UNIVERSITY OF THE CORDILLERAS
College of Engineering and Architecture
GEOTECH 1 — Geotechnical Engineering 1
Module 1 — Basic Geology and Soil Mechanics, Introductory Concepts
OBJECTIVES, CLOs & TLOs
CLO 1: The student shall be able to discuss natural or geological processes per nent to the origin of soil.
MT TLO 1: The student is able to discuss the geological processes governing the
origin of soil and the forma on of soil deposits.
OUTLINE
1. Short Recall
2. Geology and Geotechnical Engineering
2a. Geology and Geotechnical Engineering Defined
2b. Soil Mechanics Defined
2c. Importance of Geology in Geotechnical Engineering
3. Geological Processes
3a. Earth’s profile, Rock cycle, forma on of soil deposits
3b. Steno’s Principles
3c. Common Mineral Content of Soils
SHORT RECALL
1. Course Descrip on and coverage
1a. Course Descrip on
1b. Course Coverage
2. Course policies and guidelines
2a. Prerequisites — GeoE & Mech 3
2b. A endance and requirements — A endance is required but with
extensive leniency for absences; emails of explana on are to be sent for
every absence; 1 week for all requirements
GEOLOGY AND GEOTECHNICAL ENGINEERING
Geology is an encompassing branch of science that deals not only with
the physical processes related to the forma on of the solid earth. It must
be understood that knowledge and finding offered by geology are used as
base for a myriad of applica on not only in engineering but in other fields.
Limi ng this in rela on to the course however, geology answers ques ons
regarding the processes that govern the forma on of rocks, soil deposits,
mineral contents/distribu on and the like.
Geotechnical Engineering on the other hand is that branch of civil engineering that deals specifically with the use of geology, soil mechanics,
rock mechanics, hydraulics and other per nent sciences or bodies of
knowledge towards the design of engineering systems with focus on the
Soil mechanics is therefore a subset of geotechnical engineering that
deals with how soil works, in the case of our course, in rela on to its use
as a construc on material. Soil mechanics therefore deal with the intrinsic
and external stresses experienced by soil, its capacity to deal with these
stresses and there effects. For this to be achieved, per nent soil proper es
are also core points of interest of soil mechanics.
Take Figure M1-1. An oversimplified analysis in rela on to defining geotechnical engineering would be to say that the successful design of the
retaining structure is the proper applica on of geotechnical engineering.
It must be noted however that these “successful applica on of geotechni-
Figure M1-1: Retaining structure stress diagram, taken online strictly for educa onal purposes.
cal engineering” required understanding of the stresses induced by the soil
(soil mechanics), stresses induced by the water (hydrology/hydraulics), stresses induced by the surcharge (structural, soil), how these stresses will act on
the structures (mechanics), what form and magnitude of stresses this will
induce on the structure (structural analysis) and the successful structural design—i.e. dimensions, reinforcements, material strength etc—of the retaining
structure.
Soil mechanics may be defined therefore as that body of knowledge that
offers the necessary tools to answer engineering ques ons related to soil
while geotechnical engineering is the use of various bodies of knowledge for
successful design not only of geotechnical engineering systems but engineering systems as a whole as long as long as soils and rocks are involved.
Common sense would or should dictate that for a thorough understanding Figure M1-2: A sector of the earth, taken online strictly for educa onal purposes.
of soil, ques ons pertaining to the natural processes surrounding it must be answered. The sa sfac on of which would consequently to governing
and rela ng principles, situa ons and condi ons that may again prove useful for the purposes of civil engineering.
It must be understood that engineering design is a con nuously evolving process and that engineering design problems will always have uncertain es. Soil in par cular is a very complex material. It is therefore the responsibility of designers to successfully design system in spite of these
uncertain es. Keep in mind that stability, in more than a few aspects, and economy are the tenets of engineering design.
Following are discussion of basic geology principles.
GEOLOGICAL PROCESSES
You learned from your prior courses on basic geology that the
earth’s profile may be classified under composi on and Rheology
(Figure M1-2). For purposes of our course, most of those will no
longer be repeated.
A point of interest however for the purposes of civil engineering is
the theory of plate tectonics. The theory states that the Lithosphere
(Figure M1-2) is separated into plates (Figure M1-3) and these
plates are moving over the Asthenosphere. This is of par cular interest as the movements of these plates cause natural phenomena
that must be considered in design of engineering systems.
Earthquakes are of par cular interest. To explain simply, earthFigure M1-3: Tectonic plates, taken online strictly for educa onal purposes.
quakes resul ng ground shaking caused by waves caused by the Fault zones, plates slide past each other
sudden release in uncontainable energy cause by the movement of Spreading Zone, Plates slide away from each other
Subduc on zones, plates move towards each other
the tectonic plates along the fault lines. Earthquake Engineering.
At the moment, you have to understand that phenomena such as these are under your profession’s responsibility to design against.
UNIVERSITY OF THE CORDILLERAS
College of Engineering and Architecture
GEOTECH 1 — Geotechnical Engineering 1
Module 1 — Basic Geology and Soil Mechanics, Introductory Concepts
Soils are essen ally the result of the weathering – break down—of
rocks. Weathering may be physical and chemical. Physical weathering is any process that changes the size of the rock without change in
the original composi on of the original rock. The common processes
responsible for physical weathering include exfolia on, unloading,
erosion, freezing and thawing. Chemical weathering on the other
hand causes both changes in size and chemical composi on. Under
normal circumstances, the most common processes involved are hydra on, oxida on and carbona on. It must be understood that these
two processes o en happen simultaneously. For simplicity, refer to
Figure M1-5. We have no knowledge of the actual situa on on how
said forma on came to be but for purposes of the current discussion,
imaging said forma on to have been once solid. Imagine possible
situa ons according to its environment that may have caused it to
“deteriorate” to its current state. Try considering that from its once
“solid” state, where have the masses that have been weathered gone
to.
Soils may also be classified according to whether they remain or are
transported to other places. Soils that remain at the site of weathering are called residual soils. These soils retain many of the elements
that comprise the parent rock. Alluvial or fluvial soils are soils that
were transported by rivers and streams. The composi on of these
soils depends on the environment under which they were transported
and is o en different from the parent rock. Glacial soils are soils that
were transported and deposited by glaciers. Marine soils are soils
deposited in a marine environment.
Rocks, from which the weathering of come soils, are classified according to the process governing their forma on.
Igneous rocks are formed from magma emi ed from volcanoes
that has cooled and solidified
Sedimentary rocks are formed from sediments and animal and
plant materials that are deposited in water or on land on the earth’s
surface and then subjected to pressures and heat.
Metamorphic rocks are formed deep within the earth’s crust from
the transforma on of igneous, sedimentary, and even exis ng metamorphic rocks into denser rocks.
Among these three types of rocks, sedimentary rocks are of par cular interest as they cover most of the earth’s surface, around 75%,
with an average thickness of 0.8 km.
The forma on of sediments and rocks is a con nuous process usually referred to as the geologic cycle. One must understand that rocks
weathered into sediments can again be turned into rocks and the
process con nuous. In rela on to this, there are three geological
principles governing the geologic cycle established by Nicolas Steno
(1677) in 1669.
1. Principle of original horizontality, which states that sediments are deposited in layers parallel to the earth’s surface. Layers of sediment were
originally deposited horizontally under the ac on of gravity. Any rock layer
that are now folded and lted have since been altered by outside forces.
2. Principle of original con nuity states that the deposi ons are sheetlike
and are only terminated with exis ng solid surfaces. Deformi es occur
from subsequent forces in the earth.
3. The age of deposi on is directly related to the order of deposi on.
Refer to figure M1—6. According to the above principles, arrange the
events represented by le ers from earliest to most recent.
Figure M1-5: “weathered” rock forma on, taken online strictly for educa onal purposes.
Figure M1-6: Steno’s principle, taken online strictly for educa onal purposes.