Multiscale approach to geo‐composite cellular structures subjected to rock impacts

Geo‐composite cellular structures are an efficient technological solution for various applications in civil engineering. This type of structure is particularly well adapted to resisting rockfalls and can act as a defensive structure. However, the design of such structures is for the most part empirically based; this lack of research‐based design stagnates optimization and advanced development. In this paper, the mechanical behaviour of a geo‐composite cellular structure is investigated using a multi‐scale approach, from the individual cell made up of an assembly of rocky particles contained in a wire netting cage to the entire structure composed of a regular array of cells. Based on discrete modelling of both the cell and structure scales, a computational tool has been developed for design purposes. Copyright © 2007 John Wiley & Sons, Ltd.     

Bifurcation and second‐order work in geomaterials

In this paper, the ability of a material rate‐independent system to evolve toward another mechanical state from an equilibrium configuration, with no change in the control parameters, is investigated. From a mechanical point of view, this means that the system can spontaneously develop kinetic energy with no external disturbance from an equilibrium state, which corresponds to a particular case of bifurcation. The existence of both conjugate incremental strain and stress such that the second‐order work vanishes is established as a necessary and sufficient condition for the appearance of this bifurcation phenomenon. It is proved that this fundamental result is independent of the constitutive relation of the rate‐independent material considered. Then the case of homogeneous loading paths is investigated, and, as an illustration, the subsequent results are applied to interpret the well‐known liquefaction observed under isochoric triaxial loading conditions with loose granular materials. Copyright © 2006 John Wiley & Sons, Ltd.     

Developing the ability to model acid-rock interactions and mineral dissolution during the RMA stimulation test performed at the Soultz-sous-Forêts EGS site,France

The Soultz Enhanced Geothermal System (EGS) reservoir's response to chemical stimulation is assessed by numerical simulation of coupled thermo-hydraulic-chemical processes. To assess chemical interactions between host rocks and a mixture of HCl and HF as well as its potential effects on the Soultz EGS reservoir, new modelling efforts using the FRACHEM code have been initiated. This article presents the model calibration and results. Simulations consider realistic conditions with available data sets from the EGS system at Soultz. Results indicate that the predicted amount of fracture sealing minerals dissolved by injection of a mixture of acids Regular Mud Acid (RMA) was consistent with the estimated amount from the test performed on GPK4 well at Soultz EGS site. Consequently reservoir porosity and permeability can be enhanced especially near the injection well by acidizing treatment.     

Basement lithostratigraphy of the Adula nappe: implications for Palaeozoic evolution and Alpine kinematics

The Adula nappe belongs to the Lower Penninic domain of the Central Swiss Alps. It consists mostly of pre-Triassic basement lithologies occurring as strongly folded and sheared gneisses of various types with mafic boudins. We propose a new lithostratigraphy for the northern Adula nappe basement that is supported by detailed field investigations, U–Pb zircon geochronology, and whole-rock geochemistry. The following units have been identified: Cambrian clastic metasediments with abundant carbonate lenses and minor bimodal magmatism (Salahorn Formation); Ordovician metapelites associated with amphibolite boudins with abundant eclogite relicts representing oceanic metabasalts (Trescolmen Formation); Ordovician peraluminous metagranites of calc-alkaline affinity ascribed to subduction-related magmatism (Garenstock Augengneiss); Ordovician metamorphic volcanic–sedimentary deposits (Heinisch Stafel Formation); Early Permian post-collisional granites recording only Alpine orogenic events (Zervreila orthogneiss). All basement lithologies except the Permian granites record a Variscan + Alpine polyorogenic metamorphic history. They document a complex Paleozoic geotectonic evolution consistent with the broader picture given by the pre-Mesozoic basement framework in the Alps. The internal consistency of the Adula basement lithologies and the stratigraphic coherence of the overlying Triassic sediments suggest that most tectonic contacts within the Adula nappe are pre-Alpine in age. Consequently, mélange models for the Tertiary emplacement of the Adula nappe are not consistent and must be rejected. The present-day structural complexity of the Adula nappe is the result of the intense Alpine ductile deformation of a pre-structured entity.     

A critical evaluation of using bulk sediment instead of fine fraction in environmental marine studies, investigated on example of Rijeka harbor, Croatia

This work tested the preferential use of fine (<63 μm) or bulk sediment (<2 mm) in environmental research of marine sediments in the Eastern Adriatic. Fine fraction sediment containing silt and clay (<63 μm), predominating in the studied area, was examined to evaluate past and present anthropogenic inputs and to test our hypothesis that investigation of bulk sediment should be preferred. Following aqua regia digestion, chemical analyses of 58 elements were performed by ICP/OES, ICP-MS and cold vapor AAS, and statistical analysis was performed. The concentrations of the majority of the analyzed elements increased with age of the sediment, except for Ag and Sn, which had higher concentrations in recent sediments. The previous main sources of metal contamination in Rijeka harbor were now abandoned municipal-sewage outflow and oil refinery, and continuing harbor activities and antifouling paint use. All activities except of antifouling paint use have been decreasing significantly. Anomalies of selected elements were determined by the box-plot method. More anomalies were found in the bulk sediment than in the fine fraction. Results of Q-modality clustering and factor analysis in the fine fraction almost correlate with that applied on bulk sediments. Thus, it can be said that the differences between the element distribution in the bulk and fine fraction are not statistically significant. Our conclusion is that analysis of bulk marine sediment gives a better insight into the state of pollution and supports previous recommendations to use bulk sediment as a chosen media for environmental studies.     

Intercrystalline cation partitioning between minerals of the triplite-zwieselite-magniotriplite and the triphylite-lithiophilite series in granitic pegmatites

Minerals of the triphylite-lithiophilite, Li(Fe, Mn)PO₄, and the triplite-zwieselite-magniotriplite series, (Mn, Fe, Mg)₂PO₄F, occur in the late stage period of pegmatite evolution. Unfortunately, neither are the genetic relationships between these phosphates fully understood nor are thermodynamic data known. Consequently, phosphate associations and assemblages from 8 granitic pegmatites — Clementine II, Rubicon II and III, and Tsaobismund (Namibia); Hagendorf-Süd and Rabenstein (Germany); Valmy (France); Viitaniemi (Finland) — have been tested for compositional zoning and intercrystalline partitioning of main elements by electron microprobe techniques. Although the selected pegmatites display varying degrees of fractionation, and the intergrowth textures indicate different genetic relationships between the phosphates, the plots of mole fractions X _Fe=Fe/(Fe+Mn+Mg+Ca), X _Mn=Mn/(Fe+Mn+Mg+Ca), and X _Mg=Mg/(Fe+Mn+Mg+Ca) can be fitted relatively well with smooth curves in Roozeboom diagrams. Their deviations from symmetrical distribution curves are mainly dependent upon X _Mg or X _Ca, and upon non-ideal solutions. Surprisingly small differences between the partition coefficients were detected for intergrowths of different origin. However, the partitioning of shared components among coexisting phases is clearly dependent upon the conditions of formation. Compositional zoning is observed only when both Fe–Mn phosphates are intergrown mutually or with other Fe–Mn–Mg mineral solid-solutios. Thus, the zoning does not seem to be due to continuous crystallization, but to later diffusion processes. The triplite structure has preference for Mn, Mg, and Ca, while Fe prefers minerals of the triphylite series. A quantification of main element fractionation between minerals of the triphylite and the triplite series is possible in the cases where diffusion can be excluded. For the Fe/(Fe+Mn) ratios of core compositions an equation with a high correlation coefficient (R=0.988) was determined: Fe/(Fe+Mn)_Tr=[Fe/(Fe+Mn)_Li]/{2.737-(1.737)[Fe/(Fe+Mn)_Li]} (Tr=triplite series, Li=triphylite series). Consequently, the Fe/(Fe+Mn) ratio of the triplite series can now also be used in the interpretation of pegmatite evolution, just like that of the triphylite series which has been successfully applied in the past.     

Expériences de drainage et estimation de paramètres en milieu poreux non saturé

Two drainage experiments were carried out to identify the hydraulic parameters of a quartz sand by using inverse modelling. Our results, based on sensitivity and error analyses, show that (i) water content measurements are essential to estimate the parameters of the van Genuchten–Mualem retention curve, (ii) the saturated conductivity ($K_{\mathrm{s}}$) has a low sensitivity to pressure data and is not sensitive to other measures (water content and measured outflow), (iii) the inverse approach can be verified by comparing the simulated outflow to the measured one. To cite this article: H. Beydoun, F. Lehmann, C. R. Geoscience 338 (2006).     

Sedimentological and stratigraphic evolution of northern Lebanon since the Late Cretaceous: implications for the Levant margin and basin

This paper presents an updated review of the Upper Mesozoic and Cenozoic sedimentological and stratigraphic evolution of the Levant margin with a focus on the northern Lebanon. Facies and microfacies analysis of outcrop sections and onshore well cores (i.e., Kousba and Chekka) supported by nannofossil and planktonic foraminifers biostratigraphy, allowed to constrain the depositional environments prevailing in the Turonian to Late Miocene. The “Senonian” (a historical term used to define the Coniacian to Maastrichtian) source rock interval was subdivided into four sub-units with related outer-shelfal facies: (1) Upper Santonian, (2) Lower, (3) Upper Campanian, and (4) Lower Maastrichtian. This Upper Cretaceous rock unit marks the major drowning of the former Turonian rudist platform. This paper confirms the Late Lutetian to Late Burdigalian hiatus, which appears to be a direct consequence of major geodynamic events affecting the Levant region (i.e., the continued collision of Afro-Arabia with Eurasia), potentially enhanced by regressional cycles (e.g., Rupelian lowstand). The distribution of Late Burdigalian–Serravallian rhodalgal banks identified in northern Lebanon was controlled by pre-existing structures inherited from the pulsating onshore deformation. Reef barriers facies occur around the Qalhat anticline, separating an eastern, restricted back-reef setting from a western, coastal to open marine one. The acme of Mount Lebanon’s uplift and exposure is dated back to the Middle–Late Miocene; it led to important erosion of carbonates that were subsequently deposited in paleo-topographic lows. The Late Cretaceous to Cenozoic facies variations and hiatuses show that the northern Lebanon was in a higher structural position compared to the south since at least the Late Cretaceous.     

From micro scale to boundary value problem: using a micromechanically based model

Acta Geotechnica - A 3D multi-scale approach is presented to investigate the mechanical behavior of a macroscopic specimen consisting of a granular assembly, as a boundary value problem. The core...