Strength of tree roots and landslides on Prince of Wales Island, Alaska

Abstract

The stability of slopes before and after removal of forest cover was investigated. Porewater pressures and shear strengths were measured and the soil properties were determined by laboratory and it1 situ tests. A model of the soil-root system was developed to evaluate the contribution of tree roots to shear strength. The computed safety factors are in general agreement with observed behaviors of the slopes. Decay of tree roots subsequent to logging was found to cause a reduction in the shear strength of the soil-root system. La stabilite des pentes avant et aprks dkboisement a Ct C CtudiCe. Les pressions interstitielles et les rCsistances au cisaillement ont Ct C mesurCes et les propriCtCs gCotechniques ont Ct C determinies par essais en laboratoire et in situ.On a dCveloppC un modkle du systkme sol-racines pour Cvaluer la contribution des racines d'arbres B la rCsistance au cisaillement. Les facteurs de sCcuritC calculCs sont gCnCralement en accord avec le comportement observC des pentes. On a trouvC que la dCcomposition des racines aprks le diboisement produit une reduction de la rksistance au cisaillement du systkme sol-racines.

An exploratory analysis of vegetation strategies to reduce shallow landslide activity on loess hillslopes, Northeast Qinghai-Tibet Plateau, China

“…As the confining pressure continuously increases, the initial segments of stress-strain relationship curves are linear, demonstrating an elastic character. The shear strength of the root-soil composite systems agrees with the Mohr-Coulomb law (Wu 1976;Waldron 1977;Yang et al 1996;Liu et al 2006). Under identical strain conditions, the main stress difference of root-soil composite systems is notably higher than the soil without roots.…”

“…Hathaway and Penny 1975;Burroughs and Thomas 1977;Schiechtl 1980;Nilaweera and Nutalaya 1999;Greenwood et al 2004;Genet et al 2005;Norris 2005). When subject to shear stress, root tensile strength is manifest through the tensile resistance of roots (Wu et al 1979;Ekanayake and Phillips 1999;Operstein and Frydman 2000). Single root tensile strength decreases via a power relationship as root diameter increases (e.g.…”

“…smaller roots have more cellulose per dry mass than larger roots (Turmanina 1965;Hathaway and Penny 1975;Commandeur and Pyles 1991;Genet et al 2005)). Other important considerations include root system morphology, such as root biomass, root number, root diameter and root length (Wu et al 1979) and root system architecture (Stokes et al 1996;Dupuy et al 2007;Mickovski et al 2007;Reubens et al 2007). The most efficient branching pattern is generated when many roots are spread deep into the soil (Stokes et al 1996;Fan et al 2010).…”

9 Modelling river-bank-erosion processes and mass failure mechanisms: progress towards fully coupled simulations

“…Considering the mechanical effects of vegetation first, the net effect of vegetative surcharge can be either beneficial (increase in normal stress and therefore in the frictional component of soil shear strength) or detrimental (increasing the downslope component of gravitational force), depending on such factors as the position of the tree on the bank, the slope of the shear surface, and the friction angle of the soil (Gray, 1978;Selby, 1982). However, the most important mechanical effect that vegetation has on slope stability is the increase in soil strength induced by the presence of the root system, and considerable progress has recently been made in quantifying this effect (Gray, 1978;Wu et al, 1979;Greenway, 1987;Gray and Barker, 2004;Pollen et al, 2004;Pollen and Simon, 2005;Pollen, 2006). Surcharge and root reinforcement have been recently included in bank stability models (Abernethy and Rutherfurd, 1998Simon and Collison, 2002;Van de Wiel and Darby, 2004;Rutherfurd and Grove, 2004;Pollen and Simon, 2005;Pollen, 2006).…”

Uncertainty and sensitivity in a bank stability model: implications for estimating phosphorus loading

“…A composite material of roots in a soil matrix therefore has increased strength. An early relationship describing increased soil strength due to roots is a function of root tensile strength, areal density, and root distortion during shear (Wu et al, 1979). This equation tends to overestimate root reinforcement because it assumes that all roots contribute their full tensile strength during failure and that all roots break simultaneously (Pollen and Simon, 2005;Pollen et al, 2004) .…”