The Principal Problems
R.I. Waller
Retrogressive thaw slump on
Summer Island, Mackenzie Delta
1.
Frost heave associated with
freeze-back of the active layer
during the winter.
2.
Thaw subsidence - thaw of icerich permafrost and associated
terrain disturbance.
3.
Hydrological and groundwater
characteristics - problems of
water supply and waste disposal
in particular.
Dr Richard Waller, Keele University, r.i.waller@esci.keele.ac.uk
C-Change in GEES: Changing Permafrost Environments – Geotechnical Problems
Thermal Disturbance
Major construction problem, which
relates to the thermal sensitivity of
permafrost.
Modification of the ground thermal
regime can lead to two problems:
1) Thaw subsidence: ground
warming; increase in depth of active
layer.
R.I. Waller
2) Frost heave: can occur
seasonally (within active layer) or
more permanently (permafrost
aggradation).
N.B. Only a problem where material is frost susceptible and resulting
frozen ground is ice-rich.
Dr Richard Waller, Keele University, r.i.waller@esci.keele.ac.uk
C-Change in GEES: Changing Permafrost Environments – Geotechnical Problems
Surface
boundary
conditions
CLIMATE
GROUND
SURFACE
TEMP.
Surface energy
balance
GROUND
THERMAL
REGIME
Ground
thermal
properties
(+time)
Human activities cause
problems by changing
the surface boundary
conditions and
modifying the surface
energy balance.
PERMAFROST
THICKNESS
Dr Richard Waller, Keele University, r.i.waller@esci.keele.ac.uk
C-Change in GEES: Changing Permafrost Environments – Geotechnical Problems
Thaw Subsidence
• Disturbance of surface boundary conditions usually results in
an increase in surface temperatures and thermokarst
development.
• Common causes:
– Disturbance or clearance of vegetation Associated loss
of surface insulation.
– Construction of heated building.
– Stripping of surface materials: e.g. to supply construction
materials.
– Movement of vehicles: seismic lines from 1950s still
visible in ice-rich tundra regions.
Dr Richard Waller, Keele University, r.i.waller@esci.keele.ac.uk
C-Change in GEES: Changing Permafrost Environments – Geotechnical Problems
Dawson City
was the first
city to be built
on ice-rich
permafrost in
1898
Construction of
heated buildings
had inevitable
consequences...
http://www.flickr.com/photos/travfotos/249343703/
Dr Richard Waller, Keele University, r.i.waller@esci.keele.ac.uk
C-Change in GEES: Changing Permafrost Environments – Geotechnical Problems
Stripping of Surface Materials
Case Study: Banks Island
http://www.nasa.gov/centers/ames/images/content/173629main_dryvalleys4-hires.jpg
Thaw lakes on Banks Island
• Relates to construction of an airstrip
between 1959-62.
• Thawed surface gravels were
stripped and moved by bulldozer to
provide a level runway.
• Subsequent thaw of underlying icerich sands with 20-35% volumetric
excess ice content (and ice wedges).
• Development of hummocky
thermokarst terrain and widespread
landscape disturbance.
French, H.M. (1975) Man-induced thermokarst, Sachs Harbour Airstrip, Banks
Island, Northwest Territories. Canadian Journal of Earth Sciences, 12, 132-144.
Dr Richard Waller, Keele University, r.i.waller@esci.keele.ac.uk
C-Change in GEES: Changing Permafrost Environments – Geotechnical Problems
Human activities (e.g.
shading associated with
unheated buildings) can
also result in a
reduction in ground
temperature and
problems associated
with long-term frost
heave…
Surface frost heave associated with the
growth of needle ice (R I Waller)
Dr Richard Waller, Keele University, r.i.waller@esci.keele.ac.uk
C-Change in GEES: Changing Permafrost Environments – Geotechnical Problems
Controlling Factors
• Three factors determine the potential
severity of permafrost degradation:
– Ice content of the permafrost
(notably presence/absence of
excess ice).
– Thickness and insulating qualities
of the surface vegetation.
– Duration and warmth of the
summer thaw period.
R.I. Waller
Must be considered when assessing the risk and planning remedial
measures.
Dr Richard Waller, Keele University, r.i.waller@esci.keele.ac.uk
C-Change in GEES: Changing Permafrost Environments – Geotechnical Problems
Gravel Pads
• Most common solution is to build
structure on a pad of coarsegrained sediment.
• Physically separates structure
from the permafrost.
• Coarse-grained material is nonfrost susceptible - limits frost
heave.
R.I. Waller
Heated fuel oil tank resting on a
ventilated, gravel pad. Inuvik,
Canadian N.W.T.
• Commonly used in construction of
roads, airstrips, buildings etc.
• Needs careful design – aim to
provide insulation equivalent to
pre-existing surface materials.
Dr Richard Waller, Keele University, r.i.waller@esci.keele.ac.uk
C-Change in GEES: Changing Permafrost Environments – Geotechnical Problems
Gravel Pad Design
If too thin (a):
level of insulation will be reduced,
seasonal temperature fluctuations
will increase, and active layer will
deepen, causing subsidence.
If too thick (b):
level of insulation is increased,
fluctuations will decrease and
active layer will thin, leading to
frost heave.
Figure from: French, H.M. 2007. The Periglacial Environment (3rd
ed.). Wiley & Sons, Chichester.
© Wiley and Sons
Dr Richard Waller, Keele University, r.i.waller@esci.keele.ac.uk
C-Change in GEES: Changing Permafrost Environments – Geotechnical Problems
Additional Solutions
R.I. Waller
Houses in Nuiqsut (Alaska) built on wooden piles
•
Piles: If structure is
likely to generate large
amounts of heat, whole
structure is usually
mounted on piles driven
into the permafrost.
– Allows circulation of
air and greater
physical separation.
•
Thermosyphons:
Passive heat pumps can
be used to enhance the
degree of cooling. Used
in important structures
such as dams.
Dr Richard Waller, Keele University, r.i.waller@esci.keele.ac.uk
C-Change in GEES: Changing Permafrost Environments – Geotechnical Problems
Thermosyphons
R.I. Waller
Thermosyphons providing additional
cooling around a fuel oil tank
• Passive heat pumps used to enhance
cooling of foundations.
• Sealed pipe containing a volatile fluid that
transfers heat in response to a thermal
gradient (e.g. Ammonia, pressurised CO2).
• Two parts:
– Evaporator (buried in ground).
– Condensor (above ground).
• When evaporator (ground) is warmer than
the condensor (air):
– Fluid evaporates (removes heat).
– Rises into the condensor and
condenses (releases heat).
– Sinks back into the evaporator.
Dr Richard Waller, Keele University, r.i.waller@esci.keele.ac.uk
C-Change in GEES: Changing Permafrost Environments – Geotechnical Problems
Water Supply and Waste Disposal
Utilidor and “utilidettes” in Inuvik, Canadian NWT (R.I. Waller)
Dr Richard Waller, Keele University, r.i.waller@esci.keele.ac.uk
C-Change in GEES: Changing Permafrost Environments – Geotechnical Problems
Contents
•Introduction
•Site investigation
•Site considerations
•Considerations for the foundations
•Earth structures
•Buried structures
•Monitoring of geotechnical parameters
14
Siting process
• Regional analysis
High level review of an area where there is an interest to build a
nuclear power plant to identify some potential sites. This is largely
based on excluding areas that do not meet some high level criteria
such as adequate water supplies or seismic stability.
Potential sites (sites within the area of interest not ruled out by the
regional
analysis)
This analysis shall be conducted as much as possible on the basis
of existing data without engaging important survey means (mainly
for confidentiality reasons).
• Screening analysis / Site selection
Reduce the number of potential sites to a few (less than 10) candidate
sites that can then be analyzed in detail. This involves either further
exclusion criteria or very simple assessment to identify those sites that
are most likely to provide a suitable site. The sites from this step are
called candidate sites.
Candidate sites (a list of less than 10 sites that appear suitable and
can be ranked ).
• Ranking analysis /Site selection
15
final step of the process
Selection Stage
The investigation at the site selection stage is to determine the suitability of
candidate sites. On the basis of the above mentioned information on subsurface
conditions, the potential or candidate sites can be ranked according to the suitability
of the foundation.
•Unacceptable subsurface conditions.
•Groundwater
regime.
–A site with geological
conditions that could affect the safety of a nuclear
The hydrogeological
maybeallow
an estimate
of theof groundwater
location
power plant andliterature
that cannot
corrected
by means
a geotechnical
•Classification
of
sites.
and regime
(seeorIAEA
Safety
Series
No.50-SG-S6).
treatment
compensated
for by
constructive measures is unacceptable.
A siteGeological
may be classified
as
a
rock
site,
rock orvolcanic
stiff soilactivity,
site, soft
soil site,
hazards such as surfacesoft
faulting,
landslides,
or a combination
.processes,
The soil type
is further and
divided
into adue
non-cohesive
and
•Foundation
conditions.
permafrost, thereof
erosion
subsidence
collapse
to underground
cohesive
soil.
The type
of soil, depth to bedrock and the properties of the deposit may be
cavities
inferred. This allows a preliminary selection of acceptable foundation types to be
made.
16
Verification Stage
In this stage, the investigation programme should cover the site as a whole as well as
a smaller scale appropriate for layout considerations
• Geological hazards, geological and subsurface
conditions
• Liquefaction potential
• Feasible foundation types (preliminary bearing capacity
and foundation stability, preliminary settlement ranges
• Groundwater levels and regime
• Site
preparation
requirements
(earthworks,
excavations…)
• Site investigation techniques used at this stage
–
–
–
–
Seismic refraction and reflection survey
Rotary borehole drilling
In situ mechanical testing
Laboratory testing
17
Confirmation stage
• In this stage, preliminary plant characteristics such as the
loads, the physical dimensions of the buildings, preliminary
structural engineering criteria and the preferred plant layout
are know
• In this stage, sufficient in situ and laboratory testing should
be conducted to allow the estimation of the bearing
capacity, determination of settlements of structure and the
site amplification of seismic waves, establishment of soil–
structure interaction parameters (dynamic and static),
evaluation of the liquefaction potential and evaluation of a
site specific design response spectrum, if required.
• As a minimum, the following indicators of potential cavities
and susceptibility to ground collapse should be considered:
– Sinks, sink ponds, caves and caverns, sinking streams, historical
18
ground subsidence, mines, surface depressions, Rock types such
Before operation of NPP
• Pre-operational stage :
complete and refine the assessment of site characteristics by incorporating geotechnical
data newly obtained during foundation excavation and construction.
• Operational Stage :
• settlement of structures should be measured and used to confirm its safety and
integrity by comparing with prediction analyses ,
• level of the water table, should be measured and compared with predictions to enable
an updated safety assessment to be made
19
ETC-C part2
20
Sources of Data
• Historical
and current documents
– maps (topographic, geological, geophysical,soil…)
– geotechnical reports and other geotechnical literature
– earth satellite imagery
– aerial photographs water well reports and water supply reports
– oil and gas well records
– hydrogeologic maps, hydrologic and tidal data, flood, climate
and rainfall records
– mining history, old mine plans and subsidence records
– seismic data and historical earthquake records
– newspaper accounts of events of significance
– records of performance of structures in the vicinity.
• In situ investigation tests
• Laboratory tests
21
Geophysical in situ tests
Nature of materials
Cross hole seismic test
Gravel to cohesive
Uphole/downhole
seismic test
Electrical resisitivity
Gravel to cohesive
Nuclear logging
Gravel to cohesive
Gravel to cohesive
Surface
seismic All types
investigation
Microgravimetry
All types
Ground
Radar
Acoustic
Penetrating All types
Magnetic technics
All types
All types
Parameters
measured
Shear wave
velocity
Shear wave
velocity
Porosity and
water content
Water content
Types of problems
Commentaries
Site categorization,
SSI
Site categorization,
SSI
Internal erosion
1 hole instead of 2
holes
Using of logging
Surface wave
velocity
Acceleration
due to gravity
Speed of
propagation
Speed of
propagation
Magnetic field
intensity
Site categorization
Sinkholes,
heterogeneities
Cavities
Subsurface complex
Damaged zones
Dikes and dams
maintenance
Dikes and dams
maintenance
22
Areas of humidity
Subsurface complex
What is geophysics ?
• Seismology - Study of natural
[from earthquakes] and maninduced seismic waves
• Gravity - Study of variations
in earth's gravitational field
• Electrical Methods - Use of
electrical conductivity /
resistance of earth
• Electromagnetics - Study of
induced electromagnetic
fields
• Magnetics - Analysis of
variations in earth's magnetic
field
23
Field Tests to Measure
Seismic Wave Velocities
24
Geotechnical in situ tests
Nature of
materials
Flat jack test
Rock
Hydraulic fracturing test Rock
Direct shear stress test Rock
Plate bearing tests
Clay, sand, gravel
Pressure meter test
Static penetrometer
test
Dynamic penetrometer
test
Vane shear test
Parameters
measured
In situ normal stress
In situ stress state
Shear strength
Reaction modulus
Clay, sand, gravel Elasticity modulus
Compressibility
Clay, sand, gravel Cone resistance
Clay, sand, gravel Cone resistance
Relative density
Cohesive soil
Shear strength
Pumping test
Clay, sand, gravel Field permeability
Overcoring tests
Cohesive soils
and rocks
In situ stress state
Type of problem
Convergence
Convergence
Stability problems
Compaction control
Settlement
Settlement
Bearing capacity
Bearing capacity
Shear strength
Liquefaction
Bearing capacity,
slope stability
Transmissivity of
soil
Consolidation
studies
Commentaries
Used for excavations
and embankments
Needs a preliminary
hole
Called also cone
penetrometer test
Called also Standard
Penetration Test
Needs piezometers
Needs laboratory
tests
25
Drilling Program
• Invasive methods
• The purpose of the Drilling Program is to determine the:
–
–
–
–
Thickness,
Lateral Extent, and
Physical Properties of Each Layer of Soil
Presence, Depth and Pressure of Water in the Soil
• To take soil’s samples (undisturbed samples) in order to
perform laboratory tests
• Coupled with the Topographic Survey, it provides a 3D
view of the site and the soil underneath.
• If the Upper Soils are Weak, a deep Foundation system
must be developed.
Borehole Drilling
• Drilling Rig
• Continuous Hollow
Stem Augers With
Removable Drill Rod
And Center Head
Rough Spacing and Deep Guidelines
for bore holes testings
Structure Footprint
Area / Boring (min)
Depth (min)
m2
m
Poor Quality
100 - 300
6 (S)0.7+D
Average
200 - 400
5 (S)0.7+D
High Quality
300 - 1000
3 (S)0.7+D
Soil Type
Source: Coduto, 1999
Standard Penetration (SPT)
Penetration Number, N
Raising 70 lb Weight
Conventionally 140 lb Weight is
Used)
Proper Technique of Releasing the Weight to
Reduce Pulley Friction
Geotechnical Laboratory tests
Soil index and classification
Physical and chemical
properties of soils
Physical and chemical
properties of groundwater
Soil moisture- density
relationships
Type
of Type of test
soils
clayey soil Atterberg limits
Parameter
measured
Ip, wL, wP,
All types
Carbonates
and sulphates
Salt content
Dietrich- Fruhling apparatus
All types
Purpose
Compressibility and
plasticity
Soil classification
Influence on permeability
Proctor test, gammametry,
ASTM test (relative density)
h, d, w, Sr, Dr
Consolidation and permeability All types
characteristics
Shear strength and
All types
deformation capability of soil
Oedometer
Cv, Eoed
Shear test box triaxial
compression tests
Engineering properties of rock
Rock
E,
Settlement, bearing
cdrained capacity,
and undrained,
E, 
Stability, strenthening
Dynamic characteristics of the
soil.
All types
Shear test, biaxial or triaxial
compression tests
Cyclic triaxial tests, resonant Edyn, , internal Site categorization, SSI,
column
damping, pore liquefaction
30
All types
Settlement,
consolidation, bearing
capacity, consolidation
Settlement, consolidation
Triaxial test apparatus
Contents
•Introduction
• Site investigation
•Site considerations
•Foundation Considerations
•Earth structures
•Buried structures
•Monitoring of geotechnical parameters
• Quality insurance
32
Safety related topics to be examined
Bearing capacity
Settlements,
Stability
Soil-Structure
Interaction
Stability of slopes
Soil
Liquéfaction
Free field
response
spectrum
Bed-rock
Buried
structures
0,04
0,02
Acceleration [g]
Vs, ρ, G, D
Soil
profile
0,00
-0,02
-0,04
0
10
20
30
40
50
60
Time [sec.]
33
The profile
• Geometrical
description, such
as
subsurface
stratigraphic
descriptions, lateral and vertical
extent, number and thickness of
layers,
• Physical and chemical properties
of soil and rock and their values
used for classification,
•S - and P - wave and other
mechanical properties obtained by
in situ test;
•Mechanical
properties
parameters,
stress-strain
relationships, static and dynamic
strength properties obtained by
laboratory tests,
•Groundwater table,
34
Site response Modeling
The following model of soil is acceptable:
• A viscoelastic soil (materials that dissipate energy by internal
damping) system overlying a viscoelastic half-space,
• A horizontally layered system ,
• Vertically propagating body waves (shear and compression
waves),
• Non-linear effects may be approximated by equivalent linear
methods.
The equivalent linear model (s) of soil constitutive relationship
should be consistent with the strain level induced in the soil
profile by the response to the input ground motion. This leads
generally to an iterative process.
35
• Softwares available: SHAKE, CYBERQUAKE …
Difficult Soils or Conditions
•
•
•
•
•
•
•
Karst geology
Liquefaction potential
Compressible/soft soils
Collapsible soils
Expansive soils
Frost-susceptible soils
Specification
Contents
•Introduction
• Site investigation
•Site considerations
•Foundation Considerations
•Earth structures
•Buried structures
•Monitoring of geotechnical parameters
• Quality insurance
37
Foundations considerations
•Foundation work
–Preliminary foundation work
–Improvement of foundation conditions
–Choice of foundation system and construction
•Soil-structure interaction
–Static Analysis , Dynamic Analysis , Analysis
methods
•Stability
–Bearing capacity , Overturning , Sliding
•Settlements and heaves
–Static analysis , Dynamic analysis
•Induced vibration effects
38
Site Preparation & Earthwork
• Site preparation
– remove pavements, organics
– abandon utilities
– abandon/remove old foundations
– overexcavation
• Earthwork
– compaction requirements
– acceptable fill materials
39
Improvement of Foundation
Conditions
•Improvement of the foundation conditions
should be carried out when:
–The foundation material is not capable of
carrying the building loads with acceptable
deformation (settlements)
–There are cavities that can lead to subsidence
–There are heterogeneities, on the scale of
building size, which can lead to tilting and/or
unacceptable differential settlements
–Expansive soil or collapsing soil, sensitive clay
or dispersive clay
40
Choice of Foundation System
•Two systems of foundations are available for transmitting the
superstructure loads to the soil: shallow foundations and
deep foundations and the criteria leading to the choice are :
–the forces due to the structures should be transmitted to the soil
without any unacceptable deformation,
–the soil deformations induced by the earthquake should be
compatible with the design requirements of the structure,
•Uncertainties of the seismic response evaluation should be
considered in the design and construction of the foundation
system
• One single type of foundation should be used per structure
• The choice of the type of foundation depends on the type of
building. Basemat should be used for nuclear island because:
– provides homogeneous settlements under static and dynamic
loads
– barrier between the environment and the buildings inside 41
CONTENTS
•Introduction
• Site investigation
•Site considerations
•Foundation Considerations
•Earth structures
•Buried structures
•Monitoring of geotechnical parameters
• Quality insurance
42
Natural Slopes
• It is important to differentiate potentially hazardous
slopes depending on distance to NPP, slope angle, height,
geology, water content and other geotechnical conditions of
slope material,
• External effects of earthquakes and heavy rain-falls should
be considered in assessing the potential hazard ,
•A stability analysis should be made considering the seismic
effect as an equivalent static inertia force; the safety factor
should be equal or larger than 1.5 ,
• If the safety factor thus evaluated is low enough to indicate
a potential for a major sliding failure, a countermeasure for
strengthening the slope or preventing the debris from
reaching the safety related structures should be designed .
43
Dikes and Dams
• Dikes : structures running along courses of water,
• Dams: earth structures higher than 15m,
• Special attention should be paid to the permeability of the site
close to the areas of the foundations,
• The design of dikes and dams in term of safety, should be
consistent with the design of NPP (natural hazards ) and
consistent with the international regulations for design of dams
issued by ICOLD (International Commission on Large Dams
• In the design of earth structures two important phenomena
should be considered :
–the pore pressure inside the embankment ,
–the internal erosion which is caused by water flows
inside the embankment.
44
Sea-walls, Breakwaters
• Sea-walls, breakwaters, revetments are civil engineering
structures to protect NPP against wave action of an ocean or
a lake during storms and tsunami,
• These structures should be properly designed so that they
can prevent soil erosion, floodings and structural failures, and
the sustainability of safety functions should be properly
evaluated,
• Material properties of sea-walls, breakwaters, revetments
and backfill materials which include concrete blocks, rubbles
and other large size particles should be properly estimated,
•The failure consequences on these structures on safety
related ducts, pipes and other underground facilities (sideeffects) passing near or through the facilities should be
appropriately considered.
45
Contents
•Introduction
• Site investigation
•Site considerations
•Foundation Considerations
•Earth structures
•Buried structures
•Monitoring of geotechnical parameters
• Quality insurance
46
Buried Structures
•Retaining walls
–Gravity walls
–Embedded walls (as sheet walls)
•Embedded structures
–The interaction of the underground walls with
the surrounding ground is significant
–Effects of groundwater on embedded
structures should be taken into account in
design (leaks )
– The effects of embedment on impedance of
the foundation and on soil-structure interaction
47
Buried Pipes, Conduits & Tunnels
•Investigation program
– to identify areas of discontinuities or changes in the foundation
material along the route of the pipe ,
•Construction Considerations
–sufficient depth to prevent damage due to surface loading (e.g. traffic
loads) or alternatively should be designed,
–well-compacted granular material over competent foundation material
such that no damage or distortion of the piping ,
•Design Considerations
–Long, buried piping systems are primarily subjected to relative
displacement-induced strains (rather than inertial effects ),
–These strains are induced primarily by seismic wave passage and by
differential displacement between a building attachment point (anchor
point) and the ground surrounding the buried piping ,
48
Buried Pipes, Conduits & Tunnels
(ctd)
•Analysis Considerations
– Relative deformations imposed by seismic
waves travelling through the surrounding soil or
by differential deformations between the soil and
anchor points,
–Lateral earth pressures acting on the cross
section,
–Intersections move with the surrounding soil and
that there is no movement of the buried structure
relative to the surrounding soil.
–Axial deformations which depends on the wave
49
type ,
Monitoring of
Geotechnical Parameters
•Purpose of Monitoring
–provide parameters and site characteristics suitable for
predicting the performance of foundation systems under
various loading conditions.
–The monitoring of actual loads and deformations permits a
field check of the predicted behavior of the foundations and
earth structures
•Guidelines for Monitoring
–The soil behavior should be monitored during excavation,
backfilling and building construction.
–The groundwater regime under buildings and in adjoining
areas should be monitored
–The monitoring devices should be carefully chosen so that
the monitoring system provides the expected information for
the life duration of the installation. The choice and number of
the devices should rely on feedback experience with regards to50
QUALITY ASSURANCE
• A Quality Assurance program should be established to
control the execution of the site investigations and
assessments and engineering activities being performed
during the different stages of the site evaluation activities for
the NPP.
•This program should cover the organization, planning, work
control, personnel qualification and training, verification and
documentation of the activities.
• This program should be established at the earliest possible
time consistent with the site evaluation activities for the NPP .
•The process of establishing site related parameters and
evaluations involves technical and engineering analyses and
judgments which requires extensive experience and
knowledge .
51