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www.eng.chula.ac.th Laboratory Investigation of Laboratory Investigation of Laboratory Investigation of Laboratory Investigation of Laboratory Investigation of Vetiver Root Reinforcement for Slope Reinforcement for Slope Reinforcement for

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Laboratory Investigation of Laboratory Investigation of Vetiver Root Laboratory Investigation of Reinforcement for Slope Laboratory Investigation of Laboratory Investigation of Reinforcement for Slope Reinforcement for Slope Reinforcement for Slope Protection

Presented by Dr.

  • Dr. Boonrat Lohwongwatana

Dr. Dr. Dr. Faculty of Engineering, Dr. Chulalongkorn University Co Co Co- Co Co authors: Suched Co Co Co Likitlersuang Sirintra Vanno and Soamshine and and Boonyananta Chulalongkorn University

The Sixth International Conference on Vetiver Vetiver (ICV-6), 6), 6), Danang, , , Vietnam, 5 – 8 May 2015

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Mode of failure (Skepmton, 1953)

Failure Angle Slope after Failure

Total Length (L)

Foot Toe Degree of Rotation Slope before Failure

  • Max. Depth

(D)

Flows Slides Slumps

D/L = 0.5 – 3% 5 5 – 10% 15 15 – 30%

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Diverse vegetation Grass

Potential deep-seated failure Potential 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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Root Root- Root soil-water interaction

Evapotranspiration Soil Atmosphere Rainfall Water uptake Evaporation Infiltration 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 (ua – uw) vs. degree of saturation

  • => matric suction (u

=> matric suction (u

Shear strength:

 

b f w a nf f

u u c          tan tan 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 – root area ratio

b ri i

aD   

1 shear plane

1.2

n r ri i i

c A A

 

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

  • rientation.
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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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Vetiver grass – the Royal initiatives

  • The Chaipattana Foundation
  • Office of the Royal Development

Projects Royal Development Royal Development Board (RDPB)

  • Land Development Department

(LDD)

  • Corporate social responsibility of

Corporate social responsibility of PTT Public company limited.

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Chulalongkorn University Team

  • Prof. Suched Likitlersuang

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

  • Faculty of Engineering

Dr. Faculty of Engineering Faculty of Engineering Boonrat Faculty of Engineering Faculty of Engineering Lohwongwatana Department of Metallurgical Engineering, Department of Metallurgical Engineering, Faculty of Engineering

  • Faculty of Engineering
  • Assist. Prof.

Faculty of Engineering Faculty of Engineering

  • Assist. Prof.
  • Assist. Prof. Sirintra

Faculty of Engineering Faculty of Engineering Vanno

  • Assist. Prof.
  • Assist. Prof.

Department of Landscape Architecture, Department of Landscape Architecture, Faculty of Architecture

  • Faculty of Architecture

Dr. Faculty of Architecture Faculty of Architecture Soamshine Faculty of Architecture Faculty of Architecture Boonyananta Department 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 vetiver – 4.56% 6 months lowland vetiver – 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 Specimen Shear strength parameters Increasing in cohesion (kPa) Standard direct shear test Bare soil c = 6.8 kPa;  = 22.8o

  • 4 months old single

vetiver low land c = 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 land c = 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 branch 2) Thin 2nd-order branch 1) 1st-order branch 7) 3rd-order branch 6) Long end fine tip

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1) 1st-order branch

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1) 1st-order branch

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1) 1st-

  • rder

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-

  • rder branch
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7) Third-order branch

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Vetiver root tip

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Adhesion at the Interface Microscopic 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 Caps

A1_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_Shaft B2_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

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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

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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

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Mechanics of roots and root hairs

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Electron microscope observation

TR TR Intact root Deformed root q Shear zone

b b z x

Interface friction between soil and root ( between soil and root between soil and root Gray between soil and root Gray Gray & between soil and root between soil and root between soil and root & & & & Sotir between soil and root between soil and root , 1996) Root tip of Root tip of vetiver vetiver grass. Root tip of Root tip of Root tip of Root tip of vetiver vetiver vetiver Width of the micrograph is Width of the micrograph is approximately 100 Width of the micrograph is Width of the micrograph is micron. High density of root hairs. Low magnification image. The root hairs are of the order

  • f 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