Soil PropertiesDefinitionSoil in broad terms for foundation engineering is the ground supporting a structure. Soil is considered to be any loose sedimentary deposit, such as gravel, sand, silt, clay or a mixture of these materials. Granular soils (e.g. sand & gravel)
Cohesive soils (e.g. silts and clays)
Soil consists of a mass of solids particles separated by spaces or voids. The voids of a soil are usually a mixture of air and water (soil is partially saturated). In certain circumstances the voids may be completely filled with water or air only. If only air is present the soil is dry and if only water is present the soil saturated. The Figure1 shows a cross-section through a granular soil. (a)(b)
Figure 1 Cross-section through granular soil In order to study the properties we will adopt the idealised
form of the diagram shown in Figure 1. The soil mass has a total volume
V, containing a volume of solid particles Vs and a volume of voids Vv.
In most cases the void volume exists of a mixture of water (Vw) and air
(Va).
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Moisture content (m)
Degree of saturation (Sr) Air-void ratio Percentage air voids
Density () and unit weight ()
The more common way is to use the amount of mass instead of the amount of weight. Using the weight necessitates in a conversion as shown below:
Specific gravity (Gs)
The volume of voids, Vv, is obviously equal to V - Vs. For ease of calculating we will assume that all solids are compressed together and their volume considered equal to a unit volume as shown in Figure 1 and Figure 2. Porosity (n) Degree of saturation (Sr)
Percentage air voids Density () and unit weight ()
The weight is: Specific gravity (Gs) Unit weight of soil |