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110 Deforestation Around the World Fig. 4. Topographic map of Yangjiashan Creeping (YC) slope (the upper map shows its location in China). Contours are surface elevation (m). Borehole locations are labeled with a red circle (e.g., BH06-9). Color shading indicates surface maximum attainable creeping speeds larger than 1mm/s, after a 50-year recurrence storm event. The primary sliding direction (red arrow) is determined according to subsiding and swelling belts. The X- and Yaxis are distances from the SE corner (29.9N, 109.1 E). The Yangjiashan community is situated on hills composed of inter-bedded siltstones and sandstones, occasionally interspersed with altered clay layers. The rocks range from highly to completely weathered at the ground surface. The weathered rocks date from the Paleozoic and Mesozoic eras, the 200-900 m thick yellowish interbedded sandstone and siltstone dates from
Landslides Caused Deforestation the Silurian period, and the grey siltstone is from the Triassic period. The infiltration of rainfall through macro pores, which are well-developed in the soil and rock mass, plays a critical role in slope stability. The hills intersect with canyons in which increased erosion takes place during the spring and fall rainy seasons. Although many of the drainage patterns in this region have been altered by human activity, thereby increasing the slope stability, some remain unchanged, even in the inhabited areas (eastern part of the slope). Young’s modulus E(GPa) Poisson’s raioμ density ρ(kg/m 3) cohesion C(MPa) Insitu rock and soils 0.16 0.24 2150 0.38 20 Slip-surface material 0.032 0.32 1950 0.04 16 Middle/lightly weathered mudstone 1.6 0.2 2600 1.6 28 internal friction angle φ(°) Table 1. Geomechanical observations and parameters obtained by field surveys and laboratory tests of saturated specimens. Rock strength and deformation properties are obtained from triaxial compression tests using INSTRON-1346. Four saturated specimens of each layer were tested. During tests, confining pressure was applied step-wise in 3 MPa increment (i.e., 3, 6, 9, and 12 MPa), and vertical load are applied at displacement rate at 0.1 mm/s. 6.1 A prediction for the Yangjiashan slope for the 2010-2019 decade The Triassic siltstone of YC is especially sensitive to pore pressure changes. Because of the complicated stratification, the model is initialized with five borehole soil/rock profiles (18- 50 m depths within the granular soil mantle), with a horizontal resolution of 10 m in delineating the 3000 m by 5500 m simulation domain. In order to reduce spurious numerical boundary effects, the simulation domain encompasses the entire region shown in Fig. 4. The sliding material forms a characteristic alluvial fan, that is with the down-slope section thicker than the upslope section. A thin plate splines (Burrough and McDonnell, 2004) interpolator is used to obtain a sliding mass depth distribution over the grid. In the YC site, there are three model sub-layers to delineate the sliding mass, and one layer to represent the montmorillonite, within which sub-layers 10-12 are assumed to define the slip surface. This is further supported by the creep monitoring data (Fig. 5). This layer has the same chemical composition as the overlying layer but is physically fractured. We use 3 sub-layers to delineate the regolith layer because, although only ~1 m deep, it is the critical layer controlling water infiltration into the creeping slide mass. As it represents granular material under high confining pressure, the viscosity of this thin bed of finer-grained materials is smaller than that of the adjacent layers. The deep underlying rock layer is divided into 7 sub-layers, with mechanical properties specified from laboratory test results. As a link between strain and stress, viscosity Eq. (3) is the most important parameter in continuum modeling of slope movement. Under the same pressure gradient force, the smaller the viscosity, the faster the creeping rate. Non-fractured rocks have viscosity as high as 10 19 Pa•s. The creeping rate thus is minimal for non-fractured rocks. Fractured rocks (granular material), can have viscosities 10 orders of magnitude smaller, depending on confining pressure and lubrication condition (usually water content under natural conditions). A creeping curve indicates that the vertical flow shear is very large within the granular layer. Above and below the granular layer, flow shear is much smaller. For a non- 111
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DEFORESTATION AROUND THE WORLD Edit
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Contents Preface IX Part 1 Deforest
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Preface Forests are giant reservoir
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Preface XI thankful to Maja Bozicev
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Part 1 Deforestation Impacts
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Geospatial Analysis of Deforestatio
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Unsupervised Classification of Aeri
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10 Deforestation and Waodani Lands
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Sustainable Forest Management Techn
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Bunjil Forest Watch a Community-Bas
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Remnant Vegetation Analysis of Guan
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Part 3 Preventing Deforestation
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