Estimating the Effect of Shear Strength Increment Due to Root on the Stability of Makino Bamboo Forest Slopeland

Der-Guey Lin ； Wen-Tsung Liu ； Shin-Hwei Lin

《Journal of GeoEngineering》 6卷2期 (2011/08) Pp. 73-88

https://doi.org/10.6310/jog.2011.6(2).1

並列摘要

Due to the benefit of agriculture economics, Makino bamboo (Phyllostachys Makinoi Hayata) was chosen as one of the most important species for forest plantation during 1980's in Taiwan to control slopeland erosion and landslides. However, after the Chi-Chi (or 921) earthquake in 1999, shallow landslides frequently occurred at the Makino bamboo forest slopeland during typhoons. To investigate the shear strength characteristics of the soil-root system of Makino bamboo forest, a 3-D numerical root model consisted of a reverse T-shape rhizome roots and limit hair roots was developed according to the actual root morphology, and successfully applied to the numerical simulation of the in-situ pull-out tests of soil-root system. Meanwhile, the ultimate pullout resistance can be well correlated with the growth age, diameter at breast height and soil water content. Using the identical 3-D numerical root model to the pull-out test, a series of numerical simulations of direct shear tests were implemented and the shear strength increment of soil mass due to roots was estimated. Subsequently, a mechanical conversion model with simple mathematical form, which enables a direct transformation of the observed ultimate pull-out resistance of 2.28 to 6.12 kN into the shear strength increment of 2.83 to 36.45 kPa due to roots was proposed. The conversion model offered a convenient way to estimate the reinforcement effect of the Makino bamboo root system required for the 3-D slope stability analyses. For a Makino bamboo forest slopeland with slope angle varies from 20° to 50°, the maximum increment of factor safety due to the reinforcement effect of Makino bamboo root system approximates 4.6% and the contribution of the root system to the stabilization of slopeland is not as significant as expected. Conclusively, according to the field observations, it can be inferred that the tension cracks widespread over the slopeland due to the wind loading on Bamboo culms during typhoons and the sequential infiltration of rainwater into cracks are the main factors responsible for the collapse failure of slopeland.

並列關鍵字

Makino bamboo ； soil-root system ； ultimate pull-out resistance ； shear strength increment