【正文】 Foundations placed on expansive soil are often subjected to distressing movement unless special precautions are taken. Expansive soil are those which swell and contract excessively with varying amounts of moissture. Problems can be overe by installing foundations below the zone of significant change in moisture content and backfilling with nonexpansive materials, by altering the soil with an admixture such as lime or cement so that volumn changes do not occur, or by providing flexibility in the structure to acmodate movements. Underpinning of foundation is often necessary, and it may be either remedial or precautionary. Remedial underpinning is used to correct defects in existing froundations which may have settled excessively. If the structure is to be saved or returned to its original state, additional foundation support must be provided. Precautionary underpinning is used when new structure are to be installed adjacent to or beneath existing structures, as in the construction of city subways. Underpinning of foundation is a specialized construction technique. The work is generally performed in a confined space, such as the basement of a building, or in small pits excavated outside a building area. It is necessary to provide support for the loads of the existing structure while new foundations are installed. The new foundations may be footings which are placed deeper in the ground than the original foundations, or they may be piles or caissons. Underpinning of a wall footing may be performed by excavating pits adjacent to and beneath existing foundations. The pits are small, some wide by long. Horizontal sheeting is placed in the pits as excavation proceeds to prevent caving of the walls and undermining of the structure being underpinned. When the new bearing stratum is reached, forms are placed in the pit, and concrete is poured from the new bearing stratum up to within 76mm of the bottom of the old footing. After the new concrete has hardened, the 76mm space is packed by hand with a mixture of sand, cement, and a small amount of water. Called grout, themixture is packed very tightly into the space between the top of the new footing and the underside of the old footing. The pit underpinning process is repeated throughout the entire length of the wall footing. The resulting new foundation may be a continuous wall or intermittent piers. One indisputable face is this: whatever the shape of a building or structure and whatever the nature and number of its supports, the whole weight of the building must e down to, and be supported by the ground. It is therefore essential that, for any propose structure, sufficient knowledge be obtained of the nature of the supporting soil and its loadbearing capacity. The purpose of a foundation is to convey the weight of a building to the soil in such a manner: (1) That excessive settlement will not occur。 河北建筑工程學(xué)院 畢業(yè)設(shè)計（論文）外文資料翻譯 系 別 ： 土木工程 專業(yè)： 土木工程 班級： ********* 姓名： ********** 學(xué)號： ************** 外文出處： GEOLOGLCAL AND GEOTECHNICAL ENGINEERING 附 件： 外文原文 ； 外文資料翻譯譯文。 the soil and rock provide the ultimate support of the system. Foundation that are installed may be either soilbearing 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 pressue which can be used on the soil or rock and the amount of total settlement and differential settlement which the structure can withstand. The installed parts of the foundation system may be footings, mat foundations, slab foundations, and caissons or piles, all of which are used to transfer load from a supersteucture into the earth. These parts, which transmit load from the superstructure to the earth, are called the substructure. Footing Footing or spread foundations are used to spread the loads from columns or walls to the underlying soil or rock. Normally, footings are constructed of reinfored concrete. However, under some circumstances they may be constructed of plain concrete or masonary, w