Hamed A. Keykha

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.

Effect of discontinuities on the stability of rock blocks in tunnel

This paper presents the results of an investigation that was carried out using important parameters, such as discontinuities in forming rock block and instability in tunnel. Discontinuities like bedding and joints are one of the most important factors when compared with parameters, such as engineering features of rock mass. In this review, numerous features like rock quality designation (RQD), rock classification (RMR), stress and strain and distributions of discontinuities in a sample tunnel were evaluated. However, most of them were suitable in the tunnel, but because of the creation of more intersection points in critical zone, the movement of blocks in tunnel roof and wall of the tunnel are possible. It also demonstrates simple factors such as step-over joints in rock mass, having important effect in instability.

The effect of discontinuities on stability of rock blocks in tunnel

This paper presents the results of an investigation that was carried out using important parameters such as discontinuities in forming rock block and instability in tunnel. The discontinuities like bedding and joints are one of the most important factors compared with parameters such as engineering features of rock mass. In this review, numerous features like Rock Quality Designation (RQD), rock classification (RMR), stress and strain, and distributions of discontinuities in a sample tunnel were evaluated. However, most of them were suitable in the tunnel, but because of creating more intersection points in critical zone, the movement of blocks in tunnel roof and wall of the tunnel are possible. It also demonstrates the simple factors such as step-over joints in rock mass, having important effect in instability.