Use of vegetation in low carbon Geotechnical Engineering › ICEDevelopmentWebPortal... · • Conventional thinking assumes roots add an additional resistance (∆τ r) to the slip

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Professor Jonathan Knappett

Use of vegetation in low‐carbon Geotechnical Engineering

06 November 2018

13th Géotechnique Lecture Repeat– ICE YGG Evening Meeting, Sheffield

1

Scottish University of the Year 2017

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Overview

Part 1: Fundamentals of root soil interaction

• How do plant roots stabilise slopes at the Ultimate Limit State (ULS)?

• How can this effect be incorporated in geotechnical analysis & design at ULS?

• How do roots compare to traditional reinforcing techniques?

Part 2: Applications in Geotechnical Engineering

• Extending the design life of slopes (against earthquakes)

• Extending the design life of slopes (against climate change)

• Removal of trees near embankment crests (to reduce ‘leaves on the line’)

• Slope engineering with trees in steep upland areas

Summary & acknowledgements

2

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Overview


• How do plant roots stabilise slopes at the Ultimate Limit State (ULS)? ‐ Lessons from centrifuge modelling of slopes under seismic loading

• How can roots be incorporated in geotechnical analysis & design at ULS?

‐Modelling root‐reinforced soil in the Finite Element Method & Limit Analyses


Part 2: ULS Applications in Geotechnical Engineering






3

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• Stability defined by Factor of Safety (FOS) ‐ ratio of resisting to driving forces. • This can be quantified analytically or numerically…• … however, FOS cannot be directly measured in physical model tests.

Slope stability (Ultimate Limit State)

4

(σ´ + u)L

τultL

γzLcosβ

β

β

z

g

L

g

γ, φ, c

ββγzuβγzcFOS

sincostancos2

H

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• Conventional thinking assumes roots add an additional resistance (∆τr) to the slip plane from the unreinforced case, increasing FOS.

• However, as FOS cannot be directly measured, how can this be verified?

Slope stability with vegetation – historical approach

5

β

β

z

g

L

γ, φ, c

ββγz

uβγzcFOS r

sincostancos2

g

H

(σ´ + u)L

(τult +∆τr)L

γzLcosβ

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A possible solution – study seismic instability!

6

(σ´ + u)L

τultL

γzLcosβ

khγzLcosββ

β

z

khg

g

L

khg

g

γ, φ, c

• Slope has transient instability if kh > khy (yield acceleration), i.e. FOS < 1.• Magnitude and duration of these events leads to finite slip… • …this is a displacement and can easily be measured in physical model tests.

βγzkββγz

φuzkβγzcFOSh

h2

2

cossincostancossincos

tancossincos

cossintancos2

2

ββγzβγzzuβγzckhy

H

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Physical model testing ‐ centrifuge

• A centrifuge compensates for the low confining stresses in scaled models.• A gravity field N times larger than g is created, for a model at scale 1:N.• Scaling laws map model values to a representative full‐scale prototype.

7

R 3 mAxis of rotation

Soil model & actuatorsGondola

Counter‐weight

Ng

E.g. for N = 30:‐ ω = 95 rpm (1.6 revs. per second)

ω

Earthquake simulator

Beam centrifuge at the University of Dundee:

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• 3‐D printing allows realistically complex root architectures to be formed, that could not be fabricated manually.

• Acrylonitrile Butadiene Styrene (ABS) plastic provides stiffness and strength broadly representative of plant roots when printed.

Model root analogues – 3‐D printing

8

Distribution for an oak tree in a slope in Virginia (Quercus alba)

from Danjon et al. (2008)

Danjon et al. (2008). Using three‐dimensional plant root architecture in models of shallow‐slope stability. Annals of Botany 101(8): 1281‐1293

1:10 scale model:

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Initial investigations on short slopes (H = 2.4 m)

9Liang et al. (2017). Small scale modelling of plant rot systems using 3‐D printing… Landslides 14: 1747‐1765.

Dry sand (Dr ≈ 55%)

Dry sand (Dr ≈ 55%)

3‐D root architecture:

Equivalent straight root group:

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Roots reduce crest settlement (increase stability)

10

Direct shear tells a different story…

σ′v = 8 kPa

12 kPa

16 kPa

20 kPa

• Why the difference? Reinforcement cannot just be +∆τr to the fallow slip plane as previously thought… perhaps the mechanism is changing?

Centrifuge shows effectiveness of 3‐D root architecture vs. straight root group:

Liang et al. (2017). Small scale modelling of plant rot systems using 3‐D printing… Landslides 14: 1747‐1765.

Root contribution to shear strength, ∆τr: kPa

Dep

th (m

)

0 10 20 30 40 500

0.25

0.50

0.75

1.00

1.25

1.50

Unreinforced (fallow)

Straight root group

3‐D architecture

Straight root group

3‐D architecture

Time (s)

Time (s)

Cre

st s

ettle

men

t (m

)G

roun

d ac

cele

ratio

n (g

)

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Reinforcement mechanism – multi‐scale modelling

11

Beam‐and‐spring (p‐y) model ‐ ∆Fr for each root size…

Σ∆Fr for all roots for given shear plane

depth z…

Simulate all possible slip planes

(∆τr = f(z))…

Conventional 2‐D FEM analysis with smeared root contribution ∆τr over CRZ.

Liang et al. (2015). Modelling the seismic performance of rooted slopes: from individual root‐soil interaction to global slope behaviour. Géotechnique 65(12): 995‐1009.

Shear plane

CRZ

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Multi‐scale modelling – hybrid BEM‐FEM

Principal advantages:• Small deformations at global slope scale (FEM) will be large at local root scale…• …using the p‐y (BEM) approach for local root‐soil behaviour can cope with

relatively large soil‐root displacements (without mesh distortion). • Non‐linear soil behaviour is easily accounted for through readily‐available soil

constitutive models (FEM) and p‐y curves (BEM)• Method can account for variations of soil/root properties with depth.• Smeared zones in FEM account for localised effects of root spread and depth.

12Liang et al. (2015). Modelling the seismic performance of rooted slopes: from individual root‐soil interaction to global slope behaviour. Géotechnique 65(12): 995‐1009.

Centrifuge (unreinforced)Hybrid BEM-FEM (unreinforced)Centrifuge (vegetated)Hybrid BEM-FEM (vegetated)

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Insights into root stabilisation mechanism (H = 2.4 m)

13

Arching Centrifuge crest settlement

Unreinforced/fallow:

Vegetated:

Liang et al. (2015). Modelling the seismic performance of rooted slopes: from individual root‐soil interaction to global slope behaviour. Géotechnique 65(12): 995‐1009.

• Once roots are strong enough to change mechanism, further increase in root strength/number has no effect (unlike previous thinking)

Hybrid BEM‐FEM simulations: Inferred mechanism in centrifuge tests:

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Applicability across different slope heights

• Taller slopes require a higher scaling factor (1:30 here)… meaning smaller roots and more plants per model!

• Model layouts

14Liang & Knappett (2017). Centrifuge modelling of the influence of slope height on the seismic performance of rooted slopes. Géotechnique 67(10): 855‐869

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Modelling roots at different scales

• 1:30 scale root analogues represent the smallest case that can be feasibly printed given fabrication tolerances of the printer (uPrint SE).

• Element testing in direct shear shows 1:10 and 1:30 scale models behave identically at prototype scale:


1:10

1:30

Root contribution to shear strength, ∆τr: kPa

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Effectiveness of roots across different slope heights

• FEM matches measured centrifuge behaviour at both heights (2.4 m & 7.2 m)

• As before, roots are highly effective in the shorter slope.

• Roots are markedly less effective in the taller slope.


H = 7.2 m:~15% reduction in slip

Time (s)

Cre

st s

ettle

men

t (m

)

Time (s)

Cre

st s

ettle

men

t (m

)

H = 2.4 m:~85% reduction in slip

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Controlling ULS parameters for rooted soil

From a parametric study using the validated FEM:

• Vegetation is increasingly less effective in taller slopes.

• Reduction of ∆τr by up to 50% did not reduce the reinforcing effect, so:• some root death is not immediately

catastrophic; • Roots can become effective before they are

fully developed.

• It is also confirmed that once roots are strong enough to change the failure mechanism, further increasing root strength/number has no effect.

• So long as we know how ∆τr varies with lateral spread & depth the slip in a vegetated slope can be predicted (from FEM).

17

Roots less effective

Root death

Root growth

Narrow zone less effective

Liang et al. (2017). Modelling the seismic performance of root‐reinforced slopes using the Finite Element Method. Géotechnique (under review).

Change in ∆τr

Change in width of rooted zone (CRZ)

Set

tlem

ent r

atio

(roo

ted

/ fal

low

)S

ettle

men

t rat

io (r

oote

d / f

allo

w)

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Simpler design methods – Limit Analysis

• If permanent slip = key ULS performance criterion, FEM could be replaced by:• faster Limit Analysis (LA), to identify critical mechanism & corresponding khy• Newmark sliding block procedure (khy → slip).

18Liang & Knappett (2017). Newmark sliding block model for predicting the seismic performance of vegetated slopes. Soil Dynamics & Earthquake Engineering 101: 27‐40.

H = 2.4 m:

H = 7.2 m:

E.g. Using LimitState:GEO to perform LA via Discontinuity Layout Optimisation (DLO):

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From khy to seismic slip – Newmark sliding blocks

• Soil within the failure mechanism slips downslope when:

acceleration > khy• Soil is slowed to rest when:

acceleration < khy• Integral of net acceleration w.r.t.

time gives slip velocity…• … Integral of slip velocity w.r.t.

time gives slip displacement.

19

D

+ Acc. ‐ Acc.D(t) = ∆DΣ

Integrate (a – khy) for slip velocity…

Integrate slip velocity for displacement…

khy

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Accounting for large deformations – ‘regrading’

• With increasing slip, slope will flatten/ ‘regrade’ itself to a smaller effective angle:

20

i

i+1 Hi

Hi cotβi

Hi – di sinβi

di cosβi

Slip increment,di

Settlementincrement,di sinβi

di cosβi

New slope surface (i+1)

di+1(using βi+1)

Centrifuge (fallow)

With regrading

Without regrading

khy ‐ with regrading

khy ‐ without regrading

iiii

iiii dH

dH

coscotsin

tan 11

Al‐Defae et al. (2013). Aftershocks and the whole‐life seismic performance of granular slopes. Géotechnique 63(14): 1230‐1244.

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• So long as we know how ∆τr varies with lateral spread & depth the slip in a vegetated slope can be predicted (from LA + Newmark):

Newmark sliding blocks for vegetated slopes

21

khy for rooted slopes from DLO:

Liang & Knappett (2017). Newmark sliding block model for predicting the seismic performance of vegetated slopes. Soil Dyn. & Earthquake Engng. 101: 27‐40.

RegradingC

rest

set

tlem

ent (

m)

Acc

eler

atio

n (g

)

Time (s)

Centrifuge (vegetated)

LA + Newmark (with regrading)

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Overview

Part 1: Fundamentals of root soil interaction• How do roots stabilise slopes at the Ultimate Limit State (ULS)?

‐ Lessons from centrifuge modelling of slopes under seismic loading

• How can roots be incorporated in geotechnical analysis & design at ULS? ‐Modelling root‐reinforced soil in the Finite Element Method & Limit Analyses‐Measuring the properties of rooted soils using new in‐situ tests


Part 2: ULS Applications in Geotechnical Engineering• Extending the design life of slopes (against earthquakes)• Extending the design life of slopes (against climate change)• Removal of trees near embankment crests (to reduce ‘leaves on the line’)• Slope engineering with trees in steep upland areas


22

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In‐situmeasurement of rooted soil properties (1)

23

1. Fdown (N) 2. Fup (N)

Blade penetrometer: Pull‐up device:

F (N)

Dep

th BGL (m

m)

Dep

th BGL (m

m)

Meijer et al. (2016). New in‐situ techniques for measuring the properties of root‐reinforced soil – laboratory evaluation. Géotechnique 66(1): 27‐40

• To include roots within geotechnical analyses, we need to know what the properties of the rooted soil are, and how they vary with position.

• In‐situ tests could achieve this by measuring individual root‐soil interaction properties for input into the Hybrid BEM‐FEM analysis…

FuFu

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Models for root breakage force, Fu

24

ubru pdF 2023.1

14

785.0 2bru dF

212

it

ut

Ep

8

Beam model (p‐y):Root: Eb & σb

Embedded cable model:Root: Et & σt

Meijer et al. (2017). In‐situ root identification through blade penetrometer testing – part 1: interpretative models and laboratory testing. Géotechnique 68(4): 303‐319

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Field trials – Blade penetrometer test

25

Test 1

Paddockmuir Wood(Quercus Robur) Force, F (N)

Tip de

pth BG

L (m

m)

0 500 1000 1500

0

100

200

300Sound recording (root breakages)

Meijer et al. (2017). In‐situ root identification through blade penetrometer testing – part 2: field testing. Géotechnique 68(4): 320‐331

Bending model best –matches root biomechanical behaviour:

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In‐situmeasurement of rooted soil properties (2)

26

• Alternatively, tests could directly measure the stress‐strain behaviour of the smeared root‐soil composite at different positions within the ground.

• These could be directly inputted as smeared properties into FEM or LA…

Shear strength, τ (kPa)

Corkscrew tip de

pth BG

L (m

m)

Test element

Pin vane: Corkscrew extraction:FallowRooted

Meijer et al. (2016). New in‐situ techniques for measuring the properties of root‐reinforced soil – laboratory evaluation. Géotechnique 66(1): 27‐40

Laboratory evaluation

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Field trials – Corkscrew extraction test

27

Test dep

th (centre) BGL (m

m)

Meijer et al. (2018). In‐situ measurement of root reinforcement using the corkscrew extraction method. Canadian Geotechnical Journal 55(10): 1372‐1390

Root area ratio, RAR (%)

Bullionfield siteRibes Nigrum (shrub)

Hallyburton Hill sitePicea sitchensis (tree)

Extractio

n force (N)

= ∆τ r×(πDL

)

Shear displacement (mm)

Extractio

n force (N)

= ∆τ r×(πDL

)

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Overview

Part 1: Fundamentals of root soil interaction• How do roots stabilise slopes at the Ultimate Limit State (ULS)?

‐ Lessons from centrifuge modelling of slopes under seismic loading

• How can roots be incorporated in geotechnical analysis & design at ULS? ‐Modelling root‐reinforced soil in the Finite Element Method & Limit Analyses‐Measuring the properties of rooted soils using new in‐situ tests


Part 2: ULS Applications in Geotechnical Engineering• Extending the design life of slopes (against earthquakes)• Extending the design life of slopes (against climate change)• Removal of trees near embankment crests (to reduce ‘leaves on the line’)• Slope engineering with trees in steep upland areas


28

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Comparative techniques – discretely‐spaced RC piles

29

• Need to model stiffness & strength of the reinforced concrete (RC) piles.

• Stiffness (EI) controls soil pile interaction and internal pile forces.

• Moment capacity (Mult) controls whether pile fails structurally before soil fails (yields) around piles…

Al‐Defae & Knappett (2014). Centrifuge modelling of the seismic performance of pile‐reinforced slopes. J. Geotech. Geoenv. Engng. 140(6): 04014014

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Modelling concrete at small scale

30Knappett et al. (2018). Variability of small scale model reinforced concrete and implications for geotechnical centrifuge testing.9th Int. Conf. on Physical Modelling in Geotechnics, City University, London, Vol. 1: 241‐246

New micro‐concrete (plaster‐sand‐water):• Geometrically scales coarse aggregate

in concrete (at ~1:40 scale) to properly scale tensile strength;

• Simultaneously provides representative compressive strength and variability.

2 – Weigh sand & plaster

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Modelling reinforced concrete piles in the centrifuge

Knappett et al. (2011). Small‐scale modelling of reinforced concrete structural elements for use in a geotechnical centrifuge. J. Structural Engng. 137(11): 1263‐1271

Bending failure: captured in piles with sufficient

shear reinforcement

Flexural shear failure: captured in piles without sufficient shear reinforcement

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Effectiveness of vegetation vs. piling

32Liang et al. (2017). Centrifuge modelling of the influence of slope height… Géotechnique 67(10): 855‐869Al‐Defae & Knappett (2014). Centrifuge modelling of the seismic performance of pile‐reinforced slopes.

J. Geotech. Geoenv. Engng. 140(6): 04014014

Vegetation is most effective in short slopes (and sequesters carbon)

Piles are more effective in taller slopes

(but embody carbon)

(Piled cases are 500 x 500 mm square precast RC piles @ S/B = 3.5)

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Overview


• How do roots stabilise slopes at the Ultimate Limit State (ULS)?

• How can roots be incorporated in geotechnical analysis & design at ULS?


Part 2: ULS Applications in Geotechnical Engineering






33

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Applications 1 – extending design life (earthquakes)

• Consider a 7.5 m tall cutting slope with (non‐vegetated) static FOS = 1.6, within the source area for the 2009 L’Aquila & 2016 Amatrice earthquakes.

• A recent Probabilistic Seismic Hazard Analysis (PSHA) is available for this region (Meletti et al. 2016).

34

φ′ = 38o

c′ = 10 kPaγ = 19.8 kN/m3

7.5 m

From Limit Analysis (DLO):

‐ khy = 0.37g (fallow)

‐ khy = 0.40g (vegetated)

Reed (2017). Design guidance for the application of vegetation for seismic slope stabilisation. MEng project report, UoD, UKMeletti et al. (2016). Seismic hazard in central Italy… Annals of Geophys. 59(fast‐track 5): AG‐7248

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Applications 1 – extending design life (earthquakes)

• The probability P of exceeding the design Peak Ground Acceleration (PGA) for an earthquake of return period Tr over a period (design life) of y years is:

• For no‐slip, increasing the yield acceleration by vegetation extends the design life by 45 years for the same probability of failure (10%):

35

Due to vegetation

y

rTP

111

Reed (2017). Design guidance for the application of vegetation for seismic slope stabilisation. MEng project report, UoD, UKMeletti et al. (2016). Seismic hazard in central Italy… Annals of Geophys. 59(fast‐track 5): AG‐7248

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Applications 2 – extending design life (rainfall)

• Similarly to earthquakes, to guarantee performance over an increasingly longer design life, ULS design must consider a possible extreme event (removing pore suctions & lowering FOS).

• Climate change will make extreme events more likely, so the design storm for an accepted probability of exceedance will also be larger.

• A storm with Tr ≈ 30 years in 2080 is forecast to be similar to a present‐day Tr = 100 years event in the UK (Sanderson, 2010).

• How do slopes perform in such extreme events, and can vegetation help…?

36Sanderson (2010). Changes in the frequency of extreme rainfall events for selected towns & cities. Met Office Report.

Stewart et al. (2012). Frequency analysis of extreme rainfall in Cumbria. Hydrology Research, 43(5):649‐662.

2. Account for climate change

1. Extend exposure

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Centrifuge modelling of slopes with live vegetation

37

Rainfall simulator (climate chamber):

Standpipe (control water

level at slope toe)

6 m high, 1:1 silty sand slope

Compacted to density = 1.4 or 1.3 Mg/m3

(Limit analysis – unstable when upper layers fully saturated)

Juvenile Willow or Gorse(Gorse after 8 weeks growth shown)

Bengough, Knappett & Muir Wood (2015‐2019). Rooting for sustainable performance (EP/M020355/1)

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Centrifuge modelling of heavy/extreme rainfall

• 2 months of rainfall were simulated.• Month 1 – ‘heavy’ rainfall (350

mm/month) in short bursts.• Month 2 – continuous rainfall as an

increasingly extreme long‐duration storm (as per EA/DEFRA model):

38

DDF curves (Stewart et al. 2010) R. Leven catchment, Cumbria

1. ‘Heavy’ month of rainfall (15 hr rainbursts, each Tr ≈ 2 yrs)

Increasingly extreme storm

November 2009 event (Cumbria)

Centrifuge(month 2)

Centrifuge(individual month 1 burst)

Shaded zone has month 1’s rainfall

in 4 days!

Stewart et al. (2010). Reservoir safety – long return period rainfall. R&D Technical Report WS 194/2/39/TR.Stewart et al. (2012). Frequency analysis of extreme rainfall in Cumbria. Hydrology Research, 43(5):649‐662.

0 50 100Duration (hours)

0

100

300

Cum

ulat

ive

rain

fall

(mm

)

200

Tr = 2 yrs

500 yrs

10,000 yrs

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Pore water pressure response during recent tests

• For these soil & slope conditions, vegetation adapts the slope to sustain far more extreme weather, that might be consistent with future climate change.

• Upcoming tests are exploring different root architectures (Gorse) and stability of willow poles before roots have grown.

39

• Month 1: Slip after 2 No. rainbursts• Further extensive deformation during

extreme storm

• Month 1: No slip after 6 bursts• Month 2: Some small deformation following

extreme event, but no catastrophic slide

Bengough, Knappett & Muir Wood (2015‐2019). Rooting for sustainable performance (EP/M020355/1)

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Deformation response from PIV

40

Test duration: days

Test duration: days

5.50 m

Virtual inclinometer

(0.30 m back from the crest )

1.50 m

4.50 m

1.55 m

10.55 m

11

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Applications 3 – tree removal near embankment crests

• It can be desirable to remove trees on vegetated slopes close to the crests of railway embankments, to reduce ‘leaves on the line’.

• As vegetation works by beneficially changing the kinematics of slope failure, it may be possible to remove some trees while still retaining the benefits of a deepened slip mechanism:

41

Clay (fully saturated): ‐ (short term) Undrained

cu = 50 kPa‐ (long term) Drained

φ′crit = 25o, c′ = 0 kPa

Tree removal

Railway line

Would (2016). Design guidance for the application of vegetation for slope stabilisation. MEng project report, University of Dundee, UK

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42

100% removal

74% removal

52% removal

44% removal

14% removal

1:4 slope, 5 m high, drained response:


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43

• For this cohesive soil, trees could be removed over the top 20% of the slope to reduce track littering without altering stability, even in steeper slopes.

• Greater removals could be undertaken in shallower slopes if necessary.

No change

in stability

No change in

stability


14

12

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Applications 4 – slope engineering in upland areas

44

Roots stabilise source zone soil of potential debris flows

(prevent triggering)

Trees must resist pushover from wind

(windthrow)

Trees could be used as natural support posts +

foundations for catch‐fencing(provide barrier system)

Potential debris flow

Road or railway line

Picture of rest & Be Thankful

A83

Evidence of the multiple historic debris

flow events that caused road closure

E.g. Rest and be Thankful (Argyll & Bute):

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Understanding tree ‘foundation’ response

• Stabilisation of source zone material is similar to previous work.• Windthrow hazard & use in barrier systems requires knowledge of push‐over

stiffness and capacity (i.e. tree acting as a foundation under V‐H‐M loading…)

45Ongoing work, funded by Norman Fraser Design Trust and China Scholarship Council

• There is limited data available from ‘tree pull‐over’ tests (see left) collected from Forestry Commission managed woodland.

• For engineering purposes:• Trees can have significant

moment capacity;• Good indication of variability at

individual sites;• Limited information on soil

properties (only a ground type)…

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Physical modelling of trees under lateral load (current)

• 3‐D printing is being used to create models based on scanned root data (Danjon & Reubens, 2008).

• Loading tests will investigate mechanisms of resistance (e.g. root plate rotation or pull‐out?)

• This will lead towards new validated predictive models for design incorporating:• groundwater conditions;• soil properties;• root biomechanical properties.

• These can be used in deterministic or probabilistic analyses as required.

46Danjon & Reubens (2008). Assessing & analysing 3D architecture of woody root systems…Plant & Soil 303(1‐2): 1‐34

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Summary

Fundamentals:• Centrifuge and numerical modelling has provided new insights into the

behaviour of vegetated slopes.• Roots stabilise slopes by adding strengthened zones which beneficially alter

the kinematics of failure (change the mechanism).• These effects can be captured in routine FEM or Limit Analysis for

quantitative geotechnical design, through simple strength additions (+∆τr).• Input parameters for rooted soil can be determined using root‐soil interaction

models or direct from new in‐situ tests (e.g. Corkscrew pull‐out).Applications:

• Vegetation can reduce vulnerability of slopes to natural hazards or extend design life while simultaneously:• being a low‐cost, low technology solution (developing world applications);• providing natural carbon capture & storage (~2 kgCO2e/tree*);• being sustainable (through appropriate plantation management).

47* Forestry Commission, based on a study at Kielder Forest

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Acknowledgements

Funders:• EPSRC• Forest Research/Climate Xchange• China Scholarship Council• MOHESR, Iraq• Norman Fraser Design Trust • European Regional Dev. FundTechnical & IT support staff @ UoD:• Mark Truswell• Grant Kydd• Colin Stark• Gary Callon• David HusbandAnd more widely…• All colleagues in the Geotechnical

Research Group, UoD, for helpful discussions!

Collaborators/researchers/students:• Prof Glyn Bengough (UoD/JHI)• Prof David Muir Wood (UoD)• Dr Anthony Leung (formerly UoD)• Prof Paul Hallett (U. of Aberdeen)• Dr Ken Loades (JHI)• Dr Bruce Nicoll (Forest Research)• Dr Fraser Bransby (formerly UoD)• Dr Frédéric Danjon (INRA, France)• Dr Teng Liang (PhD & PDRA) • Dr Gertjan Meijer (PhD & PDRA)• Dr Asad Al‐Defae (PhD)• Dr Natasha Duckett (PhD) • Xingyu Zhang (current PhD)• Michael Reed (former MEng)• Tim Would (former BEng)

48

Documents

Use of vegetation in low carbon Geotechnical Engineering › ICEDevelopmentWebPortal... · • Conventional thinking assumes roots add an additional resistance (∆τ r) to the slip