Airborne LIDAR (Light Detecting and Ranging) is a relatively new technique that rapidly and accurately measures micro-topographic features. This study compares topography derived from LIDAR with subsurface karst structures mapped in 3-dimensions with ground penetrating radar (GPR). Over 500 km of LIDAR data were collected in 1995 by the NASA ATM instrument. The LIDAR data was processed and analyzed to identify closed depressions. A GPR survey was then conducted at a 200 by 600 m site to determine if the target features are associated with buried karst structures. The GPR survey resolved two major depressions in the top of a clay rich layer at ~10m depth. These features are interpreted as buried dolines and are associated spatially with subtle (< 1m) trough-like depressions in the topography resolved from the LIDAR data. This suggests that airborne LIDAR may be a useful tool for indirectly detecting subsurface features associated with sinkhole hazard.

Understanding the deformation mechanisms of soils and geosynthetics in response to the formation of a void below a geosynthetic-reinforced soil is crucial to provide efficient designs of geosynthetic-reinforced soil systems such as embankments and landfill liners. Centrifuge modelling of the soil and geosynthetic behaviour was conducted using a trapdoor to simulate the formation of a void in a controlled environment at realistic stress levels. A plane-strain model allowed visual observations of the deformation mechanisms using Particle Image Velocimetry. Granular soils and model clay liners were tested, as would be relevant to embankments and landfills respectively. These soils were tested with and without the reinforcement to evaluate the benefit provided by the geosynthetic. Detailed analysis of the centrifuge test results showed that arching significantly reduces the stress at the base of the soil when a void forms; this mechanism is due to stress redistributions and not the formation of a physical arch. A new method to reliably predict this reduction was provided by calculating the coefficient of lateral stress on the failure plane based on the observations of a continuous convex arc of major principal strains above the void, and the assumption that this is indicative of the stress behaviour. The observed results were also used to address the limitations in the current design methods related to the fill behaviour. Expansion in the soil was confined to a parabolic zone above the void estimated from the soil dilatancy, rather than a single, unique coefficient of expansion in the deforming soil. The zone of subsidence was characterised by the combination of a vertical prism and funnel to the surface, with the surface settlement profile better described by a Gaussian distribution rather than the parabolic profile used previously. An adaptation to the design methods for use with compacted clay liners was proposed by considering the clay as a beam with the maximum strain related to curvature and not elongation, and calculating the applied stress on the geosynthetic ignoring the clay arching. Analysis and interpretation of the centrifuge tests has thus given new insight into the soil and geosynthetic behaviour based on visual observations relevant to how these systems deform in practice. This has allowed the recommendation of more efficient design procedures and consequently will facilitate better predictions of geosynthetic-reinforced soil behaviour above voids.

In the field of cybersecurity, the top-level management make use of metrics to decide if the organization is doing well to protect itself from cyber attacks or is in tatters leaving itself susceptible against the vast threats looming around. Not only that but metrics are even used to measure the performance of the security team. The aim of this thesis is to show how economics is closely related to cybersecurity and how metrics play an important role in policy making of an organization. Furthermore, I scrutinize one of the leading security score providers for the way they detect botnet infection. Botnet infection is a part of compromised system group in their score card categories that amounts to 55\% of the total security score. So, it becomes essential for the security score providers to have the right method of grading a company since it will have an impact on how they use their resources to protect itself from outside threat and the insurance premium they pay to cover any successful cyber attacks. I have found out that the data on which the botnet infection vector is graded has false positives. I shed light on security analyst and security team on a whole in their role in making decisions according to the security score. It is even the duty of the security team to work ethically, that is, the aim should not be to improve the security score rather the aim should be to protect the organization from outside attacks and if it happens to increase the security rating then be it so.

No description available.

Current karst hazard maps in Kentucky reflect the general lithology of the state and ignore or significantly reduce the impact of the actual sinkholes present within these areas. These maps rely on equal weighting, by area, of the Karst Potential Index (KPI) map and the sinkhole inventory map. The KPI is based on a 1:500,000 geologic map and less than 500 data points of carbonate rocks. The sinkhole inventory is derived from topographic maps updated in the 1970s with approximately 10-foot resolution. This method gives a preferential weighting of the KPI over the sinkhole data. Consequently, the current method is broad in scope and ineffective in hazard assessment. There is a need for a reliable karst hazard map for land use planners, government emergency planning agencies, and other stakeholders. In this study, more detailed geology information and LiDAR (Light Detection and Ranging) data are applied to three counties (Bullitt, Logan, and Woodford) to generate a more accurate assessment of karst hazard. An assessment method based on sinkhole density is also tested. By refining the hazard score to more precise areas of concern, future stakeholders will find this data useful in emergency planning and land assessment.

This thesis analyzes some of the effects of urbanization in Pinellas County, Florida on the karst landscape. Many sinkholes have been obscured and/or modified for storm water retention by urbanization in Pinellas County, with a few sinkholes still identifiable by characteristic zoning of vegetation, soil moisture, and circular shape. Using aerial photos from 1926 and 2000, karst features were identified by circularity,vegetation, and moisture conditions. Mapping karst surface features using historic aerial photos and maps is a useful exercise that will assist our scientific understanding of karstification in Florida and the nature and extent of karst processes that have acted in the pre-urbanized past. The final product of this research is a digital spatial database and metadata of karst features discernable on the 1926 and 2000 aerial photos; a description of the karst landscape mapped for each time period; and a morphometric description (including sinkhole area, density, and topography) of the karst landscape mapped for each time period. A total of 2,703 sinkholes were identified on the 1926 aerial photos. By 2000 only 900 sinkholes were still visible, a loss of 87.31%. Most of the loss of these sinkholes was due to the rapid urbanization that happened between 1926 and 2000. A total of 499 sinkholes that had been identified in 1926 have now been modified into storm water retention ponds.

For thousands of years freshwater springs provided the foundations of human settlement in Texas, from Native Americans to Spanish missionaries to German immigrants. However, over the last generation in Texas – and across much of the United States and the rest of the world – water has become just another convenience of modern life, available at the turn of a handle or push of a button. But times are changing. In Texas a perfect storm is brewing as the population booms and water resources deplete, and many people believe water will soon overtake oil as the next big play in the state. Already there is a sustained effort by companies and investors to secure major water assets and rights. At the same time, almost paradoxically, Texans continue to overuse water for lush lawns, poorly suited agriculture, and overtaxed infrastructure without considering the long-term impacts of these habits. As recently as a generation ago, during the previous drought of record in Texas in the 1950s, most Texans either relied on rain for survival – for livestock or agriculture – or knew a family member that did. That connection to water has been all but lost over the last 50 years as reservoirs have brought reliable water supply to an increasingly urbanized population. Now flushing the toilet is as familiar as most people get with the water cycle. Sharlene Leurig, a young woman who is extremely passionate about water in both her professional and personal life, is both a throwback to a different Texas and a promising indicator of how Texans might come to grips with the new water future coming down the pipe. I follow Leurig on her quest to document springs across Texas while also meeting with veteran water experts who’ve spent their lives submerged in the issue. / text

In November 2016, 38 sinkholes formed due to subsurface erosion above undermined ground on Donkerhoek farm near Sasolburg. The fact that the sinkholes formed more than 24 years after mining in the area ceased, emphasised the need for a method to predict the likelihood of sinkhole formation due to subsurface erosion. This is especially relevant for mining houses required to quantify their mine closure risks. The purpose of this study was to investigate the mechanisms and soil properties involved in the formation of the 38 sinkholes on Donkerhoek farm through a fieldwork and laboratory testing programme and develop a method to predict the likelihood of sinkhole formation. Three areas were selected for test pit excavation: an area with large sinkholes, one with small sinkholes and a third with no sinkholes but with a history of subsidence crack formation. The same mechanism of sinkhole formation was observed in both the large and small sinkhole areas: at the soil-rock interface, soil was being eroded into a subsidence crack in the rock, resulting in an upwards migrating cavity and the eventual formation of a sinkhole on surface when the cover over the cavity collapsed. This was the first time that this mechanism was observed in the Sasolburg area, having previously only been identified in the Secunda area. The laboratory tests, carried out on samples obtained during the fieldwork, included foundation indicator, dispersivity, XRF and XRD, soil water retention curves, consolidated undrained triaxial and permeability tests. By comparison of the results from the different study areas, it was concluded that the larger sinkholes form in areas with highly dispersive soils, higher clay content, higher swell potential and a higher capacity to retain suctions when wetted. The following soil properties and factors were identified as the main contributors to sinkhole formation: • The strength of the lid, which is highly influenced by the unsaturated behaviour of the lid material. The lid strength determines the sinkhole diameter; • The erodibility of the material which is influenced by dispersivity and the material obtaining a crumb structure due to desiccation; • The activity of the soil, which influences the volume changes during drying and thereby the width and depth of desiccation cracks; and • The thickness of the soil layer overlying the rockhead. With the critical factors identified, the Van der Merwe method to predict sinkhole size was used as basis to develop an index method to predict the likelihood of sinkhole formation due to subsurface erosion above undermined ground. The method considers combinations of the following factor groups to express a high or low likelihood of the formation of large or small sinkholes in a particular area: • The strength of the lid material, mainly influenced by the unsaturated behaviour of the soil; • The capacity for cavity formation (CCF), which combines the dispersivity, erodibility and activity of the soil; and • The influence of the thickness of the soil layer overlying the rock, evaluated by calculating the ratio between crack width in the rock and the soil layer thickness. / Dissertation (MEng)--University of Pretoria, 2019. / Civil Engineering / MEng (Geotechnical Engineering) / Unrestricted

Sinkholes are a significant hazard for the southeastern United States. Although differences in climate are known to affect karst environments differently, quantitative analyses correlating sinkhole formation with climate variables is lacking. A temporal linear regression for Florida sinkholes and two modeled regressions for Tennessee sinkholes were produced: a general linearized logistic regression and a MaxEnt derived species distribution model. Temporal results showed highly significant correlations with precipitation, teleconnection patterns, temperature, and CO2, while spatial results showed highly significant correlations with precipitation, wind speed, solar radiation, and maximum temperature. Regression results indicated that some sinkhole formation variability could be explained by these climatological patterns and could possibly be used to help predict when/where sinkholes may form in the future.

Dynamic forces in the hydrologic cycle move underground water through Florida's carbonate rocks dissolving chemical components of the rocks, leaving behind caves, solution pipes, and other voids that result in a karst terrain. Ravelling is the common subsidence mechanism throughout most of Florida where unconsolidated materials filter downward into voids in the underlying limestone. A cavity in the overburden develops and enlarges over a period of many years. The enlarged cavity is also known as sinkhole. The investigations of sinkhole characteristics and potential involve studying the regional geology, hydrology and mapping historic sinkholes that have occurred in the area. Use of Cone Penetration Test (CPT) soundings, in conjunction with conventional soil borings are becoming more common in the assessment of subsurface soil conditions in the vicinity of sinkhole-related ground surface. The penetration resistance data by CPT can determine the presence and extent of raveled soil zones characteristic of sinkhole features, and the penetration pore water pressure data can be used to determine the integrity of the clay confining unit at each test sounding location. The objective of this study is to identify the possible location of the confining breach at a sinkhole in Seminole County. The methods used in the assessment of the sinkhole's subsurface conditions were Standard Penetration Test (SPT), which provided information that helped to identify the location of the ravelled zones within the soil profile, and Cone Penetration Test that gave information of the piezometric water levels obtained from the pore pressure dissipation curves. The total head was calculated from the piezometric water levels corresponding to the different elevations. The data were found to exhibit a downward behavior of the total head, starting at around elevation 50 feet, NGVD that extended towards lower elevations. The SPT boring log identified a ravelled zone starting at 31 feet approximately. From both information it was possible to establish that the hydraulic head was influenced by the proximity of the ravelled zones, where the head precipitated rapidly as the elevation decreased. From the result of this study, it was concluded that the location of the breach in the confining layer started at 61.8 feet deep below the ground surface. Potentiometric contour lines at elevation 24.40 feet denoted flow patterns of water from the surroundings of the depression towards the approximate location of the center, which is the existing of subsurface cavity.