《地基与基础毕业论文外文翻译.docx》由会员分享，可在线阅读，更多相关《地基与基础毕业论文外文翻译.docx（5页珍藏版）》请在taowenge.com淘文阁网|工程机械CAD图纸|机械工程制图|CAD装配图下载|SolidWorks_CaTia_CAD_UG_PROE_设计图分享下载上搜索。
1、Subsoils and Foundations Loadings in buildings consist of the combined dead and imposed loads which exert a downward pressure upon the soil on which the structure is founded and this in turn promotes a reactive force in the form of an upward pressure from the soil. The structure is in effect sandwic
2、hed between these opposite pressure and the design of the building must be able to resist the resultant stresses set up within the structural members and the general building fabric. The supporting subsoil must be able to develop sufficient reactive force to give stability to the structure to preven
3、t failure due to unequal settlement and to prevent failure of the subsoil due to shear. To enable a designer to select, design and detail a suitable foundation he must have adequate data regarding the nature of soil on which the structure will be founded and this is normally obtained from a planned
4、soil investigation programme . Soil investigation. Soil investigation is specific in its requirements whereas site investigation is all embracing, taking into account such factors as topography, location of existing services, means of access and any local restrictions. Soil investigation is a means
5、of obtaining data regarding the properties and characteristics of subsoils by providing samples for testing or capital which can be reasonably expended on any soil investigation programme will depend upon the type of structure proposed and how much previous knowledge the designer has of a particular
6、 region or site.The main methods of soil investigation can be enumerated as follows:1. Trail pits small contracts where foundation depths are not likely to exceed 3m.2. Boreholes medium to large contracts with foundations up to 30m deep.Classification of soils. Soils may be classified by any of the
7、following methods:1. Physical properties; 2.Geological origin; 3.Chemical composition; 4.Particle size.It has been established that the physical properties of soils can be closely associated with their particle size both of which are of importance to the foundation engineer, architect or designer. A
8、ll soils can be defined as being coarse-grained or fine-grained each resulting in different properties.Coarse-grained soils: these would include sands and gravels having a low proportion of voids, negligible cohesion when dry, high permeability and slight compressibility, which takes place almost im
9、mediately upon the application of load.Fine-grained soils: these include the cohesive silts and clays having a high proportion of voids, high cohesion, very low permeability and high compressibility which takes place slowly over a long period of time.There are of course soils which can be classified
10、 in between the two extremes described above. BS 1377 deals with methods of testing soils and divides particle sizes as follows:Clay particles less than 0.002mmSilts particles between 0.002 and 0.06mmSand particles between 0.06 and 2mmGravel particles between 2 and 60mmCobbles between 60 and 200mmTh
11、e silt, sand and gravel particles are also further subdivided into fine, medium and coarse with particle sizes lying between the extremes quoted above.Shear strength of soils. The resistance which can be offered by a soil to the sliding of one portion over another or its shear strength is of importa
12、nce to the designer since it can be used to calculate the bearing capacity of a soil and the pressure it can exert on such members as timbering in excavations. Resistance to shear in a soil under load depends mainly upon its particle composition. If a soil is granular in form, the frictional resista
13、nce between the particles increases with the load applied and consequently its shear strength also increase wish the magnitude of the applied load. Conversely clay particles being small develop no frictional resistance and therefore its shear strength will remain constant whatever the magnitude of t
14、he applied load. Intermediate soils such as sandy clays normally give only a slight increase in shear strength as the load is applied.Compressibility. Another important property of soils which must be ascertained before a final choice of foundation type and design can be made is compressibility, and
15、 two factors must be taken into account:1. Rate at which compression takes place.2. Total amount of compression when full load is applied.When dealing with non-cohesive soils such as sands and gravels the rate of compression will keep pace with the construction of the building and therefore when the
16、 structure is complete there should be no further settlement if the soil remains in the same state. A soil is compressed when loaded by the expulsion of air and/or water from the voids and by the nature rearrangement of the particles. In cohesive soils the voids are very often completely saturated w
17、ith water which in itself is nearly incompressible and therefore compression of the soil can only take place by the water moving out of the voids thus allowing settlement of the particles. Expulsion of water from the voids within cohesive soils can occur but only at a very slow rate due mainly to th
18、e resistance offered by the plate-like particles of the soil through which it must flow. This gradual compressive movement of a soil is called consolidation. Uniform settlement will not normally cause undue damage to a structure but uneven settlement can cause progressive structural damage.Foundatio
19、n types. There are many ways in which foundations can be classified but one of the most common methods is by form resulting in four basic types thus:1. Strip foundations-light loadings particularly in domestic buildings. Heavier loadings can sometimes be founded on a reinforced concrete strip founda
20、tion.2. Raft foundations-light loadings, average loadings on soils with low bearing capacities and structures having a basement storey.3. Pad or isolated foundations-common method of providing the foundation for columns of framed structures and for the supporting members of portal frames.4. Pile fou
21、ndations-method for structures where the loads have to be transmitted to a point at some distance below the general ground level. 共 45 页 第 45 页 地基与基础建筑物的荷载由组合恒载和作用荷载组成，作用荷载给结构之下的土体施加一个向下的力，而土体反过来又产生一个向上的反作用力。结构实际上是夹在这些相反的作用力之间，因此建筑物的设计必须能抵抗由构件和整个建筑物结构所产生的组合应力。下卧层的地基土必须能产生一个足够大的作用力以防结构在不均匀沉降作用下失稳破坏和土
22、体被剪切破坏。要使一个设计者能够选择设计出一种合适的基础，他就必须有足够的关于拟建场地土层性质的资料。这些资料一般通过进行土层勘测得到。土层勘测。土层勘测的要求是明确的，而场地踏勘只是考虑一些因素如地形、已有建筑物的位置、进入的途径和一些地方限制。土层勘测是获取有关地基土性能和特点的资料的一种手段，资料的获得是通过提供土样做土工实验或者提供一个肉眼观察的途径。要求提供的实际资料及合理花费在岩土工程勘察项目上的资金取决于拟建结构的类型以及该设计者对一个特殊地区或场地预先掌握了多少资料。土层勘测的主要手段列举如下：1. 探坑基础埋深可能不超过3m的小合同。2. 钻孔基础埋深达30m的中到大型合同。
23、土的类别。土层可以根据以下方式进行分类：1. 物理性能；2.地质成因；3.化学成分；4.粒径大小。土壤的物理性能已经确认与其自身的粒径有着密切的联系，而且两者对于岩土工程师、建造师和设计师来说都很重要。所有的土都可以定义为粗粒土或细粒土，每种土的性质不同。粗粒土：包括砂和碎石，这类土孔隙比小，干燥时粘聚力可以忽略，渗透性强，压缩性小，荷载作用的瞬间压缩固结就完成了。细粒土：包括淤泥和粘性土。这类土孔隙比大，粘聚力大，渗透性差，压缩性高，压缩固结需要一个较长的时间才能完成。上述两个极端之间的土当然也可以进行分类，BS1377中提到了土壤试验室定名的方法，其粒径划分如下：粘土 小于0.002粉土
24、0.0020.06砂土 0.062碎石 260卵石 60200在上面引用的粉土、砂土和碎石的两个极限值之间的粒径还可以进一步细分为细、中、粗三个等级.土的抗剪强度。由土体提供的阻止一部分土从另一部分上滑动的抗力或者叫土的抗剪强度对设计者来说很重要，因为它可以用来计算他的承载力和基坑开挖时土体作用在支护材料上的摩擦力。载荷作用下土体抵抗剪切破坏的能力取决于它的颗粒组成。如果一种土是粗粒土，那么颗粒之间的摩擦力将会随着荷载的施加而增大，它的抗剪强度也会随着外加荷载的增大而增大。相反，粘土的粒径小，不产生，摩擦力，因此它的抗剪强度保持不变不管外加荷载多大。中间的土如砂粘土一般随着外荷载的施加抗剪强度
25、只稍微有所增大。土的压缩性。在选择一种合适的基础型式和设计方案之前，需要掌握的土体的另外一个重要性能是压缩性。这里需要考虑两个因素：1. 压缩完成的速率。2. 荷载全部施加后的最终沉降量。对于非粘性土如砂和碎石，压缩完成的速率与建筑物的施工保持一致，因此，结构施工完毕后如果土体状态保持不变，将不再产生附加沉降。当施加荷载时，随着孔隙中空气或水的出以及土颗粒的自然重组。土体被压缩。粘性土中孔隙通常被水填充而处于饱和状态，它自身几乎不可压缩。因此，土体的压缩是通过孔隙中水的排出完成的。粘性土中的孔隙水排出的速率很低，主要是因为粘性土的板状颗粒阻止了水的排出。土的这个逐渐压缩的过程叫做固结。均匀的沉降通常不会给结构带来破坏，但是不均匀沉降能导致结构产生巨大的破坏。基础类型。基础的分类有多种方法，但较普通的一种方法是根据形状进行分类，由此划分为四种基本型式：1. 条形基础用于荷载较小的建筑尤其是民用建筑，荷载较大时可以用钢筋混凝土条形基础。2. 筏片基础用于荷载小，低承载力土上的一般荷载和有一层地下室的建筑物。3. 独立基础通常用作框架结构的柱下基础和门式框架承重构件下的基础。4. 桩基础用于需要将荷载传递到地面下一定距离的某一点的结构。