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Journal Cover Engineer : Journal of the Institution of Engineers, Sri Lanka
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  This is an Open Access Journal Open Access journal
   ISSN (Print) 1800-1122
   Published by Sri Lanka Journals Online Homepage  [49 journals]
  • From the Editor Vol.50 (2)

    • Abstract: No abstract available Published on 2017-04-30 00:00:00
       
  • Numerical Study and Comparison of the Settlement Behaviours of Axially
           Loaded Piles using Different Material Models

    • Abstract: The settlement behaviour of axially loaded piles is one of the prime factors that control the design of single and group piles. Therefore, this research focused on the settlement behaviour of a pile foundation located in sandy-silt under the load of a high-rise building, by simulating it using PLAXIS numerical package and giving consideration to interface effects. Four different types of analysis were investigated: (i) a Linear Elastic (LE) analysis where the soil was assumed as linear-elastic; (ii) a simple Non Linear (NL) analysis where the soil was completely assumed as a Mohr-Coulomb(MC) model; (iii) Non Linear (NL) analysis where the soil was completely assumed as a Hardening -Soil (HS) model; and (iv) a combined (NL-LE and NL-NL) analysis assuming that the soil close to the pile shaft is a nonlinear model and that the soil in the remaining area is made of either linear material or simple nonlinear material (MC). The results of the analysis suggest that the complete MC model shows good agreement with the settlement behaviour obtained from field static load tests at lower working loads. However, the incorporation of a nonlinear HS interface zone of soil is required to predict the settlement at higher working loads. In addition, it was noted that an interface thickness that is twice the pile diameter with the remaining soil modelled as MC would suffice to ascertain the load transfer mechanism of a typical pile. Published on 2017-04-30 00:00:00
       
  • River Basin Modelling for Optimum Water Usage: Uma Oya Downstream
           Development Area

    • Abstract: Water is a basic need of all living beings and the management of water in an optimum manner has therefore now received worldwide attention. This optimum management of water is achieved through the construction of reservoir systems and their optimal operation. This paper presents a simulation study carried out using Water Evaluation and Planning System (WEAP) software at the proposed Uma Oya Downstream Development Project in the Kirindi Oya basin in Sri Lanka. To investigate the impact of the proposed system, one model was developed for the existing system and another for the proposed system. Crop water requirements and irrigation schedules for three climatic conditions were determined using CROPWAT software. Climatic conditions were those of the years which received rainfalls with 20%, 50% and 80% probability of exceedance representing wet, normal and dry years respectively. Daily rainfall, runoff and other meteorological data were the information collected for the study. Availability of water for the irrigation of existing and newly proposed areas was ascertained from the model. Optimal operation patterns were developed for the newly built Alikota Ara and Kuda Oya reservoirs and the enlarged Handapanagala reservoir for different climatic conditions. Results indicated that even when the system is operating in accordance with optimum operating rules, there can be supply deficits. A study was made on the system performance with reduced irrigable areas and different crop types which were observed to bring in reduced deficits. Published on 2017-04-30 00:00:00
       
  • Geotechnical Engineering Properties of Peat, Stabilized with a Combination
           of Fly Ash and Well Graded Sand

    • Abstract: Peat has several unfavourable characteristics such as low bearing capacity, high compressibility, high content of natural water and difficulty of access and thus is not suitable for Civil Engineering constructions. One of the widely used techniques for its improvement is its chemical stabilization through the addition of chemical admixtures such as ordinary Portland cement, lime, fly ash, natural fillers etc. This research was focused on stabilizing peat using low Ca fly ash (ASTM Class F) combined with well graded sand. An experimentally based approach was followed to analyse the stabilization of peat samples with different proportions of fly ash (10, 20 and 30 % by weight) and 125 kg/m3 of well graded sand. With the increase in the fly ash content, the Maximum Dry Density (MDD) increased while the Optimum Moisture Content (OMC) decreased. The Unconfined Compressive Strength (UCS) increased with the addition of fly ash up to 10 % by weight and thereafter it began to reduce as more and more fly ash was added. The UCS increase with curing period for all of the stabilized samples. Rowe cell test results showed that there was an improvement in the compressibility of peat after stabilization. On the whole, it was found that the geotechnical engineering properties of peat can be improved by stabilizing it using fly ash and well graded sand. Published on 2017-04-30 00:00:00
       
  • A New Approach to the Study of Voltage Distribution along a Suspension
           Insulator String

    • Abstract: The cap and pin insulator string, though a simple element in a power system, has the responsibility of carrying the live conductor while insulating it properly from the tower arm. In properly designing the insulator string, it will be necessary to assess the voltage distribution along it to ensure that no unit will get unduly stressed beyond its capacity. There are standard methods available to determine the voltage distribution along an insulator string. However, all these methods have limitations. This paper describes a novel method for accurately computing the voltage distribution along a string insulator which can be used for either short or long strings with no restrictions whatsoever. The computation allows to accommodate the capacitance between the metal work of the string and the tower and the capacitance between the metal cap of the string and the guard ring. The paper also describes two new simple equations that can be used to determine the voltage distribution along an insulator string irrespective of whether it is short or long. Published on 2017-04-30 00:00:00
       
  • Changes in Rainfall in Sri Lanka during 1966 – 2015

    • Abstract: The aim of this study was to analyse the annual and seasonal rainfall trends in Sri Lanka during the 50 year period from 1966 to 2015 using rainfall data collected at 32 rain gauging stations. The seasons considered were the two principal monsoon seasons and the two inter-monsoon seasons. Non-parametric Mann-Kendall trend test and Sen’s Slope estimator method were used to examine the rainfall trends and determine their magnitudes. According to the analysis which was based on annual rainfall data, 21 of the gauging stations were showing increasing trends. The balance 11 stations were showing decreasing trends. Four of the stations, namely those at Anuradhapura, Batticaloa, Mapakadawewa and Pottuvil had significantly increasing trends. The three stations at Chilaw, Dandeniya Tank and Iranamadu Tank showed significantly decreasing trends. In general, the eastern region of the country has shown over the last half century an increasing rainfall trend and the western, northern and south western regions and the central hills of the country have shown a decreasing rainfall trend during the same period. The seasonal rainfall indicated increasing trends during the First-Inter Monsoon, Second-Inter Monsoon and Northwest Monsoon seasons at a majority of the stations. In contrast, during the Southwest Monsoon season, most of the gauging stations have shown downward rainfall trends. Published on 2017-04-30 00:00:00
       
  • Developing a Mathematical Model Based on Weather Parameters to Predict the
           Daily Demand for Electricity

    • Abstract: The System Control Centre (SCC) of the Ceylon Electricity Board (CEB) in Sri Lanka, conducts short term (hour ahead, day ahead) and medium term (up to three years) demand forecasting based on historical demands, seasonal patterns, time of the day and regional sales forecasts. However, there are no measures taken to include the influence of weather conditions in this forecasting. Temperature and humidity have become increasingly dominant determinants of the electricity demand with the increased use of space cooling equipment in commercial and household sectors. In this paper, a methodology is presented to develop a linear model to predict the daily electricity demand based on weather parameters which uses historical hourly demand data and meteorological data of four consecutive years. Meteorological parameters (temperature, relative humidity, wind speed and wind direction) are taken as independent parameters while the hourly demand is taken as the dependent parameter. Correction factors are used to include the effect of the yearly demand growth for improved correlation. Each electricity demand data point is multiplied by this correction factor based on the average demand growth (yearly) and the time of the day. The prediction model consists of 72 independent equations (24 representing a weekday, 24 representing Saturday and 24 representing Sunday). Correction factors are calculated for the calendar holidays, which have a major influence on the electricity demand. Model validation is done for historical weather data as well as for weather forecast data. Published on 2017-04-30 00:00:00
       
  • Design of a Road- side Threat Alert System for Deaf Pedestrians

    • Abstract: Listening is an important human skill which plays a vital role in our day to day life. Moreover, the reactions of people are very much correlated to the sounds they hear. Thus, deaf people have to undergo many difficulties in identifying threats when walking along roads. Many deaf pedestrians have lost their lives when walking along a road or crossing a road. Although many devices that support deaf pedestrians are being employed around the world, most of those devices are very expensive and also do not provide a detailed notification to the user. Hence, an improved deaf pedestrian assisting device is highly preferred. This paper proposes an electronic road-side threat alert system which would be a handy device to assist deaf pedestrians to identify objects moving behind them such as vehicles & other threats. With the help of this wearable device, they would be able to sense the environment around them. The proposed system is based on a microcontroller hosting a Bayesian classifier unit and an array of ultrasonic sensors for distance measuring. The notification to the deaf pedestrian is provided via a set of vibrating motors. A prototype implemented has demonstrated very good accuracy in the identification of threats at a low cost. Published on 2017-04-30 00:00:00
       
  • The Combined Effect of Temperature and Salinity on the Mechanical
           Behaviour of Well Cement

    • Abstract: Carbondioxide Capture and Storage (CCS) has been identified as the best measure to reduce the concentration of carbon dioxide in the atmosphere. Carbon dioxide expedites global warming. The captured carbon dioxide is stored in deep underground reservoirs using injection wells. The integrity of these wells needs to be ensured to have a durable carbon dioxide sequestration. Generally, the well cements of these underground wells lose their integrity primarily due to their degradation caused by aggressive curing temperatures and also due to the salinity conditions prevalent in the earth’s down-hole. Therefore, the aim of this study was to ascertain the combined effect of the temperature and the salinity on the mechanical behavior of well cement. Sulphate resistant Class G cement samples were cured in various salinity concentrations (0 to 40% of NaCl of the weight of water) and at varying curing temperatures (25, 40, 60 and 80ºC). The mechanical behavior of well cement under these varying salinity and temperature conditions was studied by analyzing its uniaxial compressive strength and the Young’s modulus. Scanning Electron Microscope (SEM) images of degraded samples showed microstructural variations caused during the degradation process. EDX (Energy Dispersive X-Ray Spectroscopy) tests were also carried out to find out the proportion of chemical ions in the degraded cement samples. The test results revealed that the uniaxial compressive strength of the samples initially increases up to an optimum salinity of 10% (by weight of water) and that it thereafter gradually decreases with increasing salinity. With the compressive strength varying with the curing temperature, the optimum temperature for 7 days of curing is found to be 40˚C and that for 28 days of curing is found to be 60˚C. On the whole, OPC sulphate resistant well cement shows its optimum strength at 60ºC and at a NaCl concentration of 10%. Published on 2017-02-09 00:00:00
       
  • Cement Stabilized Soil as a Road Base Material for use in Sri Lankan Roads

    • Abstract: The elastic modulus of the lower quality coarse–grained sandy materials available in Sri Lanka is higher than the elastic modulus of fine–grained silty and clayed materials. Although these locally available soils can be stabilized using cement, due to the non-availability of appropriate guidelines, several issues can arise when they are stabilized. The strength of the materials can be measured using the California Bearing Ratio (CBR). However in certain specifications, it is the Unconfined Compressive Strength (UCS)that is specified for stabilized material. Therefore, the first phase of this study was focused on identifying the correct way to measure the strength of stabilized materials. The study confirmed that the strength of a Cement Stabilized Soil Base (CSB) should be measured using the UCS. Furthermore, in road pavements with a stabilized base, the most critical tensile stress and strain occur at the bottom of the stabilized layer. To minimize fatigue cracking, this tensile stress at the bottom of the stabilized layer has to be controlled. However, empirical design guidelines used in pavement designs cannot be used to analyse the mechanistic behaviour of pavement layers. Hence, during the second phase of this study, cement stabilized pavements were analysed using a Mechanistic-Empirical Method (MEM). A pavement design chart for pavements with a CSB layer was developed for various subgrade and traffic classes using the MEM software KENLAYER. Published on 2017-02-09 00:00:00
       
 
 
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