Browsing by Author "de Silva, LIN"

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Applicability of HCM 2000 to determine the level of service in urban arterial roads, Sri Lanka
(Department of Civil Engineering, University of Moratuwa, 2012-12) Mampearachchi, WK; Jayasuriya, WWC; Senaratne, SAMANI; Nawagamuwa, U; de Silva, LIN
T16 obJective of this research is to identify the applicability of Highway Capacity Manual (HCM) to determine the Level of service in urban minor arterial roads in Sri Lanka. HCM has been developed by the transport research board, USA. Currently most of the local road eve opment agencies use HCM for capacity analysis of roads. There have been no researches carried out to identify the applicability of HCM to the Sri Lankan condition. To depict the quality of service of the roads quantitative measures of a traffic stream are required. Level of Service (LOS) is a quality measure describing operational conditions within a traffic stream, generally in terms of service measures such as speed and travel time, freedom to maneuver, traffic interruptions and comfort. Six LOS are defined based on service flow rates of roads. Letters designate each level from A to F with LOS A representing the best operating conditions and LOS F the worst. Though the local roads have acceptable LOS, the results obtained from both HCM 2000 andl986 have not reflected it It is required to identify the factors which affect the LOS. For that a sample of two way - two lane roads were selected. For the selected sample flow vs. density curves have been developed by considering traffic data and speed survey data. Based on the literature findings and data collected from the field, six LOS for the urban minor arterial roads have been defined.
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Civil Engineering Research for Industry Symposium 2012 (Pre Text)
(Department of Civil Engineering, University of Moratuwa, 2012) de Silva, LIN
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Finite element analysis of a deep excavation supported using a secant pile wall: a case study
(Department of Civil Engineering, 2023-09-27) Silva, VSSD; de Silva, LIN; Mallikarachchi, C; Hettiarachchi, P; Herath, S; Fernando, L
Coulomb (1776) introduced the first method to calculate the lateral earth pressure acting on retaining walls. Rankine theory was introduced as a result of improving the previous work (Rankine, 1857). Many methods are currently used to evaluate the earth pressure distributions of the retaining wall and the prop forces of the support system used in deep excavations. The Apparent earth Pressure Diagram (APD) and Distributed Prop Load method (DPL) introduced by Terzaghi, K. & Peck (1967) and Twine and Roscoe (1999) are the most widely used empirical methods to calculate the earth pressure distributions and prop forces acting on multipropped retaining walls. Finite element modelling has become the most widely used feature with rapid technological advancement. Studies have found that soil stiffness is the parameter that has the dominant control over ground movement induced by deep excavation. Elastic modulus (E50), unloading-reloading modulus (Eur), and tangent modulus (E0) are the most widely used soil stiffness parameters in design work. This study suggests recommendations for selecting appropriate parameters and correct modelling procedures in the FEM of deep excavations using measured field data using twodimensional analysis. Previous studies indicate that the elastic modulus (E50) of the soil can be increased several times to obtain the unloading-reloading stiffness (Eur) of the soil during deep excavation. The back analysis technique is commonly used in studies to calibrate the critical parameters to minimize the deviation between numerically computed results and field observation results. Back analysis was used to calibrate the elastic modulus of the soil by comparing the lateral wall deformation profile obtained from the FEM software with inclinometer readings acquired from the excavation site. Prop force and earth pressure distribution results obtained from FE analysis were compared with Peck and DPL methods considering sandy and clayey soil. Prop forces from the numerical model were compared with those from different empirical methods commonly used to estimate prop forces on multi-propped retaining structures. The study highlights that the elastic modulus (E50) values derived from the SPT N data can be multiplied by 2 to 4 times to obtain the unloading-reloading modulus (Eur) value that would reasonably predict the wall movement in the FE analysis. As the depth of excavation increases, the lateral deformation was underestimated mainly due to the impact of the corner effects. Considering sandy soil, both Peck and DPL methods produced higher prop force values for the first prop level, while the second and third prop levels had lower values compared to the results of the numerical analysis. The lower earth pressure distribution obtained from the DPL and Peck methods compared to the earth pressure distribution of the FE analysis caused this result.
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Finite element analysis of a deep excavation supported using a secant pile wall: a case study
(IEEE, 2023-12-09) Silva, VSSD; de Silva, LIN; Abeysooriya, R; Adikariwattage, V; Hemachandra, K
Accurate finite element modeling (FEM) of deep excavations is a difficult task due to the lack of availability of details about the soil strata below ground level. This study proposes a method to select the appropriate parameters and correct modeling procedures in the FEM of deep excavation using measured field test data using two-dimensional analysis. Some studies indicate that the elastic modulus (E50) of soil can be increased by several times to obtain the unloading-reloading modulus (Eur) of the soil. The back analysis technique was used to calibrate the elastic modulus of the soil by comparing the lateral wall deformation profile obtained from the FEM analysis with the inclinometer readings acquired from the excavation site. The numerical model was validated using the behavior of a retaining wall at various excavation depths and analyzed through numerical simulations. Prop forces obtained from the numerical analysis were compared with those obtained from different empirical methods commonly used to estimate prop forces on multi-propped retaining structures. The study highlights that the elastic modulus of the soil can be increased between 2 and 4 times to obtain the unloading-reloading modulus of the soil.
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Identification of WebGIS development potential and issues - a land and water case study application for Moratuwa, SrI Lanka.
(Department of Civil Engineering, University of Moratuwa, 2012-12) Chandramali, EAG; Wijesekera, NTS; Nawagamuwa, U; de Silva, LIN
Polularity of internet usuing is rapidly incerasing. Hence the demand is high for Web based GIS tools. The need to handle heavy maps and attribute datasets, often increase issues specially with aspect to the time taken to serve maps and to filter user desired information for e very. A WebGIS based land and water information management system was developed for a land extent of approximately 2.5km’- within the Moratuwa DSD of Sri Lanka. Information of roads, buildings were collected as land data while water and stream information were collected using an extensive field survey. The developed WebGIS application integrates digital base maps and feature attribute data of the selected case study area and facilitates operations through a user-interface while offering a variety of querying and reporting options. This application which was named Geoinfo WebGIS, possesses a very high potential to serve the users through i)Map to Map ii) Map to database iii) Database to Map and iv) Database to Database functions. The application was tested and verified through a consideration of user satisfaction and accuracy. Geolnfo WebGIS was developed on MS4W framework, PostgreSQL was used as the database. Non-responsive situations, high time consumption when loading the data layers, map overlaying issues and delay in refreshing the performance issues identified through the application development.
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Investigation of hydraulic performance of Gabion structures
(Department of Civil Engineering, University of Moratuwa, Sri Lanka., 2012-12) Hettiarachchi, SSL; Samarasekara, RSM; Priyankara, SS; Silva, HAM; Nawagamuwa, U; de Silva, LIN
This paper presents selected results of a detail study of the transmission refeletion performance of gabion structures usued in harbour and costal engineering applications. The performance of the structures is discussed and the results of experimental investigations relating wave reflection and transmission are reviewed and presented in a user friendly format The paper also provided important observations on the response of the design parameters'to varying incident wave
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Investigation on uplift capacity of shallow foundations on cohesionless soil
(Department of Civil Engineering, University of Moratuwa, 2012-12) Koorala, SKDCP; Kumara, MKSN; Edirisinghe, EAL.; de Silva, LIN; Nawagamuwa, U; de Silva, LIN
Shallow foundations are Abstract: commonly used in Sri Lanka for communication towers, power transmission towers and towers for wind turbines. The design of these foundations is based on several assumptions and therefore, a large factor of safety is imposed on estimated ultimate uplift capacity. In view of the above, the uplift capacity of shallow foundations on dry sand was determined ill the present research by conducting laboratory model tests on circular and square foundation models. The results were compared with the uplift capacities obtained from analytical solutions for both circular and square flat foundations. Two foundation models (circular and square) at three different depths in dry sand were tested and the uplift force and upward displacement of each model were investigated. Uplift force versus upward displacement characteristics obtained from experimental analysis was compared with the uplift capacity obtained from analytical solutions. From both experimental and theoretical results, it can be concluded that the uplifting capacity of square foundation is higher than circular foundation at each depth. Also the uplifting capacity is increased with embedded depth of foundation for both types of foundations. Another important conclusion is that, the angle between the vertical plane and the failure plane is nearly half of the friction angle of the soil.
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Is course correction needed for direction of research in concrete
(Department of Civil Engineering, University of Moratuwa, Sri Lanka., 2012-12) Holey, S; Silva, A; Perera, HTP; Wijayakulatilaka, WGMA; Nawagamuwa, U; de Silva, LIN
This paper is an endeavour to highlight importance of realizing potential of research in "value addition' or "making" process of concrete. Authors, based upon their cement manufacturing and construction industry, presented information on data generated in past five years in Sri Lanka for various purposes/studies as well as observations and interaction with concerned from the spectrum of Industry. research in experience as link of The paper, while questioning the overemphasis given to "material" part of concrete, shares the learning, which could benefit the Industry, in ensuring consistent superior quaiitv and economy of concrete and suggest the areas for future research.
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Methodology to develop a driving cycle for a given mode and traffic corridor; case study for Galle Road, Colombo, Sri Lanka
(Department of Civil Engineering, University of Moratuwa, 2012-12) Gamlath, I; Fernando, C; Galgamuwa, U; Perera, L; Bandara, S; Nawagamuwa, U; de Silva, LIN
A driving cycle is a speed time profile which represents the driving characteristics of a selected area. This can be of use to both legislative and non legislative purposes such as development of emission inventory, determination of fuel consumption etc. As driving cycles are dependent on the traffic constituents, driver behaviour and road conditions established driving cycles cannot be used in Sri Lanka. Hence the objective of this research is to develop a methodology and to constructa driving cycle(s) which represent given set of conditions in Sri Lanka such that it can be use to establish emission inventory in future. To achieve these objectives, it is necessary to collect and analyse the on road speed-time data on selected routes which will represent the driving patterns of urban or rural conditions. Due to the restriction of time and resources, study was limited to one transport corridor, anurban condition and for light vehicles only. A sample driving cycle was developed based on the data collected on the Galle Road, section from Katubedda to Fort using on board method. Cycle was developed using micro trip based cycle construction and computer application was developed to aid this purpose. In this study we observed average speed 21.37km/h, average running speed 25.78km/h, average acceleration 2.03km/h/s and average deceleration 2.02km/h/s with acceleration, deceleration, cruising and idling proportions of 27.37%, 23.70%, 31.43.6 and 17.49% respectively for selected urban condition. This study would facilitate the further studies on development of driving cycles for other conditions and could be of use for traffic engineering studies development.
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Numerical analysis on the distribution of stress through layered soils
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022-12) Wijayarathne, TIPKM; de Silva, LIN; Mallikarachchi, C
Evaluation of stress distribution through soil strata is one of the fundamentals of geotechnical analysis. Vertical stress is attributed to the loading intensity and geostatic stress. Even though many analytical methods have been developed idealising the soil as homogeneous, isotropic, and elastic material, the soil consists of layers of different characteristics in reality. In this study, stress distribution under a strip footing through a two-layered system consisting of purely sandy and purely clayey soils where the sand at the top is analysed with the Finite Element Method using Plaxis 2D geotechnical software. The Mohr-Coulomb model was used to feed the characteristics of the soils to the computer software. Different test cases were simulated by changing the soil strength parameters: friction angle of sandy soils and cohesion of clayey soils and; the thickness of two layers for selected soil types while the total depth of the soil system was 8 m. The numerical results were compared with Boussinesq solutions which are linear elastic solutions. It shows that stress at a selected point is low when the soils are loose and soft compared to the soils which are dense and stiff. The lower the thickness of the sand layer higher the stress at a selected point. Vertical stress values of Boussinesq solutions agree with the Finite Element Analysis values when moving away from the footing both in horizontal and vertical directions.
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Recognizing temporal variability of lump watershed behaviour and evaluating averaged performance of a hydrologic model
(Department of Civil Engineering, University of Moratuwa, Sri Lanka., 2012-12) Wijesinghe, WMD; Wijesekera, NTS; Nawagamuwa, U; de Silva, LIN
Majority of watersheds associated with civil engineering infrastructure projects are ungauged and most commonly used method to determine streamflow in ungauged basins is mathematical modelling with the use of Synthetic Unit Hydrograph (SUH) technique. Mathematical models require watershed characteristics to be spatially and temporally averaged. The SUH is an event based model which estimates direct runoff. Hence model calibration and verification requi: : event based evaluations with a baseflow separation effort or a method incorporating a baseflow model to combine with the SUH model and generate total runoff. In this study, a rainfall runoff model developed using SUH and a linear baseflow concept while selecting the watershed of Attanagalu Oya at Karasnagala as the study area. Other than the SUH parameters to be identified, the conceptual model used for this work consisted of 5 model parameters to be optimised. The main objective of this research was to identify the issues during calibration and verification of this five parameter model. Model calibration was carried out for 30 datasets, selecting the Mean Ration of Absolute Error (MRAE) as the objective function. Optimum model parameters for each event were determined and the most probable range of values for each parameter was computed. Using 30 datasets, model was verification was carried out by assuming that the average of each range would lead to a representative watershed model. A successful calibration produced a good match of observed and calculated streamflows with a MRAE of 0.34. Parameter optimisation revealed the inability to obtain an average initial moisture level for the entire watershed while catering both wet and dry conditions. The runoff coefficients and rainfall thresholds also indicated the need of further investigations. Event based modelling approach in this work provides an insight to the watershed behaviour and to the appropriateness of model parameters, however in order to identify the spatially and temporally averaged parameters it is necessary to carryout optimisations using a lengthy data series together with an appropriate model.
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Selecting a usability evaluation user group - a case study the development of a hydro-GIS tool aiming urban flood mitigation
(Department of Civil Engineering, University of Moratuwa, Sri Lanka., 2012-12) Pradeep, RMM; Wijesekera, NTS; Nawagamuwa, U; de Silva, LIN
Flash floods which are becoming a common occurrence due to poor planning in the ur an areas nee user friendly tools for land managers to arrive at suitable alternatives. These tools require incorporating spatially distributed assessments performing several maps overlay and hydrologic computations for the evaluation of runoff generation before and after a proposed land eve opment. The most common option for urban flood mitigation is the incorporation of land allotment based detention storages. The land managers need to capture the optimum sizes for these storages. A Hydro-GIS tool development was undertaken to ensure easy user friendly operation with automation of complex hydrologic and GIS computations. The tool with the objective of targeting nontechnical users demands high user friendliness and in order to achieve this, evaluations comparing usability becomes very important. Identification of the right number of users to evaluate usability is a requirement yet to be fulfilled. The present work successfully carried out a Hydro GIS tool development for the management of urban land development, achieving its functionality objectives while testing user friendliness with a user group of 23. Analysis shows that a group of over 13 users would arrive at an on average problem area identification rate of 90% or more.
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Study of ground vibration due to rock blasting of metal quarry: a case study
(Department of Civil Engineering, University of Moratuwa, 2012-12) Madanayaka, TA; de Silva, LIN; Dharmarathne, PGR; Nawagamuwa, U; De Silva, LIN
This study was carried out to compare vertical and horizontal bench blast(s) at a granitic gneiss rock quarry located in Colombo, Sri Lanka and predict the resulting peak particle velocities of ground vibration levels. To achieve these objectives, particle velocities and frequencies of 38 and 35 blasts respectively were measured in three perpendicular directions for horizontal and vertical bench blasts respectively with the use of Instantel Blastmate II seismographs. In the blasts, Ammonium Nitrate (ANFO)(blasting agent) primed by a Gelatine Dynamite primer were electrically initiated. Scaled distance parameters (Maximum charge weight per delay and distance between blasting points to monitoring location) were also recorded. The extensively used equation for seismic low of propagation proposed by Devine (1962) and Devine and Duvall (1963) was used for the prediction of peak particle velocities. Points were plotted with Peak Particle Velocity (PPV) in Y- axis against Scaled Distance (D/Q03) in X- axis. Regression analysis was performed to define the line of best fit. At the end of statistical analysis, an empirical relationship with good correlation was established for prediction of peak particle velocity. Frequency analysis was also done for dominant frequency and Zero crossing frequency to identify the effect of frequency of ground vibration to structural damages and defining the most suitable type of frequency analysis to define the single frequency value for ground vibration. The established relationship, frequency analysis and result obtained are presented.
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Study on rebound values on inclined planes
(Department of Civil Engineering, University of Moratuwa, 2012) Baskaran, K; Liyanage, KLDO; Munasinghe, NT; Gunawardana, WWCJ; Nawagamuwa, U; de Silva, LIN
Non-Destructive Testing (NDT) methods parameters like strength and durability of an existing structure. They offer significant advantages of speed, cost and lack of damage in comparison with test methods which require the removal of a sample. But they incorporate various limitations in practical use. This study is focused on the 'Rebound Hammer Test' which is used to assess the compressive strength by surface hardness. The rebound hammer concernedin this case, has been calibrated and charts have been developed to get the readings on vertical and horizontal surfaces only. When the structure to be investigated is consisted of an inclined surface, direct use of these charts may not be possible. During this study, basic formulation to calculate the corresponding horizontal rebound number to represent a rebound value obtained on an inclined plane was derived and verified. Taking readings on inclined surfaces of the cubes placed at different angles was done in order to observe the deviations and then the results were interpreted and analysed to obtain a suitable relationship by applying the derived formula.