Hydrogeological and geotechnical aspects of the Tennessee-Tombigbee Waterway

The Tennessee-Tombigbee Waterway is in the East Gulf Coastal Plain physiographic province The River and Canal sections were constructed on the floodplain of the Tombigbee River Locks and dams in this section are founded on sediments of Upper Cretaceous age, composed predominantly of sands, clays, and silts of the Eutaw and Gordo formations The 39-mile long Divide Cut was excavated through higher topography which is underlain by these same formations, along with the McShan formation of similar character Bay Springs Lock and Dam, at the south end of the Divide Cut, is founded on shale of the Hartselle formation, which is Mississippian in age Comprehensive studies and tests were made to evaluate and monitor potential impacts of the waterway on the hydrogeologic environment Observations to date show that adverse impacts are very minimal overall, and these are partially offset by beneficial effects Geologic and groundwater conditions were primary factors in the location and design of major features of the waterway During construction, extensive control of groundwater and dewatering effort was required The excavation, utilization, and disposal of over 200 million cubic yards of material, construction of 10 locks and dams, and over 80 miles of canal were accomplished essentially as planned and designed within budget and ahead of schedule     

Phase equilibria involving humite minerals in impure dolomitic limestones

The natural occurrence of critical assemblages among the phases clinohumite, calcite, dolomite, tremolite, forsterite, diopside, chlorite, and spinel in metamorphosed impure limestones, together with experimental and thermodynamic data, permits the calculation of phase equilibria governing the stability of clinohumite in terms of the variables P, T, and composition of a CO₂-H₂O-HF fluid. Equilibrium constant expressions are given for 23 equilibria that describe the stable phase relations between the above phases. Pure OH-clinohumite is considered to be metastable at relatively low pressures. The occurrence of clinohumite in natural marbles is the result of nonideal fluorine substitution which increases the stability of clinohumite. The stability field for clinohumite +calcite, governed primarily by the equilibrium 4forsterite+dolomite+H₂O = clinohumite+calcite +CO₂, expands to more CO₂-rich fluid compositions with increasing fluorine contents and decreasing total pressure. The F/(F+OH) ratio of clinohumite coexisting with calcite, dolomite, and forsterite is a sensitive indicator of the composition of the mixedvolatile fluid phase. The thermodynamic model is in good agreement with observed phase relations and can be used to gain useful information concerning the P-T-X _fluid conditions responsible for the formation of clinohumite.     

Widespread occurrence of magnesiocummingtonite in ultramafic schists,Cima di Gagnone,Ticino, Switzerland

Abundant magnesiocummingtonite (space group P2₁/m) with Mg/(Mg+Fe) ratios between 0.85 and 0.89 occurs in lenses of schistose metaperidotite enclosed in kyanite-zone rocks of the Lepontine Alps, Ticino, Switzerland. It forms prisms and needles that extend homoaxially from cores of tremolite. Coexisting magnesian phases are olivine, orthopyroxene, talc, magnesite, and chlorite. Except for γ∶z, optical and structural properties of one example fall on extrapolations of existing determinative curves. Analogous to synthetic F-clinoamphiboles, zz∶z has a maximum at approximately 0.7 Mg/(Mg+Fe). Anthophyllite, of almost identical composition, occurs in the same region, often intergrown with cummingtonite along lamellae ‖(010) and ‖(100). Cummingtonite is believed to have partially inverted to anthophyllite during cooling.     

国家地理信息系统展望

本文是ESRI公司于2007年初给美国政府提交的一份关于建设国家级GIS系统的报告,指出目前各领域的GIS系统已经发展到需要相互关联,以建成国家级平台创造更大的效益的阶段。报告描绘了建立国际级GIS系统的愿景,并阐述了系统的构建和实现途径,实现这样一个目标将涉及许多不同部门的参与与协作。     

Ground motion directionality in the 2010–2011 Canterbury earthquakes

This paper examines the observed directionality of ground motions in the Christchurch urban area during the 2010–2011 Canterbury, New Zealand earthquakes. A dataset of ground motions recorded at 20 strong motion stations over 10 different earthquake events is utilized to examine the ratios of various response spectral directionality definitions and the orientation of the maximum direction. Because the majority of previous related studies have utilized overlapping ground motion datasets from the NGA database, the results of this study provide a largely independent assessment of these ground motion aspects. It is found that the directionality ratio between the maximum (100th percentile) and 50th percentile orientation‐independent spectral acceleration is similar to that obtained from recent studies. Ground motions from the 4 September 2010 Darfield earthquake are shown to exhibit strong directionality for source‐to‐site distances up to R_rup = 30 km, notably further than results from a previous study, which suggests that such effects are generally limited to R_rup < 5 km. The adopted dataset also offers the unique potential to consider site‐specific effects on directionality ratios and maximum direction orientations; however, in both cases, site‐specific effects are found not to be significant in the observed empirical results. Copyright © 2014 John Wiley & Sons, Ltd.     

Occurrence of negative epsilon in seismic hazard analysis deaggregation,and its impact on target spectra computation

This paper investigates circumstances behind the occurrence of negative ε (the normalized difference between the spectral acceleration of a recorded ground motion and the median response predicted by a ground motion prediction equation) in probabilistic seismic hazard deaggregation. Negative ε values are of engineering interest because of their impact on the conditional mean spectrum (CMS), which is a proposed alternative to the uniform hazard spectrum (UHS) as a target spectrum for ground motion selection. In the case where target ε values from deaggregation are positive, the CMS calculation produces relatively lower response spectra than the UHS. Positive target ε values occur almost universally in active seismic regions at long return periods of engineering interest, but the possibility of negative target ε values is important because in the case of negative target ε, some relationships between the CMS and UHS would reverse. This paper describes the calculation of target ε, performs parametric studies to determine when negative ε values occur in deaggregation, and investigates the potential impact on target spectrum calculation and ground motion selection. The case studies indicate that special seismicity models and certain ground motion prediction equations have the most significant effect on ε values and a combination of these characteristics in Eastern North America creates the most likely situation for negative target ε to occur. CMS results are nonintuitive when the target ε is negative, but it is not clear that this is a common practical concern because negative target ε occurs only in well‐constrained areas. Copyright © 2011 John Wiley & Sons, Ltd.     

Predicting surf zone injuries along the Delaware coast using a Bayesian network

Natural Hazards - More than 2000 surf zone injury (SZI) events, including 196 spinal injuries and 6 fatalities, were recorded at the five most populated beaches along the 25 miles of...     

Dynamic response of flexible rockfall barriers under different loading geometries

Flexible steel barriers are commonly constructed on steep hillsides to mitigate rockfall. The evaluation of the dynamic response of proprietary flexible barriers is conventionally performed using full-scale field tests by dropping a weight onto the barriers in accordance with the European test standard ETAG 27. The weight typically has a spherical or polyhedral shape and cannot reproduce more complex rockfall scenarios encountered in the field. A rigid slab may load a barrier over a larger area and its effect has not been investigated. In this study, a calibrated three-dimensional finite-element model was developed to study the performance of vertically and horizontally orientated rockfall barriers under concentrated areal impact loads. A new bilinear force-displacement model was incorporated into the model to simulate the behavior of the energy-dissipating devices on the barriers. The effect of different weight geometries was studied by considering impacts by a rigid single spherical boulder and a rigid slab. Results reveal that areal loading induced by a rigid slab increases the loading on the barrier foundation by up to 40 % in both horizontally and vertically positioned barriers when compared to a concentrated load scenario with a single boulder. This indicates that barriers tested under the current test standard does not give the worst-case scenario in terms of foundation loads, and barrier designers should take into account the possible effect of increased foundation loads by reinforcing the barrier posts and/or increasing their spacing.