1. SUBGLACIAL PLOUGHING AND DRAINAGE
PATTERNS IN A GLACIATED VALLEY
(ANDORRA, SOUTHEASTERN PYRENEES)
Valenti TURU (1) & Geoffrey S. BOULTON (2)
(1) Marcel Chevalier Foundation (Andorra) igeofundacio@andorra.ad
(2) School of Geosciences, University of Edinburgh: G.Boulton@ed.ac.uk
36 slides 1

2. • 1) The Andorra glaciated valley
• Setting
• Pressuremeter tests
• 2) Rehology
• Stress/Strain diagrams
– Type 1 P/V curves: Elastoplastic
– Type 2 P/V curves: Hyperplastic
– Type 3 P/V curves: Hyperelastic-hypoplastic
• 3) Data
• Site 1: La Closa
– Consolidated layers and stratigraphy
– Prandtl penetration keel
– 14C data and ploughing
• Site 2: P. del Roure
• Site 3: P. de les Oques
• 4) Conclusions
36 slides 2

3. The Andorra glaciated valley
Geomorphology of the main valley and position of the glaciers at the last glacial advance from the Upper Pleistocene
(1) fluvial network, (2) alluvial cone, (3) debris cone and scree, (4) mountain peak, (5) glacial cirques, (6) hummocks, (7) subglacial gorge,
(8) morainic ridge, (9) reconstructed glacier margins, (10) till, (11) alluvium, (12) colluvium, (13) glacier front. Red circle main examples
36 slides 3

4. Geomechanical data
• Glacial sediments produced during Quaternary glacial periods are widespread in both mountainous and
lowland zones and influence many construction projects.
• Understanding the stratigraphy of the glacial loaded sediments of Andorra is particularly important for civil
engineers.
• One of the characteristics of such sediments is the great variability and unpredictability of the consolidation
state and accurately geotechnical and geophysical surveys are needed.
Investigation data from Andorra main va
Fondation Marcel Chevalier
-5
-10
-15
Depth (m)
-20
-25
Borehole (1596 m)
-30 Carottage (385 m)
Intact samples (195)
-35
0 10 20 30 40 50
%
Main valley, view upward, at Escaldes-Engordany
Main valley, view downward through Acquired geotechnical data at the main valley through the Valira d’Orient and Madriu confluence
36 slides 4

5. IN SITU geotechnical data
Shear test Oedometric test
Void ratio
2
1
Po
1
Pressure (
Void ratio
P/V diagram
Po’
250
(Example)
2
’
1 200
Strain (Volume cm3)
Tests 150
(Po)
2 h (Po’)
100
h* *g Pressure (
Terrain normally consolidated.
50
Bore-hole + 0
1 2
Pressuremeter test =
0 1 2 3 4 5 6 7 8
Stress (x 100 KPa) Oedometric + Shear test
36 slides 5

6. Anomalous preconsolidation values have
been observed at shallow depth
As previously stated, this test has been performed in boreholes, introducing the cell at depths between 5 and
25 meters which, in the best scenario, implies ground pressures acquired according to a gravitational gradient
between 0.1 to 0.5 MPa. However, with pressuremeter tests, overconsolidation pressures up to ten times
greater than these have been obtained, implying that glacial sediments may be strongly consolidated.
A-040.11.97
1200
Pressure
0
0 1000
h=-9m
h =-4m
Deformation (volume)
800
3
Depth
600
6
400
Po’
10 200 Po
1) Gravitational weight of s
2) Consolidation data (Po) 0
0 1 2 3
Pressure (MPa)
36 slides 6

7. Stress/Strain analysis, the pressuremeter data
Stress/strain data (pressuremeter P/V data) obtained permit us distinguish basically three types of charts:
Type 1: P/V evolution with a single yield point
Type 2: P/V evolution with various yield point
Type 3: P/V evolution without any apparent yield point and strain rebounds are observed (ratcheting)
Type 1 diagram Type 2 diagram Type 3 diagram
250
800 600
700 Po’ (4)
200
Po’ (3) 500
Strain (Volume cm3)
Strain (Volume cm3)
Strain (volume cm3)
600
Extensive ratcheting, tooth-like stress-strain diagram
150 500
400
Po’ (2)
Po’
400
100 Po’ (1) 300
300
FEDA ERT S4-P3 (-3,4 m
200
Po’ (1)
50 200
Po’ (2) Load-Unload
100 cycles La Closa S3b-P3 (-21,6 m
Po’ (3)
BM/BI S1-P1 (-4,5 m Po’ (4)
0 0 100
0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 9 10 1 12 13 14 15 0 10 20 30 40 50 60 70
Stress (x 100 KPa) Stress (x 100 KPa)
Stress (x 100 KPa)
36 slides 7

8. Type 1 P/V evolution is that which is most commonly described
in the literature, a linear stress/strain behaviour from elastic
domain is observed until a yield point is reached where start
non-linear stress/strain behaviour from the plastic domain
until reaching the Coulomb failure value
More than one yield point is observed in that type of diagrams
on the pseudoelastic domain (hyperplastic behaviour), until
the greatest Yield pressure value is reached that closes the
external hyperplasticity envelope. Far away the plasticity field
is reached (drawn) until the Coulomb failure criteria (not drawn).
Type 3 curves have lost their tensional history correspond to an
evolution toward the hyperelasticity and hypoplasticity (HEHoP)
of type 2 curves.
Hyperelasticity can explain easily the behaviour of dense packing soils
for small strains, where the stress is transferred through the porous
media and small intergranular strain occurs without new
rearrangement of grains, so the strain can be considered as
reversible.
For extreme stress ubiquitous ratcheting effects may be possible and
it’s observed in type 3 stress/strain diagrams. Typical saw-tooth-like
stress-strain diagrams are obtained in the vicinity of yield stress
predicted by the hypoplasticity models until is exceeded (HoPP
pressure).
36 slides 8

9. Pressuremeter data summary
The hyperelastic and hypoplastic behaviour of type 3
Type 1, 2 and 3 stress/strain evolution with curves derive from previous hyperplastic behaviour
from type 2 curves, while hyperplasticity of type 2 in
900 La Closa S3b-P3 (-21,6 turn derive from the elastic behaviour of type 1 curves.
La Closa S3b-P2 (-17,6
Type 1
800 La Closa S3b-P1 (-13,6 The principal mechanism to that evolution is due to
La Closa S3a-P3 (-11,8 m load-unload (L-UL) cycles, producing stiffening and
Strain (volume cm3)
700 La Closa S3a-P2 (-10,2
Type 2 kinematic hardening of the subglacial sediment.
La Closa S3a-P1 (-8,6 m
600
Stiffening
The evolution from type 2 to type 3 soil behaviour
500 should start with a critical state consolidation (HoPP
Type 3 yield), wile the HEHoP (Hyperelastic-Hypoplastic) yield
400
point appear when the soil is led to a dense packing by
300 further fine grain cleaning and rearrangement of grains.
Yield locu
200 migration Between both, type 2 expansion of the yield curve due
Kinematic hardening
100
to plastic hardening by load-unload cycles derive to
ratcheting in type 3 diagrams by extensive
0 accumulation of deformation by those cycles.
0 10 20 30 40 50 60 70
Stress (x 100 KPa)
Load-Un Load cycles are produced by the melting
dynamics of the glacier. Could be diurnal, seasonal or
climatic range in function of the subglacial possition.
36 slides 9

10. Three geomechanical evidences
Located sites
36 slides 10

11. P. del Roure
2 SITE 2
1
3
SITE 1: La Closa
S2c S1b
S2d
L1
S6
S4c S5
S3b
S4b
S4a
T1
SITE 3
P. de les Oques
36 slides 11

12. Resistivity profile
SITE 2
?
SITE 1: La Closa
S2c S1b
S2d
L1
S6
S4c S5
S3b
S4b
S4a
T1
SITE 3
Soundings at la Closa
La Closa Site
36 slides 12

13. SITE 2
?
SITE 1: La Closa
Type 2 Type 3: Hypoplastic S2c S1b
Type 1
S2d
L1
S6
S4c S5
S3b
Type 2
S4b
S4a
Type 3: Hyperelastic T1
SITE 3
Geomechanical behaviour
36 slides 13

14. Laminated sands and silts
Holocene
1a
1b
La Closa sediments
Striated gravels
Massive sands and silts
Striated gravels Laminated sands and silts 36 slides 14

15. S-N
Hyperplastic
Elastoplastic
Hyperplastic
Hyperplastic
Hypoplastic
Unconsolidated
Hyperelastic
Upwelling zone
In the drilling-sampling-in situ tests process has been observed a very weak sand layer that collapses in
a siphoning process, coutting all the stratigraphy and should be consider out of the sequence.
36 slides 15

16. S-N
Hyperplastic
Elastoplastic
Hyperplastic
Hyperplastic
Hypoplastic
Unconsolidated
Hyperelastic
Glacier base
L-UL cycles
Pervasive
shear stress Glacier base
Accretionary
pile up till
Sheared Hyperplastic
gravels Pile up till
(striated)
1 3
Hyperelastic
Hypoplastic
Prandtl
matrix pore pres logaritmic
increase arroun loop /2-
the gravel surf
The L-UL cycles produce substratum hardening and an stiffening effect that could locally overload the bearing capacity of the underlying layers.
If that happen two main types of ground collapse can happen according to the substratum compacity. If weak a punching failure occour, if heavily
dense then a general failure process starts in wich a more or less large Prandtl logaritmic loop failure produced accordinly to the frictional angle.
36 slides 16

17. S-N
14C Data
Hyperplastic
Elastoplastic
Hyperplastic
Hyperplastic
Hypoplastic
Unconsolidated
Hyperelastic
3
3 3 3
The Load and Unload cycles at the Glacier base
L-UL cycles
bottom of the glacier and produces 1
Plane
Pervasive
an accretionary pile up of till in wich shear stress
1 1 1
the organic matter is incorporated into Accretionary 3 3 3 Clast ploughing
3 3
the till matrix,being older on bottom and pile up till
Sheared 3 3 3
younguer on top. gravels
(striated)
1 3 Failure
1 1 1 plane
1 1
We observe that the age of the sandy matrix pore pres 1 1 1
layer between hypoplastic-hyperelastic increase arroun a bad pore water dissipation can produce a
the gravel surf failure plane on till by digging
till layers is the same as the overlying
till layer (age from the same till at site 2).
Subglacial clasts are dragged through the sediment by the L-UL cycles producing pore pressures in
The geomechanical behavieur of both till
excess that could weaken the sediment downtill from ploughing clasts producing a failure plane.
layers are related with the same process,
Here we observe that once the failure plane formed an decouppling till-substratum effect happen
meaning that once were the same till layer
(glacier flotation?) that slides the infill of sands and silts on the space between tills.
36 permits 17
an it has been separate by a failure plane.

18. WNW-ESE
The same weak sand layer that collapses is present on that profile an seems to be
related to the 1a layer, the younguest subglacial consolidated layer
36 slides 18

19. WNW-ESE
Failure plane
The anomalous growth of layer 1a close to the weak sandy layer is interpreted as an
accommodation failure, in a piling up synsedimentary process
36 slides 19

20. S-N
And the same for the previous profile
…. But some lateral contacts can’t be explained with a displacement above them, for that reason we need
to invoke a lateral facies contact or a previous failure contact. Sedimentary lateral facies contact is
possible but not a horizontal variation from Type 2 to Type 3 geomechanic behaviour in a so short space
(about 20 m), only in vertical direction sharp changes in the geomechanical behavieur are observed.
36 slides 20

21. S-N
PPK
PPK
Prandtl Penetration Keel
Being coherent with the geomechanical data we suggest a lateral mechanical contact.
Such contact is related with a glacier overload structure, similar to what happen in a general
failure under a shallow foundation when it exceed the bearing capacity of the soil beneath it:
a Prandtl Penetration Keel is espected to be present on the Andorra glacial valley floor.
The following slides shows the sedimentary and deformation sequence >>
36 slides 21

22. S-N
Hypoplastic/Hyperelastic 36 slides Keel and general failure
Prandtl 22

23. S-N
36 slides
High water pressures produces till decoupling following the previous failure plane 23

24. S-N
Sedimentation of the following subglacial till with a Hyperplastic behaviour (type 2)
36 slides 24

25. S-N
The sand-silt layer formed before acts as a slides
36 detachment layer. The Prandtl keel is now inactive
25

26. S-N
A general glacier retreat permit to fill the slides floor, firstly with glaciolacustrine deposits26
36 valley

27. S-N
Proglacial outwash infill sequence
36 slides 27

28. S-N
A general glacier readvance consolidate the 36 slides layers and a reactivation of the failure happen
previous 28

29. S-N
Final glacial retreat, fluvial infill and Holocene landslides invade the valley bottom
36 slides 29

30. Site 2: P.del Roure
Other resistive bodies are close to the la Closa ones
Next >>
Depth (m)
36 slides 30
Resistive bodies Distance (m)

31. Site 2:
Prat del Roure
Prandtl penetration Keel (PPK) Possible PPK
Holocene
Hyperplastic Elastoplastic
1a Hyperplastic
1b Elastoplastic
Hyperplastic 2a
Depth (m) Hyperelastic Hypoplastic
Elastoplastic
PPK Hypoplastic
?
Distance (m)
36 slides 31

32. Site 3: P. de les Oques
On the lateral side of the Andorra valley is common to observe bouldery layers overlying sand and gravels
layers with load structures. Those layers have been consolidated after deposition.
36 slides 32

33. Consolidations state of the deposits on the latereal side of the valley glacier
“Décollement”
Til
l Til
l
Til
l
Til
l Til
l
Granulometry
KPa
0 10 20 C s S S’S" G B
Light Sandy till with
brown deformed water
tractive structur
Imbricated sand a
Dark gravels. Horizont
brown bedding.
Silt and sand wit
Brown some gravel beds
Matrix supported
and load casts.
Light Silty till with
brown
Testing the shear strenght with a simple pocket vane apparatus is possible to see that the
silty-sandy layers show a decreasing pattern from top to bottom. The shear strenght are directly
related with the apparent cohesion and thus with its consolidation state. The only way to keep a
low consolidation value is the presence of high water pressure in porous media that balance the
overlying glacier pressure. So at the lateral sides of the glaciated valley high water pressures
should be common. 36 slides 33

34. Combining field observations, geophysical data and pressuremeter data we can speculate
about the continuity of the ploghing PPKs (Prandtl penetration keels) on the Andorra glacial
valley floor, see the figure on next slide:
36 slides 34

35. Conclusions
Subglacial tunnel
Subglacial tunnel Subglacial tunnel
Site 3: P. de les Oques
Site 2: P. del Roure
Site 1: La Closa
1a 1b
Highly 2a Poorly
consolidated
3a consolidated2b
layers: layers 3b
1a 680 m/s Holocene 606 m/s 1a
879 m/s 1a
2a 2a 1174-977 m/s 1b 2a
1b
1252 m/s 1b
2a
3100
2a m/s
2b 4 3a 2b 3
3b
3 4 3
3a
Prandtl penetration keel 4 3b
4
at glacial stage 1 ? Prandtl penetration keel
at glacial stage 3 5
5
Prandtl penetration keel
at glacial stage 3? Roca
Substratum
Resistivity (ohms m)
Bottom valley pressuremeter type 3 diagrams are related with hyperelastic/hypoplastic PPK’s
Bottom valley high resistivity domains are related with the subglacial drainage plumbing
Both (resistivity and geomechanical behaviour) are related on the bottom valley
Small and large scale structures are related with ploughing process
1: Weaken heavily tills
2: Prandtl Penetration Kell
36 slides 35

36. Thank you
36 slides 36

37. GEOMECHANICAL ANNEX
(If needed)
36 slides 37

38. Subglacial plumbing
Hypothetical glacier height
(c) 100 m A B
(b)
Moulins
Valley glac Static water ta
(a)
Dynamic water ta
Snout
H 2O Crevasses
0 Lateral eske
Aquifer 3
4
5 3 Tunnel R
6 Depth
Equipotentials 7 (m)
6
Flow lines 8
9
10
10
11
(e) (d)
LATERAL POSITION
CENTRAL POSITION TO THE TUNEL, A WITH REGARD TO THE TUNNEL, B
Pressure (100 x KPa) Pressure (100 x KPa)
0 5 1 1 0 5 10 15 (f) Effective pressures (100xKPa)
2
0 0
1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10
3 Lateral
Depth (m)
3
Depth (m)
2 1+3 Tunnel
effective 3 3
1 pressure 1+3
6 6
6 6
Depth (m)
Esker
Lateral
10 10
10
3 10
1) Gravitational weight of sediment effective 1 3
2) Dynamic water pressure pressure
Lines join together
3) Gravitational weight of Both lines can no
ice 36 slides
Glacier flotation condition
at the lateal of the tunnel
38
1 + 3 join, no flotati
exist beneath the
Effective pressure: 1 + 3 - drainage tunnel
2 Water pressure = Sediment weight + Ice weight

39. 1 Type 2 diagram:
1 q
q
Hyperplasticity
p’
p’
Pervasive shear --> 0 Pervasive shear --> 0
Eventual "d collement"
BOULTON & ZATSEPIN (2006)
2
q shown that the progressive
atenuation of diurnal, seasonal
and annual frequencies
reflected in pressure
p’ fluctuations at the ice-bed. At
- + the inner part of the glacier only
Pervasive shear large cycles are transmited to
the subglacial bed (climatic
cicles).
q Load-Unload Stiffening
Multiple yield field
by load-unload
3 cycles CSL
q4 4
- +
p’
q 16
8
Pervasive shear
Shape of
q16 ESP
a heavily
consolidate
clay in an
undrained 6 TSP
q 7
consolidation1 2
state Y3 3
m
4 ESP Dranaige
Pervasive q with consta
shear stress pervasive
- +
p’
drop to zero
Beginning 36 slides
of
5
q=0
1
p’ shear strai
39
Pervasive shear a L-UL cycle p’>0

40. 18/28
Type 3 diagram
Hyperelasticity - Hypoplasticity
Some particularities should be taking in account when
pervassive subglacial shear stress is present. Glacier
The zone of till where the available shear strength is less than
- +
Consolidation
the constant pervasive subglacial shear stress imposed by the
overlying glacier ice, undergoes critical state consolidation.
Small load-unload hydrological cycles (follow the numbers on Pervasive she
figure below) produce that the stress state of the subglacial
sediment moves away or close from the critical state line (CSL).
Such consolidation is known as critical state consolidation Not sheared sediment
and can be more than 1.8 times greater than the isotropic
consolidation.
600
HEHoP HoPP
Non-linear behaviour
500
Ratcheting
non-linear behaviour
(Hypoplasticity)
(Plastic domain)
Critical State Consolidation CSL
Strain (Volume cm3)
q q16 16
400 Extensive ratcheting,
tooth-like stress-strain diagram Pervasive TSP
shear stress Dranaige
drop to zero with constan
300 Beginning of q4 8 pervasive
Strain rebound a L-UL cycle
6 4 shear strain
Strain rebound 7
200
Strain rebound
2 3
Strain rebound
La Closa S3b-P3 (-21,6 m
1 Kinematic hardening
La Closa S2d-P3 (-16,2 m m q ESP
100
0 10 20 30
Hyperelasticity field Stress (x 100 KPa)
40 50 60 70
36 slides
5
q=0
p’>0
1
p’40

41. Compact cubic grain packing
Resistivity and presuremeter data in a
perpendicular profile to glacier flow.
Type 1 diagrams are located on low
resistivity facies. Type 3 diagrams are
located on high resistivity facies. Type
2 diagrams in between.
Andorra glaciated valley
y = 1257.5 * 10^(-3.8756e-2x) R^2 = 0.838
10000
Correspondence between electrical
resistivity and fine grained content
Toward hyperelasticity Legend
La Margineda
1000 Santa Coloma Roysa
Santa Coloma Riberayg
Ohms X m
Escaldes Prat del Rou
La Comella
100
10
0 5 10 15 20 25 30 35 40 45 50 55
Silt and Clays content (<0,08 mm) %
Hyperelastic terrains acts like a dense packing (cubic or hexagonal grains packing) material. The dynamic shear modulus
(P and L waves) with the pressuremeter (static) shear modulus are very nearer (ratio ≈ 1). Resistivity values suggest that
hyperelastic and hypoplastic terrains seems to be cleaned of clays and silt by the groundwater flow through the subglacial
drainage tunnels. 36 slides 41

42. Resistivity and hyperelasticity/hyperplasticity
Tunnel Tunnel Tunnel
Type 3
diagram
The consolidation of the subglacial sediments
close to hydraulic singular points (subglacial Andorra glaciated valley
tunnel drainage), are subject to an intense flow y = 1257.5 * 10^(-3.8756e-2x) R^2 = 0.838
10000
of water due to being situated near the place Correspondence between electrical
resistivity and fine grained content
of drainage where there is a high hydraulic
drop. The idea of an high water flow through Legend
porous media that produces a fine grain 1000
La Margineda
Santa Coloma Roysa
cleaning is supported by soil analysis and Santa Coloma Riberayg
Ohms X m
Escaldes Prat del Rou
geophysical data. Such process combinate La Comella
with pervasive subglacial shear stress and the
100
L-UL cycles rearrange the sediment grains to a
dense packing (close to hexagonal or a cubic
simetry). The soil will appear to be undergoing
consolidation when its stress state is close to 10
critical state and loses it’s stress/strain history. 0 5 10 15 20 25 30 35 40 45 50 55
Silt and Clays content (<0,08 mm) %
36 slides 42

43. 25/28
Prandtl penetration Keel (PPK)
Central
Lateral
Esker Tunnel Lateral
Esker
- + -
+ consolidated
- + - - + - - consolidated
Prandtl logaritmic loop The overbunden pressure from the glacier
weight plus the subglacial water drainage via
porous media through the central
tunnel, following Load-Un Load cycles
(diurnal/seasonal/climatic cycles) promote a
Penetration critical state of consolidation
Keel and produce that the terrain becomes harder
and stiffer than the sorrounding terrain
σ1 (hyperelastic-hypoplastic), overloading the
σ3 σ3 bearing capacity of the terrain and breaking
Glacier load it following a Prandtl logaritmic loop. If the
Lateral penetration keel is coupled to the glacier
Lateral
Esker Esker basal motion then a ploughing effect on the
Tunnel middle of the glacial valley is possible.
- + -
- + - - + -
Hyperelastic and
hypoplastic Keel
36 slides 43

44. Appendix: The pressuremeter
36 slides 44

45. The pressuremeter device
G 063.06.01
Controller
“Push in” with a penetrometer Gas (Nitrogen)
36 slides 45

46. The pressuremeter test
P/V diagram
Intact soil
250
200
Strain (Volume cm3)
150
Push in, soil 100
plastification ring Non linear behavieur
(disturbed soil)
50
0
0 1 2 3 4 5 6 7 8
Stress (x 100 KPa)
P/V diagram
250
Elasto-Plastic
Yield point
(Po’)
200
Pressuremeter test,
Strain (Volume cm3)
Non interpretable
(disturbed soil)
Linear behaviour
(Elastic domain)
cilindrical deformation 150
Non-linear behavio
(Plastic domain
100 ˘p
˘v
50
0
0 1 2 3 4 5 6 7 8
Test end, soil
Stress (x 100 KPa)
recover parcially
36 slides 46

47. Geomechanical data, pressuremeter tests
G 085.12.02 A 151.10.00 G 093.09.03 G 040.11.97
Driller The most frequent problems:
“Push in” Gravels between the slotted
tube and the pneumatic cells
Slotted tube
Pinch out of the pneumatic cells
1 to 1,5 m metallic tubes by gravels or coarse sands
Pneumatic cells Slotted tube braked & broken
by big boulders or even
Hydro-pneumatic conduit deformation of the slotted tube
36 slides 47