Sinkhole Dropouts Due to Underground Utility Installation on Construction Sites

The karst geologic setting of south-central Kentucky presents many challenges to engineers and construction firms. Karst areas are characterized by numerous sinkholes and subsurface drainage systems that can include caves, regolith arches, and highly irregular bedrock surfaces. The increased commercial and residential development in south central Kentucky, particularly Bowling Green which is in Warren County, has created an increased interest in the existence and location of these unmapped karst features, particularly regolith arches. Regolith arches arc formed by the downward movement affine-grained soils as a result of water infiltration from the ground surface into subsurface drainage systems. The reason for this interest in the location of unmapped karst features is the tendency for construction induced vibration and topographic changes to cause collapse of these regolith arches. It is well documented that construction and topographic changes can cause regolith arches to collapse. However, a lesser documented cause has become more common. This cause is the installation of underground utilities. The primary way underground utilities can lead to the dropout of regolith arches is by directing water into an active regolith arch. This occurs because utility lines are typically backfilled with highly permeable gravel. In the Warren County area, native soils are silts and clays which possess a very low permeability. The gravel backfilled utility creates a conduit that captures a significant amount of surface runoff. If a regolith arch is located near and underground utility line, there’s a dramatic increase in water volume entering the regolith arch than would have occurred had the utility line not been installed. This paper will document two case histories in Bowling Green, Kentucky, which is in Warren County, where dropouts have developed due to the combination of construction activity and underground utility construction

Lowland savanna of southeastern Iowa : historical and modern vegetation patterns and implications for management

Lowland savannas are a rare variant of savanna, occurring on alluvial soils, which lack quantitative data on their structure, composition, and restoration. The purpose of this thesis was to assess both historical and modern vegetation composition and structure of lowland savannas and to determine the success of recent management of a lowland savanna remnant. Lowland savanna distribution, composition, structure, and possible flood driven disturbance regime were compared to those of upland savanna and floodplain forest in the Lower Cedar River Valley of southeast Iowa, U.S.A. Furthermore, the effects of fire and abiotic variables on the flora of a degraded lowland savanna remnant were evaluated to assess restoration efforts. The General Land Office survey was used to reconstruct the pre-Euro-American settlement vegetation of the study area and both surveyors\u27 descriptions and tree density were used to determine the distribution, composition, and structure of upland savanna, lowland savanna, and floodplain forest. County GIS layers and soil surveys were used to determine disturbance regimes for these communities. In the savanna remnant, burned and unburned treatments were compared across woodland areas, as well as those dominated by invasive Phalaris arundinacea (reed canary grass). Overstory and understory vegetation composition and abundance, elevation, ground level light, depth of inundation, soil texture, soil carbon, and soil nitrogen were measured in study plots and ordinated. Overall, our data suggested that lowland savanna occurred in the study area, but was compositionally similar to both upland savanna and floodplain forest. Large shade-tolerant tree species occurred historically in lowland savanna. This study did not provide direct evidence that flooding or fire maintained lowland savannas historically, however indirect evidence suggests fire was present on the landscape. In the savanna remnant, burned areas had lowered tree density, but not increased mean basal area. Plots dominated by P. arundinacea had nearly a 50% reduction in P. arundinacea cover. High abundance of P. arundinacea was associated with high soil carbon and nitrogen, but it remains unknown if regular flooding is driving this correlation. Techniques commonly used in upland savanna restoration may not be useful in restoring lowland savannas other than for invasive species control

Chaos in a modified Henon-Heiles system describing geodesics in gravitational waves

A Hamiltonian system with a modified Henon-Heiles potential is investigated. This describes the motion of free test particles in vacuum gravitational pp-wave spacetimes with both quadratic ("homogeneous") and cubic ("non-homogeneous") terms in the structural function. It is shown that, for energies above a certain value, the motion is chaotic in the sense that the boundaries separating the basins of possible escapes become fractal. Similarities and differences with the standard Henon-Heiles and the monkey saddle systems are discussed. The box-counting dimension of the basin boundaries is also calculated.Comment: 11 pages, 7 figures, LaTeX. To appear in Phys. Lett.