地基分析与设计------外文翻译.docVIP

2-2 FOUNDATIONSUBSOILS We are concerned with placing the foundation on either soil or rock. This material may be under water as for certain bridge and marine structures, but more commonly we will place the foundation on soil or rock near the ground surface. Soil, being a mass of irregular-shaped particles of varying sizes, will consist of the particles (or solids), voids (pores or spaces) between particles, water in some of the voids, and air taking up the remaining void space. At temperatures below freezing the pore water may freeze, with resulting particle separation (volume increase).When the ice melts particles close up (volume decrease). If the ice is permanent, the ice-soil mixture is termed permafrost It is evident that the pore water is a variable state quantity that may be in the form of water vapor, water, or ice; the amount depends on climatic conditions, recency of rainfall, or soil location with respect to the GWT of Fig. 1-1. Soil is an aggregation of particles that may range very widely in size. It is the by-product of mechanical and chemical weathering of rock. Some of these particles are given specific names according to their sizes, such as gravel, sand, silt, clay, etc., and are more completely described in Sec. 2-7. Soil may be described as residual or transported. Residual soil is formed from weathering of parent rock at the present location. It usually contains angular rock fragments of varying sizes in the soil-rock interface zone. Transported soils are those formed from rock weathered at one location and transported by wind, water, ice, or gravity to the present site. The terms residual and transported must be taken in the proper context, for many current residual soils are formed (or are being formed) from transported soil deposits of earlier geological periods, which indurated into rocks. Later uplifts have exposed these rocks to a new onset of weathering. Exposed limestone, sandstone, and shale are typical o