Research for time-temperature equivalence effect of rock (I):Theory research

In order to know about the rheological properties of rock in a long range of the time scale,method of increasing temperature was brought forward to accelerate the rheological process of rock,which could extend the time scale of experimental test data.Firstly,based on the generalized linear viscoelastic constitutive equation with temperature variable,the creep behavior of rock was divided into three types according to the different strain dependences of the time,that is,Hookean deformation,Newtonian flow,and retarded elasticity.Then the general equivalence relationship between time parameter and temperature parameter was derived for each type of strain.Finally,the relation between time parameter and temperature parameter in the whole creep was considered and the general theory of time-temperature equivalence effect(TTEE) of rock was established.This research reveals: ①The temperature effect on the instantaneous strain could be modified through vertical shift.②The key point of the TTEE of Newtonian flow depends on whether in the study of linear viscoelastic behavior of rock change of temperature is completely equivalent to a shift of the logarithmic time scale or not.③By plotting the results of a creep experiment performed at different temperatures and comparing the curves obtained,one can decide whether the rock considered have TTEE.④The TTEE of the whole creep should satisfy that the horizontal shift function of Newtonian flow and retarded elasticity is consentaneous.     

Major and trace element compositions (including REE) of mineral,thermal, mine and surface waters in SW Germany and implications for water–rock interaction

The near-surface water cycle in a geologically complex area comprises very different sources including meteoric, metamorphic and magmatic ones. Fluids from these sources can react with sedimentary, magmatic and/or metamorphic rocks at various depths. The current study reports a large number of major, minor and trace element analyses of meteoric, mineral, thermal and mine waters from a geologically well-known and variable area of about 200 × 150 km in SW Germany. The geology of this area comprises a Variscan granitic and gneissic basement overlain in parts by Triassic and Jurassic shales, sandstones and limestones. In both the basement and the sedimentary rocks, hydrothermal mineralization occurs (including Pb, Cu, As, Zn, U, Co and many others) which were mined in former times. Mineral waters, thermal waters and meteoric waters flowing through abandoned mines (mine waters) are distributed throughout the area, although the mine waters concentrate in and around the Schwarzwald.The present analyses show, that the major element composition of a particular water is determined by the type of surrounding rock (e.g., crystalline or sedimentary rocks) and the depth from which the water originates. For waters from crystalline rocks it is the origin of the water that determines whether the sample is Na–Cl dominant (deeper origin) or Ca–HCO₃ dominant (shallow origin). In contrast, compositions of waters from sedimentary rocks are determined by the availability of easily soluble minerals like calcite (Ca–HCO₃ dominant), halite (Na–Cl dominant) or gypsum (Ca–SO₄ dominant). Major element data alone cannot, therefore, be used to trace the origin of a water. However, the combination of major element composition with trace element data can provide further information with respect to flow paths and fluid–rock interaction processes. Accordingly, trace element analyses showed, that:

• −Ce anomalies can be used as an indicator for the origin of a water. Whereas surface waters have negative or strongly negative Ce anomalies, waters originating from greater depths show no or only weak negative Ce anomalies.
• −Eu anomalies can be used to differentiate between host rocks. Waters from gneisses display positive Eu anomalies, whereas waters from granites have negative ones. Waters from sedimentary rocks do not display any Eu anomalies.
• −Rb and Cs can also be indicators for the rock with which the fluid interacted: Rb and Cs correlate positively in most waters with Rb/Cs ratios of ∼2, which suggests that these waters are in equilibrium with the clay minerals in the rocks. Rb/Cs ratios >5 indicate reaction of a water with existing clay minerals, whereas Rb/Cs ratios <2 are probably related to host rock alteration and clay mineral formation.

The chemical compositions of carbonate precipitates from thermal waters indicate that rare earth elements (REEs), Rb and Cs concentrations in the minerals are controlled by the incorporation of clay particles that adsorb these elements.     

A model for multiphase flow and transport in porous media including a phenomenological approach to account for deformation—a model concept and its validation within a code intercomparison study

Multiphase flow processes in unsaturated cohesive soils are often affected by deformation due to swelling and shrinking as a result of varying water contents. This paper presents a model concept which is denoted ‘phenomenological’ in terms of the processes responsible for soil deformation, since the effects of deformation on flow and transport are only considered by constitutive relations that allow an adaptation of the hydraulic properties. This new model is validated in a detailed intercomparison study with two state-of-the-art models that are capable of explicitly describing the processes relevant for the deformation. A ‘numerical experiment’ with a state-of-the-art reference model is used to produce ‘measurement data’ for an inverse-modelling-based estimation of the model input parameters for the phenomenological concept.     

Does vertical seismic force play an important role for the failure mechanism of rock avalanches? A case study of rock avalanches triggered by the Wenchuan earthquake of May 12, 2008, Sichuan,China

The Wenchuan earthquake triggered 15,000 rock avalanches, rockfalls and debris flows, causing a large number of causalities and widespread damage. Similar to many rock avalanches, field investigations showed that tensile failure often occurred at the back edge. Some soil and rock masses were moved so violently that material became airborne. The investigation indicates that this phenomenon was due to the effect of a large vertical seismic motion that occurred in the meizoseismal area during the earthquake. This paper analyses the effect of vertical earthquake force on the failure mechanism of a large rock avalanche using the Donghekou rock avalanche as an example. This deadly avalanche, which killed 780 people, initiated at an altitude of 1,300 m and had a total run-out distance of 2,400 m. The slide mass is mainly composed of Sinian limestone and dolomite limestone, together with Cambrian slate and phyllite. Static and dynamic stability analysis on the Donghekou rock avalanche has been performed using FLAC finite difference method software, under the actual seismic wave conditions as recorded on May 12, 2008. The results show that the combined horizontal and vertical peak acceleration caused a higher reduction in slope stability factor than horizontal peak acceleration alone. In addition, a larger area of tensile failure at the back edge of the avalanche was generated when horizontal and vertical peak acceleration were combined than when only horizontal acceleration was considered. The force of the large vertical component of acceleration was the main reason rock and soil masses became airborne during the earthquake.     

SPH model for fluid–structure interaction and its application to debris flow impact estimation

On 13 August 2010, significant debris flows were triggered by intense rainfall events in Wenchuan earthquake-affected areas, destroying numerous houses, bridges, and traffic facilities. To investigate the impact force of debris flows, a fluid–structure coupled numerical model based on smoothed particle hydrodynamics is established in this work. The debris flow material is modeled as a viscous fluid, and the check dams are simulated as elastic solid (note that only the maximum impact forces are evaluated in this work). The governing equations of both phases are solved respectively, and their interaction is calculated. We validate the model with the simulation of a sand flow model test and confirm its ability to calculate the impact force. The Wenjia gully and Hongchun gully debris flows are simulated as the application of the coupled smoothed particle hydrodynamic model. The propagation of the debris flows is then predicted, and we obtain the evolution of the impact forces on the check dams.     

Strain accumulation and fluid–rock interaction in a naturally deformed diamictite,Willard thrust system,Utah (USA): Implications for crustal rheology and strain softening

Structural and geochemical patterns of heterogeneously deformed diamictite in northern Utah (USA) record interrelations between strain accumulation, fluid–rock interaction, and softening processes across a major fault (Willard thrust). Different clast types in the diamictite have varying shape fabrics related to competence contrasts with estimated effective viscosity ratios relative to micaceous matrix of: ∼6 and 8 for large quartzite clasts respectively in the Willard hanging wall and footwall; ∼5 and 2 for less altered and more altered granitic clasts respectively in the hanging wall and footwall; and ∼1 for micaceous clasts that approximate matrix strain. Within the footwall, matrix X–Z strain ratios increase from ∼2 to 8 westward along a distinct deformation gradient. Microstructures record widespread mass transfer, alteration of feldspar to mica, and dislocation creep of quartz within matrix and clasts. Fluid influx along microcracks and mesoscopic vein networks increased westward and led to reaction softening and hydrolytic weakening, in conjunction with textural softening from alignment of muscovite aggregates. Consistent Si, Al, and Ti concentrations between matrix, granitic clasts, and protoliths indicate limited volume change. Mg gain and Na loss reflect alteration of feldspar to phengitic muscovite. Within the hanging wall, strain is overall lower with matrix X–Z strain ratios of ∼2 to 4. Microstructures record mass transfer and dislocation creep concentrated in the matrix. Greater Al and Ti concentrations and lower Si concentrations in matrix indicate volume loss by quartz dissolution. Na gain in granitic clasts reflects albitization. Large granitic clasts have less mica alteration and greater competence compared to smaller clasts. Differences in strain and alteration patterns across the Willard thrust fault suggest overall downward (up-temperature) fluid flow in the hanging wall and upward (down-temperature) fluid flow in the footwall.     

A new mathematical model for soil-column experiment and parameter identification

In this paper, one-dimensional soil-column experiment and its mathematical models were discussed. Due to nonlinear behaviors of solute transport in soil and groundwater, the ordinary retardation factor could be a nonlinear function of solute concentration, and the zero production term could be modified to a nonlinear term related with solute concentration, and then a new mathematical model with nonlinear terms was put forward. Furthermore, an inverse problem of identifying nonlinear source parameters was put forward according to the additional data of breakthrough curves （BTCs）. Numerical simulations for the inverse problem here were carried out by applying gradient regularization （GR） method. Finally, the method was successfully used to explore an actual soil-column experiment in Zhangdian, Zibo, Shandong Province.     

Research for time-temperature equivalence effect of rock(Ⅱ):Experimental research

With the creep test data of granite taken from Three Gorges,the existence of time-temperature equivalence effect(TTEE) of granite is investigated.Based on the creep test data at different temperatures,which are 20 ℃,60 ℃,80 ℃,100 ℃,200 ℃,300 ℃,four-component viscoelastic Burgers model is presented to characterize the creep curves.The parameters of elasticity modulus and viscosity coefficient in the constitutive model at different temperatures and their functional dependences on temperature are obtained.Then,according to the basic theory of TTEE presented in research(I),the TTEE of granite is investigated through modifying the compliance curves with vertical shift function and checking the coincidence of the modified curves with horizontal shift functions.It is concluded that:① Burgers model could appropriately characterize the creep property of granite in a short time scale.② Both elastic modulus and viscosity coefficient in the Burgers model decay exponentially with temperature.③ The coincidence of the curves at different temperatures after vertical shift modification and horizontal shift is fine,which indicates the existence of TTEE of granite.④The master curves which reflect the long time scale test data at temperatures 20 ℃,100 ℃,200 ℃ are obtained.     

An equilibrium speciation model for copper in sea and estuarine waters at 25°C including complexation with glycine,EDTA and NTA

An equilibrium speciation model has been derived for copper, glycine, EDTA and NTA in sea and estuarine waters. The model is based on the ion-pairing model of Dickson and Whitfield (1981) for the major components of seawater, and the derivation has taken advantage of recent measurements on many of the interactions involved. The model is intended for use in the calibration of complexation capacity methods, and in the interpretation of bioassay measurements. Fitting functions for the apparent association constants of the organic acids as a function of salinity have been derived, and selected speciation calculations from the literature have been reassessed.     

A micro-mechanics-based elastic–plastic model for porous rocks: applications to sandstone and chalk

A micro-mechanics-based elastic–plastic model is proposed to describe mechanical behaviors of porous rock-like materials. The porous rock is considered as a composite material composed of a solid matrix and spherical pores. The effective elastic properties are determined from the classical Mori–Tanaka linear homogenization scheme. The solid matrix verifies a pressure-dependent Mises–Schleicher-type yield criterion. Based on the analytical macroscopic yield criterion previously determined with a nonlinear homogenization procedure (Shen et al. in Eur J Mech A/Solids 49:531–538, 2015), a complete elastic–plastic model is formulated with the determination of a specific plastic hardening law and plastic potential. The micro-mechanics-based elastic–plastic model is then implemented for a material point in view of simulations of homogeneous laboratory tests. The proposed model is applied to describe mechanical behaviors of two representative porous rocks, sandstone and chalk. Comparisons between numerical results and experimental data are presented for triaxial compression tests with different confining pressures, and they show that the micro-mechanical model is able to capture main features of mechanical behaviors of porous rock-like rocks.     

A 2D mixed fracture–pore seepage model and hydromechanical coupling for fractured porous media

A novel two-dimensional mixed fracture–pore seepage model for fluid flow in fractured porous media is presented based on the computational framework of finite-discrete element method (FDEM). The model consists of a porous seepage model in triangular elements bonded by unbroken joint elements, as well as a fracture seepage model in broken joint elements. The principle for determining the fluid exchange coefficient of the unbroken joint element is provided to ensure numerical accuracy and efficiency. The mixed fracture–pore seepage model provides a simple but effective tool for solving fluid flow in fractured porous media. In this paper, examples of 1D and 2D seepage flow in porous media and porous media with a single fracture or multiple fractures are studied. The simulation results of the model match well with theoretical solutions or results obtained by commercial software, which verifies the correctness of the mixed fracture–pore seepage model. Furthermore, combining FDEM mechanical calculation and the mixed fracture–pore seepage model, a coupled hydromechanical model is built to simulate fluid-driven dynamic propagation of cracks in the porous media, as well as its influence on pore seepage and fracture seepage.

     

Application of the content–area (C–A) fractal model and prediction–area (P–A) plot for mineral prospectivity modeling in the Luchun area of Yunnan Province,China

This method of assigning weights based on expert opinion introduces bias when we are evaluating the relative importance of evidence values. In this paper, we used a prediction–area (P–A) plot method and content–area (C–A) fractal model to estimate the weight of each evidence map. In this paper, we used the content region (C–A) fractal model to divide the evidence maps to the threshold of the corresponding dimensions. The P–A plot approach is an objective data-driven approach for evaluating map weights. Using geochemical layer and remote sensing, hydroxyl layers as weight evidence maps are the highlights of this study. We use the P–A method from which we can evaluate the predictive ability of each evidence map with respect to the known ore occurrences. We used the P–A plot for weighting each evidence map and choosing the appropriate threshold for predictor maps in the Luchun area of Yunnan Province, China. The method adopted in this paper can improve the prediction efficiency of ore prospecting.     

The mantle rock (“laterite”) of the Gold Coast and its origin

Zusammenfassung Der Verwitterungsmantel (Laterit s. l.) der südlichen Goldküste besteht aus Horizonten, die sowohl verschiedene Entstehungsart als verschiedenes Alter haben. Brekzien oder Steinschichten sind unter aridem Klima als Wüstenpflaster entstanden. Zonen chemisch verwitterten Felses, Horizonte von lehmigem Sand (an deren Aufbau Termiten wesentlich beteiligt sind) und Konkretionen haben sich unter feuchtem Klima gebildet. Harte limonitische Oberflächen-Krusten deuten auf progressive Austrocknung hin. Unter diesen drei klimatischen Bedingungen gebildete Horizonte wiederholen sich mehrfach im Verwitterungsmantel der Goldküste. Ein junger, unvollständiger Zyklus ist weit verbreitet, ein älterer Zyklus tritt nur in begrenzten Vorkommen auf, und ein dritter Zyklus ist fast nur noch in aufgearbeiteten, limonitisierten Bruchstücken erhalten. Die wiederholten Klimaschwankungen machen es wahrscheinlich, daß der Verwitterungsmantel zeitlich dem größeren Teil des Quartärs entspricht. Wahrscheinlich können die Ergebnisse auf weit größere Gebiete angewandt werden.     

Selenium and other trace elements in phosphate rock of Bayovar–Sechura (Peru)

Selenium is an essential trace element in regard to human and other animals' health, but it presents a narrow range of dietary deficiency and toxic excess. Some phosphate rocks are rich in selenium. Furthermore it is necessary to control selenium's and other trace elements’ compositions in the phosphate rocks, because phosphorite ores of different geographical sites are varied, and even ores from the same outcrop can vary substantially in trace element levels.     

A distributed water–heat coupled model for mountainous watershed of an inland river basin in Northwest China (II) using meteorological and hydrological data

A distributed water–heat coupled model (DWHC) is calibrated by using daily precipitation data from 26 hydrological and meteorological stations: daily averaged air temperature data from the 11 stations and daily pan evaporation data (E601) from the 15 stations in 2000. Six tests by using different spatial interpolation methods to calculate the above daily meteorological data in each 1 km × 1 km grid, are designed to simulate the mean daily runoff generated from the research Heihe mountainous watershed in 2000. Due to spatial sparseness and asymmetry of the hydrological and meteorological stations, the results of the six tests have little differences. The interpolation method in 3-D mode considering altitude is not better than those taking no account of altitude, nor are the model results when the daily meteorological data at the two stations far from the research watershed are complemented. At last, a nearest neighbor interpolation method in 2-D mode is used to calibrate the DWHC model, in which the revised Nash-Sutcliffe Efficiency NSE, balance error B, determinate coefficient R ², root mean square error RMSE and average absolute error MAE is about 0.61, 0.08%, 0.73, 25.0 and 15.8 m³s⁻¹, respectively. However, by using the daily data in 1999 to validate the model, the NSE, B, R ², RMSE and MAE are, respectively, 0.63, −2.98%, 0.77, 34.9 and 20.3 m³s⁻¹. The reason that the model result is not favorable is mainly because of the lack of detailed soil information, meteorological data and vegetation data; even worse, the basic equations for runoff generation processes are mainly derived from the research results in other regions and meanwhile, its flow concentration method should be improved too. The water balance of the research watershed in 2000 is also discussed in this paper. Though the runoff simulation results are not favorable, the estimated evapotranspiration and runoff components are in accordance with the usual knowledge qualitatively, parts of which meet with the field measurements. According to the model results, the runoff is mainly generated from the land surfaces and shallow soil layers in this cold mountainous watershed. The alpine meadow has evident water conservation function based on the model results, field investigation and field observation results. The DWHC model also reproduces the formation processes of the thick-layered ground ice to some extent, though it is suppositional due to lack of detailed soil, vegetation and meteorological information.     

Migration and bio-absorption of ~(125)I in soil

The biogeochemical migration of iodine in soil and its effect factors were studied by the isotope tracer (125I) and experiments of leaching and absorption by Chinese cabbage to iodine under simulated condition. The results show that the quantities of tran…