ENGR. HILLARY MAE M.
TESTON
Soil is defined as “the uncemented aggregate of mineral
grains and decayed organic matter (solid particles), with
liquid and gas in the empty spaces between the solid
particles.” It functions as both a construction material and a
support medium for structures.
• Soil Mechanics: A scientific
discipline studying the • Geotechnical Engineering: A
physical properties of soil subdiscipline of civil
and its behavior under engineering applying soil and
various forces. rock mechanics to the design
of foundations, earth
• Soils Engineering: The structures, retaining walls,
practical application of soil and more.
mechanics to real-world
challenges.
• The use of soil in construction dates back to ancient times, but
scientific understanding began only in the early 18th century.
Prior to that, empirical experimentation—rather than
science—guided engineering.
Civilizations along key rivers (Nile,
Tigris-Euphrates, Huang Ho, Indus)
built dykes and structures as early
as 2000 B.C.—often without
foundation stabilization or erosion
control.
Greek engineers used pad footings,
strip foundations, and rafts.
Egyptian pyramid construction
(~2750 B.C.: Saqqarah, Meidum,
Dahshur, Cheops) raised complex
challenges in foundation design,
slope stability, and underground
structures.
• During China’s Eastern Han dynasty (~68 A.D.), pagodas
were built on soft clay and silt layers; foundation pressures
often exceeded soil bearing capacity, resulting in structural
damage.
A famous pre-18th-century
example of geotechnical
failure: the Leaning Tower of
Pisa. Built beginning in 1173
A.D., its tilt resulted from
weak clay approximately 11 m
deep. It tilted over time (max
~5 m off-plumb for a 54 m
structure), and in the 1990s
was stabilized by carefully
removing ~70 metric tons of
soil.
• These historical examples underscore that geotechnical
engineering began as trial and error—“the art of geotechnical
engineering” evolved before the science developed.
• They also highlight why modern engineers must understand
soil behavior—even the best design can fail without this
foundation
• Pre-Classical Period (1700–1776 A.D.)
Gautier (repose & unit weight), Bélidor (earth pressure, soil classification),
Gadroy (slip planes)
• Classical Soil Mechanics – Phase I (1776–1856 A.D.)
Coulomb (shear strength & earth pressure), Poncelet, Français, Navier,
Collin, Rankine
• Classical Soil Mechanics – Phase II (1856–1910 A.D.)
Darcy (permeability), Boussinesq (stress distribution), Reynolds (dilatancy),
Darwin (earth retention)
• Modern Soil Mechanics (1910–1927 A.D.)
This era represents the birth of modern geotechnical theory:
❖ Albert Atterberg: Defined consistency limits (liquid, plastic, shrinkage)
for cohesive soils and established clay-size fractions—fundamental for
soil classification.
❖ Arthur Bell (c. 1915): Developed models for lateral pressure and
resistance in clays, formulated bearing capacity theories, and introduced
the shear box test using undisturbed specimens.
❖ Wolmar Fellenius: Introduced the method of analyzing saturated clay
slope stability using circular slip surfaces.
Karl von Terzaghi: Often
called the “Father of Soil
Mechanics,” he formulated:
❖ The theory of consolidation for
clays
❖ Principles of effective stress
❖ Foundational work in shear
strength, bearing capacity,
settlement, and earth
pressure—all culminating in his
seminal work Erdbaumechanik
(~1925)
I. Geologic Features for Geotechnical Engineering
A. Plate Tectonics
B. Earthquake
C. Rock Cycle
II. Types of Rock and Properties
III. Types of Soil and Properties
Soils originate from the
weathering of rocks—
physical breakdown and
chemical alteration—
forming the mineral grains
that make up soil. The
nature and properties of the
soil largely depend on the
parent rock's mineralogy.
Residual soils – remain at the site of weathering. These soils retain many of
the elements that comprise the parent rock.
Alluvial soils – (fluvial soils) are soils that were transported by rivers and
streams. The composition of these soils depends on the environment under
which they were transported and is often different from the parent rock.
Glacial soils – soils transported and deposited by glaciers
Marine soils – soils deposited in a marine environment
The Unified Soil Classification System (USCS) is commonly used to classify soils
based on particle size and distribution
Gravels, Sands, Silts, and Clay – common descriptive terms used to
identify specific textures in soils.
❖ Coarse-grained soils – feels gritty and hard. Sands and Gravels are
grouped together as coarse-grained soils. The coarseness of coarse-
grained soils is determined from knowing the distribution of particle
size.
❖ Fine-grained soils – feels smooth. Clays and silts are fine-grained
soils. To characterize fine-grained soils, further information is needed
on the types of minerals present and their contents.
For a fine-grained soil the ratio of its surface area to its volume is larger
as compared to coarse-grained soil. Because of their large surfaces,
surface forces significantly influence its behavior.
Adsorbed water – thin film or layer of water which is bonded to the
mineral surfaces which greatly influences the way soil behaves.
Soil fabrics are mineral particles arranged into structural frameworks
during deposition. Soil fabric is the brain; it retains the memory of the
birth of the soil and subsequent changes that occur.
Flocculated structure – results when particles tend to orient parallel or
perpendicular to each other.
Dispersed structure – results when majority of the particles orient
parallel to each other.
Flocculated structure –
Flocculated structure – saltwater freshwater environment
environment
Dispersed structure
Coarse-Grained Soils Fine-Grained Soils
• good load-bearing capacities • poor load-bearing capacities
• Good drainage qualities • Practically impermeable
• Strength and volume change • Change volume and strength with
characteristics are not significantly variations in moisture conditions
affected by change in moisture • Frost susceptible
content • Engineering properties are
• Incompressible when dense controlled by mineralogical factors
• Volume change occur when loose • Thin layer of fine grained soils
• Engineering properties are even with thick deposits of coarse
controlled by the grain size of the grain soils have been responsible
particles and their structural for many geotechnical features.
arrangement.
