The effect of scale on the shear behaviour of joints is studied by performing direct shear tests on different sized replicas cast from various natural joint surfaces. The result show significant scale effects on both the shear strength and deformation characteristics. Scale effects are more pronounced in the case of rough, undulating joint types, whereas they are virtually absent for planar joints. The key factor is the involvement of different asperity sizes in controlling the peak behaviour of different lengths of joints. It is shown that as a results both the joint roughness coefficient (JRC) and the joint compression strength (JCS) reduce with increasing scale. The behaviour of multiple jointed masses with different joint spacing is also considered. It is found that despite unchanged roughness, jointed masses consisting of many small blocks have higher peak shear strength than jointed masses with larger joint spacing. These scale effects are related to the changing stiffness of a rock mass as the block size or joint spacing increases or decreases. Economic methods for obtaining scale-free estimates of shear strength are described.

Experimental studies of scale effects on the shear behaviour of rock joints

NeuroToxicology 31 (2010) 575–581 Contents lists available at ScienceDirect NeuroToxicology Review The neurotoxicity of environmental aluminum is still an issue Stephen C. Bondy * Program in Environmental Toxicology, Division Occupational and Environmental Health, Department of Medicine, University of California, Irvine, CA 92697-1825, USA A R T I C L E I N F O A B S T R A C T Article history: Received 18 September 2009 Received in revised form 24 March 2010 Accepted 10 May 2010 Available online 27 May 2010 Evidence for the neurotoxicity of extended exposure to low levels of aluminum salts is described using an animal model treated with aluminum at low levels reﬂecting those found in some water supplies. Emphasis is given to the potential role of aluminum in acceleration and promotion of some indices characteristic of brain aging. These hallmarks include the appearance of excess levels of inﬂammation in speciﬁc brain areas. Aluminum salts can increase levels of glial activation, inﬂammatory cytokines and amyloid precursor protein within the brain. Both normal brain aging and to a greater extent, Alzheimer’s disease are associated with elevated basal levels of markers for inﬂammation. These are not attributable to obvious exogenous stimuli and may reﬂect the lifespan history of the organism’s immune responses. It is possible that aluminum salts can act as a subtle promoter of such apparently unprovoked responses. s 2010 Elsevier Inc. All rights reserved. Keywords: Aluminum Drinking water brain aging Alzheimer’s disease Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aluminum is environmentally prevalent and ingested by humans. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . There is an epidemiological relation between chronic aluminum exposure and the incidence of Alzheimer’s disease . . . . . . . . . . . Aluminum exposure may also promote the onset of Parkinson’s disease. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acute exposure to aluminum can cause clinical neurotoxicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Elevated levels of intrinsic inﬂammation are associated with neural aging and this is exacerbated in several neurodegenerative diseases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Low levels of aluminum in drinking water of experimental animals, elevate basal levels of inﬂammatory activity within the CNS Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1. Introduction This review on the potential neurotoxic hazard posed by aluminum focuses on distinguishing between those aspects of aluminum neurotoxicity that are widely accepted and not controversial, and those aspects that are suggestive but not fully established. The work of this laboratory over the past 12 years is described and this falls into the latter classiﬁcation, adding to the body of evidence increasingly implicating aluminum as a potentially hazardous environmental agent. The most accepted facts relating to aluminum include: (i) it’s widespread prevalence and level of human consumption, (ii) the * Correspondence address: Department of Community and Environmental Medicine, University of California at Irvine, Irvine, CA 92697-1825, USA. Tel.: +1 949 824 8077; fax: +1 949 824 2793. E-mail address: scbondy@uci.edu. 0161-813X/$ – see front matter s 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.neuro.2010.05.009 known neurotoxicity of high levels of aluminum, and (iii) a repeated epidemiological correlation between ingested aluminum and the incidence of Alzheimer’s disease. Another relevant area of widespread consensus is the tendency of the aging brain to express elevated levels of inﬂammation and the further exacerbation of this state in several neurodegenerative diseases. Less accepted is the evidence that aluminum can be a causal factor in promoting Alzheimer’s disease. This area has been handicapped by earlier erroneous reports of heightened levels of aluminum in amyloid plaques. Tissue aluminum levels are notoriously difﬁcult to determine and later more reliable ﬁndings leading to similar conclusions have been overshadowed by these original reports. The main objective of our more recent studies has been to study the effects of extended exposure of experimental animals to levels of aluminum that have relevance for the human population. Demon- stration that these can provoke cerebral inﬂammatory responses resembling those that are found with brain senescence, can provide a mechanistic link to epidemiological reports.

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The neurotoxicity of environmental aluminum is still an issue - eScholarship

Geology Igneous Rocks Surface Processes Sedimentary Rocks Metamorphic Rocks Geological Structures Geological Maps Map Interpretation Tectonics Boundary Hazards Rocks of Britain Rocks of the US Weathering and Soils Floodplains and Alluvium Glacial Deposits Climatic Variants Coastal Processes Groundwater Ground Investigation Desk Study Ground Investigation Boreholes Geophysical Surveys Assessment of Difficult Ground Rock Strength Rock Mass Strength Soil Strength Ground Subsidence Subsidence on Clays Subsidence on Limestone Subsidence Over Old Mines Mining Subsidence Slope Failure and Landslides Water in Landslides Soil Failures and Flowslides Landslide Hazards Slope Stabilization Ground Conditions Rock Excavation Tunnels in Rock Stone and Aggregate Appendices Rock Mass Quality Q System Abbreviations and Notation Further Reading Index

Foundations of engineering geology

Fundamentals of Soil Behaviour

Coefficient of consolidation (Cv) is a measure of compressibility of soil. This coefficient is an important parameter which is used in the design of foundation of civil engineering structures and also in the slope stability analysis. In this study, the main objective is to propose a hybrid machine learning approach named MLP-BBO for the prediction of the coefficient of consolidation of soft soil. This method is based on Multi-layer Perceptron Neural Network (MLP) and Biogeography-based Optimization (BBO). For this, a total number of 164 soil samples were collected from the Tan Vu–Lach Huyen highway project and Ha Noi–Hai Phong highway project sites. In the modeling, input parameters used include clay (%), moisture content (%), liquid limit (%), plastic limit (%), plasticity index (%), and liquidity index (%). To validate performance of the models, standard methods such as Root-Mean-Square Error (RMSE), Mean Absolute Error (MAE), and correlation coefficient (r) were used. For the comparison of performance of the models, popular machine learning methods were used namely Backpropagation Multi-layer Perceptron Neural Networks (Bp-MLP Neural Nets), Radial Basis Functions Neural Networks (RBF-Neural Nets), Gaussian Process (GP), M5 Tree, and Support Vector Regression (SVR). Results of the model study indicate that the proposed method MLP-BBO has the highest predictive capability (RMSE = 0.397, MAE = 0.302 and r = 0.827), followed by the SVR (RMSE = 0.403, MAE = 0.299 and r = 0.819), the Bp-MLP Neural Nets (RMSE = 0.478, MAE = 0.398 and r = 0.805), the RBF-Neural Nets (RMSE = 0.412, MAE = 0.281 and r = 0.804), the GP (RMSE = 0.440, MAE = 0.301 and r = 0.777), and the M5 Tree (RMSE = 0.494, MAE = 0.322 and r = 0.728), in the prediction of Cv, respectively. Therefore, it can be concluded that though performance of all applied models is good in the prediction of the coefficient of consolidation of soil but performance of the MLP-BBO is the best.

A novel artificial intelligence approach based on Multi-layer Perceptron Neural Network and Biogeography-based Optimization for predicting coefficient of consolidation of soil

Construction of building and other civil engineering structures on weak or soft soil is highly risky because such soil is susceptible to differential settlements, poor shear strength, and high compressibility. Various soil improvement techniques have been used to enhance the engineering properties of soil. Soil reinforcement by fiber material is considered an effective ground improvement method because of its cost effectiveness, easy adaptability, and reproducibility. Hence, in the present investigation, papyrus fiber has been chosen as the reinforcement material, and it was randomly included into the soil at four different percentages of fiber content, i.e., 5, 10, 15, 25% by volume of raw soil. The main objective of this research is to focus on the strength behavior of soil reinforced with randomly included papyrus fiber. Direct shear, consolidation, and displacement tests were performed on papyrusreinforced specimens with various fiber contents. The results of these tests have clearly shown a significant improvement in the failure deviator stress and shear strength parameters (c and φ) of the studied soil with a percent addition of 10% (the preferred percent). Moreover, this addition ratio reduced the displacement of the soil under loading. It can be concluded that papyrus fiber can be considered an appropriate soil reinforcement material.

Strength of soil reinforced with fiber materials (Papyrus)

Landfill sealing technologies comprise low hydraulic conductivity engineered layers as part of covers and bottom liners, for which clays and geosynthetic materials are conventionally used. In last ...

Utilization of waste products as alternative landfill liner and cover materials – A critical review

The undrained shear strength of clays is an important geotechnical parameter used during construction processes. Several laboratory tests were performed on kaolinite and smectite mixed with pore fluids with different pH values. Vane shear tests were carried out and it was found that the undrained shear resistance for clays increased considerably if the pore fluid had a high or a low pH. A possible explanation could be the dissolution of Al3+ which acts as a coagulant, increasing the internal shear resistance. Geochemical computations, Al measurements and ζ-potential experiments were performed to confirm this theory. The research suggests varying the pH may make a useful contribution to soil improvement techniques.

Undrained shear strength of clays as modified by pH variations

The Influence of the Dielectric Constant and Electrolyte Concentration of the Pore Fluids on the Undrained Shear Strength of Smectite

Red mud (RM), a waste arising from the bauxite refining, was studied to assess its suitability as a compacted liner material. The geotechnical and hydraulic conductivity (K) characteristics of the RM, as well as the effect of desiccation, were evaluated. RM has index properties satisfying the requirements to achieve low K. The compaction–permeability studies showed that RM may be compacted to a dense homogeneous mass using a moderate compactive effort, while lowest K (⩽1 × 10−7 cm/s) was achieved for RM compacted slightly (0.4–4%) wet of optimum. Shear strength test revealed high values of friction angle and cohesion for compacted RM, and its tight structure was also evidenced by its low compressibility and maximum settlement under load. Desiccation adversely affected the permeability of compacted RM, but to a lesser extent than generally observed for clays. These results suggest that RM could be potentially utilised as a low-permeability barrier to be laid down under engineered landfill sites.

Giovanni Spagnoli

Papers

Strength of soil reinforced with fiber materials (Papyrus)

Utilization of waste products as alternative landfill liner and cover materials – A critical review

Undrained shear strength of clays as modified by pH variations

The Influence of the Dielectric Constant and Electrolyte Concentration of the Pore Fluids on the Undrained Shear Strength of Smectite

Assessment of bauxite refining residue (red mud) as a liner for waste disposal facilities