Stability and Evolution of Planar and Concave Slopes under Unsaturated and Rainfall Conditions

Natural slopes are often observed to have a concave, convex, or a combination concave/convex profile, yet constructed slopes are traditionally designed with planar cross-sectional geometry. In this paper, the stability of two planar slopes was compared with that of companion concave slopes, designed to have similar factors of safety (FOS) under gravity loading. The stability of these slopes was then investigated in response to a suction event followed by a precipitation event, and it was shown that both the planar and the concave slopes experienced similar changes in stability. Additional analyses were conducted with a simulated erosion mechanism to investigate how the planar and concave shapes would evolve under a sequence of three similar suction/precipitation/erosion cycles. The results suggest that for these slopes, the second and third simulated weather cycles reduced the stability of the slopes, yet had a lesser effect on the concave slopes than the planar slopes. This is in spite of the fact that the planar slopes became more “concave-like” due to the simulated erosion, and suggests slopes designed to be concave may perform better than the planar slopes

Application of Stability Charts and Reliability Concepts for Simplified Analysis of a Void in Soil Overlying Karst Bedrock

pg(s) 37-4

Effect of temperature averaging on predicted pavement life

Mechanistic-empirical pavement design methods for flexible pavements are based on the assumption that the pavement life is inversely proportional to the magnitude of the traffic-induced pavement strains. These strains vary with the stiffness of the asphalt layer, which in turn varies with temperature. Because these relationships are nonlinear, the additional pavement life consumed at higher-than-average temperatures is not offset by savings at lower-than-average temperatures. As a result, whenever average pavement temperatures are used to determine the asphalt stiffness, pavement life is overestimated. Using hourly pavement temperature data from an instrumented pavement site in Tennessee, the effects of temperature averaging on predicted pavement life are examined and it is shown, for a typical full-depth asphalt pavement section supported by subgrade soils of different strengths, that pavement life can be overestimated by 50% to 75% if the temperatures are aggregated into monthly averages. It is also shown that even hourly average temperatures can produce errors if the hourly distribution of truck traffic is not taken into account

Environmental effects on the predicted service life of flexible pavements

Mechanistic-empirical pavement design methods for flexible pavements are based on the assumption that pavement life is inversely related to the magnitude of the traffic-induced pavement strains. These strains vary with the stiffness of various pavement layers. The stiffness of the asphalt varies with temperature and the stiffness of the unbound base and subgrade materials varies with water content. Because these relationships are nonlinear, the additional pavement life consumed by wheel loads at higher-than-average temperatures or water contents is not offset by savings at lower-than-average temperatures or water contents. Furthermore, the temperature and moisture effects cannot be considered separately and superimposed, they must be considered together. In this paper, seasonal temperature and water content variations observed at instrumented pavement sites in Tennessee are idealized and the combined effects of these seasonal changes on predicted pavement life are evaluated for three typical pavement profiles. The results of the parametric study show that the temperature averaging period, the temperature gradient in the asphalt, and the timing and duration of wet base and subgrade conditions all affect the estimation of pavement life. © 2007 ASCE

Stability Charts for the Collapse of Residual Soil in Karst

Collapse of the residual soil over bedrock cavities often occurs during construction in karst terrain, particularly when the thickness of the residuum is reduced during excavation. Even if an estimate of the strength of the residual soil is known, uncertainty with respect to the size/geometry of the subterranean voids makes a detailed analysis difficult, and straightforward methods to check the stability are needed. In this study, numerical analyses were performed to develop a stability chart expressed in terms of a dimensionless stability number and the geometry of a potential void in the residual soil. The stability charts include the effect of friction angle, and are also developed to allow the investigation of the effect of the inverted strength profile typically observed in karst terrain. Such stability numbers may be useful to estimate the stability of a given site based on the expected thickness of the soil overburden and the likely range of anticipated soil void diameters

Undrained stability of residual soil in karst

Human activity on the karst landscape can result in subsidence or collapse, particularly when the thickness of the residual soil layer is reduced due to excavation. When collapse occurs beneath or adjacent to structures or highways, it may result in extensive damage. The stability of the residual soils that overlie solution cavities in limestone is often a concern during the construction, and a simple means to evaluate the stability of these residual soils may be valuable. In this study, the undrained stability of residual soil in karst terrain was investigated by the Finite Element Method (FEM). The results are summarized in a design chart in terms of dimensionless stability numbers and the geometry of a potential soil void above a cavity in the underlying limestone. The use of the stability chart for short-term stability is demonstrated by an example. Such stability numbers can be useful to estimate the stability of a given site based on the expected thickness of the soil overburden and the likely range of anticipated soil void diameters

Mechanics of column beds : II. Modeling of coupled stress-strain-flow behavior

The rheological behavior of a bed of packing material during its consolidation was investigated using an elastic-plastic model, the Frictional Material Model. This model takes into account the behavior of the packing material under compression stress, its consolidation, its internal friction, its friction against the column wall, and the dependence of the bed's permeability on the local void fraction. The complexity of the problem arises from the nonlinear behavior of the relationships between the critical parameters controlling the column bed behavior and the external stresses applied to this bed. Solutions of the model were calculated for combinations of axial compression and seepage stresses, the latter corresponding to the flow of the mobile-phase stream under typical conditions used in HPLC. The results demonstrate the importance of the internal angle of friction of the packing material used on the degree of radial and axial heterogeneity of the beds of chromatographic columns packed with this material

Observed long -term water content changes in flexible pavements in a moderate climate

A comprehensive instrumentation system was installed at four sites across the state of Tennessee to monitor seasonal variations in the environmental factors affecting flexible pavement response. This paper presents some selected findings obtained from over five years of continuous data collection. The data included temperature and water content of the various pavement layers, and weather information. Falling weight deflectometer (FWD) tests were used to observe the pavement response during different seasons. The measured seasonal variations in subgrade and base water content were observed to be small. Consistent with these observations, the seasonal variations in FWD back calculated subgrade modulus were small, suggesting that these effects may not be important in the design of pavements in moderate climates. Since the pavement systems were new construction, little pavement distress was observed over the study period. However, as the pavements age, water infiltration may increase leading to greater water content changes in the unbound materials

Genomic Surveillance of Rabies Virus in Georgian Canines

Rabies is a fatal zoonosis that is considered a re-emerging infectious disease. Although rabies remains endemic in canines throughout much of the world, vaccination programs have essentially eliminated dog rabies in the Americas and much of Europe. However, despite the goal of eliminating dog rabies in the European Union by 2020, sporadic cases of dog rabies still occur in Eastern Europe, including Georgia. To assess the genetic diversity of the strains recently circulating in Georgia, we sequenced seventy-eight RABV-positive samples from the brain tissues of rabid dogs and jackals using Illumina short-read sequencing of total RNA shotgun libraries. Seventy-seven RABV genomes were successfully assembled and annotated, with seventy-four of them reaching the coding-complete status. Phylogenetic analyses of the nucleoprotein (N) and attachment glycoprotein (G) genes placed all the assembled genomes into the Cosmopolitan clade, consistent with the Georgian origin of the samples. An amino acid alignment of the G glycoprotein ectodomain identified twelve different sequences for this domain among the samples. Only one of the ectodomain groups contained a residue change in an antigenic site, an R264H change in the G5 antigenic site. Three isolates were cultured, and these were found to be efficiently neutralized by the human monoclonal antibody A6. Overall, our data show that recently circulating RABV isolates from Georgian canines are predominantly closely related phylogroup I viruses of the Cosmopolitan clade. Current human rabies vaccines should offer protection against infection by Georgian canine RABVs. The genomes have been deposited in GenBank (accessions: OQ603609-OQ603685)