XJCV3510
Foundation Engineering Fundamentals
Professor Yan Yu
Introduction
Contents
• Geotechnical engineering is about the design, construction and operation
of structures built in, on and with soil.
• Foundation design is about the design and construction of a stable
platform
–
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–
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Case studies
Introduction to foundation design
Shallow foundations
Deep foundations
• Assessment
– 30% coursework; 70% open book exam
• Do you understand how to design a foundation?
Reflections
• Notes – are a guide
• Note taking - take notes during the lectures and in the workshops
• Ask questions – if there is anything you do not understand, ask
• Learning by rote – memorising answers to questions is not the way to
learn as it means that you do not understand foundation design
• Learning by practice – work through example sheets, past papers to
build up your knowledge
• Answering questions – answers are not unique
– Produce a cross section to show the actions causing settlement or
failure;
– Decide what information is needed to solve the problem;
– State assumptions
• Relevance of coursework – is to help you prepare for the exam by
creating a procedure to solve problems
• The open book exam – is a test of your understanding of foundation
design
Reflections
• Structural engineering is like
making a chocolate cake
– You know what you want
– You specific the ingredients
– You specify how it is made
– And you know what it will look
like
• Geotechnical engineering is like a
present
– You know what you want
– You do not know what it
contains
– You know it will make you
happy
Foundation Design
The role of the foundation
• The foundation transfers vertical (e.g. the weight of the building) and
horizontal (e.g. wind forces) to the soil
• A poorly designed foundation can render the building unfit for purpose
– building collapses due to failure of the soils beneath the building
• fails ultimate limit state criteria
– building cracks/tilts due to differential settlement of the foundations
• fails serviceability limit criteria
Differential settlement
Erosion
Sinkholes
Earthquakes
Analysis
• Structural and geotechnical engineering solutions are based on three
equations
– Equilibrium of forces
– Compatibility of deformation
– Constitutive law linking deformation to forces
• Four approaches to produce a solution
– Empirical methods based on observations
– Semi-empirical methods based on observations and theory
– Theoretical methods
– Numerical analyses
• Three ways to allow for uncertainty
– Permissible loads
– Global factor of safety
– Partial factors applied to disturbing forces and restoring forces
Difference between geotechnical and structural design
Geotechnical
Particulate material (soil)
Structural
Solid material (concrete, steel, timber)
Solid material (rock)
Anisotropic (σ’v ≠ σ’h)
Strongly anisotropic (reinforced concrete,
timber)
Anisotropic (steel)
natural
Manufactured (concrete, steel)
Selected (timber)
Fabric (fissures, faults)
Composite (reinforcement)
No fabric
Time dependent behaviour (consolidation,
creep)
Time dependent behaviour (creep)
History dependent
Specified manufactured/selection process
Unknown materials
Specified materials
Unknown properties
Specified properties
Geotechnical Design Process
• What is there?
– Geological and hydrological models
• Where has it been?
– Geological history, stress history (Ko, σ’vmax)
• Where is it now?
– State variables (e, σ’v, σ’h, u); mechanical properties (c’, ϕ’,G, kh)
• What is going to happen?
– Load/unload; change in gwl degradation; SLS, ULS
Geotechnical design
• Identify hazards
– Actions (forces) that lead to loss of serviceability or failure
– Force diagrams and failure mechanisms
• Identify potential harm and loss to people, the natural and built
environment
• Assess risk
• Produce mitigation measures
– Analytical techniques
• Simple models to establish initial dimensions
• Simple theoretical models modified by factors based on
observations to refine design
• Numerical studies for ‘what if ‘ studies
– Guidelines
• Eurocode
• Experience
Coursework
Stages of design
1.
Produce the ground model
a. Ground profile showing the topography, strata and ground water
levels
b. Profiles of effective stress, strength and stiffness
Stages of design
1.
2.
Produce the ground model
a. Ground profile showing the topography, strata and ground water
levels
b. Profiles of effective stress, strength and stiffness
Identify hazards
a. Actions (forces) that lead to loss of serviceability or failure during
construction and operation
b. Produce force diagrams and failure mechanisms
Hazards
Performance of masts and towers
serviceability
failure
Foundation failure examples
Stages of design
1.
2.
3.
Produce the ground model
a. Ground profile showing the topography, strata and ground water
levels
b. Profiles of effective stress, strength and stiffness
Identify hazards
a. Actions (forces) that lead to loss of serviceability or failure
b. Produce force diagrams and failure mechanisms
Produce mitigation measures
a. Simple models to establish initial dimensions
b. Simple theoretical models modified by factors based on
observations to refine design
c. Numerical studies for ‘what if ‘ studies
Solutions
Foundation solutions
mass concrete
reinforced concrete
shaft
monopile
pile group (lateral loaded)
pile group (raker)
Coursework
1.
2.
Aim
a. To interpret site investigation data
b. To design suitable foundations for a storage shed that are
i.
Fit for purpose,
ii. Stable,
iii. Economic
iv. And can be constructed.
Outcome
a. A design that takes into account the ground conditions and the limiting
criteria for the structures
b. A report that fully justifies your decisions and can be checked by a third
party
c. A data file for the examination
References
References
• BS 5930:1999 + A2:2010 Code of practice for site investigation
• BS 8002:2015 Code of practice for earth retaining structures
• BS 8004:2015 Code of practice for foundations
• BS EN 1991-1-7:2006+A1:2014. Eurocode 1. Actions on structures.
General actions
• BS EN 1997-1:2004+A1:2013, Eurocode 7: Geotechnical design - Part 1:
General rules
• BS EN 1997-2:2007, Eurocode 7: Geotechnical design - Part 2: Ground
investigation and testing (incorporating corrigendum 2010)
• ICE Manual of Geotechnical Engineering © 2012 Institution of Civil
Engineers
• Tomlinson, M. J., and Boorman, R., 2001. Foundation design and
construction. Pearson education