Prediction of Compaction Characteristics of Coal Bottom Ash

Compaction is the process of artificially improving the mechanical properties of soil. However, determination of compaction characteristics in laboratory using Proctor compaction test is time consuming and expensive. Hence, there is a need of correlating compaction characteristics with other physical properties of bottom ash which can be obtained easily. This paper describes an innovative solution to predict the compaction properties of coal bottom ash for the preliminary assessment prior to geotechnical engineering related field applications. The data for required parameters of bottom ash for the model development were collected through a literature survey representing different parts of the world. After stepwise regression analysis, specific gravity and uniformity coefficient were found to be the most significant input parameters to predict the compaction characteristics of bottom ash. These parameters were then used to develop the models to predict maximum dry density and optimum moisture content of bottom ash using multiple regression analysis. The developed models were accurate with a prediction accuracy less than ±3% for both maximum dry density and optimum moisture content models. These empirical models were also presented graphically. According to those predictive curves, maximum dry density increases with increasing uniformity coefficient and specific gravity while optimum moisture content reduced

Evaluation of appendicitis risk prediction models in adults with suspected appendicitis

Background Appendicitis is the most common general surgical emergency worldwide, but its diagnosis remains challenging. The aim of this study was to determine whether existing risk prediction models can reliably identify patients presenting to hospital in the UK with acute right iliac fossa (RIF) pain who are at low risk of appendicitis. Methods A systematic search was completed to identify all existing appendicitis risk prediction models. Models were validated using UK data from an international prospective cohort study that captured consecutive patients aged 16–45 years presenting to hospital with acute RIF in March to June 2017. The main outcome was best achievable model specificity (proportion of patients who did not have appendicitis correctly classified as low risk) whilst maintaining a failure rate below 5 per cent (proportion of patients identified as low risk who actually had appendicitis). Results Some 5345 patients across 154 UK hospitals were identified, of which two‐thirds (3613 of 5345, 67·6 per cent) were women. Women were more than twice as likely to undergo surgery with removal of a histologically normal appendix (272 of 964, 28·2 per cent) than men (120 of 993, 12·1 per cent) (relative risk 2·33, 95 per cent c.i. 1·92 to 2·84; P < 0·001). Of 15 validated risk prediction models, the Adult Appendicitis Score performed best (cut‐off score 8 or less, specificity 63·1 per cent, failure rate 3·7 per cent). The Appendicitis Inflammatory Response Score performed best for men (cut‐off score 2 or less, specificity 24·7 per cent, failure rate 2·4 per cent). Conclusion Women in the UK had a disproportionate risk of admission without surgical intervention and had high rates of normal appendicectomy. Risk prediction models to support shared decision‐making by identifying adults in the UK at low risk of appendicitis were identified

Utilization of fly ash-based geopolymer for well cement during CO2 sequestration: A comprehensive review and a meta-analysis

Global warming is a pressing issue caused by the increase in greenhouse gas emissions, with CO2 contributing to 64% of total emissions. To reduce anthropogenic CO2 emissions, several options have been proposed, including CO2 sequestration. A key requirement for a successful and sustainable geo-sequestration process is the use of appropriate zonal isolation provided by the cementing material used between the annular surface and injection well. Although, Ordinary Portland Cement (OPC) is typically used as the well cement, it has shown failures during the process, including degradation issues, carbonation, shrinkage and microcracking, increased permeability in CO2-rich environments, and loss of sealing properties in a short period of time. To address these problems, fly ash (FA)-based geopolymers have been introduced as a better well cement replacement. This study provides a comparative review between OPC and FA-based geopolymers in the context of CO2 sequestration. The review comprehensively analyses the behaviour of FA-based geopolymer cement with its chemical composition, the impact of preparation conditions on the mechanical behaviour of geopolymers, and CO2 permeability through FA-based geopolymer. Furthermore, a meta-analysis was conducted to develop statistical models for predicting the pertinent hydro-mechanical properties of FA-based geopolymer, including dry density, compressive strength, autogenous shrinkage strain, and CO2 permeability during the geo-sequestration process. The outcomes of the meta-analysis can aid decision-making regarding the appropriateness of applying FA-based geopolymer as a replacement for OPC to conduct a sustainable and safe CO2 geo-sequestration process under proper isolation conditions

Effect of Coal Rank on Various Fluid Saturations Creating Mechanical Property Alterations Using Australian Coals

During CO2 sequestration in deep coal seams, the coal mass may be subjected to various fluid (CO2, N2, etc.) saturations. Therefore, in order to maintain the long-term integrity of the process, it is necessary to identify the mechanical responses of preferable coal seams for various fluid saturations. To date, many studies have focused on the CO2 saturation effect on coal mass strength and less consideration has been given to the influence of other saturation mediums. Hence, this study aims to investigate coal’s mechanical responses to water and N2 saturations compared to CO2 saturation and to determine the effect of coal-rank. A series of unconfined compressive strength (UCS) tests was conducted on Australian brown and black coal samples saturated with water and N2 at various saturation pressures. An advanced acoustic emission (AE) system was utilized to identify the changes in crack propagation behaviors under each condition. According to the results, both CO2 and water act similarly with coal by enhancing the ductile properties of the coal mass and this mechanical weakening is greater for high-rank coal. Conversely, N2 saturation slightly enhances coal strength and delays crack propagation in coal and this strength enhancement can be improved by increasing the N2 saturation pressure

Prediction of Compaction Properties of Clayey Soils Stabilized with Calcium Carbide Residue

The use of Calcium Carbide Residue (CCR) for soil stabilization results in changes of the properties of natural soil. In terms of compaction properties, the addition of CCR reduces the maximum dry density (MDD) of clayey soils while increasing the optimum moisture content (OMC). This paper describes a multivariate linear regression model and a multivariate polynomial regression model which can predict the MDD, and OMC of clayey soils stabilized with CCR, respectively. In both models, the compaction properties of the natural soil and the CCR mix proportion are used as independent variables and the developed models can be used to study any clayey soil which can be classified as CH or CL according to the unified soil classification system (USCS). From the statistical analysis, it is found that the models are capable of accurately predicting the compaction properties (i.e., MDD and OMC) of clayey soils stabilized with different CCR dosages with a prediction accuracy of ±5%. Therefore, the developed correlations can be effectively used as an indirect approach to estimate the improved compaction properties of soil in the process of soft ground improvement using CCR

Coal Bottom Ash as an Anthropogenic Soil to Prevent Soil Erosion during Post Mine Rehabilitation in Sri Lanka

The clay mines are abandoned due to the higher cost and non-availability of suitable fill material creating severe environmental issues. Coal bottom ash (CBA) is an industrial waste by-product generated in coal power plants and open dumped which causes soil and water pollution. Hence, CBA is a potential anthropogenic soil for post mine rehabilitation. Soil erosion is one of the major environmental problems in post mine land with the change in soil conditions, mainly in the tropical countries like Sri Lanka. Therefore, main objective of this study is to evaluate the potential of CBA to prevent soil erosion in the post mine land. The engineering properties of the samples were evaluated, and annual soil loss due to rainfall was measured by artificial rainfall test for six different CBA and soil mixtures. CBA exhibits high potential to prevent soil erosion with higher permeability and water holding capacity values. The annual soil loss is very low when the fine fraction of the CBA-soil mixture is lesser than 20%. Further, soil erosion can be significantly reduced when CBA fraction of the CBA-soil mixture is greater than 75%. Interestingly, the micropore structure of CBA is significantly influential on the soil erodibility

Applicability of calcium carbide residues for the improvement of soft peaty clay

Most of the constructions in Sri Lanka is to be carried out on soft peaty clay. The problems with the soft peaty clay are its high-water content, being extremely compressible and having very low shear capacity. Therefore, from an engineering point of view it is very important to improve the geotechnical properties of this weak soil. Among the methods of chemical stabilization, the most common method used in world is stabilization using cement. However, using cement in such large-scale projects is unbearable for a developing country like Sri Lanka. This study is to evaluate the suitability of Calcium carbide residues (CCR) as a binder to improve soft peaty clay. Number of samples were prepared by mixing CCR with different proportions having maximum of 20% binder in soil. Improvements achieved in strength of treated peat for short term and long term were assessed by conducting unconsolidated undrained triaxial tests at 28 days and 90 days respectively. The results have shown that when the CCR content is increased, shear strength is gradually decreased in both short-term and long-term curing. However, strength improvement due to CCR is higher in long-term curing. That will be economically beneficial in projects where stabilization of soil is done in larger scale

Utilization of Bottom Ash for Clay Mine Rehabilitation

At the end of mining activities, clay mines were abandoned due to the cost and non-availability of filling materials. These abandoned clay mines cause adverse environmental and social impacts. In addition, large quantities of bottom ash (BA) are generated as a by-product of coal combustion process. This BA is disposed by open dumping in the lands, which creates severe environmental pollution. Therefore, conducted research on utilization of BA for mine rehabilitation is beneficial. The main focus of this research is applicability of BA generated from Lakvijaya power plant, Sri Lanka as a potential backfill material and a soil amendment during the clay mine rehabilitation. Initially tests were conducted to investigate the basic properties of BA. Next, chemical composition of BA was analysed to select the suitable crops for vegetation. Further pH, electrical conductivity and water holding capacity were checked and micro structural morphology of BA was determined through Scanning Electron Microscope. The results showed that BA has good engineering properties and the potential to improve agronomic characteristics of soil. It has better water holding capacity and permeability. BA can adjust soil pH to a desirable plant growth range. As BA has a very porous structure, the root system can easily develop and helps to uptake nutrients by the plant. However, a considerable percentage of trace metals is accumulated in BA which will increase the bioavailability of some trace metals to levels that poses risk to human. Thus, investigations were carried out to identify the heavy metal concentration in leachate of BA using column leaching test. Results showed that leachability potential of trace metals in BA does not exceed the allowable limits

A Review of CO2-Enhanced Oil Recovery with a Simulated Sensitivity Analysis

This paper reports on a comprehensive study of the CO2-EOR (Enhanced oil recovery) process, a detailed literature review and a numerical modelling study. According to past studies, CO2 injection can recover additional oil from reservoirs by reservoir pressure increment, oil swelling, the reduction of oil viscosity and density and the vaporization of oil hydrocarbons. Therefore, CO2-EOR can be used to enhance the two major oil recovery mechanisms in the field: miscible and immiscible oil recovery, which can be further increased by increasing the amount of CO2 injected, applying innovative flood design and well placement, improving the mobility ratio, extending miscibility, and controlling reservoir depth and temperature. A 3-D numerical model was developed using the CO2-Prophet simulator to examine the effective factors in the CO2-EOR process. According to that, in pure CO2 injection, oil production generally exhibits increasing trends with increasing CO2 injection rate and volume (in HCPV (Hydrocarbon pore volume)) and reservoir temperature. In the WAG (Water alternating gas) process, oil production generally increases with increasing CO2 and water injection rates, the total amount of flood injected in HCPV and the distance between the injection wells, and reduces with WAG flood ratio and initial reservoir pressure. Compared to other factors, the water injection rate creates the minimum influence on oil production, and the CO2 injection rate, flood volume and distance between the flood wells have almost equally important influence on oil production