Department of Civil Engineering
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Publication Open Access Vertically constructed wetlands for greywater reuse: Performance analysis of plants(Elsevier, 2023-10-02) Siriwardhana, K.D; Miguntanna, N; Jayaneththi, D. I.; Kantamaneni, K; Rathnayake, UVertical Flow constructed wetlands (VFCWs) are environmentally feasible engineered systems that mimic the functions of natural wetlands. They are alternative engineering systems that are economical, and simple in structure with reduced land area compared to Horizontal Flow Constructed Wetlands (HFCW). Thus provides a sustainable solution for greywater treatment to a considerable extent. However, VFCWs feasibility and plant performance were not tested in the context of Sri Lanka for the greywater treatment. Therefore, the purpose of this study is to evaluate the potential of household greywater treatment using a pilot-scale VFCW and examine the performance characteristics of different types of plants. Three types of plants, the Canna plant (Canna indica), Ferns plant (Matteuccia struthiopteris), and Cattail plant (Typha latifolia) were used as emergent plants and a retention tank was constructed to retain solid particles in the greywater as primary treatment. The experiments were carried out for two months using a Completely Randomized Design (CRD) for three replicates. The quality of the influent and effluent was tested fortnight for a number of water quality parameters. Results revealed that the removal efficiency of contaminants was increased. Cattail plants showed higher removal efficiency for dissolved oxygen (DO), chemical oxygen demand (COD), nitrates (NO3 1-), turbidity, and electrical conductivity. In addition, Canna plants had higher efficiencies for the removal of total dissolved solids (TDS) and phosphates (PO4 3-). Furthermore, Ferns plants presented higher efficiency only for removing sulphate (SO4 3-). Conclusively, Cattail plants presented the overall best performance in treating greywater. This can be attributed to the ability of the Cattail’s dense fibrous root system to absorb more contaminants from greywater. This research also discussed the importance of microplastic analysis in greywater treatment which is a vital part of the current day research. The results of this study will be helpful to the further advanced research. Furthermore, this methodology can be implemented to other similar plants across the globe irrespective of geographical area.Publication Embargo Relationships amongst water and sediment qualities, discharge, and allochthonous inputs of intermittent streams in tropical dry climates: Implications on stream management(Elsevier, 2023-07-19) Gomes, P.I.A; Perera, M.D.DThe interrelationships amongst water and sediment physicochemistry, catchment hydrology, and allochthonous inputs are not well established for intermittent streams, especially in tropical climates. This remains a major concern in water resources management, and understanding these streams is vital in forming targeted frameworks for protection. A two-year comprehensive study showed spatially independent water quality variations, where similar temporal patterns were observed in different streams in close catchments for many variables (such as for electrical conductivity, pH, nitrogen species, and dissolved oxygen). This was not the case for sediment quality variables; in addition, in-stream variation was high. This gave an indication of the regulatory potential of intermittent stream sediment. Redundancy analysis models showed that stream water quality was significantly correlated to, and could be explained by discharge, rainfall parameters, litter, and sediment quality. Sediment quality was not influenced by litter inputs but by discharge and rainfall-related parameters. The study reported new insights into the unique physicochemistry of intermittent streams and proposes the fact that sediment quality needs comprehensive monitoring and management both spatially and temporally.Publication Embargo Uncovering stress fields and defects distributions in graphene using deep neural networks(Springer, Cham, 2023-05-19) Dewapriya, M. A. N.; Rajapakse, R. K. N. D.; Dias, W. P. S.Deep learning provides a new route for developing computationally efficient predictive models for some complex engineering problems by eliminating the need for establishing exact governing equations. In this work, we used conditional generative adversarial networks (cGANs) to identify defects in graphene samples and to predict the complex stress fields created by two interacting defective regions in graphene. The required data for developing deep learning models was obtained from molecular dynamics simulations, where the numerical results of the simulations were transformed into image-based data. Our results demonstrate that the neural nets can accurately predict some complex features of the interacting stress fields. Subsequently, we used cGANs to predict defect distributions; this revealed that a cGAN could predict the existence of a crack even though it had never seen a cracked sample during the training stage. This observation clearly demonstrates the remarkable generalizability of cGANs beyond the training samples, suggesting that deep learning can be a powerful tool for solving advanced nanoengineering problems.Publication Open Access Risk Evaluation of Cost Overruns (COs) in Public Sector Construction Projects: A Fuzzy Synthetic Evaluation(MDPI, 2023-04-22) Chadee, A.A; Martin, H.H; Gallage, S; Banerjee, K.S; Roopan, R; Rathnayake, U; Ray, IIn the Small Island Developing States (SIDS), public sector infrastructure projects (PSIPs) fail to both meet targeted performance metrics and deliver on the intended benefits to society. In terms of the cost performance metric, cost overruns (COs) beyond the initial contract value are more of a norm than a unique occurrence. Therefore, to ensure economic sustainability for SIDS, and value for money on PSIPs, there is a need to investigate and evaluate the risk impacts on COs. The purpose of this research was to identify and evaluate the perceived cost overrun risk factors that are within the primary project stakeholders’ sphere of control, and to reduce the ongoing ambiguities that exist in the prioritization of these risks. This was achieved by extracting critical risk factors from selected comparative studies in developing countries to formulate a closed-ended questionnaire to be administered to construction professionals in Trinidad and Tobago. Thereafter, the process of fuzzy synthetic evaluation (FSE) was used to develop a risk model based on three tiers of risks: 11 critical risk factors, 3 critical risk groupings (CRGs) and an overall risk level (ORL). The results showed that the two highest-ranked critical risks were project funding problems and variations by client. The leading critical risk grouping was client-related risk (5.370), followed by professionalrelated risk (4.815) and physical risk (4.870). The ORL was 5.068. Based on the FSE’s linguistic scaling, the CRGs and the ORL are perceived to be high risks in PSIPs. This research adds to the CO body of knowledge in primarily three ways. Firstly, the study extends the comparative assessment previously undertaken in scholarship into the context of SIDS to build on the generalizability of this context-specific phenomenon. Secondly, the FSE evaluation undertaken provides a practical tool to be promoted for use in SIDS’ construction industry among practitioners to focus and prioritize the critical risks in the planning phases and improve on contemporary risk practices in the execution phases of projects. Finally, this quantitative model approach is recommended to supplement the traditional qualitative risk management practices adopted in SIDS, thus contributing towards the overall improved economic sustainability and viability of PSIPs.Publication Open Access Predicting adhesion strength of micropatterned surfaces using gradient boosting models and explainable artificial intelligence visualizations(Elsevier, 2023-06-27) Ekanayake, I.U; Palitha, S; Gamage, S; Meddage, D.P.P.; Wijesooriya, K; Mohotti, DFibrillar dry adhesives are widely used due to their effectiveness in air and vacuum conditions. However, their performance depends on various factors. Previous studies have proposed analytical methods to predict adhesion strength on micro-patterned surfaces. However, the method lacks interpretation on which parameters are critical. This research utilizes gradient-boosting machine learning (ML) algorithms to accurately predict adhesion strength. Additionally, explainable machine learning (XML) methods are employed to interpret the underlying reasoning behind the predictions. The analysis demonstrates that gradient boosting models achieve a high correlation coefficient (R > 0.95) in accurately predicting pull-off force on micro-patterned surfaces. The use of XML methods provides insights into the importance of features, their interactions, and their contributions to specific predictions. This novel, explainable, and data-driven approach holds potential for real-time applications, aiding in the identification of critical features that govern the performance of fibrillar adhesives. Furthermore, it improves end-users’ confidence by offering human-comprehensible explanations and facilitates understanding among non-technical audiencesPublication Open Access Achieving near-zero carbon dioxide emissions from energy use: The case of Sri Lanka(Elsevier, 2023-07-04) Fernando, G.L; Liyanage, M.H; Anandarajah, G; Attalage, R. A; Karunaratne, SSignatories to the Paris Agreement are to achieve net zero Green House Gas (GHG) emissions during the half-century to pursue the efforts limiting global average temperature increase by 2 °C compared to pre-industrial levels. This study models ambitious to challenging scenarios involving energy demand and supply side actions for energy system transition toward net-zero for Sri Lanka. To analyze these scenarios a least cost optimization-based bottom-up type energy system model was developed from 2015 to 2050. A Business-as-usual (BAU) scenario and four countermeasure (CM) scenarios termed Plausible, Ambitious, Challenging, and Stringent were developed. Four different carbon tax rates were used to fathom the level of carbon tax needed to achieve net-zero emissions. The CM scenarios were formulated considering different technology options and policy measures such as the diffusion of efficient technologies, availability of renewable energy sources, use of cleaner fuels, the introduction of nuclear and carbon capture and storage technologies, and green hydrogen for power generation. The result of this study reveals that the stringent scenario which includes aggressive policy measures in both the energy supply and demand sectors, such as nuclear, and renewable energy for power generation, diffusion of efficient Enduse devices, fuel switching, including the introduction of electric cars, and increased share for public transport achieves the near carbon-neutral scenario at a carbon tax trajectory of 32 US$/tCO2 in 2020 and 562US$/tCO2 in 2050. The Net Energy Import Dependency (NEID) of the country decreases to 13 % in 2050 compared to that of the BAU scenario (65 %) under the near carbon neutral scenario, which is a positive sign from the energy security perspective.Publication Open Access Evaluating expressway traffic crash severity by using logistic regression and explainable & supervised machine learning classifiers(Elsevier, 2023-07-09) Shashiprabha, M.J.P.S; Kelum, S.R.M; Meddage, D.P.P; Pasindu, H.R; Gomes, P.I.AThe number of expressway road accidents in Sri Lanka has significantly increased (by 20%) due to the expansion of the transport network and high traffic volume. It is crucial to identify the causes of these crashes for effective road safety management. However, traditional statistical methods may be insufficient due to their inherent assumptions. This study utilized explainable machine learning to investigate the factors that affect the severity of traffic crashes on expressways. The study evaluated two groups of traffic crashes: fatal or severe crashes, and other crashes that included non-severe injuries or only property damage. Five factors that contribute to crashes were analyzed: road surface condition, road alignment, location, weather condition, and lighting effect. Four machine learning models (Random Forest (RF), Decision Tree (DT), extreme gradient boosting (XGB), K-Nearest Neighbor (KNN)) were developed and compared with Logistic Regression (LR) using 223 training and 56 testing data instances. The study revealed that the machine learning algorithms provided more accurate predictions than the LR model. To explain the machine learning models, Shapley Additive Explanations (SHAP) and Local Interpretable Model-agnostic Explanations (LIME) were used. These methods revealed that all five features decreased the possibility of occurrence of fatal accidents. SHAP and LIME explanations confirmed the known interactions between factors influencing crash severity in expressway operational conditions. These explanations increase the trust of end-users and domain experts on machine learning models. Furthermore, the study concluded that using explainable machine learning methods is more effective than traditional regression analysis in evaluating safety performance. Additionally, the results of the study can be utilized to improve road safety by providing accurate explanations for decision-making processes for black-box models. © 2023Publication Open Access Analysis of Multi-Temporal Shoreline Changes Due to a Harbor Using Remote Sensing Data and GIS Techniques(MDPI, 2023-05-06) Zoysa, S; Basnayake, V; Samarasinghe, J. T.; Gunathilake, M.B.; Kantamaneni, K; Muttil, N; Muttil, U; Rathnayake, UCoastal landforms are continuously shaped by natural and human-induced forces, exacerbating the associated coastal hazards and risks. Changes in the shoreline are a critical concern for sustainable coastal zone management. However, a limited amount of research has been carried out on the coastal belt of Sri Lanka. Thus, this study investigates the spatiotemporal evolution of the shoreline dynamics on the Oluvil coastline in the Ampara district in Sri Lanka for a two-decade period from 1991 to 2021, where the economically significant Oluvil Harbor exists by utilizing remote sensing and geographic information system (GIS) techniques. Shorelines for each year were delineated using Landsat 5 Thematic Mapper (TM), Landsat 7 Enhanced Thematic Mapper Plus (ETM+), and Landsat 8 Operational Land Imager images. The Normalized Difference Water Index (NDWI) was applied as a spectral value index approach to differentiate land masses from water bodies. Subsequently, the Digital Shoreline Analysis System (DSAS) tool was used to assess shoreline changes, including Shoreline Change Envelope (SCE), Net Shoreline Movement (NSM), End Point Rate (EPR), and Linear Regression Rate (LRR). The results reveal that the Oluvil coast has undergone both accretion and erosion over the years, primarily due to harbor construction. The highest SCE values were calculated within the Oluvil harbor region, reaching 523.8 m. The highest NSM ranges were recorded as −317.1 to −81.3 m in the Oluvil area and 156.3–317.5 m in the harbor and its closest point in the southern direction. The maximum rate of EPR was observed to range from 3 m/year to 10.7 m/year towards the south of the harbor, and from −10.7 m/year to −3.0 m/year towards the north of the harbor. The results of the LRR analysis revealed that the rates of erosion anomaly range from −3 m/year to −10 m/year towards the north of the harbor, while the beach advances at a rate of 3 m/year to 14.3 m/year towards the south of the harbor. The study area has undergone erosion of 40 ha and accretion of 84.44 ha. These findings can serve as valuable input data for sustainable coastal zone management along the Oluvil coast in Sri Lanka, safeguarding the coastal habitats by mitigating further anthropogenic vulnerabilities.Publication Open Access COMPARATIVE STUDY ON THE STORMWATER RETENTION OF ORGANIC WASTE SUBSTRATES BIOCHAR, SAWDUST AND WOOD BARK RETRIEVED FROM PSIDIUM GUAJAVA L. SPECIES(University of Montenegro, 2023) Kader, S.A; Jaufer, L; Bashir, O; Raimi, M. OThis research compares the stormwater retention performances of an organic waste growing medium extracted from the widely available Psidium guajavala L species in Sri Lanka. Rainfall gauges were manually constructed to outsource accurate precipitation data, and the study was conducted throughout the entire month of January 2023. A stormwater retention curve was constructed for the Biochar, Sawdust and Wood bark substrates and the hotspots were compared. Furthermore, the results were validated using a volumetric comparison of water retention. The experimental outcomes have shown that Biochar exhibits strong water retention ability and enables the overlaying vegetation to acquire nutrients without external obstacles. The main reason for this exceptional performance was biochar's low evaporation levels and high porosity. In contrast, Sawdust was found to be the worst performer in terms of water retention due to its high thermal conductivity. These experimental studies were rationalised by outsourcing the specimen from the same tree. Our recommendations suggest that the biochar manufacturing industry needs to be improved in the future since it provides a sustainable and effective alternative in terms of eco-friendly substrates.Publication Open Access Reducing Cost Overrun in Public Housing Projects: A Simplified Reference Class Forecast for Small Island Developing States(MDPI, 2023-04-10) Chadee, A; Martin, H; Gallage, S; Rathnayake, UInaccuracies in cost estimation on construction projects is a contested topic in praxis. Among the leading explanations for cost overrun (CO), factors accounting for large variances in actual cost are shown to have psychological or political roots. The context of public sector social housing projects (PSSHPs) in Small Island Developing States (SIDS) is positioned with similar CO challenges. This study is the fifth phase of a series of research projects on the vulnerability of PSSHPs to COs, and the need to de-risk cost estimates. The aim of this study is to present a simple and practical application of Reference Class Forecasting (RCF), a promising solution utilizing an “outside view” approach, as an effective control to reduce the variance of forecasted cost inaccuracies. Using a sample set of 82 housing projects, a reference class of 23 projects was selected based on properties such as design-build procurement type and local contractor involvement. A probability distribution was then established for this reference class, and required cost uplifts to be applied were based on the level of risk a housing agency is willing to accept for PSSHPs. Finally, the accuracy of the reference class was tested using a recently completed project. The results showed that the RCF method, based on a 50th percentile risk acceptance of CO, provides a closer estimate to the actual costs of the project as compared to the contracted costs. This empirical study is the first to undertake and implement RCF in the 52 SIDS and presents the first instance of practical RCF in public housing projects worldwide, thus providing a platform for improvement in future PSSHPs’ budget forecasting. The research can be applied to lessen societal and economic welfare losses as well as significant financial risks for governments. The implementation of practical safeguards, such as RCF, together with contemporary standard project controls, provides immediate advantages for enhancing accuracy in present forecasting approaches against financial risks. It allows for improved value derived from social infrastructure projects, improved supply of public housing, and consequently progress for these nations towards achieving their sustainable development goals.