1、1.2.2 Water in a Soil Mass As regards water in the soil,we differ among gravitational water or ground water,capillary water,bound water and interlayer water of a mineral. 1.Gravitational water The gravitational water is mainly concentrated at contact point between grains that is in steady motion und
2、er the influence of gravitational forces.There is a regular water table for the water. Below the water table there exists a water-saturated zone and hydrostatic water within it,The gravitational water has a negative influence on foundation soil.This form of water exists in both coarse-grained soils
3、and finer soils,following Darcys law.It will be discussed in details in chapter 4. 2.Capillary water The capillary water,above the gravitational water table,is held by capillary force (surface tension force) that is governed by the surface tension of grains and the diameter of voids.The height, Hc,
4、to which water will rise in a capillary tube (void space) , is, theoretically,directly proportional to the surface tension force T, divided by the diameter of the tube d: So the height of the capillary zone (the occupied area of capillary water) will also be affected by the cleanness of the water； i
5、t could be much less for pollutes water. According to Terzaghi and Pech (1967) ,the Hc can be giver as: 10edcHc Where Hc maximum height of capillary size, in mm, relates to minimum pore size； e void ratio； d10 effective size, mm； c constant,1020 mm2 (for clean water) . Capillary rising depends on gr
6、ain size distribution. As always, the smaller the grain is, the higher the capillary rises, except for some of clay particles that is filled with bound water surrounding the grains. As a geotechnique engineer, you should be aware of a big difference between the capillary water and the gravitational
7、water: the water-saturated zone filled with the gravitational water has hydrostatic pressure, while pore water pressure produced by the capillary water should be negative. 3.Bound water In the fine-grained soils,the grain surface has an ionized layer around them, which is defined as bound water. Mor
8、e and more people have known that the cohesion force,which is against shearing stress, is to a large extent, resulted from the bound water. The plastic properties of clay soil such as swelling and shrinkage of clay, is mainly attached to the bound water. It is a very important factor considered in t
9、he design of a foundation. See Fig. 1-4. 4.Interlayer water The interlayer water is hidden in a mineral. For example, the mineral,montmorillonitic has a layer structure, its interlayer space,is typically filled with water,originally filled, or filled later. Depending on the abundance or deficiency o
10、f water occupy this space, a montmorillonitic soil may exhibit its marked properties of swelling and shrinkage.The montmorillonitic soil, as a loaded dTHcfoundation, is very unstable when water is present. 1.2.3 Gas in a Soil Mass As always, gas basically exists in a soil mass. We differ between ope
11、ned gas and closed gas. The opened gas is interconnected, and directly flows to atmosphere, while the closed gas retains.The former always takes place in the coarse-grained soil,which has little influence on the engineering properties of the soil. But the latter is so difficult to escape that there
12、is a high compressibility and a low permeability for the soils.Geotechnical engineers should know that the presence of gas in the soil void is of great importance in the design of a foundation. 1.2.4 The Structural Features of a Soil Mass 1.Different Layers of Soil For the sedimentary formations, no
13、 matter whether they are wind-deposited,water-deposited or glacial-deposited, it is natural that there are different layers of soil,fine-grained soil or coarse-grained soil.Fine-grained layers are often embedded in coarse-grained layers and vice versa. We can also say,from the soil mechanics point o
14、f view, high bearing capacity (or Low compressive) layers are often embedding in low bearing capacity and vice versa. These different layers of soil will cause the problems as follows: （ 1） Long-term settlement if there are weak layers (existed). （ 2） Differential settlement of buildings (superstruc
15、ture) due to the layers thickness change in horizontal direction. （ 3） Landslide along a thin and weak layer (such as clay or silt) when deep excavating for foundation. It is emphasized that the weak layers of soil will be carefully studied in the building site for a successful foundation design. 2.
16、Non-homogeneities (Homogeneousness) Absolutely, soils are non-homogeneities materials that are different in deformation and strength in all directions. The non-homogeneities characteristics of soil are caused by not only the variation of deposit conditions, but also the effect of stress history. Wit
17、h a very large variations in size and shape, most of which are sharp-edged belonging to the former, while deep-going fissures and cracks are the latter. In engineering investigation of a soil mass, we should pay attention to the local non-homogeneities such as lenses of highly compressible soils emb
18、edded in the formations that are of particular danger and often cause detrimental and big differential settlement of buildings. 1.3 Soil Configuration 1.3.1 Single-grained Structure The primary structure for a coarse-grained soil is typically single-grained one. The loose configuration shown in Fig.
19、 1-5 (a) typically takes place in an active water environment such as beach sand or river gravel. But the dense soils as shown in Fig. 1-5 (b) are typically originated in a quiet water environment. The soil with single-grained structure may serve as a natural foundation soil. 1.3.2 Honeycomb Structu
20、re For the very fine sand or silt soil, the grain arrangement looks like the honeycombs of a bee, in term of honeycomb configuration similar to that shown in Fig. 1-6. The soil with the honeycomb configuration has the properties of loose, low strength and high compressibility. 1.3.3 Fabric Structure
21、 Clay soil has its special structure, fabric configuration shown in Fig. 1-7. This concept of soil structure is arrived at through the current microscopy technique. Some clay grains may exists in randomly arranged picket or pads, which individually are made up of highly oriented particles. For this
22、configuration, you should be aware of high compressibility due to high voids in the design of a foundation. Macro structure of a soil mass, such as beds,disappeared layers, lenses and deep-going fissures, are very dangerous because they are the cause of high compressibility, low strength and differe
23、ntial settlement. 1.4 The Important Parameters for Two-phase and Three-phase Soils From the construction point of view,soils are also divided into in situ soils that are in place and undisturbed, and artificial soil by human beings such as embankment.Both in situ and disturbed soil usually have soli
24、d, water, and air, known as three-phase soils, which can be expressed in a schematic as shown in Fig. 1-8. All parameters are expressed in terms for a soil mass (three-phase soil). 1.4.1 Measurement of Voids Voids in soil are either expressed in terms of porosity or in terms of void ratio. Porosity
25、n is defined as the ratio of volume of voids,Vv, to total volume of soil V and expressed as a percentage, while void ratio e is defined as the ratio of volume of voids to volume of particle Vs, expressed as a decimal. They are differently expressed without any reason other than custom . 1.2.2 土中的水 关
26、于土中的水，我们可分为重力水或地下水，毛细水，结合水和矿物隔层水。 1. 重力水 重力水主要集中在介于颗粒间的接触点，在地心引力的影响下固定移动。这有一个规 律的地下水位。在地下水位的下面存在一个水饱和层和静力水在里面，重力水对地基土有消极影响。水的形态存在粗粒土和优质土中都符合达西定律。 这将是在第四章中详细讨论。 2. 毛细水 毛细水，在重力水位上面， 是由 颗粒 的表面张力和 孔隙率的直径管理 毛细管力 (表面张力力 )。高度 cH ，在毛细管（孔隙空间）中 水 将会 上升 ， 从理论上来讲 ， 与表面张力力 T成正比， 除以管的直径 d： 所以毛细管水层的高度（毛细水的占地面积）也将受到洁净水的影响；这更不用说是污水了。根据太沙基和 Pech（ 1967）， c H 由 dTHc
