Research Papers - Department of Civil Engineering

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Start date: 2010End date: 2019

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    Investigation of the Carrying Capacity of the Socketed Region of Bored and Cast-in-Situ Piles in Sri Lanka
    (ASTM International, 2018-06-07) Thilakasiri, S; Rathnayaka, A
    Approximately 90 % of Sri Lanka is underlain by Proterozoic gneisses consisting of Precambrian basement, with Phanerozoic sediments being restricted to the coastal areas. Due to the availability of bedrock on an average at approximately 20 m below the ground surface, end-bearing bored and cast-in-situ piles socketed into bedrock are very often used in Sri Lanka to support large structures such as high-rise buildings. However, significantly high variations of both the bedrock profile and properties are observed even within small sites. Therefore, termination of the piles within the bedrock is a very important consideration during the installation of piles to achieve the required capacity. Pile termination is generally done using the drilling rate and observing the rock cutting as the criteria for terminating piles. The relationship between the drilling rate, the quality of the rocks, and mobilized skin friction within the rock socket are investigated in this paper based on the results of instrumented pile load tests. The results of the analysis indicate that the mobilized skin friction in the rock socket does not have a direct correlation with the drilling rate but on the overall quality of the bedrock. Due to the low cost and quick execution, engineers use the skin friction distribution and end-bearing capacity obtained from signal matching of high-strain dynamic load test results for the design of piles. In this paper, mobilized pile capacities within the rock socket are investigated using measured field-instrumented maintain load test results and the results from signal matching. The results of the analysis indicate that the static load-settlement curve can be obtained from CAPWAPVR analysis, but the mobilized skin friction distribution and the end bearing cannot be accurately obtained from an acceptable CAPWAP signal matching.
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    Management of municipal solid waste open dumps immediately after the collapse: An integrated approach from Meethotamulla open dump, Sri Lanka
    (Elsevier, 2019-07) Jayaweera, M; Gunawardana, B; Gunawardana, M; Karunawardena, A; Premasiri, S; Manatunge, J; Wijeratne, N; Thilakasiri, S; Karunarathne, D; Dias, V
    Meethotamulla open dump (MOD) of Sri Lanka that has received about 290,000 metric tons of mixed MSW annually collapsed on 14th April 2017 with massive devastation. An integrated approach was attempted to control further collapse with the deployment of drone-assisted and stand-alone instrumentation. The collapsed dump was analyzed for attributes, including contours, heights, wetness, temperature levels, tension cracks, landfill gases, fire, explosion, and asphyxiation hazards with 24-h surveillance after one day of the collapse. The mode of MOD failure was implicated to be deep-seated (rotational) slope failure. A short-term plan, consisting of 12 activities was prepared and successfully implemented. The activities of the short-term plan were carried out at the dumpsite until the water level fluctuations <5 cm, inundation of the toe area receded completely, the horizontal displacement of surface markers <20 mm, lower explosive levels of CH4 and CO less than 5 and 12%, respectively, O2 level improved up to 21%, and temperature variation of the collapsed face <2 C. The short-term plan was halted when the factor of safety for slope failure of the critical face improved from 0.807 to 1.286 ensuring no signs of a subsequent collapse of the MOD. An early warning system was established in the case of an imminent collapse. This integrated approach, to our knowledge, is the first study instituted, and this holistic management effort could be easily replicated to avoid disasters from slope failures of landfills or open dumps that may occur elsewhere.
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    PublicationOpen Access
    Effective Sizing of Natural Systems for Grey Water Treatment Using Locally Derived Parameters
    (Spriger Link, 2019-08-07) Karunarathne, S
    When properly managed, grey water can be a valuable resource, which agricultural and horticultural practitioners as well as home gardeners can benefit from using to provide an excellent nutrient sources for vegetation. Natural treatment systems such as constructed wetlands emphasizing on sustainability and wastewater reuse typically for agricultural irrigation/home gardening can be considered as an ideal alternative to close the loop in terms of nutrient capture and water conservation. This paper presents a part of an analysis done to estimate the locally derived treatment wetland parameters based on BOD5 removal mechanisms of a pilot scale subsurface horizontal flow constructed wetland (SSHF CW) treating greywater. A pilot scale SSHF CW with a surface area of 8.64 m2 and a substrate depth (with 20 mm aggregates) of 0.7 m was monitored. This is a part of a long term study carried out to test the viability of SSHFCW for treating grey water for agricultural reuse. The wastewater flow measurements were taken from the inlet and the outlet of the constructed wetland while monitoring the hydraulic (HRT) and organic loading rates. Water samples from four sampling points were collected on a long term basis. Equations based on a kinetic model of a first-order piston flow reactor was used to calculate the relationship among the design parameters appropriate for local conditions. The HRT varied from 3.3 to 4.7 d for maximum and minimum inflow loading rates observed. Using the data from the current study, a resizing exercise for a subsurface horizontal flow constructed wetland was carried out. Accordingly, a household with four people, discharging 720 L/d greywater with an average influent BOD5 of 300 mg/L could be treated up a BOD5 concentration of 25 mg/L using an area of 3.60 m2 of SSHF CW, implying only 0.975 m2 of per capita land usage.
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    Pavement maintenance management system for low volume roads in Sri Lanka
    (IEEE, 2019-07-03) Perera, M. Y. I; Pasindu, H. R; Sandamal, R. M. K
    In Sri Lanka there are about 150,000 km of roads and among those about 75% are considered as rural low volume roads [1]. These roads are essential in community development, transport of people, goods and services in the rural areas. Most of these low volume roads would be actively contributing to our country's economy and wellbeing by distributing the produces from rural areas to urban areas. Limited funding, subjective and ad-hoc maintenance decision making has resulted in suboptimal maintenance level for these road networks. There is no proper maintenance system available in Sri Lanka as in the foreign countries. Lack of technical expertise and shortage of human resources, equipment and funds to carryout detailed data collection and analysis makes use of existing Pavement Management Systems difficult for local road agencies. The study will be focused on developing an asset management system to manage rural and provincial road networks in Sri Lanka.
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    PublicationOpen Access
    Importance of hydrologic simulation for LIDs and BMPs design using HEC-HMS: A case demonstration
    (Medcrave, 2017) Khaniya, B; Wanniarachchi, S. S; Rathnayake, U
    Best management practices (BMPs) and the Low impact development (LIDs) is water management tools used to mitigate hydrological impact resulting from unpremeditated urbanization. For the proper functioning of the LID and BMP features the volume of the runoff generated, peak runoff rate before and after the installation, need to be accessed. Modeling by comparing different developmental scenarios helps to characterize the impact of BMPs and LIDs practices on the surface runoff. Therefore, this paper describes a modeling approach to predict the performance of these BMPs and LIDs in an existing hydrological model. This type of modeling approach is important to understand the long-term operation of the watershed post-development plan. A single rainfall event in May 2013 has been modeled and the characteristics graphs such as outflow, precipitation, runoff, infiltration have been analyzed. Run-off volume after retrofitting infiltration trench has decreased by 351m3 at the outlet with an increase of 39 L/s in peak discharge. Time series study of reservoirs depicts low performance of infiltration trench at latter phase of rainfall event. This leads with a rational that infiltration trench cannot result favorable for longer rainfall events unless underlying soil has superior geo-technical properties with low level water table. Results manifest the benefits of using hydrologic modeling software to understand the watershed hydrology.
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    PublicationOpen Access
    Use of Natural Fibres to enhance tensile strength of concrete
    (ACADEMIC JOURNAL OF CIVIL ENGINEERING, 2017-07-21) Seneviratne, R.A.C.J; Tharmarajah, G; Archbold, p
    This paper discusses the influence of natural fibres on density, compressive strength and flexural strength of fibre reinforced concrete specimens. Coir fibre extracted from coconut husk was added to high strength concrete to produced 36 test cubes and 36 beam samples. Tests carried out on cube and beam samples show that compressive strength of high strength concrete reduces with addition of coir fibres. The reduction is noticed varying with the change of fibre content and fibre length. Further, comparison between cubes and beams indicate variation in density of the concrete as well. The test results show that a reduction in flexural strength in most cases except for 2% coir fibre reinforced concrete, where a slight enhancement was noticed in flexural strength.
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    PublicationOpen Access
    Experimental study On Addition of Pine Fibres to High Strength Concrete
    (researchgate.net, 2017-03) Seneviratne, R; Tharmarajah, G
    This study focuses on influence of pine fibres on unit weight, compressive strength and flexural strength of high strength concrete. Concrete mixes with 2%, 4% and 6% fibre content were produced while length of the fibres were varied from 10 mm to 40 mm. From the pine fibre reinforced mixes, 36 test cubes and 36 beam specimens were casted to identify the desired variations. Unit weight of the concrete showed significant variations in the test cubes. However, the variations of the unit weight observed in the beam specimens were low compared to the variations observed in test cubes. Compressive strength of the high strength concrete also reduced significantly with the addition of pine fibres. Also a reduction in flexural strength was observed. Variation of both compressive and flexural strength showed a relationship with the fibre content and fibre length as well.
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    Corrosion-resistant FRP reinforcement for bridge deck slabs
    (Thomas Telford, 2014-11-26) Tharmarajah, G; Taylor, S. E; Cleland, D. J; Robinson, D
    This paper discusses the beneficial influence of compressive membrane action in fibre reinforced polymer (FRP) reinforced in-plane restrained slabs in bridge deck slabs and the improved service performance when arching action occurs. Bridge deck slabs that are exposed to extreme environmental conditions can experience severe corrosion damage. Expansive corrosion in steel reinforcement significantly reduces the design life and durability of concrete structures; for example, on one short section of the M1 in Northern Ireland, nearly £1 million was spent last year on the maintenance and repair of bridges due to corrosion. Corrosion-resistant composite reinforcement such as basalt fibre reinforced polymer (BFRP) and glass fibre reinforced polymer (GFRP) provides a durable alternative to reinforcing steel. In this research, two BFRP reinforced slabs and two GFRP reinforced slabs were constructed using high-strength concrete with a target cube compressive strength of 65 N/mm2. The slabs represented typical full-scale dimensions of a real bridge deck slab 475 mm wide by 1425 mm long and 150 mm deep. The service and ultimate behaviour of the slabs are discussed and the results are compared with the relevant design guidelines.
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    PublicationOpen Access
    Effect of electric boundary conditions on crack propagation in ferroelectric ceramics
    (The Chinese Society of Theoretical and Applied Mechanics; Institute of Mechanics, Chinese Academy of Sciences, 2014-04) Rajapakse, R. K. N. D; Li, F-X; Sun, Y
    In this paper, the effect of electric boundary conditions on Mode I crack propagation in ferroelectric ceramics is studied by using both linear and nonlinear piezoelectric fracture mechanics. In linear analysis, impermeable cracks under open circuit and short circuit are analyzed using the Stroh formalism and a rescaling method. It is shown that the energy release rate in short circuit is larger than that in open circuit. In nonlinear analysis, permeable crack conditions are used and the nonlinear effect of domain switching near a crack tip is considered using an energy-based switching criterion proposed by Hwang et al. (Acta Metal. Mater., 1995). In open circuit, a large depolarization field induced by domain switching makes switching much more difficult than that in short circuit. Analysis shows that the energy release rate in short circuit is still larger than that in open circuit, and is also larger than the linear result. Consequently, whether using linear or nonlinear fracture analysis, a crack is found easier to propagate in short circuit than in open circuit, which is consistent with the experimental observations of Kounga Njiwa et al. (Eng. Fract. Mech., 2006).
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    Atomistic and continuum modelling of stress field at an inhomogeneity in graphene
    (Elsevier, 2018-12-15) Dewapriya, M. A. N; Rajapakse, R. K. N. D
    The influence of an atomic inhomogeneity on the resulting stress field of a nanoscopic matrix material can be remarkably different from the corresponding continuum descriptions due to the significance of surface energy and the discrete nature of matter at the nanoscale. In this work, we conducted a comprehensive molecular dynamics study to investigate the stress field at an atomic inhomogeneity, in the form of an elliptical hole or a circular hexagonal boron-nitride inclusion, in graphene. The results show that stress concentration factor at an inhomogeneity is higher than the corresponding classical continuum solution. We estimated the surface elastic constants for a modified continuum framework using the molecular dynamics results. Comparison between the atomic simulations and the modified continuum model reveals the limitations of such continuum-based models for the two-dimensional materials. Molecular dynamics results imply that the underlying atomic structure softens the effect of inhomogeneity compared to a continuum description thus causing an amplification of the stress filed. The molecular dynamics and modified continuum solutions for stress concentration are presented in simplified forms and design charts to facilitate preliminary design of graphene-based hybrid materials.