Afshin Asadi

Geotechnics of Organic Soils and Peat

Peat and organic soils commonly occur as extremely soft, wet, unconsolidated surficial deposits that are an integral part of wetland systems. These types of soils can give rise to geotechnical problems in the area of sampling, settlement, stability, in situ testing, stabilisation and construction. There is therefore a tendency to either avoid building on these soils, or, when this is not possible, to simply remove or replace soils, which in some instances can lead to possibly uneconomical design and construction alternatives. However, in many countries of the world, these soils cover a substantial land area and pressure on land use is resulting in ever more frequent utilisation of such marginal grounds.

Reinforcement Benefits of Nanomodified Coir Fiber in Lime-Treated Marine Clay

AbstractIn this study, reinforcing effect of nanomodified coir fibers with ferric hydroxide, Fe(OH)3, and aluminum hydroxide, Al(OH)3, on shear strength of limed marine clay soil was investigated. Accordingly, triaxial compression strength (TCS) testing was carried out to determine the shear strength parameters of the reinforced soil. Also, wetting/drying cycle testing was conducted to assess the durability of samples. The results from the experimental investigation show that the lime and nanomodified fibers improved the shear strength and durability through the intended modification on natural coir fiber. Moreover, an increase in the effective stress internal friction angle and the cohesion intercept were observed. To confirm the morphology alteration in fibers, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) tests were performed. Nanomodification of fibers increased their tensile strength and caused a better interaction with the limed matrix by an enhanced interfacial adhesion. The ...

Effect of Coir Fibers on the Tensile and Flexural Strength of Soft Marine Clay

The effects of the mechanical properties of the coir fiber which reinforces soft marine clay were investigated by a series of laboratory tests regarding unconfined-compression, indirect tensile properties, and three point bending. In this study, fiber content was found as the main factor that affected the strength of the soil specimens. The results indicated that for the unconfined compression test at the maximum dry density and optimum moisture content, compressive strength increased with fiber content up to 1%. A similar trend was also found in the tensile strength, flexural strength, and young’s modulus of the soil. The strength and ductility increased sharply until the threshold of 1.5% fiber content. Furthermore, the improvement in the mechanical behavior of the soil mixtures indicates that the use of fibers mixed with soft marine clay as potential building materials for land-based structures.

Settlement Problems in Peat Due to Their High Compressibility and Possible Solution Using Cement Columns

Tropical peat soils are considered as extremely soft, wet, unconsolidated deposits. These kinds of soils are geotechnically problematic due to their high compressibility or high settlement and low shear strength. Cement columns may be used to improve the settlement problem of these soils. This paper describes the results of the effects of cement columns on the compressibility of fibrous tropical peat soils. Coefficient of consolidation, compression index, coefficient of secondary compression, and coefficient of volume compressibility were obtained by a Rowe cell test for both, untreated peat soil and peat soil treated with cement column. The results indicate that installing cement columns and increasing cement ratio could reduce the compressibility of peat soils and decrease its settlement dramatically.

Application of Geophysical Techniques for 3D Geohazard Mapping to Delineate Cavities and Potential Sinkholes in the Northern Part of Kuala Lumpur, Malaysia

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 samples taken from the field to obtain the formation factor. The relationship between resistivity and the formation factor and porosity for all the samples 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.

Utilization of Alkali-Activated Olivine in Soil Stabilization and the Effect of Carbonation on Unconfined Compressive Strength and Microstructure

This paper reports for the first time the stabilization of soil using olivine and the application of novel techniques utilizing alkaline activation and carbonation. A rigorous study addressed the effect of carbon dioxide pressure and alkali concentration (10-M sodium hydroxide soil additions from 5 to 20%) between 7 and 90 days. Microstructural and compositional changes were evaluated using microscopic, spectroscopic, and diffraction techniques. Results demonstrate the advantages of using olivine in the presence of NaOH and the associated increases in soil shear strength of up to 40% over 90 days. Samples subjected to carbonation for a further 7 days led to additional increases in soil strength of up to 60%. Microstructural investigations before and after carbonation attributed the strength development to the formation of Mg(OH)2, hydrated magnesium carbonates, and M─S─H, A─S─H gel phases. The impact of this work is far reaching and provides a new soil stabilization approach. Key advantages include significant improvements in soil strength with a lower carbon footprint compared with lime or cement stabilization.

Electrokinetic Stabilization of Soft Soil Using Carbonate- Producing Bacteria

The carbonate (CO3−2) produced by Sporosarcina pasteurii was injected electrokinetically to enhance the mechanical properties of soft clay soils. In this method the Ca2+ was injected into the anode chamber and moved towards the cathode by electromigration and electroosmotic flow. Then the released CO3−2 from a blend of bacteria and urea was injected into the cathode chamber. The CO3−2 ions were moved from the cathode to the anode under electromigration mechanism. The CaCO3 was precipitated in the presence of calcium in porous medium of the soil, and consequently increased the shear strength of the soil. The polarity reversal was applied to have a homogeneous distribution of CaCO3.

Environmental Factors Affecting the Compressive Strength of Microbiologically Induced Calcite Precipitation-Treated Soil

ABSTRACT Some microorganisms such as Sporoscarcina pasteurii precipitate calcium carbonate and are suitable for biocementation. This study aimed to investigate the effects of several factors including concentration of bacteria, chemical reactants, temperature, and pH on precipitation of calcium carbonate. The results showed that after 7 and 14 days of curing, the compressive strength of silty clay soil samples increased steadily as pH increased from 5 to 9. It was observed that pH plays an important role in biocementation. The highest compressive strength (i.e. 92 kPa) was observed when the soil was treated with 50 ml of bacterial solution after 14 days of curing. In addition, it was observed that the highest compressive strength of samples was achieved when the temperature was 40°C.

Sensitivity analysis of slopes affected by possible earthquake loading and heavy rainfall: Case study

The effect of seismic loading on slope failure is studied both experimentally and analytically to establish the spatial and temporal process of failure initiation and propagation during possible earthquake loading or heavy rainfall. For such purpose different limit equilibrium modeling were carried out and factor of safeties against sliding caused by both excess earthquake loading and heavy rainfall were found. As for this study, two parameters normally taken into account which were soil properties changing as well as exerted seismic loading. Moreover to show the reality and importance of the main objective of this research, two of the constructed slopes in Malaysia were selected and modeled. The factor of safety against landslides in normal condition (without any extra seismic loading consideration) at Johor was 1.293, 1.425 and 1.301 using ordinary, bishop and Janbu methods, respectively. Also, factor of safety against slope failure at Besut was 1.508, 1.637 and 1.519 according to ordinary, bishop and Janbu methods, respectively. As a result, mentioned slopes will collapse applying even low seismic loading of 0.2 g. Internal friction angle reduction more than 25% also caused significant decrease in the slope’s factor of safety.

Preventing landslides in times of rainfall: case study and FEM analyses

Purpose – The purpose of the paper is to present a new method of controlling through susceptible slopes in order to reduce the risk of landslides.Design/methodology/approach – 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.Findings – Since the water table situation has a significant effect on stability, the present study focused on an example 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 slope...