Root Reinforcement by Hawthorn and Oak Roots on a Highway Cut-Slope in Southern England |
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Authors: | Joanne E Norris |
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Institution: | (1) Nottingham Trent University, Burton Street, Nottingham, NG1 4BU, England |
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Abstract: | Highway embankments and cutting slopes in the United Kingdom, particularly in the South East of England, are often constructed
of or within stiff over-consolidated clays. These clays are prone to softening with time leading to shallow slope failures
and costly repairs. Reinforcement by natural vegetation is potentially a cost-effective method of stabilising these types
of slopes over the medium–long term. However, there is a lack of information on how natural vegetation reinforces and stabilises
clay slopes. To investigate this problem, the potential reinforcement of selected oak (Quercus robur L.) and hawthorn (Crataegus monogyna Jacq.) roots was assessed by conducting in situ root pull-out experiments on a London Clay cutting in south-east England. Pull-out tests were carried out using specifically
designed clamps and either a hand pull system with a spring balance and manual recording of force for oak roots or a jacking
system with electronic data logging of applied force and displacement for hawthorn roots. Oak roots had a mean pull-out resistance
of 7 MPa and that of hawthorn roots was 8 MPa. The electronic data logging of applied force (pull-out resistance) and displacement
of the hawthorn roots provided additional data on the failure of branched roots which could be correlated with variations
in root morphology. The failure of the roots can be categorised into three modes: Type A: single root failure with rapid rise
in pull-out resistance until failure occurs; Type B: double peak failure of a forked or branched root and Type C: stepped
failure with multiple branches failing successively. The different types of root–soil bonds are described in relation to root
anchorage and soil stability. |
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Keywords: | Pull-out resistance root morphology root tensile strength soil reinforcement soil– root interaction |
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