Effects of anisotropic permeability on stabilization and pore water pressure distribution of poorly cemented stratified rock slopes

Slopes composed of stratified and poorly cemented rocks that fail during heavy rainfalls are typical in the outer zone of Taiwan's Western Foothills. This study investigates how hydraulic conductivity anisotropy influences pore water pressure (PWP) distributed in stratified, poorly cemented rock slopes and related slope stability through numerical simulation. The notion of representing thin alternating beds of stratified, poorly cemented rocks as an equivalent anisotropic medium for ground‐water flow analysis in finite slopes was validated. PWP was then derived in a modelled slope comprising an anisotropic medium with suitable boundary conditions. Simulation results indicate the significance of the principal directions of hydraulic conductivity tensor and the anisotropic ratio on PWP estimation for anisotropic finite slopes. For a stratified, poorly cemented rock slope, estimating PWP utilizing a phreatic surface with isotropic and hydrostatic assumptions will yield incorrect results. Stability analysis results demonstrate that hydraulic conductivity anisotropy affects the slope safety factor and slip surface pattern. Consequently, steady‐state groundwater flow analysis is essential for stratified, poorly cemented rock slopes when evaluating PWP distribution and slope stability. This study highlights the importance of hydraulic conductivity anisotropy on the stability of a stratified, poorly cemented rock slope. Copyright © 2006 John Wiley & Sons, Ltd.     

Population fluctuations of Cerithidea decollata (Gastropoda: Potamididae) in mangrove habitats of the St Lucia Estuary,South Africa

Mangrove macrobenthos species are used as ecological indicators as they are sensitive to changes in sediment properties. In this study, the population density of the common mangrove whelk Cerithidea decollata was assessed during different environmental conditions in the St Lucia Estuary, South Africa. Previously, this species was found to persist through both hypersaline and freshwater-dominated conditions. The natural variability in C. decollata populations could provide information on the potential for this widespread species to be used as an ecological indicator in mangroves. We found that snail population density as well as sediment conductivity, moisture content and organic content differed between three mangrove sites that were monitored between 2010 and 2015. The relationship between snail population density and physicochemical characteristics of the sediment was therefore investigated using a mixed-effects model, and sediment conductivity was found to be the best predictor of C. decollata abundance. The resistance of this species to environmental variability could inform on resilience to ecological shifts, which is important when measuring responses associated with climate change.     

Petrochemistry of the claret creek ring complex,northeast Queensland

The Claret Creek Ring Complex is one of several calc‐alkaline ring complexes in a Carboniferous epizonal batholith emplaced into continental crust at the junction of the Precambrian Georgetown Inlier and the adjacent Palaeozoic Tasman Geo‐syncline, northeast Queensland. Rhyolite ash‐flow sheets plus rhyolite and dacite ring dykes are intruded by two comagmatic central stocks of microgranite and grano‐diorite‐tonalite. The complex may be chemically distinguished from the surrounding, contemporaneous batholith by its low K/Na, Rb/Sr and Th/K ratios. The origin and variation of its magmas is explained by invoking progressive partial melting of low K/Na basaltic andesites. Close relatives to the magma source‐rock are preserved as microdiorite xenoliths, which have contaminated their host granodiorite‐tonalite stock.     

A geological interpretation of the Echuca magnetotelluric survey,Victoria

The northern part of the auriferous Bendigo Zone is obscured by thick Cenozoic sediments of the Murray Basin, and as such remains poorly explored. Consequently, in addition to the 2006 deep seismic line obtained in Central Victoria, a magnetotelluric (MT) survey was completed to provide a signature for the major structures previously defined in the Bendigo area. Based on these correlations a second MT line, which we present here, was completed some 50 km to the north of the original line in an attempt to trace the deep structural trends extending north to the Victorian/NSW border. Extending some 155 km across the central north of the state, data were collected at 52 sites along an east–west profile. The new electrical conductivity model generated correlates well with the results from the southern transect; it confirms previously identified structural trends to the north and identifies additional unknown deep structures, thus adding to the understanding of the geology of the covered region and to its gold-bearing potential.     

西藏南部蛇绿岩套电导率研究

大地电磁(MT)资料显示,青藏高原地壳及地幔中普遍存在着高导层.作为大陆造山带中古洋盆岩石圈残片,蛇绿岩套的电导率测量可为了解古洋盆地区地壳及地幔的电性结构提供极其有用的信息.本研究中,我们在压力为1 GPa或3 GPa下,用交流阻抗谱法测量了采自西藏南部地区的蚀变辉长岩、玄武岩、角闪橄榄岩及方辉橄榄岩四个样品的阻抗谱,并进一步得出样品的电导率,不同样品电导率与温度之间的关系满足Arrhenius关系式.在实验温度范围内,蛇绿岩套电导率的对数logσ位于-6.0~-0.5 S/m之间,且随着温度的增高,不同样品电导率增大约4~5.5个量级.样品在未脱水的情况下,低温段的活化焓变化范围在0.4~0.6 eV之间,高温段的活化焓变化范围为1.7~2.6 eV之间.同时,我们研究了样品中结构水含量及铁含量对实验电导率的影响,验证了样品电导率与铁含量之间呈正比关系.当对样品结构水含量进行归一化后,相同温度下各样品的电导率随铁含量的增加而增大,而对样品铁含量归一化后,相同温度下各样品的电导率随样品中水含量的增加而增大.将实验电导率与藏南地区大地电磁结果进行了对比,发现本研究中各样品高温段实验电导率结果均落在大地电磁结果范围内.