地基分析與設(shè)計外文翻譯-其他專業(yè)-在線瀏覽
2025-03-24 08:36本頁面
【正文】 rm clay is monly used to describe any cohesive soil deposit with sufficient clay minerals present that drying produces shrinkage with the formation of cracks or fissures such that block slippage can occur. Where drying has produced shrinkage cracks in the deposit we have a fissured clay. This material can be troublesome for field sampling because the material may be very hard, and fissures make sample recovery difficult. In laboratory strength tests the fissures can define failure planes and produce fictitiously low strength predictions (alternatively, testing intact pieces produces too high a prediction) pared to in situ tests where size effects may either bridge or confine the discontinuity. A great potential for strength reduction exists during construction where opening an excavation reduces the overburden pressure so that expansion takes place along any fissures. Subsequent rainwater or even local humidity can enter the fissure so that interior as well as surface softening occurs. A clay without fissures is an intact clay and is usually normally consolidated or at least has not been overconsolidated from shrinkage stresses. Although these clays may expand from excavation of overburden, the subsequent access to free water is not so potentially disastrous as for fissured clay because the water effect is more nearly confined to the surface. Mode of Deposit Formation Soil deposits that have been transported, particularly via water, tend to be made up of small grain sizes and initially to be somewhat loose with large void ratios. They tend to be fairly uniform in position but may be stratified with alternating very fine material and thin sand seams, the sand being transported and deposited during highwater periods when stream velocity can support larger grain sizes. These deposits tend to stabilize and may bee very pact (dense) over geological periods from subsequent overburden pressure as well as cementing and aging processes. Soil deposits developed39。 however, for foundation work our principal interest is in the uniformity and quality of the deposit. Dense, uniform deposits are usually not troublesome. Deposits with an erratic position may be satisfactory for use, but soil properties may be very difficult to obtain. Boulders and lenses of widely varying characteristics may cause construction difficulties. The principal consideration for residual soil deposits is the amount of rainfall that has occurred. Large amounts of surface water tend to leach materials from the upper zones to greater depths. A resulting stratum of fine particles at some depth can affect the strength and settlement characteristics of the site Soil Water Soil water may be a geological phenomenon。 however, construction vibrations can initiate a cavein prior to plete drying. The sides of a vertical excavation in a cohesive soil may collapse from a bination of rainfall softening the clay together with excess water enteringsurface tension cracks to create hydrostatic water pressure. In any case, the shear strength of a cohesive soil can be markedly influenced by wate
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