University of Khartoum Engineering Journal

Comparative Study on Some Chemical and Mechanical Stabilizations of Expansive Soils

Omer S. M. Hamza — 2023-04-05

This paper studies the differences between effects of chemical and mechanical stabilizations on the engineering properties of expansive soil. Undisturbed soil samples were collected form Abu-Gameem in South Sudan. The soil sample was very high expansive in accordance to the primary test conducted. Laboratory tests were undertaken to study the effect of chemical and mechanical additives individually on soil properties. Atterberg’s limits, compaction, California bearing ratio, free swell and swelling pressure tests were conducted on natural and treated soil. Quicklime was used as chemical stabilizer agent, while fine sand was used as mechanical. The lime was collected from Sabol industrial area in south of Khartoum while the sand was obtained from Omdurman in Sudan. The soil was first treated by quicklime contents as 3%, 5% and 7% by weight. Then separately was treated by fine sand contents as 5%, 10% 15% by weight. Comparing the results obtained from chemical and mechanical stabilizations, it can be reported that both of them are effective in improving the engineering properties of expansive soils. Notwithstanding, chemical stabilization improved the soil with less contents of additive. Addition of only 3% quicklime reduced soil plasticity from 45% to a suitable value (18%) while addition of 15% fine sand reduced soil plasticity to 24%. Addition of quicklime resulted in reduction of free swell index almost 4 times of its initial value, whereas slight reduction was observed when fine sand used. Significant improvement on the swelling pressure was obtained when using lime. But, the compaction characteristics were improved further when fine sand used. It could be concluded that based on the result of this study, chemical stabilization is more effective than mechanical. However, a combination of them can be used for further investigations.

Causes and Effects of Delays in Road Construction Projects in Sudan

Magdi M. E. Zumrawi — 2023-04-05

Construction delay is one of the serious concerns of the road industry in Sudan. The study aims to identify the causes of delays that have adverse effects on road projects in terms of time, cost and quality. Literature of different types of delays, their causes and effects on road construction projects were intensively reviewed. The study identified a number of causes of delays at great risk and have adverse effects on construction of road projects. A questionnaire based on 15 causes and 5 effects was sent to the clients, consultants and contractors. The collected data were analysed using the Relative Importance Index (RII). The results showed that the contractor is most commonly responsible for project delay (37%), followed by the client (33%) and the consultant (30%). The study findings reveal that the top five main delay causes are payment delay by client, funding problems, conflicts among the project parties, suspension of work due to the client or consultant, and project schedule changes. On the other hand, cost and time overrun, poor quality of work due to rush, and disputes are the main effects of delays. The study concluded that adequate construction budget and payments on time should be the main factors for the project success.

The Effect of Radiometric Resolution on Information Sharing Between Landsat8 Bands

Ola Elwasila — 2023-04-13

The technological revolution that the world is witnessing also included the development of the characteristics of remote sensing devices, which had a direct impact on increasing the accuracy of the data obtained through these devices. For example; the radiometric resolution of Landsat satellite sensors increased from 7 bits in the first Landsat sensors to 16 bits in Landsat-8. In this study, the effect of this improvement in radiometric resolution was measured to find the amount of change in the mutual information at several dynamic ranges. The study area was the state of Khartoum, and the study was conducted on four different types of land cover (agricultural, urban, water, and desert) to determine the amount of shared information between several dynamic ranges based on the land cover unit. The image obtained from the Landsat-8 satellite for the study area had a 16-bit dynamic range. However, it was down sampled to 8bits, 9 bits, 10 bits, 11 bits, 12 bits, 13 bits and 14 bits, and the amount of information shared between these dynamic ranges and the original image was calculated for the first seven bands of Landsat-8. The results showed that the amount of shared information varies based on the type of land cover, however, this amount reaches its lowest value on the water cover between the 8-bit image and the 16-bit image which is 80%. The study ended with a recommendation that the effect of change in radiometric resolution should be examined in the stage classification of images.