Foundation Engineering
C.E. 155
(Lec 1)
GEOTECHNICAL PROPERTIES OF SOILS
1. Grain Size Distribution
• Coarse-grained soil distribution is determined by means of sieve
analysis.
• Fine-grained soil distribution is obtained by Hydrometer analysis.
Hydrometer Analysis
• is based on the principle of sedimentation of soil
particles in water.
GEOTECHNICAL PROPERTIES OF SOILS
2. Weight-Volume Relationship
• Soils are three-phase systems consisting of solid soil particles, water,
and air.
• Based on this separation, the volume relationships can then be defined
Void Ratio, e,
• is the ratio of the volume of voids to the volume of soil solids in a given soil mass..
GEOTECHNICAL PROPERTIES OF SOILS
2. Weight-Volume Relationship
• Soils are three-phase systems consisting of solid soil particles, water,
and air.
• Based on this separation, the volume relationships can then be defined
Porosity, n,
• is the ratio of the volume of voids to the volume of the soil specimen.
GEOTECHNICAL PROPERTIES OF SOILS
2. Weight-Volume Relationship
• Soils are three-phase systems consisting of solid soil particles, water, and
air.
• Based on this separation, the volume relationships can then be defined
Degree of Saturation, S,
• is the ratio of the volume of water in the void spaces to the volume of voids, generally
expressed as a percentage.
The weight relationships are moisture content, moist unit weight, dry
unit weight, and saturated unit weight, often defined as follows:
Note that, for saturated soils, the
degree of saturation is 100%.
GEOTECHNICAL PROPERTIES OF SOILS
2. Weight-Volume Relationship
• Soils are three-phase systems consisting of solid soil particles, water, and
air.
• Based on this separation, the volume relationships can then be defined
Degree of Saturation, S,
• is the ratio of the volume of water in the void spaces to the volume of voids, generally
expressed as a percentage.
The weight relationships are moisture content, moist unit weight, dry
unit weight, and saturated unit weight, often defined as follows:
Note that, for saturated soils, the
degree of saturation is 100%.
GEOTECHNICAL PROPERTIES OF SOILS
2. Weight-Volume Relationship
• Soils are three-phase systems consisting of solid soil particles, water, and
air.
• Based on this separation, the volume relationships can then be defined
Degree of Saturation, S,
• is the ratio of the volume of water in the void spaces to the volume of voids, generally
expressed as a percentage.
The weight relationships are moisture content, moist unit weight, dry
unit weight, and saturated unit weight, often defined as follows:
Note that, for saturated soils, the
degree of saturation is 100%.
When a soil mass is completely saturated
(i.e., all the void volume is occupied by
water), the moist unit weight of a soil
becomes the saturated unit weight.
GEOTECHNICAL PROPERTIES OF SOILS
2. Weight-Volume Relationship
• Soils are three-phase systems consisting of solid soil particles, water, and
air.
• Based on this separation, the volume relationships can then be defined
Degree of Saturation, S,
• is the ratio of the volume of water in the void spaces to the volume of voids, generally
expressed as a percentage.
The weight relationships are moisture content, moist unit weight, dry
unit weight, and saturated unit weight, often defined as follows:
Note that, for saturated soils, the
degree of saturation is 100%.
GEOTECHNICAL PROPERTIES OF SOILS
2. Weight-Volume Relationship
• Soils are three-phase systems consisting of solid soil particles, water, and
air.
• Based on this separation, the volume relationships can then be defined
Degree of Saturation, S,
• is the ratio of the volume of water in the void spaces to the volume of voids, generally
expressed as a percentage.
General relation of Moist Unit Weight:
Note that, for saturated soils, the
degree of saturation is 100%.
w = moisture content
GEOTECHNICAL PROPERTIES OF SOILS
2. Weight-Volume Relationship
• Soils are three-phase systems consisting of solid soil particles, water, and
air.
• Based on this separation, the volume relationships can then be defined
Degree of Saturation, S,
• is the ratio of the volume of water in the void spaces to the volume of voids, generally
expressed as a percentage.
General relation of Dry Unit Weight:
Note that, for saturated soils, the
degree of saturation is 100%.
e = void ratio
GEOTECHNICAL PROPERTIES OF SOILS
2. Weight-Volume Relationship
• Soils are three-phase systems consisting of solid soil particles, water, and
air.
• Based on this separation, the volume relationships can then be defined
Degree of Saturation, S,
• is the ratio of the volume of water in the void spaces to the volume of voids, generally
expressed as a percentage.
General relation of Saturated Unit Weight of soil
:
Note that, for saturated soils, the
degree of saturation is 100%.
e = void ratio
GEOTECHNICAL PROPERTIES OF SOILS
3. Relative Density
• In granular soils, the degree of compaction in the field can be measured
according to the relative density, defined as;
GEOTECHNICAL PROPERTIES OF SOILS
4. Atterberg Limits
 Clayey soil mixed with an excessive amount of water may flow like a semiliquid.
 If the soil is gradually dried, it will behave like a plastic, semisolid, or soli material,
depending on its moisture content.
 The moisture content, in percent, at which the soil changes from a liquid to a plastic
state is defined as the liquid limit (LL).
 The moisture content, in percent, at which the soil changes from a plastic to a
semisolid state is defined as the plastic limit (PL).
 The moisture content, in percent, at which the soil changes from a semisolid to a
solid state is defined as the shrinkage limit (SL),
 These limits are referred to as Atterberg limits.
GEOTECHNICAL PROPERTIES OF SOILS
5. Hydraulic Conductivity of Soils
 In soil mechanics and foundation engineering, you must know how much water is
flowing through a soil per unit time.
 Darcy (1856) proposed the following equation for calculating the velocity of flow of
water through a soil:
GEOTECHNICAL PROPERTIES OF SOILS
6. Steady State Seepage
 For most cases of seepage under hydraulic structures, the flow path changes
direction and is not uniform over the entire area.
 In such cases, one of the ways of determining the rate of seepage is by a graphical
construction referred to as the flow net.
 For a steady flow condition, the flow at any point A can be represented by the
equation;
GEOTECHNICAL PROPERTIES OF SOILS
6. Steady State Seepage
 For most cases of seepage under hydraulic structures, the flow path changes
direction and is not uniform over the entire area.
 In such cases, one of the ways of determining the rate of seepage is by a graphical
construction referred to as the flow net.
 For a steady flow condition, the flow at any point A can be represented by the
equation;
PROBLEMS
1. For a soil given; void ratio = 0.81, moisture content = 21%, and Gs=2.68. Calculate
the ff;
a) Porosity
b) Degree of saturation
c) Moist unit weight in kN/m3
d) Dry unit weight in kN/m3
2. For a given soil, the following are given, moist unit weight = 19.17 kN/m3, moisture
content = 14.7%, and Gs=2.68. Calculate the following;
a) Void ratio
b) Porosity
c) Degree of saturation
d) Dry unit weight
END