C HA NGC H U N I NS TI TU TE O F TEC HNO LO GY专业英语班级：勘查0942姓名：崔金龙学号：0 4指导老师：刘丽莎成绩：Foundation engineeringStructures or other constructed works are supported on the earth by foundations. The word“foundation”may mean the earth itself, something placed in or on the earth to provide support ,or a combination of the earth and the elements placed on it . The foundation for a multistory office building could be a combination of concrete footings and the soil or rock on which the footings are supported . The foundation for an earth-fill dam would be the natural soil or rock on which the dam is placed . Concrete footing or piles and pile caps are often referred to as foundations without includes the soil or rock of the earth form a foundation system ,the soil and rock provide the ultimate support of the system . Foundations that are installed may be either soil-bearing or rock-bearing . The reactions of the soil or rock to the imposed loads generally determined how well the foundation system functions . In designing the installed portions , the designer must determine the safe pressure which can be used on the soil or rock and the amount of total settlement and differential settlement which the structure can withstand . A building's foundation transmits loads from buildings and other structures to the earth.Geotechnical engineers design foundations based on the load characteristics of the structure and the properties of the soils and/or bedrock at the site. In general, geotechnical engineers: 1) Estimate the magnitude and location of the loads to be supported; 2) Develop an investigation plan to explore the subsurface; 3) Determine necessary soil parameters through field and lab testing (e.g., consolidation test, triaxial shear test, vane shear test, standard penetration test); 4) Design the foundation in the safest and most economical manner .The primary considerations for foundation support are bearing capacity, settlement, and ground movement beneath the foundations. Bearing capacity is the ability of the site soils to support the loads imposed by buildingsor structures. Settlement occurs under all foundations in all soil conditions, though lightly loaded structures or rock sites may experience negligible settlements. For heavier structures or softer sites, both overall settlement relative to unbuilt areas or neighboring buildings, and differential settlement under a single structure, can be concerns. Of particular concern is settlement which occurs over time, as immediate settlement can usually be compensated for during construction. Ground movement beneath a structure's foundations can occur due to shrinkage or swell of expansive soils due to climatic changes, frost expansion of soil, melting of permafrost, slope instability, or other causes. All these factors must be considered during design of foundations .Many building codes specify basic foundation design parameters for simple conditions, frequently varying by jurisdiction, but such design techniques are normally limited to certain types of construction and certain types of sites, and are frequently very conservative.In areas of shallow bedrock, most foundations may bear directly on bedrock; in other areas, the soil may provide sufficient strength for the support of structures. In areas of deeper bedrock with soft overlying soils, deep foundations are used to support structures directly on the bedrock; in areas where bedrock is not economically available, stiff "bearing layers" are used to support deep foundations instead . Shallow foundationShallow foundations, often called footings, are usually embedded about a meter or so into soil. One common type is the spread footing which consists of strips or pads of concrete (or other materials) which extend below the frost line and transfer the weight from walls and columns to the soil or bedrock.Another common type of shallow foundation is the slab-on-grade foundation where the weight of the building is transferred to the soil through a concrete slab placed at the surface. Slab-on-grade foundations can be reinforced mat slabs, which range from 25 cm to several meters thick, depending on the size of the building, or post-tensioned slabs, which are typically at least 20 cm for houses, and thicker for heavier structures . Deep foundationsA deep foundation is used to transfer a load from a structure through an upper weak layer of soil to a stronger deeper layer of soil. There are different types of deep footings including impact driven piles, drilled shafts, caissons, helical piles, and earth stabilized columns. The naming conventions for different types of footings vary between different engineers. Historically, piles were wood, later steel, reinforced concrete, and pre-tensioned concrete. FootingFootings or spread foundations are used to spread the loads from columns or walls to the underlying soil or rock . Normally , footing are constructed concrete . However , under some circumstances they may be constructed of plain concrete or masonary ,when each footing supports only one columns ,it is square . Footing supporting two columns are used to carry loads from two columns , with one column and one end of the footing placed against a building line or exterior wall . Footings supporting walls are continuous footings . The sizes of footings are determined by the allowable bearing pressure which can be imposed on the soil or rock of the earth . Most building codes and textbook on foundations contain tables listing allowable bearing pressure for various types of soil and rock ;however, these tables give only general classifications and descriptions of the soil or rock and must be used with caution. More specific information about the soil or rock is normally obtained bydrilling test boring , extracting soil or rock samples, performing laboratory tests on the samples , and making engineering analysis to determine suitable bearing pressure. In addition to bearingpressure ,consideration must be given to the amount of settlement which may occur and the capability of the structure to withstand such settlement.If settlement is a problem it may be necessary to use an alternate founation type rather than footings or to enlarge the footing and decrease the bearing pressure . Mat foundationsMat or raft foundation are large , think ,and usually heavily reinforced concrete mats which transfer loads from a number of columns and walls to the underlying soil or rock .Mats are also combined footing ,but are much large than a footing supporting two columns . They are continuous footing and are designed to transfer a relatively uniform pressure to the underlying soil or rock . Mats are rigid and will act as a bridge over discontinuities in the soil or rock on which they are founded ,Mats founded several meters bellow the ground surface ,when combined with external walls ,are termed floating foundations .The weight of the total weight of the soil excavated from the ground surface to the bottom of the mat be equal to approach the total weight of the structure . In thiscase ,little or no new load is applied to the underlying supporting soil ,and settlements of a structure may be minimal after construction .基础工程建筑物或者其它已建成的工程是由基础下面的地基土来支撑着的，所以“基础”这个词表示土本身或者在土内布置的物体作为支承体，或作为土和在它上面布置的构件的联合体。