Anthropogenic Pb accumulation in forest soils from Lake Clair watershed: Duchesnay experimental forest (Québec, Canada)

Mineral soil horizons (Ae, Bhf1, Bhf2, Bf, BC and C) were carefully collected from two podzolic soil profiles in the Lake Clair watershed (Québec) in order to assess anthropogenic trace metal accumulation. Petrographic and selective analyses were performed to establish the soil mineralogy and properties. Furthermore, a complete sequential extraction procedure has been applied to help understanding the complex chemical speciation of Pb in forest soils. Chemical speciation of Pb showed a strong vertical gradient: 85% of this metal is mainly partitioned in refractory minerals in the C-horizon whereas in the upper Bhf1 and Ae-horizons, less than 50% of Pb is associated with this fraction. In the Ae-horizon, for example, 35%, 30% and 12% of total Pb, respectively, is associated with the exchangeable, labile organic matter and amorphous Fe-Mn oxides fractions. The distribution of Pb and Cr in the studied forest soils mainly reflects progressive contamination of the watershed by anthropogenic atmospheric sources. The anthropogenic source is indicated by elevated Cr and Pb concentrations in the topsoil (Bhf and Ae) horizons and by strong negative correlation between ²⁰⁶Pb/²⁰⁷Pb ratios and total Pb concentrations. According to these isotopic values, penetration of anthropogenic Pb does not exceed 10 cm in both soil profiles. Below this depth, both Pb concentrations and isotopic ratios remain nearly constant and similar to values observed in pre-anthropogenic sediments from Lake Clair. These values are interpreted as the natural geochemical backgrounds of the watershed. Based on that behaviour, calculated anthropogenic Pb net inputs amounted to between 1.24 and 1.8 g/m².     

Coalescence of offset rock joints under biaxial loading

Crack coalescence in rock masses was studied by performing a series of biaxial compresion tests on specimens made of rock-like material. Specimens of size 63.5 × 27.9 × 20.3 cm, made of 72% silica sand, 16% cement (Type I) and 12% water by weight were tested. The joint inclination angle was maintained at 45°, while the offset angle i.e. angle between the plane of the joint and the line that connects the two inner tips of the joints, was changed from 0° to 90° with an increment of 15°. Three levels of lateral stress were used; 0.35 MPa, 0.7 MPa and 1.5 MPa on each sample. HP data acquisition system was used to record the data for each sample. In each sample, four LVDTs were fixed to measure the axial and lateral displacement along the sample. The failure mechanisms were monitored by eye inspection and a magnifier to detect crack initiation and propagation. For each test, the failure surfaces were investigated to determine the characteristics of each surface. Wing cracks initiated at the tip of the joint for the low confining stress applied, while at higher confining stresses wing cracks also initiated at the middle of the joint. Secondary cracks initiated at the tip of the joint due to shear stress. Three modes of failure took place due to coalescence of the secondary and wing cracks. The bridge inclination was the main variable that controlled the mode of failure. For bridge inclination of 0°, the coalescence occured due to shear failure and for bridge inclination of 90° the coalescence occurred due to tensile failure while for the other bridge inclinations coalescence occured due to mixed tensile and shear failure.     

Seismic based characterization of total organic content from the marine Sembar shale,Lower Indus Basin,Pakistan

The exploration and production of unconventional resources has increased significantly over the past few years around the globe to fulfill growing energy demands. Hydrocarbon potential of these unconventional petroleum systems depends on the presence of significant organic matter; their thermal maturity and the quality of present hydrocarbons i.e. gas or oil shale. In this work, we present a workflow for estimating Total Organic Content (TOC) from seismic reflection data. To achieve the objective of this study, we have chosen a classic potential candidate for exploration of unconventional reserves, the shale of the Sembar Formation, Lower Indus Basin, Pakistan. Our method includes the estimation of TOC from the well data using the Passey’s ΔlogR and Schwarzkofp’s methods. From seismic data, maps of Relative Acoustic Impedance (RAI) are extracted at maximum and minimum TOC zones within the Sembar Formation. A geostatistical trend with good correlation coefficient (R²) for cross-plots between TOC and RAI at well locations is used for estimation of seismic based TOC at the reservoir scale. Our results suggest a good calibration of TOC values from seismic at well locations. The estimated TOC values range from 1 to 4% showing that the shale of the Sembar Formation lies in the range of good to excellent unconventional oil/gas play within the context of TOC. This methodology of source rock evaluation provides a spatial distribution of TOC at the reservoir scale as compared to the conventional distribution generated from samples collected over sparse wells. The approach presented in this work has wider applications for source rock evaluation in other similar petroliferous basins worldwide.     

Spatial Topology and its Structural Analysis based on the Concept of Simplicial Complex

This paper introduces a model that identifies spatial relationships for structural analysis based on the concept of simplicial complex. The spatial relationships are identified through overlapping two map layers, namely a primary layer and a contextual layer. The identified spatial relationships are represented as a simplical complex, in which simplices and vertices, respectively, represent two layers of objects. The model relies on the simplical complex for structural representation and analysis. To quantify structural properties of individual primary objects (or equivalently simplices), and the simplicial complex as a whole, we define a set of centrality measures by considering multidimensional chains of connectivity, i.e. the number of contextual objects shared by a pair of primary objects. With the model, the interaction and relationships with a geographic system are modeled from both local and global perspectives. The structural properties and modeling capabilities are illustrated by a simple example and a case study applied to the structural analysis of an urban system.     

Precipitation in the Anatolian Peninsula: sensitivity to increased SSTs in the surrounding seas

Effects of the increased sea surface temperatures (SSTs) in the surrounding seas of the Anatolian Peninsula on the precipitation it receives are investigated through sensitivity simulations using a state-of-the-art regional climate model, RegCM3. The sensitivity simulations involve 2-K increases to the SSTs of the Aegean, eastern Mediterranean and Black seas individually as well as collectively. All the simulations are integrated over a 10-year period between 1990 and 2000. The model simulations of this study indicate that the precipitation of the peninsula is sensitive to the variations of the SSTs of the surrounding seas. In general, increased SSTs lead to increases in the precipitation of the peninsula as well as that of the seas considered. The statistically significant increases at 95% confidence levels largely occur along the coastal areas of the peninsula that are in the downwind side of the seas. Significant increases do also take place in the interior areas of the peninsula, especially in the eastern Anatolia in winter. The simulations reveal that eastern Mediterranean Sea has the biggest potential to affect the precipitation in the peninsula. They also demonstrate that taking all three seas into account simultaneously enhances the effect of SSTs on the peninsula’s precipitation, and extends the areas with statistically significant increases.     

Contributions of Basin-edge-induced Surface Waves to Site Effect in the Dinar Basin,Southwestern Turkey

Ground motion amplifications in the Dinar basin, and contributions of the surface waves generated from basin edges are investigated in frequency and time domains. Amplification functions are computed from the aftershock data of the October 1, 1995 Dinar earthquake (M_W=6.4) using the Standard Spectral Ratio method which requires a pair of instruments; one located at the site under investigation (generally on alluvium) and the other on a reference site, preferably a nearby rock site. First, a time window covering the whole signal is used to compute the amplification function, and, successively, the noise, P wave, S wave and the surface wave time windows are used in computation to observe their contributions to the amplification function. It is seen that the maximum amplifications observed at about 2.0 Hz on the amplification functions of the stations located in the basin are largely due to basin edge induced surface waves. These waves have significantly increased the duration of signals recorded within the basin. Particularly, on the vertical component records, the amplitudes of surface waves are larger than the S-wave amplitudes. The periods of waves amplified maximally due to the basin structure coincide with the natural periods of 4–6-story buildings which were heavily damaged in Dinar. This indicates that the site effects may have been important regarding the damage which occurred during the Dinar earthquake of October 1995.     

An Empirical Method for Analysis of Load Transfer and Settlement of Single Piles

An empirical method is developed for estimating the load transfer and deformation of drilled, in situ formed piles subjected to axial loading. Firstly, governing equations for soil–pile interaction are developed theoretically, taking into account spatial variations in: (a) shaft resistance distribution and (b) ratio of load sharing between the shaft and base. Then generic load transfer models are formulated based on examination of data from 10 instrumented test piles found in the literature. The governing equations and load transfer models are then combined and appropriate boundary conditions defined. Using an incremental-iterative algorithm whereby all the boundary conditions are satisfied simultaneously, a numerical scheme for solving the combined set of equations is developed. The algorithm is then developed into an interactive computer program, which can be used to predict the load-settlement and axial force distribution in piles. To demonstrate its validity, the program is used to analyse four published case records of test piles, which other researchers had analysed using the following three computationally demanding tools: (a) load transfer (t–z), (b) finite difference and (c) finite element methods. It is shown that the proposed method which is much less resource-intensive, predicts both the load-settlement variation and axial force distribution more accurately than methods: (a–c) above.