Soil Reinforcement Vegetation Effect An analysis applied to the Earth moving volume of California High Speed Railway System

摘要

The revegetation growing on a mass of soil brings about in this, an important increase of its shear strength. On the one hand, in the superficial zone of itself, in whose inside concentrates the great density of roots, the additional soil shear strength Δτ_(vr), due to themselves, in the depth z_r reached by the main packet of roots, depends on radicular density and is Known as "vegetation reinforcing effect". On the other hand, beyond the reinforced zone, as far as z_3 depths at those the moisture of soil belongs to suctions equal or larger than pF3, is well-Known the increment of soil shear strength Δτ_(vd), "vegetation drying effect". The soil masses limited for a sloping surface (be sloped land with native vegetation or cutting slope with implanted vegetation), and therefore yielded to shear stresses on the slide surface that they can produce inside them, will be stable with a definite safety coefficient FS, if the soil shear strength along of these slide surfaces surpass in this ratio the shear sliding stresses leaded to by the gravity force. The expected average growth of vegetation (native or implanted) on a slope, during a period of time (total biomass production UG (underground) + AG (above ground)), may be estimated beginning with production climatic rates WUE (water use efficiency) and LUE (light use efficiency), depending on the hydric balance of the slope (BH= P-E), its orientation (ε°) and inclination (θ°) that in turn have influence between them. Depending on the magnitude of vegetation development achieving on a definite slope (height H and inclination θ), function from the climatic characteristics on site and from the solar orientation (obligates by functional layout) the additional soil shear strength that may be mobilized in front of a potential instability, it will depend on its geometry and on the vegetative development of its surface. Learning on the mentioned phytoclimatic characterizations, and in the use, for example, of the Taylor abacus which estimation of the critical sliding circle, it is analysed, for soils from coulombian behaviour, the stage of reinforcement achieved at them, according, the importance of vegetation growth in its surfaces. As an example, and reducing the accuracy of data by the approximate generalization from global aspects, it is applied this type of analysis to an important and nearly future civil work construction with larger earth-moving volume and cuts length from moderate heights the California High Speed Railway System (CHSRS) in U.S.A. This type of point of view can be of interest for the geoenvironmental design of linear works infrastructures and for the financing of "green works" that carries with themselves.