ORCID Profile
0000-0002-2804-7797
Current Organisations
EnvoGéotechnique Limited
,
International College of Auckland
,
Wilton Joubert Consulting Engineers
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Publisher: American Society of Civil Engineers (ASCE)
Date: 02-2017
Publisher: ASTM International
Date: 09-07-2018
DOI: 10.1520/GTJ20170353
Publisher: Thomas Telford Ltd.
Date: 10-2015
Abstract: This paper describes a new method called electro-biogrouting for the improvement of soft soil with low hydraulic conductivity. In this method, bacteria, urea and calcium ion are injected by an applied electric field. Initially, the calcium ions are moved across the specimen by electromigration from the anode to the cathode. Then, the urea, which is non-ionic and solvable, is transported by electro-osmotic flow from the anode to the cathode. Finally, the bacteria with negative surface charge are induced as particles by electrophoresis mobility from the anode to the cathode. Polarity reversal is applied to ensure homogeneous distribution of agents. As the bacteria expose the urea, the urease enzyme is released, and carbonate ions are produced, which results in CaCO 3 precipitation in the porous media of the soil. This increases the shear strength of the soil up to 1080%. The CaCO 3 was detected using the acid washing technique.
Publisher: Elsevier BV
Date: 12-2019
Publisher: Thomas Telford Ltd.
Date: 12-2015
Abstract: This study addresses the use of alkali-activated binder to evaluate the feasibility of using this promising technique to stabilise soils. One of the well-known agro-wastes, palm oil fuel ash (POFA), was used as a source binder. Also, sodium hydroxide (NaOH) and potassium hydroxide (KOH) were used as alkaline activators. The influence of four factors including the kind of alkaline activator, the use of source binder, the curing condition and the water content of the soil on the strengthening performance of soil was evaluated according to the improvement of the unconfined compression strength (UCS). At the same alkaline concentration, both sodium hydroxide and potassium hydroxide were able to enhance the strength development rate of specimens. However, potassium hydroxide-POFA-stabilised soil yielded the highest UCS value following a long curing time (90 and 180 d of curing). The size and charge density of the alkaline activator play significant roles in controlling the rate and extent of the activation process for the strength performance. With regard to soil strength improvement, when the POFA content in the activation process increased from 0% to 15%, the UCS value increased substantially, irrespective of the alkaline activator type. This achievement implies a tremendous effect of this agro-waste on the strength behaviour of treated soil.
Publisher: Informa UK Limited
Date: 06-2011
Publisher: Informa UK Limited
Date: 18-09-2019
Publisher: Academic Journals
Date: 30-11-2011
DOI: 10.5897/IJPS11.777
Publisher: Springer Science and Business Media LLC
Date: 06-2009
Publisher: Elsevier BV
Date: 05-2013
Publisher: Springer Science and Business Media LLC
Date: 26-04-2014
Publisher: Elsevier BV
Date: 12-2017
Publisher: Hindawi Limited
Date: 2013
DOI: 10.1155/2013/629476
Abstract: This work describes the application of the electrical resistivity (ER) method to delineating subsurface structures and cavities in Kuala Lumpur Limestone within the Batu Cave area of Selangor Darul Ehsan, Malaysia. In all, 17 ER profiles were measured by using a Wenner electrode configuration with 2 m spacing. The field survey was accompanied by laboratory work, which involves taking resistivity measurements of rock, soil, and water s les taken from the field to obtain the formation factor. The relationship between resistivity and the formation factor and porosity for all the s les was established. The porosity values were plotted and contoured. A 2-dimensional and 3-dimensional representation of the subsurface topography of the area was prepared through use of commercial computer software. The results show the presence of cavities and sinkholes in some parts of the study area. This work could help engineers and environmental managers by providing the information necessary to produce a sustainable management plan in order to prevent catastrophic collapses of structures and other related geohazard problems.
Publisher: Elsevier BV
Date: 08-2016
Publisher: Elsevier BV
Date: 2015
Publisher: ASTM International
Date: 26-09-2017
DOI: 10.1520/ACEM20170001
Publisher: MDPI AG
Date: 07-12-2020
DOI: 10.3390/MIN10121096
Abstract: In this study, we investigated the breakage behavior of a bed of olivine sand particles using a drop-weight impact test, with drop weights of various shapes (oval, cube, and sphere). An Attainable Region (AR) technique, which is a model-free and equipment-independent technique, was then applied to optimize the impact energy during the breakage process and also to get particles in defined particle size classes. The findings revealed that the different drop weights produce products within the three different particle size classes (feed, intermediate, and fine). A higher mass fraction of materials in the fine-sized class (−75 μm) was obtained when the spherical drop weight was used relative to the cubic and oval drop weights. The drop height was found to have a significant influence on the breakage process. The AR technique proved to be a practical approach for optimizing impact energy and particle size during the breakage of a bed of olivine particles, with potential application in sustainable soil stabilization projects.
Publisher: Thomas Telford Ltd.
Date: 10-2019
Abstract: This paper presents the results of experiments designed to investigate the effect of acid rain on the compressibility behaviour of residual soils. Sedimentary residual soil (SRS) and igneous residual soil (IRS) with different mineral compositions were collected from two locations in Malaysia. The specimens were infiltrated by artificial acid rain (AAR) at varying pH values of 2, 3, 4, 5 and 5·6 and at different fluxes of 1, 5 and 20 years. At the end of each AAR flux interval, compressibility, zeta potential, atomic adsorption spectroscopy, X-ray diffraction and scanning electron microscope analyses were performed to study the behaviour of the soil in an acidic environment. It was found that AAR has a strong effect on soil structure consequently, the compressibility of both SRS and IRS increased as the pH value decreased and/or as the flux of AAR increased. Microstructural analyses confirmed that this process destroyed the bonds between clay particles/aggregates and induced significant changes in mineral structure due to the dissolution of alumina and silica from SRS and IRS, resulting in the formation of ‘loose’ structures with larger voids.
Publisher: Thomas Telford Ltd.
Date: 06-2015
Abstract: An investigation of the electrokinetic properties of Sporosarcina pasteurii and Sporosarcina aquimarina bacteria is presented here. The surface charge of bacteria in different pH values was characterised by zeta potential measurements. Results show that both type strains are pH dependent and have negative zeta potential in the low and high pH range. S. pasteurii has a more negative charge in comparison to S. aquimarina. The bacteria size of S. pasteurii was 2–3 µm, whereas S. aquimarina has a size of 1–2 µm in culture media, which has a potential to transport these type strains into fine soils. The results of the electrophoresis mobility of S. pasteurii bacteria show that the bacteria were transported under electric fields. These results demonstrate that electrokinetics can be used for bacterial transport in soils with low hydraulic conductivity.
Publisher: Elsevier BV
Date: 10-2019
Publisher: Elsevier BV
Date: 06-2015
Publisher: International Journal of Geomate
Date: 08-2019
Publisher: Elsevier BV
Date: 2013
Publisher: American Society of Civil Engineers
Date: 02-11-2009
DOI: 10.1061/41082(362)26
Publisher: Thomas Telford Ltd.
Date: 06-2016
Abstract: In this study, coir fibres were modified with nanoparticles of calcium hydroxide and magnesium hydroxide via a chemical treatment in order to increase the tensile strength of the fibres and their interaction with soil. To evaluate the modification and its effects, unconfined compressive strength tests, indirect tensile strength tests, flexural strength tests and triaxial compressive strength tests were carried out at 7, 28 and 90 days of curing age on lime-treated soil reinforced with modified and unmodified fibres. The obtained results showed that nano-modification of fibres enhanced the mechanical properties of the lime-treated clay soil due to the tensile strength of the augmented fibres. The results showed that the compressive strength, the indirect tensile strength and the flexural strength of s les treated with modified coir fibres increased by 64%, 122% and 56%, respectively compared to that of s les treated with unmodified fibres. Moreover, an increase in the effective internal friction angle and the cohesion intercept was observed. Also, the results of scanning electron microscopy and energy dispersive X-ray confirmed a desired alteration in morphology of the fibres.
Publisher: MDPI AG
Date: 23-07-2023
DOI: 10.3390/MIN13070976
Abstract: This study aimed to investigate the structure and shape of carbonate crystals induced through microbial activity and carbon dioxide reactions in the sand. The strength of sandy soil treated with carbonate minerals was subsequently determined using unconfined compression strength (UCS) tests. Sporoscarcina pasteurii bacteria were used to produce an aqueous solution of free carbonate ions (CO32−) under laboratory circumstances called microbial-induced carbonate precipitation (MICP). In CO2-induced carbonate precipitation (CICP), carbon dioxide was added to a sodium hydroxide solution to form free carbonate ions (CO32−). Different carbonate mineral compositions were then provided by adding Fe2+, Mg2+, and Ca2+ ions to carbonate ions (CO32−). In the MICP and CICP procedures, the results of scanning electron microscopy (SEM) and X-ray powder diffraction (XRD) revealed a distinct morphology of any type of carbonate minerals. Vaterite (CaCO3), siderite (FeCO3), nesquehonite (MgCO3(H2O)3), and dolomite (CaMg(CO3)2 were produced in MICP. Calcite (CaCO3), siderite (FeCO3), nesquehonite (MgCO3(H2O)3), and high-Mg calcite (Ca-Mg(CO3)) were produced in CICP. According to UCS data, siderite and high-Mg calcite/dolomite had more effectiveness in increasing soil strength (63–72 kPa). The soils treated with nesquehonite had the lowest strength value (25–29 kPa). Mineral-treated soils in CICP showed a slightly higher UCS strength than MICP, which could be attributable to greater particle size and interlocking. This research focused on studying the mineralogical properties of precipitated carbonate minerals by CICP and MICP methods to suggest a promising environmental method for soil reinforcement.
Publisher: American Society of Civil Engineers (ASCE)
Date: 06-2016
Publisher: Elsevier BV
Date: 06-2018
Publisher: American Society of Civil Engineers
Date: 13-11-2013
Publisher: Elsevier BV
Date: 04-2017
Publisher: Springer Science and Business Media LLC
Date: 03-2010
Publisher: American Society of Civil Engineers (ASCE)
Date: 06-2017
Publisher: Elsevier BV
Date: 02-2020
Publisher: Elsevier BV
Date: 07-2012
Publisher: American Society of Civil Engineers
Date: 09-11-2015
Publisher: Elsevier BV
Date: 08-2014
Publisher: Springer Science and Business Media LLC
Date: 22-02-2019
Publisher: CRC Press
Date: 06-2017
Publisher: Emerald
Date: 26-04-2011
DOI: 10.1108/09653561111126067
Abstract: The purpose of the paper is to present a new method of controlling through susceptible slopes in order to reduce the risk of landslides. Geotechnical and geological characteristics were collected and different FEM analyses were carried out in a case study of the Alasht valley in Northern Iran in order to determine susceptibility to landslides and consider appropriate countermeasures. Gravel drain piles have a real feel of reducing the pore water pressure in times of seismic loading, so they are used as a remediation method. The results clearly show their effects and an increase in safety as a result. Since the water table situation has a significant effect on stability, the present study focused on an ex le of using a seepage controlling system and its effect on the safety factor for different slopes in the area of Alasht, Northern Iran. Several FEM analyses were carried out on a landslide susceptible case. The results from FEM analysis of different slopes in the study area show a high susceptibility to landslides for six sites. Installing a gravel drain pile surrounded by a non‐woven geotextile layer leads to an increase in the safety factor against landslides. As a result, after installing gravel drain piles in the upper parts of slopes in order to control run out and ground water rising up in times of heavy rainfall, the safety factor against landslides in both static and seismic loading improved significantly. The literature regarding controlling seepage in order to reduce the risk of landslides is limited. This paper collects and analyses geotechnical and geological data from the Alasht valley as an ex le to show the high risk of susceptibility to landslides.
Publisher: Informa UK Limited
Date: 25-04-2017
Publisher: Elsevier BV
Date: 12-2016
Publisher: Informa UK Limited
Date: 04-11-2014
Publisher: Thomas Telford Ltd.
Date: 11-2023
Abstract: This research study was conducted to improve the properties of highly plastic clay using carbonate minerals produced using carbon dioxide. The carbonates such as magnesite, siderate and calcite were produced using laboratory-scale carbonation experiments and were used to treat clay s les. The index properties, shear strength and consolidation behaviour of the treated clay s les were then investigated. The results showed that the plasticity index and activity of the treated clay decreased, and shear strength and consolidation behaviour improved. The study confirmed that magnesite had improved clay properties due to the uniform and homogeneous distribution of small crystals of magnesite in the clay compared with those of siderite- and calcite-treated soil. As the process sequesters carbon dioxide, it could be developed as an environmentally friendly soil improvement method subject to further research studies.
Publisher: Research Publishing Services
Date: 2009
DOI: 10.3850/GI068
Publisher: Thomas Telford Ltd.
Date: 12-2019
Abstract: Factors that influence microbially induced carbonate precipitation (MICP) include bacterial species, bacterial cell concentration and urea and calcium ion (Ca 2+ ) concentrations for determining the most effective laboratory conditions for calcium carbonate (CaCO 3 ) precipitation by Sporosarcina pasteurii and Sporosarcina aquimarina bacteria. In this study, the most effective laboratory conditions for MICP by S. aquimarina were 12·8 × 10 9 bacterial cells/ml, 0·25 M urea and 2 M calcium chloride (CaCl 2 ). On the other hand, the most effective conditions for S. pasteurii were 9 × 10 9 bacterial cells/ml, 1 M urea and 2 M calcium chloride.
Publisher: ASTM International
Date: 30-05-2018
DOI: 10.1520/JTE20170305
Publisher: Thomas Telford Ltd.
Date: 06-2017
Abstract: This paper describes the first study demonstrating the potential of olivine as a soil stabiliser. Olivine has been shown to provide a reactive source of magnesium oxide capable of sequestering carbon dioxide. The effects of olivine additions on consistency limits, compaction characteristics and unconfined compressive strength (UCS) of soil are described. The effect of carbon dioxide pressure, and carbonation period, on the UCS of olivine-treated soil is of great importance in defining treated properties. Results highlight the benefits of olivine in soft soil stabilisation with reference to the UCS. Use of 20% olivine decreased the plasticity index and optimum moisture content while increasing the maximum dry density of the soil. The greatest strength was developed after carbonation at 200 kPa for 168 h in the soil containing 20% olivine. Structural and compositional analysis using scanning electron microscopy and X-ray diffraction confirmed the benefits of olivine in terms of decreasing the discontinuity of soil. This was attributed to the crystallisation products responsible for strength development after carbonation, respectively. The paper is significant as it presents a more environmentally friendly method of stabilising soils compared with alternative methods using high embodied energy binders such as cement.
Publisher: Elsevier BV
Date: 04-2016
Publisher: CRC Press
Date: 18-02-2014
DOI: 10.1201/B15627
Location: Iran (Islamic Republic of)
Location: Iran (Islamic Republic of)
Location: Iran (Islamic Republic of)
Location: Iran (Islamic Republic of)
No related grants have been discovered for Afshin ASADI.