Performance of an instrumented slope covered with shrubs and deep-rooted grass

Rahardjo, H., et al., 2014. Soils and Foundations

Original research (primary data)
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Green technology, an integrated design approach that combines vegetation and engineering design methods, can be applied to improve slope stability. Orange Jasmine is a small tropical evergreen shrub which has deep root systems and is considered to be a drought-tolerant plant that adapts well to a wide range of climatic and soil conditions. It can also grow in infertile soils, limestone soils or loam. Vetiver grass has been widely cultivated in many tropical and subtropical regions of the world for soil and water conservation, land rehabilitation, and embankment stabilization. Vetiver grass has deep roots (2-4 m) and adapts well under extreme conditions of temperature, soil, moisture, soil acidity, and alkalinity. The role of Orange Jasmine and Vetiver grass in minimizing rainwater infiltration, for improving the stability of slopes, was investigated on a soil slope in Singapore with its tropical climate. Two slope sections, covered with Orange Jasmine and Vetiver grass, were instrumented with tensiometers, installed at different depths within the slope, and a rainfall gauge. The instruments were connected to a real-time monitoring system to study the pore-water pressure, the rainfall, and the groundwater level in the slope throughout a one-year period. The pore-water pressure characteristics within the slope sections covered with Orange Jasmine and Vetiver grass are analyzed and presented in this paper. The analyses indicate that both Orange Jasmine and Vetiver grass played a significant role in reducing rainwater infiltration into the slope, minimizing the loss of matric suction, and hence, the shear strength of the soil during rainfall and, as a result, maintained the stability of the slope. Vetiver grass and Orange Jasmine appeared to be similar in effectiveness in terms of reducing the rainwater infiltration into the slope.

Case studies

Basic information

  • Case ID: INT-172-1
  • Intervention type: Created habitats
  • Intervention description:

    green technology slope: tested effects of planting two different types of plants “One portion of the slope (50m2) was covered with Orange Jasmine, another portion of the slope (50 m2) was covered with Vetiver grass” The Orange Jasmine was planted with a lateral spacing of 450 mm and a downslope spacing of 450 mm. The Vertiver grass was planted with a lateral spacing of 250mm and a downslope spacing of 450 mm. This spacing was sufficient for avoiding the over- lapping of root growth between adjacent vegetation.

  • Landscape/sea scape ecosystem management: No
  • Climate change impacts Effect of Nbs on CCI Effect measures
    Soil erosion  Positive Soil stability analysis for a rainfall intensity of 22.2 mm/h that occurs continuously for 1 day based on a 25-year return period “The “total cohesion” method was used to analyze the stability of the original slope and the slope sections covered with Orange Jasmine and Vetiver grass. In the model, the soil layers were divided into several sub-layers. The effect of rainwater infiltration on the matric suction was reflected by the change in total cohesion in each layer. The total cohesion was obtained from the summation of the effective cohesion and the shear strength contribution due to the matric suction (i.e., (ua uw)tan φb)”
  • Approach implemented in the field: Yes
  • Specific location:


  • Country: Singapore
  • Habitat/Biome type: Created other |
  • Issue specific term: Not applicable


  • Notes on intervention effectivness: “The adjacent original slope section, covered with cow grass, was used as a control to study the performance and the effectiveness of the sections covered with Orange Jasmine and Vetiver grass”
  • Is the assessment original?: Yes
  • Broadtype of intervention considered: Not applicable
  • Compare effectivness?: No
  • Compared to the non-NBS approach: Not applicable
  • Report greenhouse gas mitigation?: No
  • Impacts on GHG: Not applicable
  • Assess outcomes of the intervention on natural ecosystems: No
  • Impacts for the ecosystem: Not reported
  • Ecosystem measures: N/A
  • Assess outcomes of the intervention on people: No
  • Impacts for people: Not reported
  • People measures: N/A
  • Considers economic costs: No
  • Economic appraisal conducted: No
  • Economic appraisal described:
  • Economic costs of alternative considered: No
  • Compared to an alternative: Not reported

Evaluation methodology

  • Type of data: Quantitative
  • Is it experimental: Yes
  • Experimental evalution done: In-situ/field
  • Non-experimental evalution done: Not applicable
  • Study is systematic: