Centrifuge modelling of reverse fault–foundation interaction

The propagation of reverse faults through soil to the ground surface has been observed to cause damage to surface infrastructure. However, the interaction between a fault propagating through a sand layer and a shallow foundation can be beneficial for heavily loaded foundations by causing deviation of the fault away from the foundation. This was studied in a series of centrifuge model tests in which reverse faults of dip angle 60° (at bedrock level) were initiated through a sand layer, close to shallow foundations. The tests revealed subtle interaction between the fault and the shallow foundation so that the foundation and soil response depend on the foundation loading, position, breadth and flexibility. Heavily loaded rigid foundations appeared best able to deviate fault rupture away from the foundation but this deviation could be associated with significant foundation rotations. However, a lightly loaded foundation was unable to deviate a reverse fault and the fault emerged beneath the foundation. This led to gapping beneath the foundation as well as significant rotations and may cause severe structural distress. As well as providing insight into the mechanisms of behaviour, the data from the tests is used to validate finite element analyses in a separate article.     

Camel grazing affects species diversity and community structure in the deserts of the UAE

Camel grazing plays a crucial role in the desert ecosystems of the UAE. In this study, we compare areas grazed by small antelope (Al Maha Resort – the AMR) with areas grazed by both camels and small antelope (Dubai Desert Conservation Reserve – the DDCR). A total of 126 plots were selected during the growing season 2006/07 on three soil substrates: gravel plains, sand flats and sand dunes. In each plot, several vegetation parameters were assessed: density, frequency, percent cover and diversity indices. The replacement of camels with wild antelope has significantly increased the number of species on gravel plains, vegetation density on sand dunes and diversity indices on both sand flats and sand dunes, but significantly decreased plant cover on sand flats and sand dunes. The increase in species diversity in the AMR was attributed to moderate grazing by antelope. Replacement of camels by antelope in the AMR has resulted in change in plant community composition of the three substrate types. Species recovered after protection from camel grazing are palatable, especially for camels, except Heliotropium kotschyi and Aerva javanica. The absence of most of the palatable species from the DDCR was attributed to both selective foraging and overgrazing by camels.     

Design and commissioning of a laminar soil container for use on small shaking tables

This paper describes the design, fabrication and commissioning of a single axis laminar shear box for use in seismic soil–structure interaction studies. A laminar shear box is a flexible container that can be placed on a shaking table to simulate vertical shear-wave propagation during earthquakes through a soil layer of finite thickness. The laminar shear box described in this paper was designed to overcome the base shear limitations of a small shaking table at The University of Western Ontario. The design details of the box are provided in addition to results of dynamic tests performed to commission the box. A synthetic clay comprising sodium bentonite mixed with diluted glycerin was used as the model soil and 1-G similitude theory was employed to maintain model to prototype similarity. The model soil was compacted into the container in lifts to achieve soil stiffness that increased with depth. A series of shaking table tests and numerical analyses that were performed to study the performance of the laminar box and non-linear seismic behavior of the model clay are described. The results of this study show that the laminar box does not impose significant boundary effects and is able to maintain 1-D soil column behavior. In addition, the dynamic behavior of the model clay during scaled model tests was found to be consistent with the behavior measured during cyclic laboratory tests.     

Efficient 3D nonlinear Winkler model for shallow foundations

This paper presents a new practical modeling approach, based on the beam-on-a-nonlinear Winkler foundation (BNWF) model, to simulate the 3D rocking, vertical and horizontal responses of shallow foundations using structural elements that are readily available in the element library of commercially available structural analysis programs. An assemblage of a moment-rotation hinge, shear hinge connected in series with an elastic frame member attached to the bottom end of ground story columns was proposed to model the response of the footing under combined action of vertical, horizontal and moment loading. To couple the responses of these hinges, two bounding surfaces equations were introduced and derived mathematically: a surface that defines the interaction between the rocking and vertical capacities of the footing along its width and length; and a surface that defines the interaction between the horizontal capacities of the footing along its width and length. Simple calculation steps to evaluate the geometric and mechanical properties of the proposed assemblage of structural elements are provided. The proposed modeling approach was verified using experimental results from large scale model foundations subjected to cyclic loading. Based on this study, it was found that the proposed assemblage can be reliably used in modeling the rocking and horizontal responses of shallow foundations under cyclic loading.     

Platinum group minerals in podiform chromitites of the Bou Azzer ophiolite, Anti Atlas, Central Morocco

Summary The Neoproterozoic Bou Azzer ophiolite complex hosts numerous, small lenticular bodies of massive and disseminated chromite. Metallurgical-grade high-Mg and high-Cr spinels (cores with 48–62 wt% Cr₂O₃) reveal complex alteration patterns of successive Cr and Mn enrichment and loss of Al towards the rims, while the Mg# ratios [(Mg/(Mg + Fe²⁺)] remain almost constant. Concentration patterns of platinum-group elements are typical for ophiolitic chromitite poor in sulfides, with predominance of the IPGE, variable Rh, and low Pt and Pd. The most abundant platinum-group mineral is Rh-bearing laurite that occurs either included in spinel or in silicate matrix, whereas Os-Ir-Ru alloy is always included in spinel. Laurite inclusions reveal complex intergrowth textures with Rh-Ru-Pt rich alloy, and with Rh-rich sulfide. Most laurites display trends to sulfur-poor compositions leading to local formation of very fine-grained Ru-Os-Ir alloy phases. Ni-Co-Fe sulfides, arsenides and sulfarsenides devoid of PGE are associated with the alteration of chromite. Textural position and chemical composition of the base metal inclusions, as well as comparison of alteration features between chromite and accessory chromian spinel in the Co-Ni-As ores of the Bou Azzer ophiolite indicate a close connection. It is suggested that hydrothermal fluids percolated through the marginal zones of the ophiolite belt during greenschist facies metamorphism and deposited Ni-Co-Fe arsenides, sulfarsenides and minor sulfides as accessories within altered chromitites, and also in structurally favourable zones as Ni-Co-As ores. Author’s address: Dr. Frank Melcher, Federal Institute for Geosciences and Natural Resources, Stilleweg 2, 30655 Hannover, Germany     

Phosphorus removal efficiency from wastewater under different loading conditions using sand biofilters augmented with biochar

Treated wastewater is a valuable resource, particularly in countries facing water shortage such as Jordan. Nevertheless, excess nutrients, especially phosphorus, may have detrimental impacts on receiving waterbodies. Treated wastewater in Jordan often exceeds the recommended levels set by the Jordanian Standards for wastewater reuse and discharge. Therefore, it is important to reduce phosphorus loads to acceptable levels before discharge. Biofiltration is a low-cost technology that has shown good potential for wastewater treatment. The performance of biofilters largely depends on the media used. In this study, local sand and sand augmented with biochar prepared from the olive oil processing waste (SBC) were used as filter media for phosphorus removal from clarified secondary treated wastewater. The two media types were tested under different hydraulic and phosphorus loading conditions to simulate shock, flooding, and inundation conditions. The results showed that sand media was more effective in removing phosphorus (90.8 ± 2.6%) than sand amended with biochar (83.3 ± 3.2%). Both media showed resilience under extreme loading conditions. Although phosphorus removal efficiency was negatively affected following the extreme loading events, the observed effects were temporary. The simulated inundation event further showed that the media was able to retain the adsorbed phosphorus. Furthermore, the phosphorus concentration in the effluent remained within the prescribed discharge guidelines at all times.     

Ionic conductivity in gem-quality single-crystal alkali feldspar from the Eifel: temperature,orientation and composition dependence

We measured the ion conductivity of single-crystal alkali feldspar originating from two different locations in the Eifel/Germany, named Volkesfeld and Rockeskyller sanidine and having potassium site fractions \(C_\mathrm{K}\) of 0.83 and 0.71, respectively. The dc conductivities resulting from electrochemical impedance spectroscopy over the temperature range of 300–900 \(^{\circ }\hbox {C}\) show a weak composition dependence but pronounced differences between the b-direction [\(\perp (010)\)] and \(c^{*}\)-direction [\(\perp (001)\)] of the monoclinic feldspar structure. Conductivity activation energies obtained from the observed linear Arrhenius plots are close to 1.2 eV in all cases, which is closely similar to the activation energies of the \(^{22}\mathrm{Na}\) tracer diffusivity in the same crystals. Taking into account literature data on K tracer diffusion and diffusion correlation effects, the present results point to a predominance of the interstitialcy mechanism over the vacancy mechanism in mass and charge transport on the alkali sublattice in potassium-rich alkali feldspar.     

Late Proterozoic older granitoids from the North Eastern desert of Egypt: petrogenesis and geodynamic implications

Major, trace, and REE data for three localities of calc?Calkaline older granitoid rocks exposed in the north Eastern Desert of Egypt are presented. These rocks were selected to cover wide compositional spectrum of the Egyptian older granitoid varieties. They are petrographically represented by granodiorite, tonalite, quartz?Cdiorite, and quartz?Cmonzodiorite. The rocks are comparable with the peraluminous, unfractionated calc?Calkaline suites and fall within the volcanic arc and I-type granite fields. So, they can be regarded as belonging to the volcanic arc collision stage (665?C614?Ma). The granitoids are geochemically similar to other rocks recorded from continental margin arc-systems being exhibit light-REE enriched patterns with variable but chiefly positive Eu anomaly. The latter has reverse relationship with the ??REE, which was attributed to the fractionation of hornblende during partial melting. These patterns are comparable with models involving partial melting of amphibolitic source. This source must represent basalts, gabbros, or volcanics of an island arc system that were transformed to the level of the island arc crust during continental growth where the P?CT conditions are suitable for partial melting. Thus, it is plausible that the studied rocks were derived by partial melting of LREE-enriched, garnet-free, and amphibole-bearing (i.e., hydrated) mafic source. Wadi Milaha granitoids are consistent with the derivation by a high degree of partial melting (30?C40%) of amphibolite protolith in the deep crust. However, the two other localities (Wadi Umm Anab and West Gharib) are matching with 20?C30% partial melting. Within each locality, variation in rock types from granodiorite to tonalite is said to be dominated by variable degree of restite separation during magma ascent. The high water and volatile contents in Wadi Milaha granitoids allowed higher degree of partial melting (30?C40%). Moreover, the lower volatile contents in the other two localities (Wadi Umm Anab and West Gharib) gave lower degrees of partial melting (20?C30%). These processes may resemble important geodynamic features of the Arabo-Nubian Shield evolution in the north Eastern Desert of Egypt.