Civil Engineering

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    MODELING LEVEL CROSSINGS’ TRAVEL TIME AND DELAY CHARACTERISTICS OF ADDIS ABABA LIGHT RAIL TRANSIT (AA-LRT)
    (Hawassa University, 2019-04-17) DARIC TESFAYE
    Traffic modeling is simplified representation of a part of traffic reality that provides a better understanding and interpreting of the complex traffic interactions. The objectives of this study is modeling level crossings travel time and delay characteristics of Addis Ababa light rail transit (AA-LRT) using simulation and mathematical models and evaluate the operational characteristics of the level crossings. In the process of achieving the objectives, the study investigate about peak period vehicle volumes, compositions, routings, LRV arriving frequency ,speed and the delays experienced. To meet the objective of this research intersection geometry data from field and traffic flow data at selected intersections is done by video recording and manual counting. In addition travel time data using light rail transit and minibus taxi is collected by traveling using these modes to a statistical number of repetitions. Suitable data inputs in forms of traffic volume, vehicle composition, vehicle routing, speed, train headway, travel time and delay at different incidences including level crossings are prepared. These suitable data inputs are introduced into VISSIM and SPSS analysis soft wares. Finally, the results were interpreted and the key research findings were presented in two types; i.e. through VISSIM simulation and SPSS statistical models. At the CMC level crossing the baseline without LRT scenario the average delay of traffic is 134.62s/veh ,the actual scenario with 00:05:41 LRV headway the average delay of traffic is 135.2 s/veh the delay increased by 0.43% and twice arrival frequency scenario the delay is 136.22s/veh with an increase in delay of 0.76% from the actual conditions. At the Sebategna level crossing the baseline without LRT scenario the average delay of traffic is 22.31s/veh ,the actual scenario with 00:06:30 LRV headway the average delay of traffic is 23.53 s/veh the delay increased by 5.47% and twice arrival frequency scenario the delay is 33.11s/veh with an increase in delay of 40.7% from the actual conditions. Additionally as observed in the mathematical model equation, the train’s travel time is dependent on running time, delay at grade intersection, open door close door time, close door start movement time and stop open door time in descending order. It is concluded that the average additional delays at level crossings increase from the base scenario and with increasing light rail crossing frequencies. In addition, delay at the level crossing is the second important variable that contributes for the variability of train travel time at peak hours.
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    SIMULATION OF PILE LOADING TEST IN A LAYERED SOIL WITH VERTICAL LOADING BY USING FINITE DIFFERENCE METHOD BASED SOFTWARE
    (2020-10-13) BEREKET GEBRESELASSIE GIRMAY
    Pile loading tests are usually performed in various projects to determine the ultimate pile capacity. However, the cost of running these tests and the time it takes is one of the difficulties that engineers face in current geotechnical practices. Finite difference method and finite element methods have comparable accuracy. However, finite difference method based tool was used for the analysis due to its simplicity, computational efficiency and simple structure codes. The research presents a numerical simulation of pile loading test using a finite difference program “FLAC 3D”. The chosen software is memory and simulation time efficient. It solves almost all kinds of geotechnical problems, but the only downside is that it initially takes some time to get the feel of the software, but once understood, it can solve any problem and it also supports a wide range of material models. The objective of this study is to simulate a pile load test with vertical loading in a layered soil, in order to estimate the load-settlement characteristics and to determine the effect of young’s modulus, angle of internal friction, lateral earth pressure coefficient, and the dilation angle on the load-settlement curve. Input parameters of the simulation were collected from Nib, United, and Zemen international bank's new headquarter projects. In the case of piles with incomplete data, the parameters were estimated from site experience data and/or using different equations obtained from a literature. The proposed numerical model has been validated with field data and published results provided by other studies. The validation produced good results with a minor deviation except for nib bank piles. The significant deviation in nib bank piles is due to the generalized soil parameters used in the analysis. The numerical analysis underestimated the ultimate pile capacity. However, Lateral pressure coefficient manipulation yields improved results. Underprediction of load-settlement curves of nib bank piles was due to lower young’s modulus values estimated from various equations. The study on one of the piles showed that the base resistance carries the upper hand of the total capacity. The importance of using finer mesh near high-stress gradient zones was examined and it has been found that finer mesh generated based on the developed relation produced a good performance. If the required constitutive model, initial and boundary conditions, and good quality input data are available, the proposed numerical model can be used as an alternative method for the design purpose on projects involving pile foundations