Mohd Raihan Taha

Locating the general failure surface of earth slope using particle swarm optimisation

In this study, a new particle swarm optimisation (PSO) approach is proposed for evaluating the factor of safety (FS) in a slope stability analysis based on the limit equilibrium method. The safety factors of the general slip surfaces are calculated using a concise algorithm of the Morgenstern–Price method, which satisfies both the force and the moment equilibriums. Each new slip surface is randomly generated by a straight-line technique. The performance of the proposed algorithm is evaluated using a set of three benchmark functions and three slope stability problems from the literature. The results indicate that the new method can provide high-quality, accurate and efficient solutions for computing the FS. Moreover, this method can predict a more critical failure mechanism of earth slope and outperform both the other methods in the literature and the standard PSO.

Morphological and electron transport studies in ZnO dye-sensitized solar cells incorporating multi- and single-walled carbon nanotubes

Dye-sensitized solar cells (DSSCs) incorporating zinc oxide (ZnO) nanostructures and carbon nanotubes (CNTs) were fabricated using a chemical bath deposition method. The nanoflake structures captured by a field-emission scanning electron microscopy analysis traced the appearance of multi-walled carbon nanotubes (MWCNTs) and single-walled carbon nanotubes (SWCNTs) in the photoanode thin film. The photovoltaic performance of the photoanode was quantified by means of an electrochemical impedance spectroscopy (EIS) unit with GAMRY-Physical Electrochemistry. The ZnO?SWCNT-based DSSC exhibited good photovoltaic performance with power conversion efficiency (?), photocurrent density (Jsc), open-circuit voltage (Voc) and fill factor (FF) of 1.31%, 15.31?mA?cm?2, 0.224?V and 0.36, respectively. The EIS unit was also employed to quantify the charge transport resistance (Rct), transport resistance (Rt) and effective electron lifetime (?eff) of the DSSC. The impedance analysis of the ZnO?SWCNT-based DSSC also determined greater highly efficient electron transport due to long effective electron diffusion length than the film thickness of the photoanode.

Soil-water characteristic curves and hydraulic conductivity of nanomaterial-soil-bentonite mixtures

This study evaluates the influence of nanomaterials (nano-copper and nano-alumina) on the suction and hydraulic conductivity of compacted soil-bentonite mixture with different plasticity indexes. The soil suction and hydraulic conductivity of the compacted soil-bentonite mixtures were measured before and after the addition of nanomaterials. Soil-water characteristic curves were then developed for compacted soil samples (with and without nanomaterial) using a pressure membrane apparatus. It was found that saturated water content was lower in the soil samples mixed with nanomaterials. The soil hydraulic conductivity also decreased with increasing nanomaterial content, except for S3 soil sample with nano-copper content. The decrease of hydraulic conductivity was possibly caused by the reduction of the effective porosity due to pore clogging. The results from testing samples after one to four drying times show that the largest rise in soil hydraulic conductivity occurred at first or second drying. Adding nanomaterials can reduce the soil hydraulic conductivity by as much as seven times for soil samples with high clay (bentonite) content.

Numerical model of antecedent rainfall effect on slope stability at a hillslope of weathered granitic soil formation

Modeling rainwater infiltration in slopes is vital to the analysis of slope failure induced by heavy rainfall. Although the significance of rainwater infiltration in causing landslides is widely recognized, there have been different conclusions as to the relative roles of antecedent rainfall to slope failure. In this study, a numerical model was developed to estimate the effect of antecedent rainfall on an unsaturated slope, the formation of a saturated zone, and the change in slope stability under weak rainfall and rainstorm event. Results showed that under a rainstorm event, slope failure occurred at comparably similar time although the antecedent rainfall drainage periods prior to the major rainfall were different (i.e., 24-h, 48-h and 96-h). However, under weak rainfall condition, differences of the antecedent rainfall drainage periods have significant effect on development of pore-water pressure. A higher initial soil moisture conditions caused faster increase in pore water pressure and thus decreasing the safety factor of the slope eventually increasing likelihood of slope failure.

Strength and Microstructure of Mortar Containing Nanosilica at High Temperature

The effect of high temperature on the mechanical properties and microstructure of nanosilica-incorporated mortars has been studied. Results show that the incorporation of nanosilica increases both compressive and flexural strengths significantly at both ambient and after a 2-hour exposure to 752°F (400°C) temperatures; the strengths increase with the increase of nanosilica content. A significant decrease in strength was recorded for all control and nanosilica-incorporated mortar specimens after a 2-hour exposure to 1292°F (700°C) heat; however, nanosilica-incorporated specimens show higher residual strength than those without nanosilica. Microstructural analysis shows that nanosilica reduces the calcium hydroxide crystals to produce more calcium silicate hydrate, the process that contributes to the strength and the residual strength of the material. In addition, the material exhibits a stable structure state up to 842°F (450°C), while exposure to higher temperatures results in a decomposition of hydration products.

Enhancement of dye-sensitized solar cell efficiency using carbon nanotube/TiO2 nanocomposite thin films fabricated at various annealing temperatures

To increase energy conversion efficiency of dye-sensitized solar cells (DSSCs), carbon nanotubes (CNTs) were added to TiO2 gel-like solution. Modified acid-catalyzed sol-gel method was used with the doctor blade coating technique to obtain thin films of CNT/TiO2 nanocomposite photoanode. CNT/TiO2 paste was applied onto the conductive glass to generate a 0.25 cm2 active area which was later annealed at 350°C, 450°C, and 550°C for 60 min. Characterization of the CNT/TiO2 paste was performed using x-ray diffraction. Results showed that the crystalline phase of the particles was anatase. The micrograph obtained using field emission scanning electron microscopy demonstrated that the pastes are highly porous. Brunauer-Emmett-Teller analysis was performed to determine the CNT/TiO2 surface area and particle size. The DSSC with the CNT/TiO2 photoanodes annealed at 550°C showed the highest incident photon-to-charge carrier efficiency value of 0.95% compared with the DSSCs with photoanodes annealed at 350°C and 450°C (0.70% and 0.83%, respectively). The observed efficiencies of the DSSCs with CNT/TiO2 photoanode annealed at the three different temperatures were 2.62%, 2.65%, and 3.13%. The electrochemical impedance spectroscopy analysis showed that the DSSCs with photoanodes developed using the highest annealing temperature (550°C) have higher electron lifetime of 70.423 ms and lower effective recombination rate of 1.42 × 10−2 s−1, thereby improving the performance of CNT/TiO2 DSSCs.

Expert System to Control Construction Problems in Flexible Pavements

This article discusses how highway engineers face complicated problems that are influenced by various conditions during the construction of flexible highway pavements. Identifying these problems and recommending effective solutions demand considerable engineering expertise, which is difficult to obtain at all construction sites. The development of an expert system can effectively help engineers control and analyze such problems. In addition, an expert system can effectively archive the storage and distribution of expertise among pavement engineers. This article describes the development and evaluation of such an expert system. The first stage in the development of the proposed system was the elicitation of knowledge from written sources and from experts through literature reviews and interviews, respectively. The acquired knowledge was analyzed and classified and then represented in a form containing rules and the rules were subsequently coded as software. This article describes the development and evaluation of the Expert System for the Control of Construction Problems in Flexible Highway Pavements.

Regularized versus non-regularized neural network model for prediction of saturated soil-water content on weathered granite soil formation

Modeling unsaturated water flow in soil requires knowledge of the hydraulic properties of soil. However, correlation between soil hydraulic properties such as the relationship between saturated soil-water content θs and saturated soil hydraulic conductivity ks as function of soil depth is in stochastic pattern. On the other hand, soil-water profile process is also believed to be highly non-linear, time varying, spatially distributed, and not easily described by simple models. In this study, the potential of implementing artificial neural network (ANN) model was proposed and investigated to map the soil-water profile in terms of ks and θs with respect to the soil depth d. A regularized neural network (NN) model is developed to overcome the drawbacks of conventional prediction techniques. The use of regularized NN advantaged avoid over-fitting of training data, which was observed as a limitation of classical ANN models. Site experimental data sets on the hydraulic properties of weathered granite soils were collected. These data sets include the observed values of saturated and unsaturated hydraulic conductivities, saturated water contents, and retention curves. The proposed ANN model was examined utilizing 49 records of data collected from field experiments. The results showed that the regularized ANN model has the ability to detect and extract the stochastic behavior of saturated soil-water content with relatively high accuracy.

Adsorption of DDT and PCB by Nanomaterials from Residual Soil

This paper presents the findings of a study on adsorption of dichlorodiphenythreechloroethen (DDT) and polychlorinated biphenyls (PCBs) on three nanomaterials including Multi walled Carbon Nanotube (MWNT), nano-clay and nano-alumina. DDT and PCBs are of significant concern due their high toxicity and long environmental half-lives. Experiments were conducted using batch adsorption procedures at different DDT and PCBs concentrations, from 10 to 60 mg/L. The amounts of MWNT, nano-clay and Nano-alumina used were 0.25%, 0.50%, 0.75%, 1%, 2% and 10%. The adsorption of PCBs solution onto the MWNT, nano-clay and nano-alumina was characterized by an initial rapid adsorption which eventually became constant within 22, 20, and 17 hours, respectively. The adsorption of DDT solution onto the MWNT, nano-clay and nano-alumina was also characterized by an initial rapid adsorption which gradually became constant within 22, 22 and 16 hours, respectively. Results of this study indicated that MWNT was a better adsorbent material compared to nano-clay and nano-alumina for both contaminants in this study. While at 10% of MWNT 88.9% and 77% of DDT and PCB were removed by MWNT, respectively. The effect of pH and temperature were also investigated.

Effect of Three Bioenzymes on Compaction, Consistency Limits, and Strength Characteristics of a Sedimentary Residual Soil

Bioenzymes are organic degradable materials, currently introduced as soil improvement additives. In this experimental study, three types of bioenzymes from three different countries were used to improve Universiti Kebangsaan Malaysia (UKM) soil. UKM soil has properties quite similar to soils recommended as suitable by bioenzyme suppliers. The effect of the three bioenzymes on Atterberg limits, compaction characteristics, and unconfined compressive strength was studied. Controlled untreated and treated samples for two dosages at curing times up to three months were prepared and tested after completion of the curing period. Some results showed little improvement in compaction characteristics, and unconfined compressive strength, but no notable improvement was noticed in Atterberg limits. X-ray diffraction (XRD), X-ray fluorescence (XRF), and field emission scanning electron microscopy (FESEM) tests were conducted for untreated and treated soil samples after two months of curing. XRD and XRF did not show any change in mineralogy and chemical composition between controlled untreated samples and samples treated with the three bioenzymes. However, the FESEM images revealed a denser packing of particles for soil samples treated with two of the bioenzymes.