There are, however, several other causes of settlement apart from consolidation（固结）due to load. These causes are incalculable（不可计算的）and must be carefully guarded against（预防）. They include frost（霜冻）action, chemical change in the soil, underground erosion（侵蚀）by flowing water, reduction of the ground water level, nearby construction of tunnels（隧道）or vibrating machinery（机械）such as vehicles.

但是，除了荷载引起的固结外，还有其他一些沉降的原因。这些原因是不可计算的，必须小心预防。它们包括霜冻作用、土壤中的化学变化、流水引起的地下侵蚀、地下水位的减少、附近隧道的施工或者振动的机械如车辆。
Static load can cause elastic (temporary) or plastic （permanent） settlement, consolidation settlement being permanent. However, when plastic flow（塑性流）is mentioned in English, it generally means the failure of a soil by overload in shear. Consolidation settlement occurs mainly in clays or silts.

静荷载会引起弹性（暂时的）或塑性（永久的）的沉降，其中固结沉降是永久的。但是，在英语中提到塑性流，它通常意味着超载引起土壤的剪切失效。固结沉降主要发生在粘土或淤泥中。
From dynamic load alone the commonest settlements are found in sands or gravels, caused by traffic or other vibration, pile driving（打桩）or other earth shocks（冲击）. A drop（降低） in the ground water level will often cause the soil to shrink and a rise may cause expansion（膨胀）of the soil. Ground water is lowered by the drainage（排水）which can be caused by any deep excavation（深开挖）. The shrinkage which can occur with drying（干燥）is well shown by the clay underlying Mexico City, a volcanic ash. After seven weeks drying this clay shrinks to 6.4 percent of its initial volume. It is an unusual clay with the very high voids ratio（孔隙比）of 93.6 / 6.4 = 14.6.
在砂或砾石中发现了仅由动荷载如交通或其他振动，打桩或其他土地冲击引起的最普通的沉降。地下水位的下降常常引起土壤的收缩，上升可能引起土壤的膨胀。由任何深开挖引起的排水可导致地下水位的降低。干燥引起的收缩可通过墨西哥城下的粘土即火山灰来很好地说明。在七个星期的干燥后，该粘土比它的初始体积收缩了6.4%。它是一种与众不同的粘土，具有很高的孔隙比，为93.6/6.4=14.6。
Underground erosion is the removal of solids（固体颗粒的流失）, usually fines（细颗粒）, from the soil by the flow of underground water. The solids can be removed as solids（固态） or in solution（溶解状态）, though only a few rocks are soluble enough（充分溶解）to be removed in this way. Rock salt（岩盐）is the commonest example of a soluble rock. Potassium salts（钾盐）also are soluble.

地下侵蚀是由于地下水的流动引起的固体颗粒通常是细颗粒从土壤中流失。固体颗粒能在固态或溶解状态时流失，尽管只有一些岩石能以这种形式充分溶解后流失。岩盐是可溶解的岩石中最普通的例子。钾盐也是可溶解的。
The permeability（渗透性）of a soil is important for calculations of underground flow（地下潜流）, for example of oil or water to a well, or of water into a trench（排水沟）dug for a foundation, or of water through an earth dam（土坝）. Of the loose soils which can be dug with spade（铲）, clays are the least permeable, silts slightly more（稍大）, sands yet more（更大）, and gravels even more. In other words, the permeability is in direct proportion to（与..成正比）the grain size of the soil.

土壤的渗透性对计算地下潜流是重要的，例如计算井中的石油或水，或计算为基础开挖的排水沟中的水，或计算通过土坝的水。在可用铲开挖的疏松土壤中，粘土的渗透能力是最小的，淤泥稍微大一些，砂更大一些，砾石甚至还要大。换句话说，渗透性与土壤的颗粒尺寸成正比。
When a well is being pumped（抽水）, the water flows towards（流向）it from every direction and the ground water surface (water table地下水位) around it sinks. As the distance from the well increases, the water table is lowered rather less, so that around the well it becomes shaped like a funnel（漏斗形）, though it is usually called a cone of depression（降落锥体）.

当井在抽水时，水从每个方向流向井中，在它周围的地下水表面（地下水位）便下沉。随着离开井的距离的增加，地下水位降低得相当少，以致井的周围变成漏斗形，但它通常称为降落锥体。


Unit 17 第十七单元
Tendering Procedure 招投标
Introduction
This document presents（介绍）a systematic approach for tendering and awarding of contracts（签订合同）for international construction projects. It is intended to assist the employer / engineer to receive sound competitive tenders（公开投标）in accordance with the tender（招标）documents so that they can be quickly and efficiently assessed. At the same time, an effort has been made to provide the opportunity and incentive（鼓励）to contractors to respond easily to invitations to tender for（投标）projects which they are qualified to implement. It is hoped that the adoption of this procedure will minimize tendering costs and ensure that all tenderers receive a fair and equal（公正与公平）opportunity to submit（提交）their offers（建议）on a reasonable and comparable（同等的）basis.