Permeability of Soils
Permeability: property of soil which permits water flow through it
through the voids.
Role of soil permeability:
Leakage (seepage) through and under dams
Stability of slopes etc.
Flow In Soil
When water flow through soils, it exerts forces called seepage
forces on individual soil grains.
Seepage forces affect the effective stress in soil mass.
When water level in the riser tube is at elevation B, -> water
level in sta
Capillarity arises due to surface tension
Surface tension results from differences in forces of attraction
between the molecules of materials at the interface.
U c hc w
U w z w g z w
Pressure at point 1 = Pressure a
Soil classification system enables one to use the engineering
experience of the others.
Facilitates communication/transfer of information among
groups of engineers.
The system is based on the particle size and the distributio
Clay Minerals and Soil Structure
Very fine grained soil; has plasticity, cohesive, water
E.g.: Kaolinite, Illite, etc.
Small particles very active electrochemically
Clay minerals evolved from chemical weathering
The Origin of Soils
Relative loose agglomeration of minerals and
inorganic materials found above the bedrock.
The particles are the results of disintegration of
3 Major rock types
1. Igneous rocks from cooling and hardening of
Determining the subsurface condition:
What materials are below the ground surface
The extent of the materials
Properties of the materials
Obtain existing informati
A Civil Engineering structure is almost always constructed to be in contact
with the ground. On a construction site, the ground supports the structure,
and thus the ground will be subjected to the loads from the structure.
The ability of the
Mechanical method to improve engineering properties of soil
Increase strength improve bearing capacity
Compaction equipment in the field:
Hand operated tampe
Lateral Earth Pressure
Soil is subjected to vertical pressure/stress either due to its own weight or due to
external loadings. Under the vertical pressure it exerts lateral pressures in its
attempt to reach equilibrium due to its granular natur
Stresses in Soils
In situ stress at a given point
1. In situ effective overburden vertical stress:
2. Porewater pressure: u
3. Increase of stress on element A due to constructed structural
load. e.g. embankments, foundations, ta
Soil mass as it exists in nature consists of:
Solid soil particles (soil grains)
For analysis, the soil mass is represented by the Phase Diagram
A diagram showing the three phases of soil sample with
Soil consistency describes the behavior and characteristics of
wetted fine grained soil with varying amount of water content.
The presence of water in voids affects the engineering behavior of
fine grained soil, they may change state as w
Grain Size Distribution
Soil consists solid grains of various sizes, the size and shape of the soil solids
influence the engineering characteristic of the soil. The distribution of grain size in
a soil can be seen below:
Well Graded: Gradation curv
Empty can mass Mass before dry
Mass pycnometer T(i)
M of p+water
Diameter of mold (in)
Height of mold
Volume of mold
Mass of Mold (g)
Mass of Mold and Sand
Mass of Sand
Dry Density Sand (m/v)
Mass cone and bucket
Mass sand and cone
Mass sand in cone
Compressibility of Soil
All materials deform when subjected to loads
A stress increase caused by construction of foundation (or
other loads) will result in compression of soil
14. Compressibility of Soil.doc