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LECTURE NOTESON
GEOTECHNICAL ENGINEERING
Prepared by:
Anipineni naga
jyothi
Department of Civil Engineering
1
, GEOTECHNICAL ENGINEERING
UNIT-I INTRODUCTION AND INDEX PROPERTIES OF
SOILS:
Soil formation, clay mineralogy and soil structure, moisture content, weight-volume
relationships, relative density. Grain size analysis, sieve analysis, principle of hydrometer
method, consistency limits and indices, I.S. classification of soils
UNIT-II PERMEABILITY, EFFECTIVE STRESS AND SEEPAGE THROUGH SOILS :
Capillary rise, flow of water through soils, Darcy’s Law, permeability, factors affecting
permeability, laboratory & field tests for determination of coefficient of permeability,
permeability of layered soils; Total, neutral and effective stress, upward and downward
seepage through soils, quick sand condition, flow nets: characteristics and uses.
UNIT-III STRESS DISTRIBUTION IN SOILS AND
COMPACTION:
Boussinesq’s and Westergard’s theories for point load, uniformly loaded circular and
rectangular areas, pressure bulb, variation of vertical stress under point load along vertical
and horizontal plane, Newmark’s influence chart for irregular areas.
Mechanism of compaction, factors affecting compaction, effects of compaction on soil properties,
field compaction equipment and compaction quality control.
UNIT-IV
CONSOLIDATION :
Types of compressibility, immediate settlement, primary consolidation and secondary
consolidation, stress history of clay, e-p and e-log p curves, normally consolidated soil , over
and under consolidated soil, pre-consolidation pressure and its determination, Terzaghi’s 1-
D consolidation theory, coefficient of consolidation square root time and logarithm of time
fitting methods, computation of total settlement and time rate of settlement.
UNIT-V SHEAR STRENGTH OF
SOILS:
Importance of shear strength, Mohr and coulomb failure theories, types of laboratory tests
for strength parameters, strength tests based on drainage conditions, strength envelops,
shear strength of sands, dilatancy, critical void ratio, liquefaction, shear strength of clays.
2
, UNIT-I
INTRODUCTION AND INDEX PROPERTIES OF SOILS
Introduction to Soil Mechanics:
The term "soil" can have different meanings, depending upon the field in which it is
considered.
To a geologist, it is the material in the relative thin zone of the Earth's surface within
which roots occur, and which are formed as the products of past surface processes. The
rest of the crust is grouped under the term "rock". To a pedologist, it is the substance
existing on the surface, which supports plant life.
To an engineer, it is a material that can be:
• Built on: foundations of buildings, bridges.
• Built in: basements, culverts, tunnels.
•
Built with: embankments, roads, dams.
•
Supported: retaining walls.
Soil Mechanics is a discipline of Civil Engineering involving the study of soil, its
behaviour and application as an engineering material. Soil Mechanics is the application
of laws of mechanics and hydraulics to engineering problems dealing with sediments and
other unconsolidated accumulations of solid particles, which are produced by the
mechanical and chemical disintegration of rocks, regardless of whether or not they
contain an admixture of organic constituents.
Soil consists of a multiphase aggregation of solid particles, water, and air. This
fundamental composition gives rise to unique engineering properties, and the description
of its mechanical behavior requires some of the most classic principles of engineering
mechanics.
Engineers are concerned with soil's mechanical properties: permeability, stiffness, and
strength. These depend primarily on the nature of the soil grains, the current stress, the
water content and unit weight.
3
, Formation of Soils
In the Earth's surface, rocks extend upto as much as 20 km depth. The major rock types
are categorized as igneous, sedimentary, and metamorphic.
• Igneous rocks: formed from crystalline bodies of cooled magma.
• Sedimentary rocks: formed from layers of cemented sediments.
• Metamorphic rocks: formed by the alteration of existing rocks due to heat from
igneous intrusions or pressure due to crustal movement.
Soils are formed from materials that have resulted from the disintegration of rocks by
various processes of physical and chemical weathering. The nature and structure of a
given soil depends on the processes and conditions that formed it:
• Breakdown of parent rock: weathering, decomposition, erosion.
• Transportation to site of final deposition: gravity, flowing water, ice, wind.
•
Environment of final deposition: flood plain, river terrace, glacial moraine,
lacustrine or marine.
• Subsequent conditions of loading and drainage: little or no surcharge, heavy
surcharge due to ice or overlying deposits, change from saline to freshwater,
leaching, contamination.
All soils originate, directly or indirectly, from different rock types.
Soil Types
Soils as they are found in different regions can be classified into two broad categories:
(1) Residualsoils
(2) Transported soils
Residual Soils
Residual soils are found at the same location where they have been formed. Generally,
the depth of residual soils varies from 5 to 20 m.
Transported Soils
Weathered rock materials can be moved from their original site to new locations by one
or more of the transportation agencies to form transported soils. Transported soils are
classified based on the mode of transportation and the final deposition environment.
(a) Soils that are carried and deposited by rivers are called alluvial deposits.
4
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