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Laboratory Investigation of Laboratory Investigation of VetiverVetiver Root Laboratory Investigation of Reinforcement for Slope

VetiverVetiverVetiver Root Root Laboratory Investigation of Laboratory Investigation of VetiverReinforcement for Slope Reinforcement for Slope Reinforcement for Slope Protection

Presented by Presented by Dr.Dr. BoonratBoonrat LohwongwatanaPresented by Presented by Dr.Dr.Dr.Faculty of Engineering,

BoonratBoonrat LohwongwatanaLohwongwatanaDr. BoonratBoonratFaculty of Engineering, Faculty of Engineering, Chulalongkorn

LohwongwatanaLohwongwatanaChulalongkornChulalongkorn University ChulalongkornChulalongkorn

CoChulalongkorn

CoCo-University University University University

CoCo---authors:Suched

CoCoCo authors:authors:authors:Suched LikitlersuangSuchedSuched Likitlersuang

SirintraLikitlersuangLikitlersuangLikitlersuang

SirintraSirintraSirintra VannoLikitlersuangLikitlersuang

VannoVanno and SirintraSoamshine

Sirintra VannoVannoVanno and and SirintraSirintraSoamshineSoamshine BoonyanantaSoamshineSoamshine BoonyanantaBoonyanantaChulalongkorn

BoonyanantaBoonyanantaChulalongkornChulalongkorn University

TTThe he he Sixth International Conference on Sixth International Conference on VetiverVetiver (ICV(ICV-(ICV-(ICV-(ICV 6), 6), 6), DanangDanang, Danang, Danang, Danang Vietnam, 5 Vietnam, 5 –– 8 May 2015

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Mode of failure (Mode of failure (SkepmtonSkepmton, 1953)

Failure AngleSlope after Failure

Total Length (L)

Foot

Toe

Degree of Rotation

Slope before Failure

Max. Depth(D)

Flows Slides Slumps

D/L = 0.5 D/L = 0.5 –– 3% 5 5 –– 10% 15 15 –– 30%

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Diverse vegetation

Grass

Potential deep-seated failurePotential shallow failure

Grass root

Live pole

Soil nail

Live pole

Self-regenerative and sustainable (almost maintenance free)

(root of small tree/shrub)

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Two effects of vegetation on soil slope

[1] Hydrology - Plant roots may increase subsoil permeability at the same time the vegetation will intercept rainfall and transpire water, eventually leading to lower water pressures (i.e., higher suctions) in the slope.

[2] Mechanical - The presence of the roots will lead to reinforcement in the penetrated regions.

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RootRoot-Root-soilsoil-soil-water interactionEvapotranspiration

Soil

Atmosphere

Rainfall

Water uptake

EvaporationInfiltration

Plant

Complex plant-soil-atmospheric interaction(Greenwood et al., 2004; Blight, 2005; Pollen-Bankhead & Simon, 2010)

Solar energy

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Unsaturated soil mechanics

•• Soil water characteristic curve (SWCC)=> matric suction (u=> matric suction (u=> matric suction (uaa –––– uuuwuuw) vs. degree of saturation

•=> matric suction (u=> matric suction (u

• Shear strength: bfwanff uuc tantan bfwa uuu tan

Net normal stress

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Root structures

Fan C.C. and Chen Y.W. (2010)

(a) Linden hibiscus (H-type); (b) Japanese Mallotus (VH-type); (c) Chinese tallow tree (V-type); (d) ironwood (VH-type); (e) white popinac (R-type)

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Shear plane Shear plane –– root area ratio

bri iaD

1shear plane

1.2 n

r ri ii

c AA

Wu et al. (1979): Shear reinforcement was calculated from the sum of the forces required to break each individual, crossing the shear plane by where 1.2 is a correction factor for root orientation.

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Objectives

• To understand the mechanism of vetiver root reinforcement for slope protection

Overall strength = Soil + Water + Root system + Interface

• To evaluate the shear strength contribution of the vetiver root for soil slope

• To demonstrate the role of vetiver root for slope stabilization

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VetiverVetiver grass grass –– the Royal initiatives

• The The ChaipattanaChaipattana Foundation• Office of Office of Office of the the the Royal Development Office of

Projects the the the Royal Development Royal Development Office of Office of the

Projects Projects Projects Board (RDPB)• Land Development Department Land Development Department

(LDD)• Corporate social responsibility of Corporate social responsibility of

PTT Public company limited.

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ChulalongkornChulalongkorn University Team• Prof. Prof. SuchedSuched LikitlersuangLikitlersuangLikitlersuang

Department of Civil Engineering, Department of Civil Engineering, Faculty of Engineering

•Faculty of EngineeringDr. Faculty of EngineeringFaculty of EngineeringDr. Dr. BoonratFaculty of EngineeringFaculty of Engineering

BoonratBoonrat LohwongwatanaDr. Dr. BoonratBoonratBoonrat LohwongwatanaLohwongwatanaDepartment of Metallurgical Engineering, Department of Metallurgical Engineering, Faculty of Engineering

•Faculty of EngineeringAssist. Prof. Faculty of EngineeringFaculty of EngineeringAssist. Prof. Assist. Prof. SirintraFaculty of EngineeringFaculty of Engineering

SirintraSirintra VannoAssist. Prof. Assist. Prof. SirintraSirintraSirintra VannoVannoDepartment of Landscape Architecture, Department of Landscape Architecture, Faculty of Architecture

•Faculty of ArchitectureDr. Faculty of ArchitectureFaculty of ArchitectureDr. Dr. SoamshineFaculty of ArchitectureFaculty of Architecture

SoamshineSoamshine BoonyanantaDr. Dr. SoamshineSoamshineSoamshine BoonyanantaBoonyanantaDepartment of Art, Music and Dance Education, Department of Art, Music and Dance Education, Faculty of Education

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Sample preparation

Mr. Adithep Vangbunkong(Master student, Department of Civil Engineering)

Lowland Highland

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Root observation

The average growth rate of vetiver roots = 30 cm/month (1 cm/day)

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Image processing Image processing –– root area ratio

6 months highland 6 months highland vetivervetiver ––– 4.56%

6 months lowland 6 months lowland vetivervetiver ––– 3.36%

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Direct shear tests

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Large direct shear test

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Results of direct shear tests

Test SpecimenShear strength

parametersIncreasing in

cohesion (kPa)

Standard direct shear test

Bare soil c = 6.8 kPa; = 22.8o -4 months old single

vetiver low landc = 7.7 kPa; = 29.7o 0.9

4 months old single vetiver high land

c = 13.7 kPa; = 28.8o 5.9

Large direct shear test

Bare soil c = 2.5 kPa; = 21.8o -6 months old group

vetiver low landc = 5.1 kPa; = 28.4o 2.6

6 months old group vetiver high land

c = 8.5 kPa; = 29.2o 6.0

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Study of vetiver root surfaces

3) Fine tip

8) Root cap

4) Knotted fine tip

5) Thick 2nd-order branch2) Thin 2nd-order branch1) 1st-order branch

7) 3rd-order branch

6) Long endfine tip

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1) 1st-order branch

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1) 1st-order branch

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1) 1st-order branch

2) Thin 2nd-order branch

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2) Thin 2nd-order branch

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2) Thin 2nd-order branch

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3) Fiber pullout

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4) Knotted fine tip

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5) Thick 2nd-order branch

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7) Third-order branch

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Vetiver root tip

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Adhesion at the InterfaceMicroscopic scale effect is important

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Soil planted roots

A1_Elbow A2_Spindles

A3_EggShape Caught

A4_Cut section A1_Shaft

A1_Root tip lower down A1_Root tip A2_Spindles2

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Sand planted roots

B1_Shaft B1_B2 Overlap B2_and Sand? B3_

B3_B1_Tip next to B2 B2_and Sand? B2_and Sand?

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Root CapsA1_Root tip

A1_Root tip lower down

• Elongated cells ready to expand.

B1_Tip next to B2

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Sample A vs B Comparison: Particles

B1_ShaftB2_and Sand?

• We observe both soil and sand particles embedded in the roots

• Particles can be differentiated from roots based on surface morphology

A3_EggShape Caught

A3_EggShape Caught 2x Zoom

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Root Hairs and their spindles

• Filamentous tip growth is much more extensive in sample A (soil)

• Some root hairs are visible in sample B (and previous plug sample), but are significantly shorter and sparser

B3_

B3_A2_Spindles A2_Spindles2

Root segment, pulled apart and surrounded

by soil

Sample F: Comparison of EM vs. LM

F – LM

(uncoated)

F – LM (coated)

Limited depth of

focus

Segment 1

(root

details

clearly

visibly

in EM)

F – EM

Fractur

e

surface

Sample A fracture surface

Fracture sruface

Root hairs (invisible in LM)

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Tensile delamination - root

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Core fiber pull out

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Findings

• Root hairs are important anchorage for Vetiver grass.

• Dense filamentous structures are substantially more developed in the soil-planted sample

• Vasculature is well-defined in cross-sectional samples.

• Future study of fractured roots and failure modes. A4_Cut section zoomed 2x

Mechanics of roots and root hairs

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Electron microscope observation

TRTR

Intact root

Deformed root

q

Shearzone

b

b

z

x

Interface friction Interface friction between soil and root (between soil and root between soil and root ((Graybetween soil and root GrayGray &

between soil and root between soil and root between soil and root & & & & Sotir

between soil and root between soil and root SotirSotir, 1996)

Root tip of Root tip of vetivervetiver grass. Root tip of Root tip of Root tip of Root tip of vetivervetivervetiver grass. grass. Width of the micrograph is Width of the micrograph is approximately 100 Width of the micrograph is Width of the micrograph is approximately 100 approximately 100 micron.

High density of root hairs. High density of root hairs. Low magnification image.

The root hairs are of the order of micron level and their interfacial area is contributing significantly to the friction due to their increased surface area.

This mechanism provides adhesion between root and soil during shear which could be directly linked cohesion term in Mohr-Coulomb failure criterion framework.

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Acknowledgement• The AUN/SEED-Net (JICA) • The Chaipattana Foundation• Office of the Royal Development Projects Board• The Sustainable Energy Foundation - PTT Co., LTD• Dr. Songkiert Tansamrit and P’ Yai – PTT Co., LTD• Dr. Pitayakon Limtong from LDD• Mr. Atichart Ruksajitr – The Chaipattana

Foundation