Throughout the world, large populations directly depend on the food, fuel and fiber produced by agroecosystems. These agricultural systems must be resilient to both increasing population pressures ...and changing environmental conditions. In many cases these systems are rainfed and, in these instances, increased rainfall variability and the elevated risk of extreme events associated with global climate change have the potential to adversely affect agricultural productivity. Adaptive management strategies are therefore necessary to support the long-term sustainability of these systems. An important consideration in developing management practices is the structure of the landscape, or spatial arrangement of land use practices. Landscape structure affects the resilience of agricultural systems in a fundamental way. Hydrological function and the consequent transport of soil are influenced by the configuration of land use practices. Location-specific management practices are thus required for different portions of any given landscape, and while this is understood, there is limited research supporting spatially explicit allocations of specific management practices. To understand and quantify the importance of landscape structure, this research models the effect of spatial arrangements of management practices. Different spatial arrangements are tested using the Unit Stream Power-based Erosion Deposition (USPED) model to assess potential for soil conservation. Multiple landscape configurations are simulated by placing regionally appropriate crop types in management zones based on physical characteristics of the watershed. For example, certain policy-related documents suggest that different management practices are more appropriate for specific portions of an area based on physical characteristics of the watershed. Four management scenarios were designed using variables such as topographic position, slope, and flow accumulation as the basis for assigning agricultural practices. In turn, the effectiveness of each of the scenarios is measured by a series of simulations to assess the sensitivity of the landscape to different management approaches as expressed by soil transport. Scenarios are compared against benchmark landscape configurations, including in situ practices and a randomly allocated configuration. The results of these model scenarios suggest soil transport is sensitive to the spatial arrangement of management practices. Management configurations designed to limit soil transport in areas of large upstream contributing areas show measurable reductions in potential soil transport. Counterintuitively, configurations based on watershed position and slope resulted in higher levels of soil transport than the in situ observations. The presented approach represents a useful model for understanding best management practices, exploring potential optimal land-management configurations, and serves as a framework for broader scale analyses.
A numerical investigation was conducted to evaluate the geotechnical safety and slope
stability of Municipal Solid Waste (MSW) landfills, considering the effects of
geosynthetic reinforcements, ...biodegradation of the waste, and associated changes in
material properties, and extreme wind force simulating hurricane conditions. Three
different landfill slopes, 1:1, 1:2, and 1:3 having the height of 122m and width of 2134m,
were analyzed using Limit Equilibrium Method (SLOPE/W) and Finite Element
Modeling (ANSYS). Techniques developed in this study were used to analyze a case
history involving a geogrid reinforced mixed landfill expansion located in Austria. It was
found that few years after construction of the landfill, there is a significant decrease in the
FS due to biodegradation. Extreme wind loading was also found to cause a substantial
loss in the FS. The geosynthetic reinforcement increased the slope stability and
approximately compensated for the damaging effects of biodegradation and wind
loading.
Includes bibliography.
Thesis (M.S.)--Florida Atlantic University, 2016.
FAU Electronic Theses and Dissertations Collection
Experimental and theoretical studies have demonstrated that behaviour of unsaturated soils is governed by two independent stress-state variables, soil suction and net normal stress. Most documented ...case histories focused on responses of soil suction but often overlooked possible influences due to net normal stress. The principal objectives of this research are to investigate seasonal performance of a saprolitic hillslope due to changes of soil suction and net normal stress and to identify in situ groundwater flow mechanisms. Moreover, effects of the two variables and drying-wetting cycle on stress-dependent soil-water characteristic curve (SDSWCC) and permeability function, k(ψ) of a saprolite are measured and investigated.Three interconnected research methodologies, namely full-scale field monitoring (Part I), laboratory investigations (Part II) and two- and three-dimensional (2D and 3D) flow analyses (Part III), are adopted. In Part I, a saprolitic hillslope situated in Hong Kong was selected to be heavily instrumented. Two-year seasonal variations of soil suction and net normal stress were closely monitored by heat dissipation matric water potential sensors and earth pressure cells, respectively. Slope movements were also measured. To provide input parameters for flow analyses in Part III, SDSWCC and k(ψ) of the saprolite were measured by two new test apparatuses directly in Part II. A series of 2D and 3D transient flow analyses were performed in Part III to back-analyse measured pore-water pressure (PWP) responses in Part I.Evident seasonal slope movements are observed throughout the 2-year monitoring period. When a heavy rain fell in wet seasons, measured increases of both positive PWP and equivalent “effective” stress led to a “deep-seated”-type of down-slope ground deformation. An inelastic horizontal displacement of 40mm was resulted and a shear strain of 8% was estimated at 5.5 depth. In dry seasons, owing to suction recovery of 190kPa and substantial reduction of total horizontal stress, “cantilever”- and “translational”-type of up-slope movements were resulted at the top 5m of the ground. After subjecting to 2 cycles of dry-wet seasons, up-slope rebounds in dry seasons appear not to recover down-slope displacements measured in previous wet seasons fully. A general down-slope rachetting is identified.Under the heavy rainfalls, significant rise of the main groundwater table which was at 11m depth is observed. This is mainly attributed to 3D cross-slope groundwater flow on top of a shallowed decomposed rock stratum. The increase of positive PWP in deeper regions due to the GWT rise and the observed “deep-seated” mode of ground deformation shape imply a reduction of stability for “deep-seated” slope failure.Drying and wetting full-suction SDSWCCs and stress-dependent k(ψ)s of the saprolite were measured at vertical net normal stresses of 0, 40 and 80kPa. At a given suction, the k(ψ) decreased by up to 1 order of magnitude when average net normal stress increased from 4 to 78kPa. A noticeable hysteresis loop is observed between the measured drying and wetting k(ψ)s. On the contrary, hysteresis between the drying and wetting k(θ)s (where θ is volumetric water content) appear to be not very significant at any stress level.
Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2011
A structural system consisting of micropiles fixed by a cap beam can be used to provide an engineered solution for stabilization of landslides. For this technology to gain wider acceptance by ...practicing engineers, a reliable design procedure is required. The most widely-cited method is described in the micropile design manual published by the Federal Highway Administration (Sabatini, et al., 2005). The method is based on the assumption that landslide forces are transferred to the micropile wall by two mechanisms: (1) side shear between the sliding soil mass and the micropiles above the slide plane and (2) as a concentrated force acting at the slide surface and distributed to the micropiles, each of which is modeled as a single free-headed pile. This model fails to account for (a) load transferred between the micropiles through the cap beam, i.e., the micropile wall is a structural system, not a collection of individual, free-standing elements and (b) load transferred laterally from the moving mass of soil, as opposed to a concentrated force at the slide surface. The limiting condition using this method is bending resistance of the individual micropiles. However, case studies of instrumented micropile walls in Alabama, Ohio, Canada, and Wyoming demonstrate that micropiles develop resistance to sliding primarily through mobilization of axial load, and that bending moments are much smaller than predicted by the FHWA method. In this thesis, a new design procedure is proposed in which the micropile wall is modeled and analyzed as a structural frame. Using this approach, micropiles resist distributed soil loads through axial tensile and compressive forces rather than in bending. The computed axial loads control the design of the structure and provide a more realistic representation of structural performance. Based upon determined maximum axial loads, micropiles can then be designed structurally, and geotechnically for proper embedment based upon pile side friction. The proposed method is described and example calculations are presented to illustrate its application to slope stabilization.
The objective of this study is to investigate the stability problems in tailing (i.e. mine waste) dams. A tailing dam is an embankment dam (made of natural borrow or tailing material) constructed to ...retain slurry-like mining wastes that are produced as a result of operation of mines. In the last 30 years, the stability of tailing dams has drawn much attention as a significant number of tailing dam failures have been recorded worldwide. These instability problems caused significant loss of life and damage to property in addition to environmental hazards. In this study causes of failure of tailing dams and their stability problems are investigated with respect to their geometric and material characteristics. Seepage and stability of tailing dams are studied through limit equilibrium method and finite element method. The effects of uncertainties in material properties on the stability of tailings dams is investigated. Within this context, Kastamonu-Kure copper tailings dam is used as a case study and material properties are determined by laboratory tests.
Straw wattles are common erosion control devices used to trap sediment. Thisthesis studies the relationship of straw wattles on slope stability through a case studydemonstrating their use on steep ...slopes (1.5H:1V) for the US20 highway realignmentproject. Several surficial slope failures have occurred on these fill slopes, often bracketedby straw wattles, which were hypothesized to contribute to the slope failures. To date,little is known about straw wattle placement and its effect on surficial slope stability.Prior studies have evaluated slope stability against slope height, slope angle, vegetation,rainfall, and other variables but have not assessed the influence of straw wattle placementon surficial stability.Several laboratory tests were performed to characterize the fill soil and the strawwattles for numerical modeling and evaluation. Straw wattles were shown to quicklyabsorb a substantial amount of water (a water content of 400% within 15 minutes) andrequire a substantial amount of time to dry (several days at high temperatures). Severalmodeling scenarios were run (varying the slope angle, slope height, straw wattle spacingand climate condition) to determine the overall effect of straw wattles on deep andsurficial slope stability. Overall, straw wattles were shown to have no significant effecton surficial slope stability, particularly compared to modeling uncertainty and soilvariability. Of the 366 models run, 26% showed a change in factor of safety (0.006 onaverage) against surficial slope failure when straw wattle spacing was increased. Overhalf of the 26% showed a decrease in factor of safety.Other influencing factors such as slope angle, ground water elevation andenvironmental conditions have a much more significant impact on slope stability. Theslopes themselves were found to have a low factor of safety (≤1, at the limit ofequilibrium) against surficial slope failures and a reasonable factor of safety (>1.5)against deeper failures, regardless of straw wattle spacing. Investigations using 3D laserscanning verified that straw wattles were installed along the same slope contours,therefore, not allowing water to pond behind the straw wattle and decrease the factor ofsafety against surficial slope failure.
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