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Introduction:
Geotechnical Site Investigation (CE 829)
What is geotechnical site investigation?
Instructor: Tariq M. Bajwa , PhD
NUST, Pakistan
Office # 112 (NIT Building)
Email: tariq.bajwa@nice.nust.edu.pk Ground investigation
Site investigation
Same or different
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Introduction: Introduction:
Planning and CD o Planning – Flow chart
How do we do site investigations?
Desk study & WOS
How do we plan GSI?
Key steps involved in GSI Geotechnical Hazards & RM
Main investigations
Report
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Desk study and walk over survey: Introduction:
Desk study : Why do we do desk study?
Why do we asses GH? Groundwater
• Desk studies are a well known but often under-used method of gathering and assessing existing
information about a site that is to be used for some form of construction works. Slope instability
Probable ground condition (topography, soil and rock types, Subsidence
ground water, contaminated soil)
Compressible soils
Previous uses of the site (made up of ground and contaminated
ground
Principle objectives Swelling soils
Environmental and ecological considerations GH identification
Weak soils
wetland area – endangered species of
flora and fauna
Examples Weathering of soil and rock
archaeological interest
Freezing soils
o a subsequent walk-over survey to identify likely geotechnical Dispersive soils
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hazards to the proposed structure and conceptual design.
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Geotechnical hazards : Introduction:
o Hazards associated with the ground:
Atterberg limits
Why do we do site investigations?
Shear strength
The combination of clay soil with tress - swelling
Consolidation
The combination of clay soil with sloping ground
– unstable ground Hydraulic conductivity
Dilatancy
Examples The combination of chalk and a cover of sand and Parameters determination
clay – dissolution features (referred as sink holes) Swelling
A quarry indicative of existence of the made ground Surface area
– contaminated ground
Particle size distribution
The combination of loose granular soils and a
seismically active area – liquefaction from Stiffness
earthquake Tariq M. Bajwa, PhD 18/09/2019 / Dr. Tariq Bajwa 8
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Introduction: Introduction:
How do we assess parameters? Dewatering
Why geotechnical site investigations?
Direct shear test Vertical sand drains
Compaction
Triaxial compression test Blasting
Laboratory tests
Soil stabilization techniques Vibro- flotation
Unconfined compression test Chemical additives
Grouting
Field tests?
Vane shear test Geosynthetic
Geophysical test? Sand columns
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Introduction: Introduction:
Why geotechnical site investigations? Why geotechnical site investigations - Example?
Examples:
Dewatering – permeability, Dynamic compaction – % fine content, Grouting – void ratio,
fissures, cracks, joints, and extent of weathering
Figure: Methods and particle size range for in-place treatment of soils
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Introduction: Introduction:
Why geotechnical site investigations - Example? Why geotechnical site investigations?
the success rate of any ground-improvement technique depends upon how
much we have understood the subsurface conditions at the project site.
Understanding the index and engineering properties of soils is essential
before using the soil-stabilization techniques.
Figure: Particle size ranges to which different grout materials apply
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Introduction: Introduction:
Why geotechnical site investigations? Why geotechnical site investigations?
The depth and type of foundation to be used • A good site investigation minimizes the chances of disputes that
may arise between the contractors and owners due to insufficient
Skilled/unskilled manpower
Other decisions based on subsurface information in the tender documents or even due to
the GSI Expertise required to implement the project
unpredictable ground conditions encountered during the execution of
Techniques, and equipment needed to execute
the work on sites the project.
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Introduction: Introduction:
Report? • AGS 2001: We must continue to encourage clients to consider best value rather than lowest cost
Introduction of the report, i.e. about the project stage and its contents
Project overview, i.e. name and background of the project 1- Identification of ground hazards
Regional geology, local stratigraphy, groundwater occurrence, and description of the location
2- Provision for better management of ground risk
Scope of work, methods and equipment used, and work schedule
Summary of all subsurface exploration data including information about the groundwater table and soil stratification
Critical stress factor 3- Provision of better value for clients and users
All field and laboratory test results: Interpretation and analysis of the subsurface data (with methods and formulae used
for calculations and the codes and standards used for analysis)
4- Efficient processes which continuously improve
Major geotechnical issues and possible alternatives based on site investigation data
5- Provision of relevant, reliable information
Engineering recommendations for design
Recommendations for geotechnical special provisions (as applicable) supported with proper reasoning and justifications 6- Effective supply chain management.
Conclusions
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Introduction: Introduction:
(AGS 2001) Benefits:
• to assess the general suitability of the site and its environs
1- Preparation – desk study and walk over survey • to enable an adequate and economic design to be prepared, including the design of temporary
2- Design works, ground improvement techniques and groundwater control schemes
3- Procurement • to plan the best method of construction, and to foresee difficulties and delays which may arise
for whatever reason
Key performance 4- Management – project, risk, and quality
• the design of remedial works if any failures have occurred
indicators 5- Supervision
• to explore sources of indigenous materials for use in construction
6- Reporting – factual, interpretative, and ground level • to select sites for the disposal of waste or surplus materials
7- Outcome – client satisfaction, project review, • to carry out safety checks on existing slopes, dams or structures
8- User feedback • to determine the changes which may arise in the ground and environmental conditions, either
naturally or as a result of the works, on adjacent works and on the environment in general.
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Three Projects - Example Thank you very much / Dr. Tariq Bajwa
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