Abdul Samad Abdul Rahman

Simulation technique for voltage collapse prediction and contingency ranking in power system

Currently, power demand in the world has grown at a rate faster than the infrastructure development. This has caused the power system network to be stressful that could disrupt system stability leading to voltage collapse in the entire system. This incident led to a cascading blackout in the whole system and required a voltage stability analysis to be properly conducted. Line outage in a power system could also lead to the event of voltage collapse which implies the contingency in the system. Line outage contingencies are ranked so that the line which highly affects the system when there is an outage occurs in this line in terms of voltage instability could be identified. The contingency ranking process can be conducted by computing the line stability index of each line for a particular line outage and sort them in descending order. The contingency which is ranked the highest implies that it contributed to system instability. This paper presents a new voltage stability index referred to a line used to rank the line outage contingency. The information from the contingency ranking indicates the severity of the voltage stability condition in a power system due to line outage.

Peat soil treatment using POFA

Palm oil fuel ash (POFA) is a by-product from palm oil mill. It is found that this ash contains pozzolanic which possess cementitious properties that enable it to replace cement. This leads to this research to study the possibility of POFA to replace Ordinary Portland Cement (OPC) in stabilizing peat soil. POFA which were collected from Bukit Kerayong was dried than sieved through 445 µm sieve. In order to get fineness POFA, ash which passes through 445 µm sieve were then grinded. As for the peat soil, it was dug out approximately 0.5m from the surface of Sungai Belankan, Sepang. It was first heated up in the oven and sieved to remove the large fibres. Several series of physical properties test were conducted in this study. The tests conducted were liquid limit test, specific gravity test, particle size distribution test, compaction test, organic content test and moisture content test. On top of that, the classification for peat soil was found as low to medium degree of decomposition, which is according to von Post scale, it can be classified as H4. The peat has high amount of moisture content which is 211%. For engineering properties which is also the main objective for this test, an unconfined compression test was conducted for a total of 15 samples with 38mm of diameter and 76mm of height. These samples were divided into four groups named P0, P1, P2, P3 and P4 with 0% additive, 30%OPC, 20%OPC + 10%POFA, 15%OPC + 15%POFA and finally 10%OPC + 20%POFA respectively. Each group experienced 3 different curing periods of 0, 7 and 14 days and named as A,B and C respectively. Based from the deviator stress vs. axial strain graph, the highest recorded UCS value is 128 kPa which was tested on sample P2C. It was even higher than the value of P1C which is 92.1 kPa. Hence, it shows that there are possibilities for POFA as one of a pozzolanic material to replace cement in peat soil stabilization.

Clay Stabilization Using OPC and Bottom Ash as Additives

Clay can be found in many parts of Malaysia. It is very susceptible to settlement due to its low shear strength. Therefore, stabilization is needed especially for a wide construction area. Nowadays, the use of waste materials as construction material is crucial because this practise will help to protect the environment. One of the waste material that has low economical value and less explored by researches is bottom ash (BA). This material is produced from the electric power plant. This material has pozzolanic properties which is able to substitute cement in ground improvement. The objective of this study is to determine the unconfined compressive strength of clay after stabilization with the ordinary portland cement (OPC) and BA. The disturbed soil sample was taken from Pulau Indah, Klang, Malaysia. The basic and engineering properties tests were conducted on the clay samples. Moreover, 18 samples were prepared in cylinder form for unconfined compression test (UCT). The samples were then cured for 0, 7 and 14 days in order to see the strength development over time because the pozzolanic reaction is affected by time. Therefore, the strength of the soil mix will increase with the increase in cement content and curing time. Hence, this waste material can be used for ground improvement work in order to protect the environment.

Volume Change Behaviour of Clay by Incorporating Shear Strength: A Review

Soft clay settlement is well known as a major problem in the civil engineering structures such as highways, buildings and bridges. The problem arises due to the current settlement analysis which is derived from the effective stress concept. It considers the volume change increase with the increase in the effective stress, whereas the settlement problem is not always happened in this fashion. In fact, the inundation problem that causes the sudden settlement during the effective stress decrease really put a tremendous blow to this concept. It is proved that the empirical effective stress concept that is widely used by the engineer is not the appropriate analysis. In fact, this is one of the main factors that cause many settlement problems. The objective of this paper is to review several settlement models available in the literature and to distinguish the applicability of the model to predict soil settlement. It also reviewed the volume change behaviour by incorporating shear strength concept that is more appropriate to predict the settlement. Hopefully, this paper will help the new researcher to uncover the unique behaviour of clay settlement and at the same time will reduce the settlement problem cases.

The Effect of Rice Husk Ash (RHA) Mixtures on Geotechnical Properties of Soil

Nowadays, a major issue in construction industry is about soil stability. RHA is one of the potential stabilizers and can be easily found in Malaysia. RHA can create a negative effect on the environment if it is being dumped as a waste since it can cause air pollution from its fine grains when blown by the wind. Therefore, this study will utilize this waste and it hopefully can reduce the above-mentioned hazard. The samples were prepared with different proportions of RHA which are 4, 8, and 12% of the soil mass. On top of that, the samples were added with Ordinary Portland Cement (OPC) to ignite the pozzolonic reaction between the soil particles and the additives. The amount of cement used in every sample is 2% of the soil mass. Unconfined Compression Test (UCT) was conducted to determine the maximum strength that can be sustained by the modified samples. The higher strength can be gained with addition of RHA together with OPC. It is recommended that 8% of RHA content with 2% cement is the optimum amount for practical purposes. In conclusion, RHA and OPC are suitable to be used for soil stabilization.

The Effect of Fly Ash and Bottom Ash Pile in Problematic Soil Due to Liquefaction

Generally, a construction structure is located on a by soil preferably a good and sound soil properties. However due to limited location of a good and sound soil properties, engineers were challenge by constructing a structure on a problematic soil condition. Mostly, the engineer will be facing building a structure on a loose sandy soil and worst it has a higher chance of liquefaction. This sandy soil can cause the problem to the structure of the building especially if the bearing capacity of the soil is not adequate. For example, the settlement, cracking will happen due to the earthquakes phenomena and worst-case scenario the building will have to undergo a liquefaction attack aftershock. Thus, to overcome this serious problem, the soil properties must be improved by a suitable method such as soil stabilization. The objective of this research is to assess the effectiveness of using fly ash and bottom ash on soil stabilization in liquefaction condition. In this research, piling was used to increase the density of the soil. This will help to reduce the number of settlement during liquefaction process. The amount of cement (5% of soil weight) and fly ash with bottom ash is used with different percentages (10, 20, 30, 40%). The sand will be mixed with the bottom ash and fly ash in different percentages. After conducting a series of tests, it is concluded that 30% of bottom and fly ash give a better result in reducing the settlement value than other mixture.

Prediction of soil stress-strain response incorporates mobilised shear strength envelope of granitic residual soil

The concept of effective stress has been the principal concept in characterizing soil volume change behavior in soil mechanics, the settlement models developed using this concept have been empirical in nature. However, there remain certain unexplained soil volume change behaviors that cannot be explained using the effective stress concept, one such behaviour is the inundation settlement. Studies have begun to indicate the inevitable role of shear strength as a critical element to be incorporated in models to unravel the unexplained soil behaviours. One soil volume change model that applies the concept of effective stress and the shear strength interaction is the Rotational Multiple Yield Surface Framework (RMYSF) model. This model has been developed from the soil-strain behavior under anisotropic stress condition. Hence, the RMYSF actually measure the soil actual elasto-plastic response to stress rather than assuming it to be fully elastic or plastic as normally perceived by the industry. The frameworks m...

Bioengineering Stabilization Method to Counter Rainfall-Induced Slope Failure

The application of vegetation as part of slope stability and to control erosion has proved to be cost-effective for stabilizing the surface of the slope. This research describes the unique characteristics of Vetiver grass and Vetiveria Zizanioides Nash and it is the potential use for stabilizing slopes and erosion control. This study refers to the past research on the generic characteristics of Vetiver grass. Also, reports on the laboratory tests that had been conducted determine the strength of Vetiver grass roots at an existing slope. It concludes that in the basis of tests are success and effectiveness over many years that the grass and its associated applications can be effective, durable, and low cost method of vegetative stabilization of slopes under tropical and extreme conditions.

Lateral movement and settlement of sandwiched soft soil using physical model

Soft marine clay is a well-known problematic soil in geotechnical engineering. Soft marine clay soil is one of the problematic soils which are commonly found along the coastal areas of West Malaysia. In Klang area where the samples are taken, the thickness of the soft marine clay may vary from 20 to 40m. The general physical properties of the soft soil are presented in this study. In general, the unit weight of the soft clay is about 14 to 16 kN/m3. The result for Liquid Limit (LL) of the soft clay is very high which about 50% to 150%. Plasticity Index (PI) varies from 20% to 80%. The compressibility properties of the soft soil are mainly assessed from the laboratory consolidation test results. This study involves the laboratory test studies where the specimen of soft soil is obtained in disturbed condition. Prior to the experimentation, the physical model is prepared. The physical model is under constant condition of exposure in the laboratory to ensure any possible errors pertaining to the surrounding environment are mostly eliminated. The results of this experiment show that the lateral movement of soft soil is proportional to the depth of normal excavation and failure occur parallel to the soft soil plane in the geotechnical tank. Maximum settlement occurs at the centre of tank. In conclusion, it can be accepted that the soft soil has a smooth characteristic and can cause lateral movement of the above soil layers by dispersing its mass horizontally.