CERS - 2021

Permanent URI for this collectionhttp://192.248.9.226/handle/123/17780

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    item: Conference-Full-text
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    item: Conference-Abstract
    Characteristic analysis of embedded wave barrier material beside railway tracks
    (Department of Civil Engineering, University of Moratuwa, 2021-11) Abiram, P; Hidallana-Gamage, HD; Hettiarachchi, P
    Rail transport is one of the most effective modes of transporting goods and people among various access points. It has several benefits compared to some of the other modes of transport, such as safety, cost effectiveness, time saving, and high capacity. Forces from the result of passing vehicles and irregularities at the wheel-rail interaction, penetrate through wheel into the track, and generates vibration. The scenarios of increasing traffic congestion and civil infrastructure development in Sri Lanka, have led to the concern about the improvement of railway transportation free from propagation of vibration through ground. Using embedded barrier material within a trench beside the railway track is an effective active control strategy practiced in most of the Railway transportation sectors around the world. In this research, characteristics of the material which is used as a vibration controlling layer embedded beside the railway track within the subsoil are analysed. Initially a finite element model of a railway track was developed, and then it was validated with the field vibration measurements available in the literature. Later a parametric study was carried out by varying the properties of the vibration controlling layer within the subsoil. The vibration characteristics were compared at 2 and 3 m depths, for different Elastic modulus, density, and void ratios of the material. It was evident that barrier material with lower elastic modulus provides a better vibration screening performance. If the available barrier material has a high elastic modulus, it should be constructed deep enough to provide a better vibration screening performance. For a given depth of an embedded barrier layer, there will be an optimum unit weight, which provides a high performance of screening. It was also found that, 2 m deep barrier provides better performance than the 3 m deep barrier for a given unit weight. Increasing the void ratio will increase the pores inside the material, and hence will increase the performance of the barrier. A shallow barrier provides better performance up to a certain value of void ratio, beyond which the performance is independent of the depth of the barrier. Overall, findings of this research elaborate the optimum material characteristics of a vibration controlling layer for train induced ground vibration in different depths.
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    item: Conference-Abstract
    Composite effects of pozzolans in producing high strength recycled aggregate concrete
    (Department of Civil Engineering, University of Moratuwa, 2021-11) Fernando, AM; Gamage, JCPH; Hettiarachchi, P
    Over the years, the unceasing growth and development in the construction industry has resulted in both positives and negatives. The extensive use and disposal of many of the materials used in construction have resulted in the depletion of natural resources, together with piling up of large amounts of construction and demolition waste in landfills, causing adverse effects on the environment, the economy as well as society. The most extensively consumed material in the construction industry can be identified as concrete. Procurement and transportation of raw materials for cement and aggregates which are the two major constituents used in concrete production add significant disturbances to the ecological system. Thousands of research studies have shown the feasibility of using recycled aggregates to produce both normal and high strength concrete with comparable properties to conventional concrete. However, it requires a more allinclusive approach in producing an environmentally friendly solution. This paper discusses the procedure followed in producing cost effective and economical high strength concrete through the composite use of pozzolans namely fly ash, silica fume and rice husk ash (RHA), in both stages of aggregate treatment and concrete production. Results from aggregate testing showed a 26%and 59% reduction in aggregate water absorption and porosity, respectively. Further, enhancements in terms of aggregate specific gravity and crushing value were obtained. Concrete which contained RHA in both stages, attained a compressive strength of 55.4 MPa, which was even higher than the control mix containing natural aggregates. The same mix of concrete showed a 12% increase in its surface resistivity. This indicates the possibility of achieving high strengths, even with the use of RA derived from parent concretes of lower grades, and not many studies have focussed on this aspect of high strength recycled aggregate concrete production (HS-RAC).
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    item: Conference-Abstract
    Development of design guidance for circular reinforced concrete columns incorporating crack width
    (Department of Civil Engineering, University of Moratuwa, 2021) Jayaweera, GCS; Hidallana-Gamage, HD; Indrajith, WPR; Hettiarachchi, P
    The maximum crack width of Reinforced Concrete (RC) structures should be controlled for satisfying the serviceability and durability requirements of the civil engineering structures. Therefore, care must be taken at the initial design stages for maintaining the possible crack widths within a permissible range which has been specified under the design standards. However, the crack width analysis of RC structures is not easy because of the complexity of the parameters which affect the crack width. If crack width calculation is skipped, the width of the cracks in real concrete structures can be larger than the maximum limiting allowable value. Circular RC columns and piles are widely used structural components in modern civil engineering construction projects. As an example, circular RC piles and columns can be seen in many expressway construction projects in Sri Lanka to support viaduct structures. The main aim of this research is to develop design guidance for circular RC columns to estimate the crack width. In the Sri Lankan construction industry, there is no specific simplified guidance in terms of charts and tables for crack width estimations of circular RC columns. Hence, it is important to develop such design guidance for circular RC columns. Although there are a variety of applications of circular RC columns in the industry, this research deals with the crack width analysis of circular RC columns in straight viaduct sections. A comprehensive study was carried out regarding the behaviour of the cracks in circular RC columns in viaduct sections as per the design standard, BS 5400. Autodesk Structural Bridge Design software was used to perform crack width estimations, and MIDAS Civil software was used to do the Finite Element (FE) analysis and validation process. The crack width can be estimated to a 0.01 mm accurately by using the charts developed in this research. This design guidance is simple to understand, and use. Hence, engineers can perform their preliminary crack width estimations with less effort using correctly specified methods. Crack width estimation charts were developed for both uniaxial bending and biaxial bending cases of short circular RC columns with a diameter of 1.5 m, C 25/30 concrete, a nominal cover of 45 mm, and the main rebars all of the same diameter. According to the parametric study done for the circular RC columns subjected to uniaxial bending, the following details were found. Crack width reduces with increasing bar diameter and number of main rebars. Crack width is low in the columns with high-grade concrete. When the ratio of Mq/Mg as defined in BS 5400 is decreased, the crack width also decreases. A significant variation of the crack width can be seen in the cases where, the ratio, Axial load (ULS)/(Column diameter)2 is in the range of 0.5 to 2.5 N/mm2. The width of the crack is significantly higher in the case of having higher bending moments with low axial forces. This research can be extended to develop design guidance for estimating the crack width following latest standards such as Eurocodes and produce more charts by accounting for the requirements of the design engineers. The comprehensive design charts developed in this research will be useful in estimating the crack widths in circular RC columns without the need to follow time-consuming methods. Therefore, the findings of this research will be helpful to enhance the efficiency of the design work.
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    item: Conference-Abstract
    Improve the lateral stability of variable height steel truss type pedestrian bridges in Sri Lanka
    (Department of Civil Engineering, University of Moratuwa, 2021-11) Liyanage, MLLN; Hidallana-Gamage, HD; Hettiarachchi, P
    This paper investigates the methods of improving the lateral stability of variable height truss type steel bridges that are used for pedestrian purposes in Sri Lanka. A bridge is a structure that provides passage without blocking the way underneath over an obstacle. A truss is one of the key engineering features related with bridges in the emerging civil engineering contest. Several truss type steel bridges have been built for pedestrian use in the recent past. Modified Warren and variable height bridges can be commonly seen in the Southern Province of Sri Lanka over the major river crossings. When designing a pedestrian bridge for local conditions, it is very important to consider the loads due to pedestrians, wind, and sometimes light weight vehicles in the rural areas. So, it is preferred to investigate the applicable truss types and their shortcomings by conducting a detailed analysis. The aim of this research is to provide an overview of the Finite Element (FE) method with the focus on lateral stability of the variable height steel truss type pedestrian bridges, their analysis, and various applications. The applicability of steel hollow and composite sections to improve the lateral stability of steel truss type bridges were studied. A comprehensive literature review was carried out to identify the behaviour of different member sections under applied loads. FE analysis was performed using the SAP2000 software to investigate the behaviour of truss type steel bridges. The loads acting on the pedestrian bridges were calculated based on BS 5400: Part 2: 1978, where the design code BS5950: 2000 was used for the design of member sections. Later, MIDAS CIVIL software was used when analysing the truss bridges having concrete infilled composite sections for the top chord members by accounting for the buckling analysis. Span vs tonnage graphs were developed for the Variable Height Arch, Inverted Arch and other selected bridge types to investigate their steel usage for different spans. Almost all the bridges consume similar tonnage up to 25 m span, and their tonnages notably varied thereafter. Results from this study indicated that variable height bridges with concrete infilled sections consume less steel tonnage compared to those with hollow sections and other truss types. Furthermore, it was evident that the steel truss bridges with circular hollow sections consume slightly less steel tonnage compared to those with rectangular hollow sections for all the spans. This trend could be seen for both hollow and infilled sections. Overall, it can be concluded that the lateral stability of variable height bridges can be improved by using infilled sections, reducing their buckling effect, which is the main shortcoming of variable height steel truss type bridges.
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    item: Conference-Abstract
    3D full field deformation measurement using digital image correlation
    (Department of Civil Engineering, University of Moratuwa, 2021-11) Lowhikan, SS; Mallikarachchi, HMYC; Hettiarachchi, P
    3D deformation and strain are crucial parameters in engineering design and construction. Precise 3D full-field measurement is useful in identifying the response of the structure under a given loading condition. Digital Image Correlation (DIC) is a non-contact optic-based technique that may prove to be ideal for full-field deformation applications. It has the potential to become an inexpensive, simple, and accurate solution for deformation measurement. All DIC measuring systems now available consist of expensive software packages and experimental facilities which are difficult to access. Therefore, a cost-effective method must be developed to use in the local context efficiently. This research mainly focuses on the development and validation of the cost-effective precise noncontact- based deformation measurement technique. In the proposed method, 3D full-field deformation of the deforming object is measured using two digital cameras and an image processing toolbox available in the MATLAB commercial package. Further, the proposed method efficiency is enhanced by developing it as a standalone application, which can be installed and used by any technician conveniently and utilized for various laboratory Civil Engineering applications. Enhancing the proposed DIC algorithm to improve resolution in 3D applications and extending to phase-changing materials and developing Graphical User Interface (GUI) and general guidelines to be used by a technician were defined as objectives of this research. The proposed measuring system consists of two digital cameras mounted on a rigid frame as it is targeted to capture the specimen and connected to a computer. A random speckle pattern must be applied on the specimen’s surface to track the deformation. The proposed image processing algorithm was developed in MATLAB by using a computer vision toolbox. Later Graphical User Interface was developed using MATLAB App Designer. The developed system was used to obtain the results and validated for rigid body motion tests of concrete cube and cylinder, compression test of concrete, uni-axial tensile test of a dog bone aluminium specimen and shrinkage cracks of mortar experiments. In conclusion, a cost-effective and reliable measurement system was developed by using DIC techniques and MATLAB computer vision toolbox, with its performance validated experimentally by assessment of measurements of the in-plane strain of materials. Even though it has some limitations, the developed algorithm and application can be effectively used for laboratory-scale Civil Engineering related experiments. Also, the application that was developed can be handled by technicians who do not have much knowledge nor understanding of programming languages. The Graphical User Interface that was developed is easy to use and saves considerable time. The performance of the system that has been developed can be assessed and improved for greater precision.
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    item: Conference-Abstract
    Study on ways to minimize honeycombs in concrete construction
    (Department of Civil Engineering, University of Moratuwa, 2021-11) Manojh, N; Baskaran, K; Hettiarachchi, P
    During concrete construction, there may be some defects formed due to carelessness of humans. The defects formed include honeycombs, those due to poor formwork installation, shrinkage cracks, segregation, and exposed reinforcement to environment etc. These may have happened due to poor site experience, poor design, and carelessness of workers. One of the main defects is honeycombs. Honeycombs are porous volumes of coarse grain aggregates bonded together by cement. In practice, these defects are formed when the fresh concrete ingredients segregate e.g., due to granular convection effects. The presence of honeycombs causes loss of durability, loss of load bearing capacity and corrosion of reinforcement bars. So, there is a need to minimize the honeycombs in construction site to enhance the durability of concrete structures. Under this study, the causes, remedial measures, how to identify, and how to avoid were studied. The main objective of the present study is to find methods to identify the location of core honeycombs. Ultrasonic Pulse Velocity (UPV) test and measuring vibration levels using a vibrometer while striking the surface with a rubber mallet are the two approaches attempted in the present study. A questionnaire survey and an experimental analysis were done as part of research. Questionnaire survey was done among the batchmates on whether they have encountered honeycombs during their Industrial training. Experimental analysis was performed on six beams (600 mm x 250 mm x 150 mm) of Grade 30 concrete (with reinforcement three beams and without reinforcement three beams). The beams were cast with intentionally created honeycombs inside the beam in different depth using Polystyrene. Beams were cast with reinforcement of 4T12 bars and R6 stirrups at spacing 100 mm. On the faces of each beam a grid having lines at 100 mm interval in the horizontal direction and 50 mm interval in the vertical direction was made to carry out the UPV and Vibrometer testing. The experimental results show that by using UPV equipment it is possible to locate the core honeycombs precisely in the concrete panels with plaster and without plaster. However, accuracy of detecting honeycombs using Vibrometer in beams with or without plaster is less. In the plastered case, surface should be smoothened by Plaster of Paris for better results.
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    item: Conference-Abstract
    Characterising the self-opening behaviour of single creased Kapton polyimide films
    (Department of Civil Engineering, University of Moratuwa, 2021-11) Navaratnarajah, S; Mallikarachchi, HMYC; Hettiarachchi, P
    Use of thin folded membranes for deployable structures is becoming increasingly popular especially in aerospace applications such as a deployable solar arrays, sun shields, and solar sails. The folding and compaction process of thin membranes, which introduces permanent, nonrecoverable, localized plastic deformation, changes the geometric shape and material properties. Therefore, precise prediction of folding and deployment behaviour is essential for the mission's success as incorrect folding, storage, and deployment could result in damaging the membrane or not achieving the expected deployed configuration. Virtual simulation is a feasible solution in comparison with physical testing which requires reduced gravity, friction, and air-drag-free environment in design optimization of these structures. However, accurate idealisation schemes will significantly reduce number of elements meaning lower the degrees of freedom and hence reduce the computational cost. Therefore, a proper understanding of the mechanics of creased membrane structures is the key, in formulating such idealisations. The underlying mechanics in the deployment of creased membrane structures from the folded state to the deployed state involves two phases. First, the structure self-opens from the fully folded state to the stress-free stable state. It then requires an external force to deploy from stress-free state to fully deployed state. This can be referred to as forced opening. The focus of the previous studies was limited to the characterisation of crease behaviour during forced opening but not the self-opening which is also crucial in the design of gossamer structures. In this research, an attempt has been made to characterise the crease mechanics of single creased thin Kapton polyimide membranes during their self-opening behaviour using two different experimental approaches. One experimental study investigates the rotational motion of a panel in a single creased membrane immediately after creasing where angle, angular velocity, and angular acceleration variation were obtained to develop the moment-rotation response. The second experimental study evaluates the moment-rotation response of crease during quasi-static folding of the single creased membrane once it achieved the stress-free stable state. It has been found that the moment-rotation response during the self-opening behaviour shows a linear trend for all thicknesses considered. The effect of membrane thickness and width on the crease rotational stiffness was also investigated in the experimental study. Accordingly, crease stiffness increases with increasing thickness and is independent of the width of the specimen. A simple analytical study was performed to predict the rotational stiffness of the crease which shows a good qualitative agreement with physical experiment results. Finally, the results from the self-opening study were combined with the forced opening study which was done by previous researchers. Based on the results it is reasonable to assume the fold-line stiffness to be linear during the whole deployment with a constant crease stiffness. This value can be easily incorporated as spring stiffness in the finite element model by idealising the crease region as a rotational spring to reduce the computational cost.
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    item: Conference-Abstract
    Study on economical protective measures against concrete spalling
    (Department of Civil Engineering, University of Moratuwa, 2021-11) Senevirathne, WTL; Baskaran, K; Hettiarachchi, P
    Concrete spalling is a major problem in reinforced concrete structures, especially in public buildings, which were constructed some time ago. In Sri Lanka, many public buildings such as schools and hospitals exhibit this problem. Authorities prohibit the use of the building area, where there is potential for concrete spalling instead of immediately repairing, because the repairing work is expensive and time consuming. This research is to study economical protective measures to prevent falling of spalled cover concrete chunks until the proper repair is done. The research is conducted in two experimental series. Series one consisted of eight small scale concrete slab panels, which were installed with four different materials (plywood sheet, thin aluminium sheet, plastic mesh, and stainless steel wiremesh) by two installation methods (concrete wedge anchors and screws with wall plugs). Initially concrete slab panels were cast, and after 28 days the materials were installed with two distinct installation methods. Then the material installed structure was subjected to area load and failure loads were recorded. Second experimental series was performed with the same size concrete slab panels, three materials (stainless steel wire mesh, plastic sheet, and thin aluminium sheet) and one installation method (wedge anchors) which were used in first experiment. Initially slab panels were cast and kept to gain strength, then the selected three materials were fixed with the above installation method. After that, the material installed slab panels were subjected to cyclic wetting and drying using three percent sodium chloride solution by weight of water to create a spalling condition by the electrolysis process. Then the relevant observations of the material installed structure and concrete slab panels were made with the time. After 28 days, material installed structure was subjected to area load and failure loads were recorded as same as the first experiment. Stainless steel wire mesh installed with concrete wedge anchors showed the highest load carrying capacity.
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    item: Conference-Abstract
    An integrated framework to select building materials for construction projects in Sri Lanka
    (Department of Civil Engineering, University of Moratuwa, 2021-11) Senanayake, HH; Jayasinghe, C; Kariyawasam, KKGKD; Hettiarachchi, P
    Construction Industry has contributed to more than one third of global carbon emissions. Adoption of sustainable development approaches could minimize such environmental and social impacts. To guide the construction industry more towards sustainability, one of the key requirements is to develop a standard framework to rate the suitability or greenness of building materials. Such a framework should also address the country-specific priorities and assess whole life performance starting from extraction of raw materials to the disposal of material after usage. This study provides an improved standard framework to rate green building materials that could help policymakers to implement rules, regulations, and tax benefits in near future with the aim of encouraging the use of sustainable building materials. The framework was improved from the existing building material rating system in Sri Lanka by making changes for the fields and measurements and by assigning weightages based on country specific priorities. The developed approach provides a green building material rating for the materials considering the relative importance of seven factors including natural resource consumption, recycled / reused / regenerated component, energy demand and CO2 emission in manufacturing and transportation stages, and indoor environment. This framework was assessed by a case study of five materials, and it was found that the framework provides an integrated solution to measure greenness of building materials. According to the framework developed, highly green-rated materials have the potential to reduce natural resource consumption, enhance energy efficiency and water efficiency, reduce greenhouse gas emissions, enhance indoor environment quality, and improve social well-being. This study shows that some products provide sustainable solutions only in one or two fields and those products are not fully green although the exceptional performance in the one or two fields makes the product attractive to the customers. Moreover, this study found that governing bodies should pay attention to knowledge sharing with not only manufacturing firms but also with rural industries as they tend to lag behind the large firms in producing fully green building materials. The integrated framework developed and tested in this study could be leveraged by the governing bodies, the industry, and the wider world to identify the greenness/sustainability of building materials quantitatively.
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    Ranking of walling materials using eco-efficiency for tropical climatic conditions: a survey-based approach
    (Department of Civil Engineering, University of Moratuwa, 2021-11) Gurupatham, SV; Jayasinghe, C; Perera, P; Hettiarachchi, P
    Construction is an important sector that consumes a significant amount of resources worldwide and produces a lot of waste. Buildings as a whole share nearly a quarter of total electricity generation in tropical countries, which has adverse effects on the natural environment and their national economies. Improving the energy efficiency of the building is based on the choice of materials and technologies that complement the local climatic conditions. Compressed stabilized earth blocks are considered an innovative and proven building envelope upgrade that improves building efficiency both economically and ecologically given their cradle-to-grave phase. However, the cradle-to-grave life cycle impacts of compressed stabilized earth blocks compared to conventional walling materials still need to be assessed under tropical climatic conditions over the long run. Hence, the objective of this study is to compare compressed stabilized earth blocks with conventional walling materials such as burnt clay bricks and cement sand blocks. The life cycle thinking approach has been integrated into the eco-efficiency analysis to compare and evaluate the materials mentioned above taking into account their total lifespan, from cradle to grave. A case study approach has been followed in order to compare the walling materials. The cost component has been computed in every stage of building life cycle and the net present value has been computed through a cash flow. The life cycle assessment has been considered in the form of emissions as both embodied as well as operational emissions. Hence, the eco-efficiency index has been quantified. The result of the case study indicated that when the eco-efficiency index of burnt clay bricks is taken to be 1, cement sand blocks showed 0.959 (decrease of 4%) and compressed stabilized earth block showed 1.013 (increase of 13%) showing the highest eco efficiency. Further when plaster was not applied, the index increased to 1.054 showing 4% increment than the plastering situation. As a result, compressed stabilized earth block was selected as the most efficient material with environmental benefits. In addition, since it can be used as a walling material even without the application of plaster, costs and environmental impacts could be further reduced when used without plaster. The results of this research will encourage building developers, contractors, and practitioners to choose the most desirable material for their projects taking into account the costs and environmental impacts of the life cycle of materials.
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    item: Conference-Abstract
    Effect of a shear key on the behaviour and stability of cantilever type retaining walls
    (Department of Civil Engineering, University of Moratuwa, Sri Lanka., 2021-11) Gowshikan, A; De Silva, LIN; Hettiarachchi, P
    Retaining walls are categorised into several types, of which cantilever retaining walls are the commonly used retaining wall type. The stability of these walls should be ensured for its longterm use without any anticipated failures. A retaining wall can fail due to four main failure mechanisms: sliding, overturning, bearing capacity, and deep-seated failure. Shear keys are the structures incorporated in the cantilever retaining walls to increase their resistance to sliding, thus, increasing the Factor of Safety against sliding. The development of passive earth pressure due to the soil in front of the shear key will generate an additional resistance against sliding. This study aims to identify the optimal location and depth of the shear key to yield maximum use from it. Both the theoretical approach based on limit equilibrium and numerical modelling have been adopted in the analysis. Limit equilibrium analysis was carried out using the Excel spreadsheet application, and two different scenarios were considered based on the distribution of lateral loads due to active soil conditions. Rankine's method was used for active and passive earth pressure computation. For the shear key, three different locations were considered: at the toe, middle of the base, and heel, and five different depths were considered: 0.4 m, 0.6 m, 0.8 m, 1.0 m, and 1.2 m. Soil strength properties were taken by referring to the commonly used backfill soil materials in Sri Lanka. The design soil parameters considered for the analysis were calculated using BS 8002:1994. From the Limit Equilibrium approach, the values of Factor of Safety (FOS) against sliding and overturning, varying with the shear key's depth and location, were obtained as graphical representations. Finite Element Analysis was carried out using PLAXIS 2D software to analyse the variation of the overall stability with the increasing depth of the shear key and validate the location of the point of rotation assumed in the limit equilibrium approach. Both the retaining wall and shear key were modelled as plate elements in PLAXIS 2D. The results of limit equilibrium analysis suggested that the use of a shear key enhances the stability of the retaining wall against sliding. The location of the shear key does not influence the stability of the retaining wall against sliding. It was also found that the increased depth of the shear key reduces the stability of the retaining wall against overturning, and the optimum location of the shear key is at the heel of the wall base. Results from the Finite Element Analysis show that the overall stability of the retaining wall increases with an increase in depth of the shear key. The point of rotation is assumed to be located underneath the toe of the wall and at a depth of the shear key. From the Finite Element Analysis, changes in the direction of displacement were visible around the assumed location of the point of rotation for all three locations of the shear key. Hence, the assumed location of the point of rotation is reasonable in this study.
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    item: Conference-Abstract
    Nature based landslide mitigation - an application of bio engineering
    (Department of Civil Engineering, University of Moratuwa, 2021-11) Athapaththu, P; Nawagamuwa, UP; Hettiarachchi, P
    The use of vegetation for slope stability has been practiced in developed countries such as Hong Kong. This study identifies the effect of roots of the tea plant (Camellia sinensis) and vetiver grass (Chrysopogon zizanioides) on slope stabilization in the central highlands of Sri Lanka. The main objective of this research is to compare the influence of clonal tea plants and seedling tea plants on slope stability, find the influence of vetiver on slope stability, and propose a combined slope stabilizing method for tea lands. This slope stability is studied according to the root indices based on root cohesion, root morphology, and root distribution with depth. Root morphology of tea is a tap root system and vetiver has a fibrous heart root system. The root depth of clonal tea plants is around 1 m, and it increased up to 2 m for seedling tea plants. Slope stability analysis was done for selected vegetations and different slopes with different soil properties complying with Sri Lankan soil conditions. Deterministically, FOS was computed for slopes using Bishop’s Limit Equilibrium analysis in Slope/W software. For the slope stability analysis, several soil parameters were selected for accurate results. Soil unit weight (γ) was taken as 18 kN/m-3 and analysis was done for cohesion values of 5,10,15 kPa and friction angle of 20,25,30 degrees. Analysis was done for the five different geotechnical parameter combinations for without vegetation soils where constant friction angle (200) with cohesion values of 5,10,15 kPa. And constant cohesion value (5kPa) under different friction angles (200,250,300). Slopes with vegetation were analysed as areas with increased soil cohesion. For areas reinforced with tea, cohesion was considered by adding 10kpa (root cohesion) to the existing soil condition and for vetiver, it is considered as 6kPa. Unit weight and friction angle were considered as the same. FOS for all vegetations types was calculated for the selected slope angles (300 450, 600, 700) and slope heights (5m,10m) with different soil properties (C, Ф). Critical slope angle where FOS = 1 and Safe slope angle where FOS = 1.2 for each type of vegetation was found and compared for each case. Further, terraced slope stabilization was analysed using a combination of tea and vetiver and road cut slope stabilization using tea and vetiver grass was analysed using Slope/W. On analysis, the results show that the FOS for slope increases with the vegetation cover. Plantation beneficially affects slope stabilization. Vegetation increases the critical slope angle and safe slope angle for any soil condition. Seedling tea performs better than clonal tea in slope stabilization therefore seedling tea plantations can be recommended for unstable slope conditions and the combined analysis of tea and vetiver showed that adding vetiver zones at a sufficient contour interval increased the stability of terraced slopes and could be used to stabilize the unstable slopes cut within tea estates for purpose of access roads.
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    item: Conference-Abstract
    Modeling of erosion and sedimentation process
    (Department of Civil Engineering, University of Moratuwa, 2021-11) Boyagane, WMYB; Nawagamuwa, UP; Hettiarachchi, P
    Soil erosion is one of the major environmental problems in tropical regions. It causes negative impacts including the removal of nutrient-rich topsoil, destroys aquatic habitat, dams, and pond siltation, clogs rivers by deposition of sediment, and causes water pollution in the rehabilitation process. Soil texture is an important factor affecting soil erosion. The productive soil surface is detached, transported, and accumulated at a distant place from the initial place by a complex dynamic process called soil erosion. Soil erosion can be grouped into two different stages as geologic erosion and accelerated erosion. Formation and loss of soil by natural processes to maintain the balance of soil-forming processes can be identified as geological erosion. Accelerated erosion consists of deterioration and loss of soil by anthropogenic activities. Climatic changes (rainfall/precipitation or wind), landscape relief, soil and bedrock properties, vegetation cover, and human activities are the main factors that are influencing the soil erosion process. In this study, an artificial rainfall experiment in the laboratory scale was conducted to investigate the mechanism of soil erosion under the different soil compositions. Revised Universal Soil Loss Equation (RUSLE model) is the most common one to estimate soil loss. These experiments were done to study how the amount of soil loss varying with slope angle and rainfall intensity which are the most influencing factors in the RUSLE model. Three soil samples were taken from different places such as Bathalagoda, Gedarakumbura waththa, and Siyabalanga around Kurunegala District such that different soil mineralogy can be obtained. Maximum dry density and optimum moisture content were calculated by the Proctor compaction test. According to those values, soil samples were compacted in a wooden tray and exposed to an artificial rainfall. The tray was exposed to rainfall for 30 minutes and after that soil loss was calculated. Soil loss was calculated while changing slope angle and then changing rainfall intensity. Then the soil loss variation with the RUSLE model was studied. Results of this study indicate that there are some deviations between the RUSLE slope steepness factor with the experimental values when clay particles are present. Although there is a linear relationship between slope angle and amount of soil loss in the RUSLE model when there are clay particles present in the soil that relationship deviates reasonably. After the slope angle increases up to a certain level, there is a sudden increase in soil loss even with a considerable amount of clay particles. Hence the presence of clay particles provides some resistance to soil particles to erode below a certain slope angle. When there is less amount of clay particles, soil loss with the increase of slope angle behaves similar to the RUSLE model. With the increase of rainfall intensity, there is an exponential increase in soil loss as in the RUSLE model. Less soil erosion occurs if fine particles are very low, due to high infiltration at low rainfall intensities. It was observed that when the percentage of clay particles increases, the amount of soil loss decreases.
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    item: Conference-Abstract
    Compressibility characteristics of unsaturated soil
    (Department of Civil Engineering, University of Moratuwa, 2021) Krichikeshan, I; Kulathilaka, SAS; Hettiarachchi, P
    Conventional Terzaghi's consolidation theory is developed for saturated soil. However, in practice the concept is used with unsaturated soils as well. The behaviour of unsaturated soils is quite different due to the presence of the air phase and the contractile skin- the boundary between air and water phases. In many places in the country residual soils formed by the weathering of parent metamorphic rock are present at the surface level and there is a zone of unsaturated soils just below the ground surface. Loads from many structures are applied on this zone and the understanding of the compressibility of this zone is very important. Also, there is high variability in this zone. The objective of this research is to identify the variation of compressibility characteristics of different soils with the saturation level. Due to the existence of air phase in unsaturated soil, excess pore water pressure is not equal to the load applied when the soil is compressed under an undrained loading condition. To get an accurate reliable equation we need to consider both pore water pressure and pore air pressure. If the excess pore air pressure and excess pore water pressure are allowed to dissipate, the excess pore water and air pressure will dissipate gradually with time. The volume change of the unsaturated soil is not equal to the water drainage in unsaturated condition. And also, it is necessary to consider the saturation level. The main parameter that causes the difference from saturated soils is matric suction. As such in this research a controlled uniform saturated sample is obtained, and it was brought to equilibrium under different matric suctions. The compressibility characteristics of the same soil under different matric suctions are evaluated. The parameters are evaluated under the framework of Terzaghi model. An attempt was made to establish a relationship between the matric suction and the consolidation parameters. Identical samples were tested on conventional Oedometer and a Rowe Cell of diameter 75 mm. The void ratio, natural moisture content, compressibility index are the features which can be obtained from standard Oedometer consolidation test and Rowe cell consolidation test. Available data states that the compressibility characteristics of unsaturated soils are usually very nonlinear and cannot be considered in some conditions. Compressibility of unsaturated soil depends on many factors. Some of them include particle size distribution, saturation level, temperature, permeability. Compression index (Cc) and Recompression index (Cr) decrease in the initial stage and then increase with matric suction. mv value for the saturated sample was greater than unsaturated soil and with the increase of stress level, the mv value of all the samples decreased.
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    item: Conference-Abstract
    Use of the concept of capillary barriers to optimize the support of deep vertical excavations in unsaturated soils
    (Department of Civil Engineering, University of Moratuwa, Sri Lanka, 2021-11) Prasanna, R; Kulathilaka, SAS; Hettiarachchi, P
    Deep excavation in the construction industry became vital because of the lack of availability of land in the populated urban areas to provide facilities such as parking. In a deep excavation it is necessary to ensure stability and that the deformations in the surroundings are within acceptable limits. As such, deep excavations need to be supported by properly designed earth retaining structures with adequate lateral supports. In excavations below ground water level expensive systems such as secant pile walls or diaphragm walls are needed. In unsaturated soils, simpler systems such as soldier pile walls can be used. The forces on the system are low during dry periods due to the prevailing high matric suction. But during the rainy seasons, due to the infiltration of water into the unsaturated soil matric suction will reduce leading to a reduction in shear strength. If the retaining system is designed with saturated strength parameters as a conservative measure the cost would be high. Infiltration of rainwater can be reduced with the use of the concept of capillary barriers and the design of the earth retaining system can be optimized. A capillary barrier is an unsaturated cover system with two layers with varying hydraulic properties that functions in response to change in negative pore water pressure. It consists of a fine layer on top of a coarse layer. A capillary barrier is effective if the combined effect of evaporation, transpiration and lateral diversion exceeds the infiltration from the precipitation. In this research study attempts were made to establish the critical parameters for the capillary barrier system like inclination and thicknesses of layers. Analyses for the applicability of the capillary barrier system on the deep vertical excavations on local Sri Lankan soils was done with rainfall experiments on a laboratory physical model. Results of the physical laboratory experiment were verified with the numerical analysis of the model using SEEPW Geoslope 2012 software. Another analysis was done studying the effect of rainfall on the prop forces on a soldier pile wall supporting a 6m deep excavation done in an unsaturated soil with a deep groundwater table. Infiltration was studied under the natural conditions and with the capillary barrier. This study was done with MIDAS GTS NX software under 3 Dimensional conditions. From the analysis, length of 600 mm was selected for both capillary barrier and site extent of the physical laboratory model with infiltration rate of 10mm/hr. Results of numerical analysis show that the capillary barrier of this model cut the infiltration of rainwater for a 20-hour continuous rainfall. Results of the numerical analysis on actual deep excavation shows that the prop forces reduce by a significant amount in the presence of the capillary barrier. Percentage of increase in the prop forces decrease by 45% to 27% at different prop levels. These two studies show the effectiveness of the capillary barrier in economizing design of earth retaining systems in unsaturated soils.
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    item: Conference-Abstract
    Improvement of compressibility characteristics of waste material by dynamic compaction
    (Department of Civil Engineering, University of Moratuwa, 2021-11) Rathnayaka, RIA; Kulathilaka, SAS; Hettiarachchi, P
    Open dumping is the most prevalent method of waste disposal in Sri Lanka. These sites, which are currently used as waste dump yards in urban areas, will have to be rehabilitated to be converted to be used as parks, roads or for other different construction projects. Establishing the strength and stiffness characteristics of these waste materials at different levels of degradation and how these characteristics can be enhanced to suit the proposed developments is a major challenge. The mechanisms of settlement that govern the solid waste material are numerous and complex. Bowders et al. (2001) reported that there are many reasons behind this behaviour of waste such as extreme heterogeneity of the wastes, their own particle deformability, the large voids present in the initial waste fill, and their biodegradability. According to Watts and Charles (1990) and Manassero et al. (1996), the settlement behaviour of MSW is often classified as occurring in several distinct phases. Primary consolidation of solid waste occurs due to the self-weight of the waste or application of surcharges such as fill over the time. Primary compression is then followed by the secondary compression. Secondary compression occurs due to biodegradation process in waste fill, and it can take years for this settlement to complete depending upon various phases of waste that it consists of. This paper presents a study of the effectiveness of dynamic compaction as a technique of enhancing the compressibility characteristics of waste dumps. MSW was subjected to dynamic compaction in a laboratory test setup, and another MSW sample was kept uncompacted. Next, MSW samples in both compacted as well as in non-compacted state were subjected to loading in a Rowe Cell of diameter 150 mm and height 50 mm and results were analysed to establish the compressibility characteristics, namely coefficient of volume compressibility (mv), compressibility index (Cc), coefficient of consolidation (Cv) and coefficient of secondary compression (Cα). Finally, results were compared to assess the effect of dynamic compaction on compressibility characteristics of MSW and the effectiveness of the process is compared with that of preloading. Compression index of MSW that was subjected to dynamic compaction was reduced to about 50% of the compression index of the non-compacted MSW. Recompression index values of noncompacted MSW values are less than about 10% of compression index values of non- compacted MSW samples. Similarly, results obtained for coefficient of volume compressibility shows greater reduction by preloading compared to dynamic compaction. Both preloading and dynamic compaction show significant effectiveness in reducing the coefficient of secondary consolidation. In conclusion, compressibility characteristics of MSW can be improved significantly using both preloading and dynamic compaction. According to results observed in this study preloading can be considered as the more effective method. However, depending on the composition and the degradation level of the MSW sample used these results can be changed. Considering the time, it takes to achieve the required compressibility reductions by preloading, dynamic compaction can be considered as another advantageous option.
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    item: Conference-Abstract
    Laboratory modelling of infiltration into unsaturated residual soils
    (Department of Civil Engineering, University of Moratuwa, Sri Lanka, 2021-11) Somarathne, PAU; Kulathilaka, SAS; Hettiarachchi, P
    Rain induced failures in slopes made of residual soils are a major concern in Sri Lanka. Sri Lankan sloping grounds are made of colluvial soils, residual soils, and rocks at different levels of weathering. Soils at upper levels in most slopes are in an unsaturated state during dry season. The high matric suction near to the surface enhances the shear strength. Infiltration rainwater during the rainy season reduces the matric suction and could create perched water table conditions. Ground water table could also rise. A detailed understanding of the infiltration process is necessary to get an insight into rain induced slope failures. Infiltration process can be modelled with GEOSLOPE software, but it needs to be verified with data acquired from field instrumentation. A field study would be quite complex due to the prevailing nonhomogeneous conditions. As such, initial studies are done under simplified laboratory conditions. In this research infiltration process is studied with a laboratory model of a uniform soil mass prepared in a barrel. The matric suction changes predicted by numerical model are verified by laboratory measurements. Initial study was done by filling the barrel with a lateritic fill of low permeability (Ksat = 1.0 x 10-7 m/s). In the current study a sandy soil with high permeability of 1.0 х 10-4 m/s was used. Sand was placed in layers with proper compaction. Rainfalls of different intensities were simulated. To simulate the rainfall the required quantity of water for 15 minutes was calculated and applied uniformly over the model at 15-minute intervals by a perforated cup. A constant head was achieved by having an overflow from the cup. The matric suctions and moisture contents during the rainfall events were measured using tensiometers and moisture sensors. Measurements were done after the event also to model the process of evaporation. The experimental results were compared with results from numerical modelling with GEOSLOPE SLOPE/W 2012 software. SWCC was modelled using the Fredlund and Xing model. Results of this study showed that, in first few hours after applying the rainfall the matric suction was reduced rapidly at the top of the sand column and with time it propagated to the bottom of the sand column. Thereafter, matric suction reduced gradually. When it was subjected to a continuous heavy rainfall positive pore water pressures were developed. Matric suctions increased after the cessation of the rainfall. Experimental observations and numerical predictions were in close agreement. In the tests done with lateritic soils high matric suctions prevailed after the compaction and rainfall caused a reduction in matric suction but positive pore water pressures were not developed.
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    item: Conference-Abstract
    River discharge – water level relationship at wide floodplains
    (Department of Civil Engineering, University of Moratuwa, 2021-11) Herath, HMJH; Herath, TMN; Hettiarachchi, P
    The relationship of the river discharge and water level of a river flow can be explained by Manning’s equation. However, in case of a flood situation, when overbank flow occurs, the flow cross-section related to the flow will be changed. The rating curves which give the discharges at the gauging stations are usually derived for the water levels below the flood level. Therefore, extending the same rating curve for water levels higher than the flood level will give an underestimated discharge value because the additional flow area of the floodplain is not accounted. For this study, Hanwella floodplain of the Kelani River Basin and Manampitiya floodplain of Mahaweli basin were chosen because of the availability of wide floodplains at the gauging stations. A two-dimensional HEC-RAS hydrodynamic model-based study was carried out to check the inconsistencies of the water level - discharge data at these wide flood plains. The flow hydrographs were used as inputs at the upstream boundary of the model and the simulated water levels were monitored at gauging stations. The water levels obtained were not in the order of recorded water levels and it confirmed the inconsistency of the discharge data which were obtained by using the rating curves. The discharge values were varied until a satisfactory water level distribution was obtained at the gauging location and the model was verified with manually calculated flow discharges using the Manning’s equation considering the wide flood plain cross sections. This study confirmed the inconsistency of the available discharge data and the existing rating curves at Hanwella and Manampitiya were rectified with the corrected discharges. About 58% increase in the discharge was estimated at 10 MSL at Hanwella gauging station and a 72% increase in the discharge was estimated 36 MSL at Manampitiya gauging station when compared to the discharges estimated using the existing rating curves.
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    Water resources availability and low flow discharge analysis of Kelani River basin in wet zone under changing climate conditions
    (Department of Civil Engineering, University of Moratuwa, 2021-11) Punsara, KGC; Rajapakse, RLHL; Hettiarachchi, P
    This study estimates the effects of climate change on water resources availability and low flow streamflow discharge in the wet zone Kelani Basin in Sri Lanka. Models are available for flood study purposes in the respective basin, but for the estimation of low flows, more precise hydrological models are required. Analysis of the water resources availability under low flow conditions is essential for future infrastructure projects, ongoing urbanization, irrigation releases, and hydropower generation as well as for proactive planning, decision making, and establishing alternative sources. The selected pilot areas for this study are Norwood and Deraniyagala subbasins of Kelani river. This research further evaluates the future change in streamflow of Kelani river due to climate change using a climate scenario analysis based on predicted climate variations in the basin. Standard Precipitation Index (SPI) analysis was performed to identify meteorological drought conditions that occur in the study area. The cumulative SPI results of shorter periods were generated by using the 12-month timescale which is above or below the generally used normal value. Further, the SPI values for a longer period tend to zero if a typical wet or dry trend has not occurred for a considerable period. The HEC-HMS rainfall-runoff model was used to simulate streamflow under different scenarios, based on the accessibility to data, data reliability, and flexibility of the model. The model results indicated the capability of HEC–HMS model to simulate streamflow in the basin with reasonably higher accuracy with Mean Ratio of Absolute Error (MRAE), Nash Sutcliff Efficiency (NASH), and R-squared correlation (R²) as objective functions. The MRAE showed more sensitivity to low flow and medium flow regions and less sensitivity to high flow region while NASH showed more sensitivity to high flow region compared to low flow regions. The non-parametric estimator (εp) was used to estimate the rainfall elasticity of streamflow which is an initial estimation of the impacts of climate change on runoff generation and subsequently on water resources availability. According to the rainfall elasticity of streamflow analysis, elasticity values of 0.75 and 1.00 were obtained for the Norwood and Deraniyagala subbasins, which indicate that a 1.00% change in rainfall results in a 0.75% and 1.00% change in streamflow discharge in two sub-basins, respectively. The data for synthetic climate change scenarios were generated by adjusting the historical time series of hydro-climate data. The HEC-HMS model was run for selected 18 combinations of evaporation and precipitation in order to simulate changes in the hydrological processes due to potential climate change while incorporating climate uncertainty. The synthetic climate change scenario analysis results indicate up to a 40% reduction in streamflow in the dry season due to the climate change for the 2016-2035 period. This model is a feasible tool for testing the impact of future water management plans and policymaking on low flow management, while the findings and outcome of the research will be useful for scenario analysis and implementation.