Centrifuge modelling of root reinforcement of slopes

This paper reports a series of geotechnical centrifuge model tests conducted to investigate the mechanical reinforcement of slopes by vegetation. Some of the model slopes contained young willow trees, which were grown in controlled conditions to provide different root distributions and mechanical properties. Slopes were brought to failure in the centrifuge by increasing water pressures. The failure mechanisms were investigated photographically and using post-test excavation. By measuring the soil properties and pore pressures in each test when failure occurred, slope stability calculations could be performed for each slope failure. These back-calculations of stability suggest that only a small amount of reinforcement was provided by the root system even when it was grown for 290 days before testing. In contrast, the use of the measured root properties and a commonly used root reinforcement model suggests that significant reinforcement should have been provided by the roots. This disparity is probably due to either inappropriate assumptions made in the root reinforcement model or soil alteration produced by root growth. Such disparities may exist in the application of root reinforcement models to full-scale slopes and therefore require additional study. The modelling technique outlined in this paper is suitable for further investigation of root mechanical interactions with slopes.

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Influences of root-induced soil suction and root geometry on slope stability: a centrifuge study

Canadian Geotechnical Journal ◽

10.1139/cgj-2015-0263 ◽

2017 ◽

Vol 54 (3) ◽

pp. 291-303 ◽

Cited By ~ 13

Author(s):

A.K. Leung ◽

V. Kamchoom ◽

C.W.W. Ng

Keyword(s):

Slope Stability ◽

Soil Suction ◽

Intense Rainfall ◽

Centrifuge Modelling ◽

Clayey Sand ◽

Mechanical Reinforcement ◽

Root Reinforcement ◽

Real Roots ◽

Soil Bioengineering ◽

Transient Seepage

Soil bioengineering using vegetation has been recognised as an environmentally friendly solution for shallow slope stabilization. Plant transpiration induces suction in the soil, but its effects on slope stability are often ignored. This study investigates the influences of transpiration-induced suction and mechanical reinforcement of different root geometries (i.e., tap- and heart-shaped) to the slope stability subjected to an intense rainfall with an intensity of 70 mm/h (prototype scale; corresponding to a return period of 1000 years), via centrifuge modelling. New model roots that have scaled mechanical properties close to real roots were used to simulate transpiration-induced suction in the centrifuge. Transient seepage analyses were performed using SEEP/W to back-analyse the suction responses due to transpiration and rainfall. Subsequently, the back-analysed suction was used to assess the factor of safety of the slopes using SLOPE/W. It is revealed that heart-shaped roots provided greater stabilization effects to a 60° clayey sand slope than tap-shaped roots. The heart-shaped roots induced higher suction, leading to 14% reduction of rainfall infiltration and 6% increase in shear strength. Although transpiration-induced suction in a 45° slope was reduced to zero after the rainfall, mechanical root reinforcement was found to be sufficient to maintain slope stability.

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