Eric C. Drumm

Evidence of a wall friction effect in the consolidation of beds of packing materials in chromatographic columns

Abstract Experimental observations demonstrate the intensity of the friction between the bed of a packed chromatographic column and its wall. The wall supports the bed but, in the process, causes the strong radial heterogeneity of the bed which has been previously reported and is now well documented. Friction against the wall is not entirely harmful, however. Without wall friction, the bed would contract with increasing head pressure. the bed in a typical analytical column would be a few mm longer in the absence of mobile phase flow than under standard operation conditions. Experiments demonstrate the existence of bed friction against the column wall in an axial compression column. They show that the friction coefficient depends on the nature of the solvent, the axial compression stress applied to the bed, and the bed length.

Classifying and Assessing the Geologic Contribution to Rockfall Hazard

Rockfalls from roadcuts are a major hazard and pose problems for transportation agencies across the country. In the context of rockfall hazard management, however, no consensus exists about the role of geology in assessing rockfall hazard. This study investigates the geologic contribution to rockfall hazard through application of rockfall hazard rating systems to roadcuts in Tennessee and through additional data collection to reveal correlations between hazard characteristics and geologic attributes. The geologic character of 80 roadcuts in central and eastern Tennessee was evaluated using the Tennessee Rockfall Hazard Rating System (RHRS), which is a revision of the National Highway Institute (NHI) RHRS. Scores for both RHRSs were compared to evaluate whether the improved reproducibility of scoring for the Tennessee RHRS yielded unintended losses of scoring accuracy and sensitivity. Additional geologic attribute data beyond those used in the RHRS system were collected to determine with logistic regression analysis whether relationships among the geologic attributes, rockfall type, and block size exist. Results indicate the revised geologic component of Tennessee’s RHRS is more informative and permits description of a wider spectrum of geologic conditions thandoestheNHI version.Logisticregressionanalysis indicates rockfall type correlates to lithologic variation and the number of discontinuity sets; and block size correlates to structurally controlled rockfall, lithologic variation, mechanical layer thickness, and number of discontinuity sets. Consequently, roadcuts containing potential rockfall modes with two or more discontinuity sets, no lithologic variation, and mechanical thicknesses that exceed 1.0 m are expected to have greater Geologic Character scores.

Application of limit plasticity to the stability of sinkholes

Abstract A solution is obtained using classical plasticity theory and the method of characteristics to evaluate the stability of soils adjacent to a cylindrical void. The soil strength contains both cohesive and frictional components, which allows the solution to be used to evaluate the drained stability of residual soils overlying cavitose bedrock. The method yields a lower bound solution for the magnitude of a surface loading required to cause instability of the system, and provides a description of the slip line defining the failure zone. The results are compared in dimensionless terms for various combinations of cavity diameter and overburden thickness. For a given overburden thickness, small cavities are more stable than large cavities. However, for a given cavity diameter, large overburden thicknesses are shown to be more stable than small thicknesses. This is contrary to conventional slope stability where stability generally decreases with increasing height. The difference is attributed to the role of a circumferential stress component in the axisymmetric solution, which may be significant for small-diameter cavities. Equations are suggested for the determinaton of the vertical stress required to generate an instability, and for estimation of the size or surface extent of damage. These results have significance in soil stability analyses in karst terrain and in the construction of deep foundations such as drilled shafts. The improvement of methods to detect and measure voids in soil ( Fischer and Canace, 1989 ) will make this method particularly attractive.

Stability evaluation for the siting of municipal landfills in karst

Abstract During the siting, construction, and maintenance of facilities in the karst terrain, the stability of the residual soils that overlie the cavitose limestone is often a concern. The development of arching in the residual soils and the associated distribution of stress is important to the stability. The economics of the landfill construction are usually improved by excavating a portion of the residual soil to increase the capacity of the landfill. However, it is generally accepted that for a given diameter of potential limestone cavity, the residual clay soil becomes less stable as the thickness of the soil cover decreases. Geotechnical engineers are often called upon to evaluate the stability of the residual soils as a part of the permitting process or prior to the construction of critical structures such as municipal landfills; yet, simple, rational methods are not available. Simplified methods are needed to estimate the thickness of the soil required to provide stability against soil collapse and the subsequent formation of sinkholes or distress to the surface structures. A simplified method is proposed, which consists of the evaluation of stability with respect to two potential modes of failure within the residual soil. Stability with respect to the first mode depends upon the development of arching in the residual soil, while the second failure mode corresponds to the yielding and plastic flow of the soils into the soil dome and/or rock void. The finite element method was used to conduct parametric studies of both stability modes for a typical residual clay soil over a range of cavity diameters. The results are presented in the form of a design chart. The application of the chart is demonstrated by an example. If a candidate site with a proposed cover soil depth appears to be stable for the anticipated range of cavity diameters, then a more comprehensive subsurface investigation and additional analysis can be conducted to evaluate the stability with respect to the proposed waste loading.

Approximate Solution to the Sokolovskiĭ Concave Slope at Limiting Equilibrium

AbstractThe growth of precision autoguidance systems on construction equipment suggests that nonplanar slopes and landforms now can be constructed readily. Slopes with concave cross sections not only appear more like natural slopes, but can also have superior stability and erosion resistance. Thus, it is desirable to have the description of concave slopes that provide mechanical stability for a given set of soil properties. In this paper, an approximate solution that defines the geometry of critical concave slopes (factor of safety ≈1) in a frictional medium is developed, based on the slip-line field method. The approximate solution is compared with previous numerical results and validated via limit-equilibrium method and FEM analyses. The proposed solution is simple in form, and, when implemented with precision construction equipment, will allow the construction of embankments and reclaimed mine lands that appear more like those in nature and yet are more resistant to erosion.

CALIBRATION OF FIVE-SEGMENT TIME DOMAIN REFLECTOMETRY PROBES FOR WATER CONTENT MEASUREMENT IN HIGH DENSITY MATERIALS

Time domain reflectometry (TDR) is a method of measuring high-frequency signal propagation times. TDR systems are widely used for in situ measurement of soil water content. Water content is one of the principal factors that governs many soil properties and is of special significance to shallow foundation pavement systems. Water content is calculated based on the measured dielectric properties of the soil system. Originally, TDR systems for water content measurement were developed for use in soils with low bulk densities, similar to those found in agriculture. Four highway test sites in Tennessee were instrumented with five-segment TDR probes in the soil subgrade and in the unbound aggregate sub-base. These materials are denser than agricultural soils. After several months of data collection and field verification, the TDR predicted water content and gravimetric water content did not coincide. For this reason, a study was performed with the TDR equipment using each of the four test site subgrade soils and an unbound aggregate sub-base sample. Ten previously published TDR water content relationships were evaluated to determine which relationship most accurately predicted water content for the subgrade soils and for the unbound aggregate sub-base using the five-segment probe. During the course of the study, it was necessary to evaluate the manufacturers relationship between the measured propagation time and the corrected propagation time, which accounts for the epoxy fill between the probe waveguides. The relationship was revised to reduce significant variation in corrected propagation times between segments. It was found that the relationship between inverse signal velocity and soil water content proposed by Herkelrath et al. (1991) most accurately predicted water content for all subgrade soils; however, this relationship required the derivation of a soil-specific slope and intercept. The equation proposed by Baran (1994) most accurately predicted water content for the unbound aggregate sub-base. Both of these relationships appeared to provide a better prediction than the widely used Topps relationship.

Curve Numbers for Low-Compaction Steep-Sloped Reclaimed Mine Lands in the Southern Appalachians

AbstractIn the coal-mining region of the Appalachians, the Forestry Reclamation Approach (FRA) is currently promoted by the U.S. Dept. of Interior, Office of Surface Mining (OSM). FRA’s goal in establishing native forest cover on reclamation sites requires the use of loose spoils rather than traditionally compacted spoils during hillslope reconstruction. Loose spoils improve tree planting survival and enhance overall forest growth. Although FRA has been shown to be successful on low-gradient slopes without excessive runoff leading to erosion, rainfall-runoff relationships have not been studied on steep slopes (>20°) where most surface-mine reclamation typically occurs. A curve number (CN) range representing low-compaction steep-sloped conditions was needed for Appalachian FRA sites. Three active surface-mine sites in East Tennessee were monitored during a 1-year period (June 2009–July 2010) for rainfall (5-min intervals) and runoff hydrology (discharge volume, peak discharge) using a unique Pinson-type co...

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.

Preliminary Screening of Residual Soil Stability in Karst Terrain

The stability of the residual soils that overlie cavitose limestone is often a concern during the siting, construction, and maintenance of facilities in karst terrain. Voids or domes often form in the residual soil above the rock cavities, and unless the thickness of the residual soil is sufficient for the development of arching, the soil may collapse and sinkholes may form. A preliminary screening method is proposed to estimate the thickness of residual soil required to provide stability for a given range of potential soil-void diameters. The method considers two modes of instability for sites with shallow (less than 25 m) overburden. Stability with respect to the first mode (cover collapse) depends on the development of arching in the residual soil and suggests a minimum allowable cover thickness for stability. Stability with respect to the second mode (cover subsidence) corresponds to the yielding and plastic flow of the soils into the soil and/or rock void and suggests a maximum cover thickness above which subsidence should be evaluated. Sites with very thick overburden (more than 25 m) are generally not considered problematic. The limiting conditions for the first stability mode are compared with estimated sinkhole dimensions reported in the literature and the application of the stability chart is demonstrated by an example.

Surface erosion and sediment yields on steep-sloped coal mining reclamation sites in the Appalachian Region.

Reclamation activities on coal mining sites to prevent excessive erosion have traditionally been very successful with the establishment of grass covers, on sites where the slopes are moderate to low. Establishment of native forest cover on reclaimed sites has become a priority directive of the US Department of Interior, Office of Surface Mining. However, standard construction techniques are based on slope stability criteria using high levels of compaction, resulting in poor soil medium for tree survival. A team of researchers at the University of Tennessee are engaged in studies with the overall objective to develop design criteria for stable steep slopes (∼28–35%), minimal erosion, and successful reforestation. A part of the overall project, the focus of this presentation provides a summary of the hydrological and erosion monitoring results at three experimental study sites on active coal mining locations in East Tennessee. Each site was equipped with a fully automated weather station, and consisted of four measurement plots. Sediment yields were measured using Pinson divider budgets following an H-flume and sedimentation tank. Initial results characterized pre-cover conditions in which erosion ranged from approximately < 1 ton to 10+ ton per event. Particle size distributions of the transported sediment from the hillslopes were also characterized. Results from this study will guide erosion control and detention pond design practices at early stages of coal mining reclamation, prior to reestablishment of native forest cover.