《专业英语》课件Unit_8.pptx
《《专业英语》课件Unit_8.pptx》由会员分享,可在线阅读,更多相关《《专业英语》课件Unit_8.pptx(12页珍藏版)》请在文库网上搜索。
1、Unit8SoilMechanicsTextSoils are aggregates of mineral particles,and together with air and/or water in the void spaces,they form three-phase systems.A large portion of the earths surface is covered by soils,and they are widely used as construction and foundation materials.Soil mechanics is the branch
2、 of engineering that deals with the engineering properties of soils and their behavior under stress.The primary mechanism of soil creation is the weathering of rock.All rock types(igneous rock,metamorphic rock and sedimentary rock)may be broken down into small particles to create soil.Weathering mec
3、hanisms are physical weathering,chemical weathering,and biological weathering.1 Human activities such as excavation,blasting,and waste disposal,may also create soil.Over geologic time,deeply buried soils may be altered by pressure and temperature to become metamorphic or sedimentary rock,and if melt
4、ed and solidified again,they would complete the geologic cycle by becoming igneous rock.Physical weathering includes temperature effects,freeze and thaw of water in cracks,rain,wind,impact and other mechanisms.Chemical weathering includes dissolution of matter composing a rock and precipitation in t
5、he form of another mineral.Clay minerals,for example can be formed by weathering of feldspar,which is the most common mineral present in igneous rock.TextA naturally occurring soil sample may have particles of various sizes.Over the years,various agencies have tried to develop the size limits of gra
6、vel,sand,silt,and clay.Some of these size limits are shown in Table 8.1.Referring to Table 8.1,it is important to note that some agencies classify clay as particles smaller than 0.005mm in size,and others classify it as particles smaller than 0.002mm in size.However,it needs to be realized that part
7、icles defined as clay on the basis of their size are not necessarily clay minerals.Clay particles possess,the tendency to develop plasticity when mixed with water;these are clay minerals.Kaolinite,illite,montmorillonite,vermiculite,and chlorite are examples of some clay minerals2.Table 8.1 Soilsepar
8、ate size limitsTextTextTextAn important function in the study of soil mechanics is to predict the stresses and strains imposed at a given point in a soil mass due to certain loading conditions.This is necessary to estimate settlement and to conduct stability analysis of earth and earth-retaining str
9、uctures,as well as to determine stress conditions on underground and earth-retaining structures.Estimation of the increase in stress at various points and associate displacement caused in a soil mass due to external loading using the theory of elasticity is an important component in the safe design
10、of the foundations of structures3.The ideal assumption of the theory of elasticity,namely that the medium is homogeneous,elastic,and isotropic,is not quite true for most natural soil profiles.It does,however,provide a close estimation for geotechnical engineers and,using proper safety factors,safe d
11、esigns can be developed.A knowledge of the increase of pore water pressure in soils due to various loading conditions without drainage is important in both theoretical and applied soil mechanics4.If a load is applied very slowly on a soil such that sufficient time is allowed for pore water to drain
12、out,there will be practically no increase of pore water pressure.However,when a soil is subjected to rapid loading and if the coefficient of permeability is small(e.g.,as in the case of clay),there will be insufficient time for drainage of pore water.This will lead to an increase of the excess hydro
13、static pressure.TextAny given mass of soil consists of solid particles of various sizes with interconnected void spaces5.The continuous void spaces in a soil permit water to flow from a point of high energy to a point of low energy.Permeability is defined as the property of a soil that allows the se
14、epage of fluids through its interconnected void spaces.When a soil layer is subjected to a compressive stress,such as during the construction of a structure,it will exhibit a certain amount of compression.This compression is achieved through a number of ways,including rearrangement of the soil solid
15、s or extrusion of the pore air and/or water.According to Terzaghi(1943),“a decrease of water content of a saturated soil without replacement of the water by air is called a process of consolidation.”When saturated clayey soilswhich have a low coefficient of permeabilityare subjected to a compressive
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- 专业英语 专业 英语 课件 Unit_8