Impacts of glaciers on engineering geology: examples ancient and modern
-
Upload
fundacio-marcel-chevalier -
Category
Science
-
view
70 -
download
1
Transcript of Impacts of glaciers on engineering geology: examples ancient and modern
![Page 1: Impacts of glaciers on engineering geology: examples ancient and modern](https://reader031.fdocuments.in/reader031/viewer/2022021921/58ecceb31a28ab1f188b45e9/html5/thumbnails/1.jpg)
Impacts of glaciers on engineering geology: examples ancient and modern
Geoffrey Boulton
University of Edinburgh
Quaternary Research Association
Durham, December 2016
![Page 2: Impacts of glaciers on engineering geology: examples ancient and modern](https://reader031.fdocuments.in/reader031/viewer/2022021921/58ecceb31a28ab1f188b45e9/html5/thumbnails/2.jpg)
sediment pressure pswater
pressure pw effective pressure pe
Pressure
Depth
Effective pressure with depth
• Shear strength – pe tanΦ
• Shear stress at glacier base ≈ 10-110 kPa
• Till tanΦ = 0.35 - 0.55
• Critical effective pc for failure = 18 – 314 kPa
• Equivalent to 1.8 – 31.4m of water
Pe > pc
pc
Stable
Consolidation
![Page 3: Impacts of glaciers on engineering geology: examples ancient and modern](https://reader031.fdocuments.in/reader031/viewer/2022021921/58ecceb31a28ab1f188b45e9/html5/thumbnails/3.jpg)
No basal melting Basal meltingGlacier loading & shearing
No surface load No surface loadLOADING HISTORY
PRESSURE HISTORY ATDEPTH “D”
TIME0
sediment pressure
water pressure
DENSITYCHANGE
+ve
-veshear dilation
normal consolidation
overconsolidation
Consolidation History
![Page 4: Impacts of glaciers on engineering geology: examples ancient and modern](https://reader031.fdocuments.in/reader031/viewer/2022021921/58ecceb31a28ab1f188b45e9/html5/thumbnails/4.jpg)
Rutford ice stream, West Antarctica+ Giorgos PapageorghiouAndy Smith, Emma Smith
Breidammerkurjökull, Iceland+ Sergei Zatsepin
La Gran Valira, Andorra+ Valenti Turu
Examples from:
Ancient
Modern
![Page 5: Impacts of glaciers on engineering geology: examples ancient and modern](https://reader031.fdocuments.in/reader031/viewer/2022021921/58ecceb31a28ab1f188b45e9/html5/thumbnails/5.jpg)
!2100m&
!2150m&
!2200m&
!2250m&
!2300m&
!2350m&
Rutford
Ice Stream
E
l
l
s
w
o
r
t
h
M
o
u
n
t
a
i
n
s
020
km
Project location
o
77S
o
80W
o
85W
o
78S
Fletcher
Promontory
Grounding
Line
Ic
e
f
lo
w
WAIS
Antarctic
Peninsula
Rutford
Ice Stream
05
km
Fig$1$
5 km
Ice stream flow
Rutford ice stream bedIce thickness: 2 km
![Page 6: Impacts of glaciers on engineering geology: examples ancient and modern](https://reader031.fdocuments.in/reader031/viewer/2022021921/58ecceb31a28ab1f188b45e9/html5/thumbnails/6.jpg)
Passiveseismicemissionsfromtheice/bedinterface
![Page 7: Impacts of glaciers on engineering geology: examples ancient and modern](https://reader031.fdocuments.in/reader031/viewer/2022021921/58ecceb31a28ab1f188b45e9/html5/thumbnails/7.jpg)
Evidence of deforming / non-deforming zones
b) Acoustic impedance
Low = Deforming
High = Stable
a) Active Seismicity
c) Radar reflectivity at ice/bed interface& derived effective pressure from AVO
Aseismic soft deformation
Stick-slip atIce/bedinterface
SafetyFactor=1(Pcrit =35kPa≈3.5mwater)
Deforming
![Page 8: Impacts of glaciers on engineering geology: examples ancient and modern](https://reader031.fdocuments.in/reader031/viewer/2022021921/58ecceb31a28ab1f188b45e9/html5/thumbnails/8.jpg)
ProgradingleeEroding
stoss
Lineofsection
D SS D
Mobilestreamlinedbedform
![Page 9: Impacts of glaciers on engineering geology: examples ancient and modern](https://reader031.fdocuments.in/reader031/viewer/2022021921/58ecceb31a28ab1f188b45e9/html5/thumbnails/9.jpg)
• Veryloweffectivepressures(highwaterpressures)attheice/bedinterface
• Dilatantbehaviour iswidespread
• Drainageofmeltwater fromthebedisafundamentaldeterminantofshearingbehaviour andconsolidation
• Highwaterpressureconditionsinfluencesedimentmobility
Conclusions
![Page 10: Impacts of glaciers on engineering geology: examples ancient and modern](https://reader031.fdocuments.in/reader031/viewer/2022021921/58ecceb31a28ab1f188b45e9/html5/thumbnails/10.jpg)
Breidamerkurjokull, Iceland: monitoring changes due to glacier loading
Trench
Advancingkinematicwave
Terminusadvancesovertrench
![Page 11: Impacts of glaciers on engineering geology: examples ancient and modern](https://reader031.fdocuments.in/reader031/viewer/2022021921/58ecceb31a28ab1f188b45e9/html5/thumbnails/11.jpg)
15m
+20m tobasement
AQUIFER
TILLGLACIER
Stratigraphyattheglaciermargin
![Page 12: Impacts of glaciers on engineering geology: examples ancient and modern](https://reader031.fdocuments.in/reader031/viewer/2022021921/58ecceb31a28ab1f188b45e9/html5/thumbnails/12.jpg)
Samplingwaterpressurechanges
![Page 13: Impacts of glaciers on engineering geology: examples ancient and modern](https://reader031.fdocuments.in/reader031/viewer/2022021921/58ecceb31a28ab1f188b45e9/html5/thumbnails/13.jpg)
Pressure-kPa
Days
Pressuresattransducersites
![Page 14: Impacts of glaciers on engineering geology: examples ancient and modern](https://reader031.fdocuments.in/reader031/viewer/2022021921/58ecceb31a28ab1f188b45e9/html5/thumbnails/14.jpg)
0
1.0
2.0
40 80 120 160 200Pressure- kPa
Pi
Pw
waterflow
waterflow
Impactsofdownwarddrainageintoanaquifer
Depthofshearingonday105.75
Depthofshearingonday106.25
ICE
TILLTILL
AQUIFER
Drainage
WaterpressurefallsIcepressureincreases
Pi+Ps
![Page 15: Impacts of glaciers on engineering geology: examples ancient and modern](https://reader031.fdocuments.in/reader031/viewer/2022021921/58ecceb31a28ab1f188b45e9/html5/thumbnails/15.jpg)
Evidence of shear displacement during the mini-surge
![Page 16: Impacts of glaciers on engineering geology: examples ancient and modern](https://reader031.fdocuments.in/reader031/viewer/2022021921/58ecceb31a28ab1f188b45e9/html5/thumbnails/16.jpg)
Tunnelmouth
Groundwaterdominatestunnelwaterflux
Groundwaterheadseasonalfluctuation
Watertable&Inferredgroundwaterflow
Trajectoryoftunnelmouthretreat=esker
Heavierconsolidationnearesker
Lineofsection
Groundwaterflow– subglacial tunnel- esker
![Page 17: Impacts of glaciers on engineering geology: examples ancient and modern](https://reader031.fdocuments.in/reader031/viewer/2022021921/58ecceb31a28ab1f188b45e9/html5/thumbnails/17.jpg)
Depthbelow
surface-m
Till
Aquifer
1.0
2.0
0
Pw
Pi+Ps
Pressure
Upwarddrainagetoatunnel
TILL
Streamtunnel
AQUIFER
ICE
![Page 18: Impacts of glaciers on engineering geology: examples ancient and modern](https://reader031.fdocuments.in/reader031/viewer/2022021921/58ecceb31a28ab1f188b45e9/html5/thumbnails/18.jpg)
Conclusions
• Diurnal,annualandweathereventsinfluencewaterfluxanddrainage
• Theyinfluenceconsolidationstateandshearingbehaviour
• Thedirectionofdrainage(up/down)determinestheconsolidationpatterns
• Meltwater tunnelsplayamajorroleindeterminingdrainagegeometry
![Page 19: Impacts of glaciers on engineering geology: examples ancient and modern](https://reader031.fdocuments.in/reader031/viewer/2022021921/58ecceb31a28ab1f188b45e9/html5/thumbnails/19.jpg)
Fig. 2. Geomorphological map of the ablation zone of the main valley in Andorra. The different positions of glacier fronts and moraines correspond to the MIE stage and tosuccessive post-MIE glacial stages. Legend: 1, runoff; 2, alluvial fans and talus cones; 3, debris-flow fans or slipped masses; 4, peak; 5, glacial cirque; 6, lateral (single solidblack line) and frontal moraine (double solid black line); 7, bedrock step; 8, valley-floor sediments (alluvial, glaciofluvial, till); 9, kame; 10, dashed ornaments: undifferentiatedtill (basal and lateral); 11, past ice-front position at different glacial stages (Tills 0–5).
WU
RM
IAN
GL
AC
IAL
EV
OL
UT
ION
OF
AN
AN
DO
RR
AN
PA
LA
EO
LA
KE
Glacialretreatphases:GranValira d’Andorra
![Page 20: Impacts of glaciers on engineering geology: examples ancient and modern](https://reader031.fdocuments.in/reader031/viewer/2022021921/58ecceb31a28ab1f188b45e9/html5/thumbnails/20.jpg)
Maximum elevation of the glacier surface
Hydraulic headat glacier sole
875
2250 kPa
1500 kPa 2000 kPa
2000
Modelling subglacial groundwater flow - Andorra
![Page 21: Impacts of glaciers on engineering geology: examples ancient and modern](https://reader031.fdocuments.in/reader031/viewer/2022021921/58ecceb31a28ab1f188b45e9/html5/thumbnails/21.jpg)
T5
T4
T3
T2
SantaCo
lomaiceload
-T5
LaM
argine
da–T4
SanJulia-T
3
T4
T3
T5
Gran-Valira –compositestratigraphy&pre-consolidation
![Page 22: Impacts of glaciers on engineering geology: examples ancient and modern](https://reader031.fdocuments.in/reader031/viewer/2022021921/58ecceb31a28ab1f188b45e9/html5/thumbnails/22.jpg)
Data
600 1000 1400 1800
1aEvent
2aEvent
3aEvent
Unit 1Unit 2
Unit 3
Overconsolidation - kPa
0
20
40
60
80
Dep
th -
met
res
Unit 4
Modelling consolidation events
Model Data
T5T4
T3
Singlesimulation
Simulation1
Simulation2
Simulation3
![Page 23: Impacts of glaciers on engineering geology: examples ancient and modern](https://reader031.fdocuments.in/reader031/viewer/2022021921/58ecceb31a28ab1f188b45e9/html5/thumbnails/23.jpg)
Conclusions
• Majorroleofsubglacial streamsincontrollingdrainagegeometry
• Eachglacialphasesuperimposesitsownconsolidationimprint
• Broadpatternsofvariationarepredictableandshouldbeembeddedinsiteinvestigations
• Inwinter,thesystemdrainedfully
• SYSTEMANDSEDIMENTDRAINAGEGEOMETRYARETHEKEYSTOVARIATION
![Page 24: Impacts of glaciers on engineering geology: examples ancient and modern](https://reader031.fdocuments.in/reader031/viewer/2022021921/58ecceb31a28ab1f188b45e9/html5/thumbnails/24.jpg)
sediment pressure pswater
pressure pw effective pressure pe
Pressure
Depth
Shearing behaviour
• Shear strength – pe tanΦ
• Shear stress at glacier base ≈ 10-110 kPa
• Till tanΦ = 0.35 - 0.55
• Critical effective pc for failure = 18 – 314 kPa
• Equivalent to 1.8 – 31.4m of water
Pe > pc
pc
pe< pc
Deforming
Stable