3-D numerical investigations into the shear strength of the soil-root system of Makino bamboo and its effect on slope stability.

Abstract This study attempts to quantify the reinforcement effect of the Makino bamboo ( Phyllostachys makinoi Hayata) root system on the stability of slopeland through numerical analyses and in situ tests. Based on the field surveys of Makino bamboo root morphology, a three-dimensional (3-D) numerical model of the soil–root system consisting of the reverse T -shape tap root and hair roots was developed and successfully applied to the finite element simulations of in situ pull-out tests. In the simulations, the soil mass was simulated by a soil element with a perfect elastic–plastic (or Mohr–Coulomb) material model whereas the root system was simulated by a ground anchor element with a linear elastic material model. In addition, a mechanical conversion model with simple mathematical form, which enables a direct transformation of the ultimate pull-out resistance into the shear strength increment of soil–root system was proposed. The conversion model offered a convenient way to quantify the reinforcement effect of the Makino bamboo root system required for the 3-D slope stability analyses. The numerical results indicated that the shear strength increment of the Makino bamboo soil–root system ranged from 18.4 to 26.3 kPa and its effect on the slope stability was insignificant when compared with those adverse influence factors such as the steep slope angle (=50–70°), shallow root depth (=0.8–1.0 m) and large growth height (>10 m) of the Makino bamboo forest slopeland. It can be also speculated that the tension cracks widespread over the slope surface due to the wind loading acting on the bamboo stems and the sequential rainwater infiltration is the dominating factor in the collapse failure of slopeland. For a Makino bamboo forest slopeland with medium slope (25°  β β β  > 40°). Conclusively, the contribution of the Makino bamboo root system to the stability of slopeland is not as significant as expected.

[1]  C. Phillips,et al.  A method for stability analysis of vegetated hillslopes: an energy approach , 1999 .

[2]  Normaniza Osman,et al.  Parameters to predict slope stability—Soil water and root profiles , 2006 .

[3]  Tien H. Wu,et al.  STUDY OF SOIL-ROOT INTERACTION , 1988 .

[4]  A. R. Ennos,et al.  The Anchorage of Leek Seedlings: The Effect of Root Length and Soil Strength , 1990 .

[5]  N. Coppin,et al.  Use of Vegetation in Civil Engineering , 1990 .

[6]  Alexia Stokes,et al.  A numerical investigation into factors affecting the anchorage of roots in tension , 2005 .

[7]  S. Frydman,et al.  The influence of vegetation on soil strength , 2000 .

[8]  Ching-chiang Kuo,et al.  Using ecotechnology to redirect Taiwan's construction work away from conventional method , 2006 .

[9]  R. Ziemer,et al.  Effect of tree roots on a shear zone: modeling reinforced shear stress , 1991 .

[10]  Tien H. Wu,et al.  In‐Situ Shear Test of Soil‐Root Systems , 1988 .

[11]  R. J. Rickson,et al.  Slope Stabilization and Erosion Control: A Bioengineering Approach , 1994 .

[12]  A. R. Ennos,et al.  The Mechanics of Anchorage in Wheat Triticum aestivum L.: II. ANCHORAGE OF MATURE WHEAT AGAINST LODGING , 1991 .

[13]  Alexia Stokes,et al.  Plant biomechanical strategies in response to frequent disturbance: uprooting of Phyllostachys nidularia (Poaceae) growing on landslide-prone slopes in Sichuan, China. , 2007, American journal of botany.

[14]  L. J. Waldron,et al.  The shear resistance of root-permeated homogeneous and stratified soil. , 1977 .

[15]  D. H. Barker,et al.  Ground and water bioengineering for erosion control and slope stabilization , 2004 .

[16]  Alexia Stokes,et al.  An Experimental Investigation of the Resistance of Model Root Systems to Uprooting , 1996 .

[17]  Donald H. Gray,et al.  Biotechnical and Soil Bioengineering Slope Stabilization: A Practical Guide for Erosion Control , 1996 .

[18]  L. Waldron,et al.  SOIL REINFORCEMENT BY ROOTS: CALCULATION OF INCREASED SOIL SHEAR RESISTANCE FROM ROOT PROPERTIES , 1981 .

[19]  C. O'loughlin.  The importance of root strength and deterioration rates upon edaphic stability in steepland forests , 1982 .

[20]  T. Fourcaud,et al.  A density-based approach for the modelling of root architecture: application to Maritime pine (Pinus pinaster Ait.) root systems. , 2005, Journal of theoretical biology.

[21]  Alexia Stokes,et al.  The influence of plant diversity on slope stability in a moist evergreen deciduous forest. , 2010 .

[22]  V. Operstein,et al.  Numerical simulation of direct shear of rootreinforced soil , 2001 .

[23]  T. Wu,et al.  Strength of tree roots and landslides on Prince of Wales Island, Alaska , 1979 .