Engineering Geology

What is Engineering Geology?

Engineering geology is the application of

geological data, techniques and principles to
the study of rock and soil, and ground water
for the proper location, planning, design,
construction, operation and maintenance of
engineering structures.
The Association of Engineering Geologists (2000):

“Engineering Geology is defined by the Association of

Engineering Geologists as the discipline of applying
geologic data, techniques, and principles to the study
both of
a)naturally occurring rock and soil materials, and surface and sub-
surface fluids and
b) the interaction of introduced materials and processes with the
geologic environment, so that geologic factors affecting the
planning, design, construction, operation and maintenance of
engineering structures (fixed works) and the development,
protection and remediation of ground-water resources are
adequately recognised, interpreted and presented for use in
engineering and related practice.”
 How did the subject begin?

Development of
Engineering Geology

Many Failures of Engg projects

Failures NOT due faulty Engg design, but
Problems of the ground on which they were built
 Failure of Engineering Structures
• Tunnel Failure : 1923-27, Moffat Tunnel, USA;
Water tunnel, Sydney
• Dam Failure : 1928, St. Francis Dam, California
• Material failure : aggregate – cement
reactions
• Leaning Tower of Pisa
Reasons: GEOLOGICAL, NOT FAULTY
ENGINEERING PRACTICE/DESIGN
 The tower began to sink after
construction had progressed to the
second floor in 1178. This was due to a
mere three-metre foundation, set in
weak, unstable subsoil, a design that
was flawed from the beginning.

Construction was subsequently

halted for almost a century. This
allowed time for the underlying soil
to settle. Otherwise, the tower
would almost certainly have
toppled.

Leaning Tower of Pisa

Aerial view of the leaking St. Francis Dam before the break in 1928
 The Engineering Geology came
into existence.

Engineering community realized

the importance of Geology factor
in civil engineering.

After failure

Before failure
Main reasons for dam failure: NOT ENGINEERING BUT GEOLOGICAL
1, Sedimentary rocks on the west lost strength when it is wet;
2, The fault separating the west and east rock formations started to leak water;
3, Schist on the east increases pore pressure and lost shear strength after wet.
Engineering geology represents a vital link between

Engineering and Geology

Engineering geology provides a means to appreciate and
identify geologic features that could have short and long
term consequences to the overall performance of
engineering structures and projects.

It is also a study of how we are affected by geological

phenomena, and how we can affect the environment and
trigger geologic processes.
 What is the subject matter of
Engineering Geology?

Rock, soil, water, the interaction among

these three constituents, as well as with
engineering materials and structures.
• Strength, mechanical properties of Rock, Soil,
Geological structures
Why Engineering Geology matter?
Serve civil engineering to provide information in 3
most important areas:
–Resources for construction :
• Aggregates, fills and excavations.
–Finding stable foundations:
•Present is the key to the past –geology
•Past is the key to the future -engineering
–Mitigation of geological hazards
•Identify problems, evaluate the costs, provide
information to mitigate the problem
 General Outline of Engineering Geology
Rock description and identification
Engineering properties of rocks (e.g., foundation), material for construction
(e.g., aggregates);
Rock weathering and soil development;
Map reading, both topographic and geologic;
Structure aspects –bedding, joints, and faults;
Mass movement and landslides;
Running water-erosion, flood effects, water impoundment;
Groundwater control during construction, water supply, pollution,
subsidence, slope instability;
Shoreline erosion and protection;
Earthquakes and earthquake engineering;
Glacial deposits;
Arid environments;
Subsurface geology, condition of stress at depth (for excavation, tunneling
etc.)
 Related subjects of Eng Geology
There is a continuous transition between geology and
engineering science and that most of us, as applied
earth scientists, operate in this transition.  There are
several related professional disciplines:
• Engineering Geology: the application of geology to
obtain information and understanding of geological
structures, materials and processes, as needed for
engineering analysis and design.
• Geological Engineering: the application of a
combination of geology and engineering science to
design, involving rock, soil, groundwater and mineral
resources.
Geotechnical Engineering: the application of the
science of soil mechanics, rock mechanics, engineering
geology and other related disciplines to engineering
and environmental projects.

Geo-environmental engineering: the application of a

combination of geology and engineering science to the
solution of environmental problems.

Environmental geology: the application of geology to

obtain information and understanding of geological
structures, materials and processes, as needed for the
solution of environmental problems.
 Engg Geol vs Geology
• Differs mainly in scope
• Geology = involves large area (basin scale, craton
scale, continental scale etc), information too general
for engg purpose (location of faults, joints, contact, soil
cover), depth of concern- deep, crust, mantle, core,
classification mostly aimed at origin, and many cases
complex for engg purpose
• Engg Geology = small area (concerned with site),
surface and sub-surface information too specific (joint
sets, orientation, soil cover, weathering, contacts,
subsurface lithological information (cavities etc.), thin
top layer of crust is of concern, classification should be
simple and practical
Work/Role of Engineering Geologist
The exact responsibilities varies from country to country
depending upon national and local practice.

Thus many “engineering geologists” are essentially geologists

who deliver basic geological data to engineers, without
interpretation.

At the other end of the scale some engineering geologists

might design foundations and slope stabilisation, thereby
spending much of their time as geotechnical engineers.

Much clearly depends on the training and experience of the

geologist involved, and the attitudes of the organisation in
which he or she is employed.
 Role of an Engg Geol.
• Terrain Evaluation – for site selection,
geomorphic condition, soil cover, slope
condition, drainage network
• Study Earth Processes – Dynamics & Kinetics
(Forces and Movements), neotectonics, active
tectonics, active faults, seismicity
• Geological Hazard Ass – EIA, mitigation
measures, floods, landslides etc.
William Smith (1769-1839), a British Engg is considered to be the first Enng Geol
In india – Application of Engg Geol dates back to 1859 – advice was sought from GSI –
In Railway track alignment between Kolkata and Patna through Raniganj Coal field
 Premises of Eng Geology
Behind every discipline there must be a
basic philosophy or a way in which that
discipline approaches its problems.
The philosophy of engineering geology is
based on three simple premises.
These premises are:

1.All engineering works are built in or on the

ground.

2. The ground will always, in some manner, react

to the construction of the engineering work.

3. The reaction of the ground (its “engineering

behaviour”) to the particular engineering
work must be accommodated by that work.
 Organisation, Design and Site Investigations
For a site investigation to be successful it must be well planned and
undertaken in an orderly manner, using appropriate and well
maintained field and laboratory equipment, operated by experienced
and skilled personnel.

Expertise in the mechanics of investigation (boring, testing etc.) is a

routine requirement in all investigations.

The most difficult problem is how and where, and when, to use the
various ‘tools’ available to the site investigator.

A paradigm of site investigation has built up over recent years which

proposes the idea of the developing investigation advancing in stages to
a satisfactory conclusion, each stage being built on a sound foundation
of knowledge established by the previous stage.
 Stages of Investigation
The stages do not need to be separate; they may merge into each other
and additional stages may be inserted.

1.Project Conception Stage

2.Preliminary Stage
3.Feasibility Stage
4.Construction Stage
5.Post-Construction Stage
Project Conception Stage
After the decision to initiate a project has been taken, a desk
study is undertaken of all available geotechnical, geological
and topographical data. The proposed site and its environs
should be examined by an experienced engineering geologist.

The objective of this stage is to try to identify potential

problems that may arise from site geotechnical conditions in
relation to the proposed engineering work.
Preliminary/reconnaissance Stage investigation

Basic knowledge of the site

Broad framework of geological setting

This would be undertaken using relatively simple and

inexpensive techniques, such as existing records
(maps, photographs, etc.), geological and engineering
geological mapping, geophysics and perhaps some
boreholes.

Use remote sensing data, toposheets, any other

record
 Feasibility Stage investigation
Field investigations on site and Lab tests
Subsurface information – geophysical surveys
Foundation Stability
Availability of construction material

COST BENEFIT RISK

Consequence of failure ----- Damage Control

Probability of Failure ------ Preventive Measures

Construction Investigation Stage
One of the unfortunate facts of site investigation is that
the observation and conclusions made in the investigation
reports resulting from the main investigation are seldom
absolutely and totally correct.

The construction of the project quite often reveals

discrepancies between the ground conditions forecast
and the ground conditions encountered.

Readjustment, modifications -- required

(Rate of siltation- increase height of Dam, change of
alignment of tunnel etc)

Perfect coordination between Engg and Geol - essential

Post-Construction Investigation Stage
Certain features or behaviour, such as settlement, may take many years to become
complete after construction of the project.

If observed behaviour is not the same as anticipated behaviour this may indicate that
the properties of the ground are affected by some unforeseen and previously
undetected factor. Further investigations may be required to resolve this anomaly.

Monitoring of behaviour of the engineering project and comparison with predicted

performance is of vital importance for all engineering.
It must be remembered, that major engineering disasters mostly take place some time
after completion of the work.

Anomalies of project behaviour must be observed,

their cause established and remedial measures
undertaken before severe damage or perhaps failure
can occur.
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