Biomediated soil improvement in the mitigation of liquefiable sandy soil

Soil liquefaction is one of the catastrophic effects that result from earthquakes. It is a phenomenon that occurs when loose, saturated, cohesionless soil loses its strength and stiffness as a result of rapid loading. Several techniques have been employed to mitigate the effects of soil liquefaction. However, these techniques either require high energy for its execution, or the chemical admixtures used may have adverse effects on the environment. Consequently, biocementation via microbial induced carbonate precipitation (MICP) and enzyme induced carbonate precipitation (EICP) was explored as a technique to mitigate soil liquefaction. The bacterial strain used in the MICP process was Bacillus megaterium. Meanwhile, a plant-derived urease enzyme was used in EICP. In this study, experimental based research was conducted to examine the feasibility of biocementation in the mitigation of liquefaction in sandy soil. The research is divided into three main phases. The first phase examines the effect of environmental factors (pH, temperature and salt content) on the growth of B. megaterium. Test tube tests were conducted to determine the amount of calcium carbonate (CaCO3) precipitates at different cementation reagent concentrations. Based on the test tube test’s results, the EICP method of treatment was adopted to continue with the second and third study phases, due to the amount of calcite produced in the process. The second phase evaluates the effectiveness of EICP treatment on sandy soil through a series of unconfined compressive strength (UCS) tests. The effects of factors, such as curing temperature (4, 10, 20, 30, 40 and 50ºC), the concentration of cementation reagent (0.25, 0.5, 0.75, 1.0 and 1.25 M), number of treatment cycles (1, 2 and 3 cycles) and relative density (loose, medium and dense), palm oil fuel ash (POFA) content were examined on the biocemented soil. The third phase evaluates the effect of biocementation on the cyclic resistance of sandy soil, in terms of confining pressure, Cyclic Stress Ratio (CSR) and relative density, through a series of cyclic triaxial tests. The liquefaction potential of treated soils was investigated with respect to the development of excess pore pressure. The optimum environmental growth conditions, in terms of pH, temperature and salt content, were pH 7, 30°C and 1% (w/v) NaCl, respectively. Findings from the test tube tests showed the mass calcium carbonate precipitate increased when the concentration of cementation reagent (CCR) was increased from 0.5-1.0 M; irrespective of the curing period for both MICP and EICP. Findings from the UCS tests showed a linear relationship between UCS values at various cementation reagent concentrations and average calcium carbonate content. Furthermore, the strength of biocemented sandy soil was attributed to not only the calcite content formed within the soil but also the extent of soil density. The increase in cycles of treatment via surface percolation led to higher strength and CaCO3 content, irrespective of CCR. Image analysis, using Image J software, confirms the reduction in the area of pore spaces within the SEM images, with an increase in the number of cycles of treatment. The addition of POFA to the biocemented soil helped in reducing the ammonium content released. Results from the cyclic triaxial test showed that the EICP treatment improved the sand’s resistance against the generation of pore water pressure, as indicated by the greater number of cycles required to induce liquefaction. It can be concluded that biocementation via EICP can be an effective method of mitigating liquefaction in sandy soil

Geotechnical assessment of palm oil fuel ash (POFA) mixed with granite residual soil for hydraulic barrier purposes

This paper assesses the geotechnical properties of granite residual soil treated with palm oil fuel ash (POFA), a waste from the palm oil factory for the purposes of hydraulic barrier in landfills. Granite residual soil treated with up to 40% palm oil fuel ash (by dry weight of the soil) was compacted using standard proctor compactive effort at the optimum moisture content. Index properties, hydraulic conductivity (k), volumetric shrinkage strain (VSS) and unconfined compressive strength (UCS) tests were carried out. Results showed that the index properties of samples met the minimum requirement for it to be used ass a liner. The maximum dry density and optimum moisture content decreased and increased respectively. The influence of POFA treatment on the geotechnical properties generally showed an improvement with up to 15% POFA which gave the acceptable results with regards to its usability as a hydraulic barrier material in landfill

Understanding the Challenges of 21st Century Urbanization in Northern Nigeria’s Largest City, Kano

Kano, the largest city in Northern Nigeria, has experienced tremendous and unprecedented urban growth since the late 10th Century, following the emergence of the city as one of the oldest and most prominent urban centers for Trans-Saharan trade that linked Sub-Saharan Africa with North Africa, Northern Arab, and other European countries. The city’s rapid urbanization is mainly attributed to the influx of people as a result of socio-economic trading activities. However, the inability of relevant government authorities to actively respond to the city’s rapid urbanization, coupled with the demographical and spatial expansion, has contributed to the enormous contemporary challenges. Therefore, the present study examined the various challenges faced due to the tremendous urbanization in Kano city, Nigeria. The study identified the city’s challenges to include infrastructure decay, environmental pollution, problem of urban mobility and traffic congestion, unemployment, and increased crime rates. It also analyzed the implementation of several strategies and initiatives of the relevant government authorities in tackling these problems while carefully recommending further solutions aimed at addressing these contemporary challenges. This is with a view of having a cosmopolitan city that continuously attracts the inflow of populace due to its socio-economic status without jeopardizing the city’s sustainable growth

Geochemical Evaluation of Contaminated Soil for Stabilisation Using Microbiologically Induced Calcite Precipitation Method

Abandoned mines contaminated with heavy metal wastes pose health risk and environmental hazard. Common methods in managing these wastes include pond storage, dry sacking, underground and ocean disposal and phytho-stabilisation but these does not address the associated risks regarding migration of contaminated liquid or when the soil structure is compromised during natural disaster such as earthquake. Due to these limitations, microbiologically induced calcite precipitation method (MICP) is an exciting alternative as it is sustainable and environmentally friendly. This research evaluates mine waste obtained from two sites; Mamut and Lohan Dam, both located at earthquake-prone Ranau Sabah, Malaysia, in term of their physical, mineralogy and morphological characteristics for stabilisation using MICP. Physically, mining wastes from Mamut are of well graded soil with sand (53.9%) and gravel (43.5%), classified as SW (USCS) and A-1-a (AASHTO). Meanwhile, waste from Lohan Dam are of sand (49.9%) and gravel (10.1%), classified as SM (USCS) and A-4 (AASHTO). Constant head test of the soils from the sites showed results of 3.607 x 10-1 and 3.407 x 10-2 cm/s respectively indicate high permeability. Mineralogy assessment using inductively coupled plasma atomic emission spectroscopy (ICP-OES) showed high level of iron (Fe) with 528.08 and 2931.38 mg/L respectively. Other heavy metals detected include copper (Cu), 24.39 and 4.33 mg/L, lead (Pb), 2.53 and 0.53 mg/L, manganese (Mn), 5.71 and 3.64 mg/L and arsenic (As), 0.71 and 0.31 mg/L; some higher than Malaysia’s Ministry of Health and United Nations’ Food and Agricultural approved standards. Morphological observation of the size, shape and soil texture under scanning electromagnetic (SEM) further indicate the necessity and suitability of both sites for stabilisation using MICP

Numerical Modeling of Encased Stone Columns Supporting Embankments on Sabkha Soil

The present research work is concerned with the construction of road embankments on a specific soil called Sabkha in Algeria. This soil is not only soft and very humid during the flooding seasons but also has frequent small areas of very soft soil which we here call Locally Weak Zones (LWZ). LWZ is characterized by low strength and high compressibility. The paper presents the results of two-dimensional axisymmetric numerical analyze that were carried out using PLAXIS 2D 2017, for the modeling of an embankment supported by stone columns on Sabkha soil. The study focuses on the evaluation of the maximum bulging of the stone column and on the settlement of the embankment. It has been demonstrated that Ordinary Stone Columns (OSC) were ineffective due to excessive bulging (221.16 mm) caused by the lack of lateral pressure. On the other hand, the Encased Stone Columns (ESC) showed good behavior, namely a much reduced bulging (42.09 mm) and a reasonable settlement (0.962 m vs. 1.560 m for an OSC) so that it is possible to build safe very high embankments. The numerical analysis also shows that the length of the encasement should just be greater than the depth of the LWZ. Besides, an extensive parametric study was conducted to investigate the effects of the variations of embankment height, stiffness of geosynthetic, the depth of the locally weak zone, area replacement ratio (ARR), and the stone column friction angle, on the performance of the (ESC) - embankment composite in (LWZ). Some important guidelines for selecting the ideal encased stone column (ESC) to support embankments on over locally weak zone were established through this numerical study

Attenuation capacity of soil mixed with palm oil fuel ash (POFA) liner for treating leachate

This paper presents the results of a study on the effectiveness of mixtures of granite residual soil with palm oil fuel ash (POFA) to attenuate leachate contaminants. Granite residual soil samples were mixed with 0 to 15% POFA. A short term filtration processes and hydraulic conductivity test were conducted simultaneously using a falling head apparatus with natural leachate as the permeant. The values of natural attenuation capacity of the compacted soil mixed with various percentage of POFA were determine by carrying out several water quality tests on the influent and effluent. The parameters measured were Total Suspended Solids (TSS), Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD) values and some selected heavy metal (Chromium, Copper, Manganese, Lead and Zinc). The results showed the highest reduction in hydraulic conductivity (65.4%) was achieved by the compacted soil mixed with 10% POFA. The removal rate of all parameters studied except for copper increased with the increment of POFA content

Hydraulic conductivity of compacted granite residual soil mixed with Palm Oil Fuel Ash in landfill application

Laboratory tests were carried out on compacted granite residual soil treated with 0 to 15% Palm Oil Fuel Ash (POFA), with a view to evaluate its hydraulic conductivity for its application in landfilling. The Soil–POFA mixtures were compacted using both Standard and Modified Proctors compactive efforts at 2% dry of Optimum Moulding water Content (−2%), at Optimum Moulding water Content (0%), at 2 and 4% on the wet side of Optimum Moulding water Content (+2 and +4%). The samples were permeated with water and the effect of moulding water content; compactive effort and POFA content were examined. The samples that met the minimum threshold of 1 × 10−9 m/s were used in plotting the acceptable zones criterion at various POFA mixtures. The results gave indications of reduction in the hydraulic conductivity values, with increase in compactive efforts, moulding water content and POFA content up to about 10%. This was the most suitable soil–POFA mixture for the hydraulic application

Desiccation induced shrinkage of compacted lateritic soil treated via enzymatic induced calcium carbonate precipitation technique

Exploring the biological process to enhance the engineering properties of soil have received enormous recognition in recent years. Enzymatic induced calcium carbonate precipitation (EICP) is one of the bio-inspired methods of utilizing free urease to precipitates calcite from urea and calcium ions for bettering the geotechnical properties of poor soils. In this research, the EICP technique was used to improve the volumetric shrinkage strain of compacted soil liner. In this work, the residual soil was treated with various concentrations of cementations ranging from 0.25 to 1.0 M, and the soil was subjected to Atterberg limit tests, compaction test using British standard light (BSL) and reduced British standard light (RBSL) and desiccation drying volumetric shrinkage strain test. The study's findings revealed a remarkable improvement in the liquid limit and plasticity index of the treated residual soils compared to natural soil. It was also found that the volumetric shrinkage strain of the treated soil reduces progressively from 5.24% of natural to 1.49% at 1.0 M cementation solution when the soils were prepared at 0% OMC and BSL compaction effort. Based on the consideration of permissible VSS of less than 4%, the best treatment was obtained at 1.0 M for both BSL and RBSL prepared samples. Similarly, the best compaction plane is found in the treated with 1.0 M cementation solution

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Abstract Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

Suitability of using compacted granite residual soil treated with palm oil fuel ash as hydraulic barrier in sanitary landfill

Modern landfills employ a composite liner system consisting of a geomembrane or geosynthetic clay liner overlying a compacted soil liner. For soils either natural or mixed with additive to satisfy the requirement of a liner, it must have low hydraulic conductivity, adequate shear strength and minimal shrinkage. An experimental investigation was conducted on granite residual soil treated with up to 15% palm oil fuel ash (POFA) to assess its suitability for liners in waste containment systems. Soil samples were prepared at moulding water content ranging from -2, 0, +2 and +4% of the optimum moisture content (OMC) and compacted with two compactive energy levels (standard and modified proctor). The tests carried out were divided into physical (moisture content, specific gravity, sieve analysis, Atterberg limit compaction), chemical (cation exchange capacitymineral composition, chemical oxides, structural morphology, elemental composition of leachate) and mechanical properties (hydraulic conductivity, volumetric shrinkage strain, unconfined compressive strength, compatibility studies) of both the natural soil and the mixture with POFA. Specific surface area was carried out on the POFA sample. The optimum properties of the soil mixture were then tested by carrying out the compatibility study. Compatibility study, which is the interaction between the leachate and the barrier material was determined based on the short – time hydraulic conductivity test using the leachate as the permeant. The concentrations of heavy metals contain in leachate before and after test were also assessed. The results of the index properties of soil and soil – POFA mixture carried out provided a useful way to identify, classify and assess the engineering properties of the soil.The natural soil contained 53.13% fine content and that value increased to 59.14% with 15% POFA content. The index properties of samples met the minimum requirement for it to be used as a liner. Soils with high fine content have smaller particles that reduce the volume of voids present allow less hydraulic conductivity and also higher liquid limit are related to lower hydraulic conductivity. Chemical composition of POFA showed a fair result of 67.80% in comparison to the minimum requirement of 70% for pozzolanic reaction as stated by ASTM. While on the otherhand, the addition of POFA showed a modification in the structure of the soil from a porous to a dense structure. The maximum dry density and optimum moisture content decreased and increased respectively for both compactive efforts. For both compactive energies, the hydraulic conductivity generally decreased with increase in moulding water content, the lowest were obtained at the wet side of the compaction curve especially at +2% of the optimum moisture content. At modified proctor compactive effort and +2% of the OMC, hydraulic conductivity values of 6.51×10-9, 2.23×10-10, 2.31×10-11 and 1.31×10-9m/s were obtained at 0, 5, 10 and 15% POFA, respectively. However, beyond +2% of the OMC, there was a slight increase in hydraulic conductivity values. For the volumetric shrinkage strain (VSS), there was increase in VSS values with higher moulding water content and also at higher initial degree of saturation for all compactive efforts. The largest VSS value of 5.91% was obtained at soil containing 15% POFA and +4% of the OMC. The influence of POFA treatment generally showed a decrease in the VSS with the increase in POFA content. On the other hand, shear strength values increased with the addition of POFA and at higher compactive effort, with the highest strength recorded at 10% POFA using modified proctor compactive effort. However, the values decreased at higher moulding water content irrespective of POFA content and compactive effort. Based on the acceptable zone on the compaction plane, 10% POFA gave the widest range ofmoulding water content in which minimumset of values based on the hydraulic conductivity, shear strength and volumetric shrinkage were achieved. For a compatibility study, results showed that there was a general decrease in hydraulic conductivity values at different percentages of POFA, with the highest reduction rate of 65.4% recorded at 10% POFA mixture. This could be as a result of suspended solids in the leachatewhich were absorbed at the surface of the soil there by reducing percolation with time. On the other hand the concentration of some metals was drastically reduced when permeated through the compacted material