CECHR Annual Symposium 2016
Engineering role of vegetation: Slope stability problems Dr Anthony K. Leung a.leung@dundee.ac.uk, Lecturer in Civil Engineering Date: 24th February 2016
Background Rainfall-induced shallow slope failure (< 2 m) Traditional engineering methods of shallow slope stabilisation
Soil nailing
Shotcreting
Mok Tse Che Road, Sai Kung
Anderson Road
http://mandjdrilling.com/?ID=30&SubID=50
High embodied carbon and energy
Accelerating climate change Increased instability problems Vicious circle! Low CO2, environmentally friendly techniques are needed
2
http://hkss.cedd.gov.hk/hkss/chi/studi es/lic/Html_04/index04.htm
http://www.workinginhongkong.com/gallery/pub lic/mid%20levels%20hong%20kong%20photos/sh otcreted%20slope.JPG
Background Slope bioengineering method – revegetation Before
Tree Vehicles Transpiration
Live pole responsible for mechanical reinforcement
Potential slip surface Fibrous roots responsible for root-water uptake to induce suction
After
Environmentally and ecologically friendly Atheistically-pleasing; enhance biodiversity; carbon offset
Mechanical effects of root reinforcement Hydrological effects of transpiration
http://hkss.cedd.gov.hk/hkss/eng/green/green/greening.htm
3
Infrastructure slope
Vegetation research at Dundee
Mechanical effects of root reinforcement on slope stability Rooting for sustainable performance (Recently funded by EPSRC) Seismic performance of vegetation slopes (Funded by Chinese Scholarship Council) Influence of plant roots on soil resistance to earthquake-induced liquefaction (Funded by Leverhulme Trust)
Centrifuge modelling 3-D printed root model 4
100
(A) Excluded
Soil matric suction, kPa
80
Vegetation research at Dundee
Ue
Ps
60
Cm
Ca
Sv
Hydrological effects of plant transpiration 40
Lv f = y0+a*x y0 -22.2911
BioEngineered Plant-Integrated Cover (BioEPIC) slope Effects of plant-induced suction on slope hydrology, stability and deformation? 20
Ee
Ia
0
a 103.5919 r2 0.95 p-value <0.0001
Bs
-20
0.0
0.2
0.4
0.6
0.8
Soil matric suction, kPa Penetration resistance, MPa
1007
5
>10 native species for testing their induce suction
6 80 5
Ps
60 4
r2 0.85 p-value 0.0008
Ca
Cm
Ca
Sv
Sv
403
Ps
Lv Lv
Cm
2 20 1
f = y0+a*x y0 -22.2911 a 103.5919
Ee
Ia Ia
0 0
(A) (B)
f = y0+a*x y0 -0.9398 a 5.9372
Excluded Excluded Cs Ue Ue Cs
1.0
Ee
r2 0.95 p-value <0.0001
Bs Bs
-20 0.0 0.0
7
a
Cs
6
0.2 0.2
0.4 0.4
0.6
Root:shoot ratio, g g f = y0+a*x y -0.9398
0.8
1.0 1.0
-1
(B)
Centrifuge modelling Development of new artificial root systems Transpiration Schefflera heptaphylla
Rhodomyrtus tomentosa 0.72
Melastoma sanguineum
Leaf
0.78
0.75
0.15
0.79
(After Leung, 2014)
Root
(a)
0.375 0.09 (Outer diameter)
0.75
0.09 (Outer diameter)
0.75
0.1
0.1
Connected to vacuum source
(b)
0.375 0.09 (Outer diameter) (c)
Suction controlled system (Ng et al. 2014)
High AEV porous filter
(d)
Ng, C.W.W., Kamchoom, and Leung, A. K. 2015. Centrifuge modelling of the effects of root geometry on the transpirationinduced suction and stability of vegetated slopes. Landslides. In press. 6
Centrifuge modelling of â&#x20AC;&#x153;vegetatedâ&#x20AC;? soil slope Rainfall intensity = 70mm/hr
15-g
Nozzle
Vacuum delivery panel
Nozzle
6.39
P1 P2 P3
1.50
P4
0.3 0.3 0.6 0.6 1.2 1.2 2.3 2.3
Elevation 7
15 artificial roots
450
(Silty sand, RC=95%) 2.70
1.73
6.39
5.25
1.50
Artificial root
1.2 1.2 0.75 0.75 0.45 0.45
Instrumented plane
Side
0.75
0.15
0.15
0.1 0.75
0.78 0.75
0.78
0.78
Centrifuge modelling of “vegetated” soil slope (After Leung, 2014) (After Leung, 2014) (After Leung, 2014) Root Root suction Root Effects of root geometry on “transpiration”-induced
(a)
Tap
0.1
0.1
0.1
Heart
P1 P2 P3
Plate
P1 P2 P3
P4
P5
0.75
0.75 0.75
0.09 0.375 (Outer diameter) 0.09 (Outer diameter)
0.75
0.09 (Outer diameter)
0.75 0.75
0.1
0.1 0.1
Connected to Connected to Connected to vacuum source vacuum source vacuum source Suction Suction Suction controlled controlled controlled system system system (Ng et al. (Ng et al. (Ng et al. 0.090.375 0.09 0.09 0.375 0.09 0.3750.375 0.375 2014) 2014) 2014) (Outer (Outer (Outer (Outer 0.09 diameter) diameter) diameter)0.09 diameter) High AEV (Outer High AEV (Outer High AEV (a) (b) (b) (c) (c) porous diameter)(a) (b)(c)diameter) porous porous (d) (d) (d filter filter filter
P1 P2 P3
P4
P6
P5
P4
P6
P5
P6
Ng, C.W.W., Kamchoom, and Leung, A. K. 2015. Centrifuge modelling of the effects of root geometry on the transpirationinduced suction and stability of vegetated slopes. Landslides. In press. 8
Thank you for your attention!