is a trend toward testing on the site instead of in the laboratory，and man y important properties are now evaluated in this way．

今天，市政工程极大地依赖于实验的大量数据来巩固经验以及与之相关的新的问题来建立解决方案。获得这样的土质实验的典型例子，无论如何是很极其困难的；因此有一种在实验室做比例模型来代替这种现场实验的趋向，并且许多重要的性质都是由这种方法得到的。

Engineering properties of soils．The properties of soils that determine their suita bility for engineering use include internal friction，cohesion，compressibility，elasticity，permeability，and capillary．

土的工程性质决定土的工程适用性的性质包括：内摩擦力，内聚力，压缩性，弹性，渗透性以及毛细性。

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 l owers the internal friction．The tendency of a soil to slide under the weight of a s tructure may be translated into shear；that is，a movement of a mass of soil in a

plane，either horizontal，vertical，or other．Such a shearing movement involves a d anger of building failure．

内摩擦力是土体抵抗滑动的力。砂土和砾石土比粘土有更大的内摩擦力；后期水气的增加会降低内摩擦力。土在重结构压迫下滑动的趋势可以转化成剪力；即使一部分土体在一个平面内水平的竖直的或其他方向的移动。这样一种剪切移动会给建筑带来危险。

Also resisting the danger of shear is the property of cohesion，which is the mut ual attraction of soil particles due to molecular forces and the existence of moisture between them．Cohesive forces are markedly affected by the amount of moisture p resent．Cohesion is generally very high in clays but almost nonexistent in sands or s lits．Cohesion values range from zero for dry sand to 2，000 pounds per square foo t for very stiff clays

内聚力可以减少这种剪切危险，这是由土颗粒间分子力产生的土颗粒之间相互吸引作用以及土粒间存在水气造成的。内聚力明显受土粒间大量湿气影响。内聚力在粘土中通常很大而在砂土和淤泥土中几乎不存在。内聚力值从干砂土的0到很粘稠的粘土2000磅每平方英尺之间变化。

Compressibility is an important soil characteristic because of the possibility of compa cting the soil by rolling，tamping，vibration，or other means，thus increasing its den sity and load－bearing strength．

因为可以通过碾压，夯实，振捣或其他方法压实土以增大其密度和提高其承载强度，所以可压缩性是土的一个重要特性。

An elastic soil tends to resume its original condition after compaction．Elastic（ex pansible）soils are unsuitable as sub-grades for flexible pavements since they compa ct and expand as a vehicle passes over them，causing failure of the pavement

弹性土在受压后趋向于恢复到初始条件。弹性（延性）土不适合作为柔性人行道的地基因为他们会在上面交通的作用下压缩延展导致地基沉陷。

Permeability is the property of a soil that permits the flow of water through i t．Freezing－thawing cycles in winter and wetting－drying cycles in summer alter the packing density of soil grains．Permeability can be reduced by compaction．

可渗透性是土体允许水流通过其中的性质。冬季的冻融循环和夏季的干湿循环改变了土颗粒的填实密度。压缩可以减小渗透性。

Capillarity causes water to rise through the soil above the normal horizontal pla ne of free water．In most soils numerous channels for capillary action exist；in clay s，moisture may be raised as much as 30 feet by capillarity．

毛细性导致自由水延土中孔隙上升到正常水平面以上。在多数土中都存在毛细性所需要的许多管道；在粘土中，水汽可在毛细作用下上升达30英尺。

Density can be determined by weight and volume measurements or by special measuring devices．Stability of soils is measured by an instrument called a stabilome ter，which specifically measures the horizontal pressure transmitted by a vertical l oad．Consolidation is the compaction or pressing together of soil that occurs under a specific load condition; this property is also tested．

土壤密度可以通过测量土的重量和体积来计算出或是通过特殊仪器测得。土的稳定性可以通过一种叫做稳定性试验机的设备来测量，它可以测量由交通荷载产生的水平压力。固结是由特殊荷载条件下产生的压缩或是土粒挤压在一起而发生的；这一性质也可以测量出。

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 m ay range from visual inspection to elaborate subsurface exploration by boring and la boratory testing．Collection of representative samples is essential for proper identifica tion and classification of soils．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 with horizontal distance．It is not good practice to collect composite samples f or any given horizon（layer），since this does not truly represent any one location and could prove misleading．Even slight variations 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 important steps．

基地勘探

土质调查是对将要承受工程冲击的天然及其扩展部分的土层数据的采集。花费在基地勘探上的工夫取决于工程的大小以及工程的重要性；勘探方法从肉眼观察到精细的地表下钻孔采集土样并做实验室测试。采集代表土样对于土层准确地鉴别和分类十分重要。采样数量取决于数据要求的精确度，土质的分类以及工程量的大小。通常情况下，在一个地方的天然剖面中，深度方向比水平方向有更多的土质分类参数。采集复合样品对于任何已知水平层来说都是不合适的，因为这样不能真实代表任何一处并且可能会误导。即使是水平层很细小的参数变动也要仔细表注出。土壤粒径的非类以及液限塑限的确定都是十分重要的步骤。

An understanding of the eventual use of the data obtained during site investiga tion is important．Advance information on site conditions is helpful in planning any s urvey program．Information on topography，geological features（outcrops，road and stream cuts，lake beds，weathered remnants，etc．），paleontological maps，aer ial photographs，well logs，and excavations can prove invaluable. Geophysical expl oration methods yield useful corroboratory dataMeasurement of the electrical resistivi ty of soils provides an insight into several soil characteristics．Seismic techniques oft en are used to determine the characteristics of various subsurface strata by measuri ng the velocity of propagation of explosively generated shock waves through the str ata．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 the bedrock and return to the surface as a reflecte d wave

对原位实验中获取的数据的最终用途的了解很重要。场地条件的进一步信息对于规划任何勘探项目都是很有帮助的。地形学，地理数据（地面露头，道路河流切面，湖底，气候残留物等），古生物图，航拍照片，井道日志，开挖情况等信息都是很有价值的。地理勘测方法修正出有用的数据。电阻测量可提供若干土质内部参数。地震技术通过测量穿过土层的爆炸冲

击波的波速来确定不同的地下土层参数。冲击波穿过不同土层的速度差别很大。通过测量冲击波从发出到触及基岩反射回来所需的时间可以确定基岩的深度。

Dependable subsurface information can only be obtained by excavation．A probe rod pushed into the ground indicates the penetration resistance．Water jets or auger s are used to bring subsurface materials to the surface for examination．Colour cha nge is one of the significant elements such an examination can reveal．Various drilli ng methods are employed to obtain chips from depth．Trenches or pits provide mor e complete information for shallow depths．Pneumatic or diamond drilling may be re quired if hard rock is encountered．At least a few of the boreholes should exceed t he depth of significant stress that is established for the structure．

所需要的表层信息只能通过开掘来获得。探针插入土中以显示穿透阻力。水枪或是麻花钻机用来将地表下的材料带到地表以上以获取土层信息。土的颜色的改变是此类实验可以显示的一个重要元素。多种钻探方法用于从地下获取土条。地堑或是坑可以提供浅层土质更完整的信息。如果遇到坚硬的岩石可以使用气钻或是钻石钻。至少要有一部分钻孔的深度要超过建筑结构的压力深度设计值。

Avoidance of structural disturbance of the samples is not critical for some tests b ut is very important for in－place density or shearing strength measurements．

避免取样对结构扰动的影响对一些实验不是很严格但是对原位密度以及剪切强度的测量影响很大。

Complete and accurate records，such as borehole logs，must be prepared and mai ntained，and the samples themselves must be retained for future inspection

完整和精确的记录，例如钻孔记录必须准备好保管好，并且样品自身也必须保管好供将来校对时用。