Effect of Curing On the Strength Behaviour of Lime-Fly Ashexpansive Soil Mixes

Expansive soils occupying almost 3 lakh km2 in the Indian subcontinent found to be highly problematic due to their extensive swelling and shrinkage nature. This rapid volume change leads to upliftment of foundations, differential settlements, heaving, rutting, etc. on the overlying structures. Concerning with the above problems an effective, economical and long-term method lime stabilisation was selected. In this work it is attempted to study the effect of curing period on the strength behaviour expansive soil treated with lime and fly ash by conducting triaxial shear (UU) test for 0, 3, 7, 14, 28 days with some twenty different proportions

Bearing Capacity of A Strip Footing Resting On Treated And Untreated Soils

Expansive soils are highly susceptible to volumetric changes leading to rapid loss in the bearing capacity of footings resting on them. Among several techniques available to treat expansive soils, lime or fly ash stabilization gained prominence during the past few decades due to its abundance and adaptability. Chemical stabilization is widely used to treat expansive soils as it develops base exchange and cementation processes between clay particles.When expansive soils are treated with chemicals, it is essential to obtain the load-settlement response of footing resting on stabilized ground. In this study, Finite Element Analysis is performed using the commercial software, PLAXIS 2D, to obtain the load-settlement response of a strip footing resting on untreated and treated expansive soil. The bearing capacity of strip footing resting on treated soil is found to be about 150% higher than that of footing resting on untreated soil

Resistance Factor Calculations for Load Resistance Factor Design (LRFD) of MSW Landfill Slopes

It is obvious to note that there is a significant amount of variability connected with shear parameters of municipal solid waste (MSW) landfills. To ensure uniform safety and reliability, the design approaches in the US have progressively transformed to the load and resistance factor design (LRFD) format. It may be desirable to the successful development and adoption of reliability-based resistance factors for the design of landfill slopes taking into account the significant variability of shear strength parameters. The exhaustive studies reported on shear parameters of MSW are compiled and reviewed. The mean, standard deviation, and coefficient of variation (COV) associated with shear parameters are obtained using statistical analysis. The probability density functions (PDFs) are plotted for unit weight, cohesion, and friction angle. The PDFs show that high range of variability associated with shear parameters and should be given due consideration in the optimum designs. Therefore, the present work reports a procedure for determining the resistance factors for stability number (in terms of unit weight, cohesion) and friction angle of MSW in accordance with LRFD of MSW landfill slopes that target a specific reliability index. A simple first-order reliability method (FORM) is reported to compute the ranges for the resistance factors. Perhaps, this is the first study to propose resistance factors for the design of MSW slopes. The stability number (in terms of unit weight, cohesion) and friction angle of the MSW are treated as random variables. The Spencer method of slices has been employed to formulate the performance function against the sliding failure of finite slopes. It is illustrated that the uniform safety levels can be obtained by using the proposed resistance factors

Computation of the Probabilistic Critical Centers and Reliability Indices of MSW Landfill Slopes Using the Spencer Method of Slices

The shear strength properties of Municipal Solid Waste (MSW) are of special importance when evaluating the stability of landfill slopes. Geoenvironmental engineers are well aware of the existence of many sources of uncertainties associated with shear strength parameters of MSW due to various reasons. The significant uncertainties associated with the shear strength and shear stresses render deterministic modeling potentially misleading. The traditional engineering approaches like method of slices used for evaluating MSW slopes are frequently questionable as they do not adequately account for uncertainties included in analytical modeling and natural variability. In order to quantify the slope stability precisely by taking into account the variability, the Reliability Based Design Optimization (RBDO) framework is presented. The mean and standard deviations associated with unit weight, cohesion and angle of internal friction of the MSW are taken into account in the probabilistic optimization. Reliability analysis is performed using first order reliability method (FORM). A limit state function is formulated against sliding slope failure using Spencer method of slices. The influence of coefficients of variation (COV) of stability number and friction angle on critical center coordinates and reliability index is presented in the form of charts

The ENIGMA-Epilepsy working group: Mapping disease from large data sets

Epilepsy is a common and serious neurological disorder, with many different constituent conditions characterized by their electro clinical, imaging, and genetic features. MRI has been fundamental in advancing our understanding of brain processes in the epilepsies. Smaller‐scale studies have identified many interesting imaging phenomena, with implications both for understanding pathophysiology and improving clinical care. Through the infrastructure and concepts now well‐established by the ENIGMA Consortium, ENIGMA‐Epilepsy was established to strengthen epilepsy neuroscience by greatly increasing sample sizes, leveraging ideas and methods established in other ENIGMA projects, and generating a body of collaborating scientists and clinicians to drive forward robust research. Here we review published, current, and future projects, that include structural MRI, diffusion tensor imaging (DTI), and resting state functional MRI (rsfMRI), and that employ advanced methods including structural covariance, and event‐based modeling analysis. We explore age of onset‐ and duration‐related features, as well as phenomena‐specific work focusing on particular epilepsy syndromes or phenotypes, multimodal analyses focused on understanding the biology of disease progression, and deep learning approaches. We encourage groups who may be interested in participating to make contact to further grow and develop ENIGMA‐Epilepsy

White matter abnormalities across different epilepsy syndromes in adults: an ENIGMA-Epilepsy study

The epilepsies are commonly accompanied by widespread abnormalities in cerebral white matter. ENIGMA-Epilepsy is a large quantitative brain imaging consortium, aggregating data to investigate patterns of neuroimaging abnormalities in common epilepsy syndromes, including temporal lobe epilepsy, extratemporal epilepsy, and genetic generalized epilepsy. Our goal was to rank the most robust white matter microstructural differences across and within syndromes in a multicentre sample of adult epilepsy patients. Diffusion-weighted MRI data were analysed from 1069 healthy controls and 1249 patients: temporal lobe epilepsy with hippocampal sclerosis (n = 599), temporal lobe epilepsy with normal MRI (n = 275), genetic generalized epilepsy (n = 182) and non-lesional extratemporal epilepsy (n = 193). A harmonized protocol using tract-based spatial statistics was used to derive skeletonized maps of fractional anisotropy and mean diffusivity for each participant, and fibre tracts were segmented using a diffusion MRI atlas. Data were harmonized to correct for scanner-specific variations in diffusion measures using a batch-effect correction tool (ComBat). Analyses of covariance, adjusting for age and sex, examined differences between each epilepsy syndrome and controls for each white matter tract (Bonferroni corrected at P < 0.001). Across ‘all epilepsies’ lower fractional anisotropy was observed in most fibre tracts with small to medium effect sizes, especially in the corpus callosum, cingulum and external capsule. There were also less robust increases in mean diffusivity. Syndrome-specific fractional anisotropy and mean diffusivity differences were most pronounced in patients with hippocampal sclerosis in the ipsilateral parahippocampal cingulum and external capsule, with smaller effects across most other tracts. Individuals with temporal lobe epilepsy and normal MRI showed a similar pattern of greater ipsilateral than contralateral abnormalities, but less marked than those in patients with hippocampal sclerosis. Patients with generalized and extratemporal epilepsies had pronounced reductions in fractional anisotropy in the corpus callosum, corona radiata and external capsule, and increased mean diffusivity of the anterior corona radiata. Earlier age of seizure onset and longer disease duration were associated with a greater extent of diffusion abnormalities in patients with hippocampal sclerosis. We demonstrate microstructural abnormalities across major association, commissural, and projection fibres in a large multicentre study of epilepsy. Overall, patients with epilepsy showed white matter abnormalities in the corpus callosum, cingulum and external capsule, with differing severity across epilepsy syndromes. These data further define the spectrum of white matter abnormalities in common epilepsy syndromes, yielding more detailed insights into pathological substrates that may explain cognitive and psychiatric co-morbidities and be used to guide biomarker studies of treatment outcomes and/or genetic research

Meethotamulla Landfill Failure Analysis: A Probabilistic Approach

This paper assesses the possible conditions that might have resulted in the recent catastrophic failure of the Meethotamulla landfill slope at Colombo. This paper presents a probabilistic approach to find the different combinations of parameters that might have caused the collapse of landfill slope. A performance function is formulated, and the reliability of the slope is assessed using first-order reliability method (FORM). The factor of safety associated with various slip surfaces are computed with different combinations of mean and COV. The results obtained from the reliability analysis based on FORM agree closely with the reported post-failure investigations. The analysis elucidated the possible causes of landfill slope failure. The outcome of the analysis can be utilized for finding a remediation with improved knowledge about the shear strength parameters of the solid waste. The probabilistic analysis conducted in the present work reveals that the mean value of shear strength parameters of MSW and its associated variability responsible for the collapse of Meethotamulla garbage dump are friction angle, ϕ=20∘ and stability number, c/γH=0.05. The reliability analysis proved that the most likely reason for the dump failure is the reduction in shear strength parameters of the MSW. The excessive rainfall might have triggered the reduction in shear strength parameters. The analysis of Meethotamulla garbage dump disaster demonstrated that it is very essential to conduct reliability analysis as realistically as possible to find the conditions that have triggered the collapse

Reliability Based LRFD of Geomembrane Liners for V-Shaped Anchor Trenches of MSW Landfills

The main objective of design of V-shaped anchor trenches is to ensure safety against the pullout failure in Geomembrane (GMB) liners efficiently. Uncertainties related to soil-liner interface frictional angle, allowable GMB tensile force, and the unit weight of the cover/backfill soil can be quantified through probabilistic means. Load and Resistance Factor Design approach involves reliability theory in the evaluation of load and resistance factors. The present study focuses on the application of reliability based load and resistance factor design of V-shaped anchor trenches. This paper gives a clear guideline for the successful performance of anchor trenches against pullout failure in handling the variability of soil-liner interface frictional angle, allowable GMB tensile force, and the unit weight of the cover/backfill soil. Target reliability approach is used to estimate the probability of pullout failure of GMB liner. The results of the study can be used to understand the response of the anchor trench for variable loads. The study recommends the resistance and the load factors for the design of V-shaped anchor trenches of MSW Landfills

Reliability Based Design Optimization of Geosynthetic Anchor Trenches for Municipal Solid Waste (MSW) Landfill Slopes

Anchored trenches are designed to resist the sliding action, pullout, contraction and upliftment of the cover materials that are caused due to self-weight, pullout loads, temperature variations and wind action respectively. The shear strength properties of MSW slopes are highly variable due to waste decomposition with time. Therefore careful anchor trench analysis must be performed in order to model parameter uncertainty. This paper pertains to a study on the reliability evaluation of three types of anchor trenches (simple runout, rectangular and L shaped) for MSW slopes under a probabilistic framework. It is shown that L-shaped anchor trenches are more effective than the simple runout and rectangular anchor trenches

Optimum Design of Municipal Solid Waste (MSW) Dumps: A Reliability-based Approach

The increase of population, rapid urbanization and improved living standards of the people have all led to the exponential growth of municipal solid waste (MSW) generation in India as well as in the rest of the world. The scarcity of enough land and capital, it is always a challenge to establish a new landfill facility. Consequently, the authorities are being forced to use the existing MSW landfills though they exceeded their design capacities turning out them to massive MSW dumps. The continuous dumping of MSW leads to steeper slopes which pose a threat to the MSW slope stability. Improper compaction practices, lack of daily soil/geosynthetic covers, the absence of drainage and leachate collection systems at the dump sites accelerates the chances of catastrophic failures in MSW dumps. The MSW is a highly heterogeneous and complex material and subjected to various stress conditions due to placement and compaction practices, leachate/pore fluid pressures, decay and disintegration, physical, chemical and biological changes. It is necessary to study and understand the variability associated with the geotechnical properties of the MSW to deliver safer designs. The construction of a landfill commences with installation of soil and GMB liners to avoid the contaminant transport. The design without considering uncertainties associated with the shear parameters of the MSW and the soil-liner interface friction angle may yield potentially misleading conclusions in terms of slope safety levels. The deterministic approaches ignoring the variability of these design parameters, which are random in nature, may cause a higher or lower probability of failure of the system. It can also be noted that the factor of safety approach yields either too conservative or unsafe designs