Statistical analysis of vitrinite reflectance data—a new approach

The reflectance of vitrinite (collotelinite) particles is a widely used parameter as a geothermometer for the estimation of the thermal maturity of organic matter enclosed in rocks. However, several problems have occurred during the last decades, which can be traced back to basically three causes: human mistakes, technical problems, and problems associated with the structural and compositional inhomogeneity of organic matter. Whilst in most cases the first two types of uncertainties can be handled by standardization, the third can cause significant problems during interpretation due to its generally inestimable character. The suppression of vitrinite reflectance and statistical problems originated from small sample size, and outliers belong to this latter type.International standards, such as the ASTM and the ISO, define the vitrinite reflectance parameter as a statistical average of measured data, disregarding the fact that the average is an unresisting and unrobust statistical parameter. In other words, the average is very sensitive to outliers and distribution.The aim of this research was to find and test a better, more resistant, and robust statistical parameter used by traditional parametric and nonparametric statistics, which can be applied in practice instead of the average. Three categories of statistical problems were studied on coal and disperse organic matter (DOM) samples: the distribution of measured values, the effect of data number, and the effect of outliers on statistical parameters. The statistical experiments carried out on numerous original and generated sample sets show that the median (med) and the most frequent value (Mn), a special weighted average, are better parameters to estimate the thermal maturity of organic matter especially above 1% reflectance value.     

Modelling hygro-thermo-mechanical behaviour of engineered clay barriers — validation phase

The Canadian Nuclear Fuel Waste Management Program (CNFWMP) is evaluating the concept of disposal of nuclear fuel waste in an engineerted vault at a depth of 500 to 1000 m in the plutonic rock of the Canadian Shield. In common with engineered barrier system designs being developed in other countries, the waste would be contained within durable containers that, in turn, would be isolated from the host rock by clay-based materials.

The objective of the CNFWMP is to develop a disposal concept that will protect human health and the natural environment far into the future. Assessments of the conceptual vault designs are based on system theory in which an attempt is made to correlate experiences with theoretical concepts of planned systems in such a way that the resulting coordination is sound and convincing. By necessity, since experiments with a total disposal system can never be performed, both the design and the performance assessment rely on experiments performed on physical models of vault elements over relatively short times and on information inferred from calculations (mathematical models) that simulate the probable behaviour of the system in the space-time domainof interest. For a simulation model to be successful, that is applied within a real world situation, the model must provide information regarding the behaviour of the system of interest that is clearly better, in some way, than the mental image or other abstract model that would be used instead. The results of a series of tests performed within the activity known as validation serve as tangible evidence regarding the success of a model in representing the system of interest.

This paper focusses on the validation of the models that describe the hygro-thermo-mechanical behaviour of the engineered clay-barriers proposed for application in the Canadian disposal system concept. The strategy being used to address the key issues in modelling to minimize the model error and to maximize the usefulness of the simulation model, based on testing procedures, is reviewed. Finally, a concept of the validation of codes/models that describe the unsaturated behaviour of engineered clay barriers, is described.     

Coexisting pyroxenes — a multivariate statistical approach

A population of 117 coexisting nonalkaline pyroxene pairs has been studied statistically to evaluate compositional and thermal effects on the element distribution. K_DMg^opx−cpx is influenced by the Fe/Mg-ratio, by the Ca content—especially of clinopyroxene—and by the content of tetrahedral Al. Fe and tetrahedral Al are found to be negatively correlated. A principal component analysis based on the variation of Si, Al^IV, Al^IV, Fe, Mg, Mn, Ca is performed. Dropping of highly correlated variables does not affect the result significantly. The first principal component reflects the major chemical variation in Fe and Mg. When using Ferrous and ferric iron as separate entries of the analysis, either the second or the third component demonstrates a temperature dependence. It is, however, not possible to obtain pure temperature and chemical components due to the composition not being uncorrelated to temperature of formation. From these components a graph reflecting temperature of formation has been constructed.     

The Vajont slide: Instrumentation— Past experience and the modern approach

The Vajont slide case history is reviewed from the instrumentation point of view.

In the first part, the situation before the major slide of October 9, 1963 is presented, in relation to the studies made and measures adopted to control the rate of movement. The measurements which were made are then discussed with respect to the slide and the theories that were developed at the time on the failure mechanism.

In the second part, the Vajont slide is considered from the modern geotechnical point of view. If engineers had had the benefit in 1960 of the knowledge we have now, over twenty five years later, what kind of instruments would they have installed and what measurements would they have made? The answers to these questions are discussed with reference to the possible prediction of the slide failure and the choice of a strategy to control the rate of failure.

Some aspects of the questions raised in the geotechnical community by the Vajont slope are still unresolved today, and require further research before we can safely predict the behaviour of a slide in a condition of incipient failure when, for reasons still not fully understood, the safety factor drops far below one.     

New approach to milling circuit control—robust inverse Nyquist array design

The aim of this paper is to present an application of robust inverse Nyquist array control design method to a milling circuit in Majdanpek Copper Mine. An existent model of a milling circuit was adopted to respond to robust inverse Nyquist array methodology demand by introducing model uncertainty, and optimal robust controller of milling circuit is designed. The proposed controller is robust for reference signals. The robustness of multivariable feedback systems with designed controller is tested and compared with different, previously designed multivariable controllers. Simulation results, in time domain, demonstrate the preferable performance of the designed robust controller in setpoint tracking. Implementation of the new controller without any investments in new equipment significantly improves performance of the milling process.     

Prediction of elastic settlement of rectangular raft foundation — a coupled FE–BE approach

A numerical method of analysis is proposed for computation of the elastic settlement of raft foundations using a FEM–BEM coupling technique. The structural model adopted for the raft is based on an isoparametric plate bending finite element and the raft–soil interface is idealized by boundary elements. Mindlin's half-space solution is used as a fundamental solution to find the soil flexibility matrix and consequently the soil stiffness matrix. Transformation of boundary element matrices are carried out to make it compatible for coupling with plate stiffness matrix obtained from the finite element method. This method is very efficient and attractive in the sense that it can be used for rafts of any geometry in terms of thickness as well as shape and loading. Depth of embedment of the raft can also be considered in the analysis. Copyright © 1999 John Wiley & Sons, Ltd.     

Coupling of solid deformation and pore pressure for undrained deformation—a discrete element method approach

This paper presents a numerical scheme for fluid‐particle coupling that uses the discrete element method by taking into consideration solid deformation and pore pressure generation. A new water particle element is introduced to calculate pore water pressure due to porosity changes. The water particle element has the same size and shape as the solid element and experiences the same amount of deformation. On the basis of the effective stress principle at the element contact, the total force is equal to the sum of the force transmitted through the solid element contact and the water particle force due to pore water pressure. Analytical solutions of traditional soil mechanics problems, such as isotropic compression and consolidated triaxial undrained test, are used to quantitatively validate the proposed model. The numerical results show good agreement between the model and the analytical solutions. The model therefore provides an effective method to calculate pore pressure in a porous medium in discrete modeling.     

Depositional history of the North Taymyr ice‐marginal zone,Siberia—a landsystem approach

The sediment–landform associations of the northern Taymyr Peninsula in Arctic Siberia tell a tale of ice sheets advancing from the Kara Sea shelf and inundating the peninsula, probably three times during the Weichselian. In each case the ice sheet had a margin frozen to its bed and an interior moving over a deforming bed. The North Taymyr ice‐marginal zone (NTZ) comprises ice‐marginal and supraglacial landsystems dominated by thrust‐block moraines 2–3 km wide and large‐scale deformation of sediments and ice. Large areas are still underlain by remnant glacier ice and a supraglacial landscape with numerous ice‐walled lakes and kames is forming even today. The proglacial landsystem is characterised by subaqueous (e.g. deltas) or terrestrial (e.g. sandar) environments, depending on location/altitude and time of formation. Dating results (OSL, ¹⁴C) indicate that the NTZ was initiated ca. 80 kyr BP during the retreat of the Early Weichselian ice sheet and that it records the maximum limit of a Middle Weichselian glaciation (ca. 65 kyr BP). During both these events, proglacial lakes were dammed by the ice sheets. Part of the NTZ was occupied by a thin Late Weichselian ice sheet (20–12 kyr BP), resulting in subaerial proglacial drainage. Copyright © 2002 John Wiley & Sons, Ltd.     

Non-cylindrical, flexural slip folding in the Ardwell flags—a statistical approach

Non-cylindrical, flexural slip folding is described from the well-known coastal section between Ardwell Bay and Kennedy's Pass, near Girvan, southwest Scotland. Bedding plane slip is recognised by the ubiquitous slickenside striations on bedding surfaces, and these linear elements define the ac kinematic plane of fold formation. This intersects the axial surfaces of folds (ab) in the common direction a which is the movement direction during fold propagation. Statistical treatment of the orientation of structural and kinematic elements yields important conclusions concerning fold formation: the Ardwell folds are markedly non-cylindrical and this is a primary feature amplified during the Ardwell Fold Phase.     

Modelling surface run-off and trends analysis over India

The present study is mainly concerned with detecting the trend of run-off over the mainland of India, during a time period of 35 years, from 1971–2005 (May–October). Rainfall, soil texture, land cover types, slope, etc., were processed and run-off modelling was done using the Natural Resources Conservation Service (NRCS) model with modifications and cell size of 5×5 km. The slope and antecedent moisture corrections were incorporated in the existing model. Trend analysis of estimated run-off was done by taking into account different analysis windows such as cell, medium and major river basins, meteorological sub-divisions and elevation zones across India. It was estimated that out of the average 1012.5 mm of rainfall over India (considering the study period of 35 years), 33.8% got converted to surface run-off. An exponential model was developed between the rainfall and the run-off that predicted the run-off with an R² of 0.97 and RMSE of 8.31 mm. The run-off trend analysed using the Mann–Kendall test revealed that a significant pattern exists in 22 medium, two major river basins and three meteorological sub-divisions, while there was no evidence of a statistically significant trend in the elevation zones. Among the medium river basins, the highest positive rate of change in the run-off was observed in the Kameng basin (13.6 mm/yr), while the highest negative trend was observed in the Tista upstream basin (?21.4 mm/yr). Changes in run-off provide valuable information for understanding the region’s sensitivity to climatic variability.     

Towards an understanding of the southern Appalachian Piedmont crustal transition—A multidisciplinary approach

The Piedmont of the southern Appalachians is characterized by significant geophysical and geological anomalies which indicate there is a major crustal transition. Multiple hypotheses, including a suture zone and a subducted continental margin, have been presented to explain the variations. Although crustal seismic reflection data have provided significant constraints, there are ambiguities inherent in the interpretation of such data. The ambiguities can be reduced by careful consideration of related geophysical and geological observations. Although the importance of correlating crustal reflection data with known geologic features by tracing reflections to drill holes or to the surface cannot be overestimated, only rarely are such correlations possible. In almost all interpretations of crustal reflection structure it is necessary to constrain the model with methods such as seismic refraction, gravity, magnetics, conductivity, and surface geology (including palinspastic reconstructions). When information from these techniques is incorporated into interpretations of the Piedmont crustal structure, the model which appears to be most consistent with the observations is one in which the upper crust of the Piedmont is decoupled from the lower crust, and in which the lower crust thins eastward. The lower crust may be a subducted Precambrian continental margin and its associated transition toward thinner, basinal crust.     

Finite-element analysis of fold propagation — a problematic application?

Finite-element analysis has been used to simulate the progressive development of folds in a single layer of higher viscosity embedded in a matrix of lower viscosity and subjected to layer-parallel compression. In contrast with other studies of the problem, the layer is given an initial deflection which is not a periodic function of distance along the layer, but is instead localized and bell-shaped. The object is to see whether developing buckle folds will become periodic of their own accord.Two models have been studied, both with viscosity ratios of 10 : 1 between layer and matrix, and both with initial deflections of the same amplitude. In Model 1, however, the initial deflection has a greater span than in Model 2. During progressive deformation of the models, the initial deflections amplify, becoming buckle folds. The spans converge toward the same value, but the deflection in Model 1 amplifies faster than in Model 2. No new folds appear in Model 1, but in Model 2 new synclines appear to either side of the initial antiformal deflection. The zone of folding therefore propagates along the layering.The rate of propagation in the finite-element models is not as great as in corresponding models made from physical materials. It is suggested that this discrepancy may be due to cumulative systematic errors in the numerical method, which, in its present form, may not be entirely suitable for treating problems of instability and propagation during geological deformation.     

Strain analysis of a shear zone in a granodiorite—discussion

This paper comments about the use of phenomenological relations between stress and strain parameters in the field of natural deformation of rocks. Three criteria are proposed in order to ensure the validity of such an approach.     

Subsidence breccias in kimberlite pipes—an application of fractal analysis

A particular variety of volcanogenic country rock breccia is described; a contact breccia that has been identified at Venetia, River Ranch and Wimbledon kimberlite pipes. The contact breccia is clast supported with no juvenile kimberlite component, has tightly packed, angular fragments (with occasional rounding of smaller particles), and has a shear-fabric dipping towards the center of each kimberlite pipe or volcanic event. Clasts have preferred orientations parallel to the fabric. Photographs of the breccia in the open pit face and measured data from drill core are analyzed specifically to quantify the clast size distributions and clast shapes by means of fractal analysis. The fractal dimension is one means of characterizing the breccia because the dimension can be specific to a fragmentation mechanism. Clast size distribution fractal dimensions in the coarser particles (greater than circa 3 cm) range from greater than 3 for nonsheared breccia, down to circa 2.3 for the sheared breccia. Breccia characterization based on this fractal analysis suggests that fragmentation occurred initially from confined high-energy explosions, followed by collapse and abrasion by subsequently gravity-induced rockmass subsidence. All studied contact breccias produced a distinctive fractal signature in the finer particles (<3 cm) of circa 1.6 that can be explained by a comminution fragmentation process in that particular particle size range. It is suggested that these subsidence breccias require a substantial volume deficit at depth within the volcanic pipe in order to explain their origin and size. The methodology used in this study could be used to characterize any other volcanic breccia and further model their origins.     

Iron speciation in interaction with organic matter: Modelling and experimental approach

The present study aims to model iron speciation when interacting with natural organic matter. Experimental data for iron speciation were achieved with insolubilized humic acid as an organic matter analogue for 1.8 × 10^− 3 M and 1.8 × 10^− 4 M iron concentrations and 2–5 pH range. Combining EPR spectroscopy and chemical analysis allowed us to fit NICA-Donnan model parameters for both organic complexation of iron and oxides precipitation.