ICSBE 2020

Table of Contents

1. Frontmatter

2. Geotechnical Advances for Sustainable Built Environment

   1. Frontmatter

   2. Assessment of Shear Strength Parameters of Marine Dredge Sand

      P. G. G. M. Ranbandara, A. M. R. G. Athapaththu, R. U. Thilakarathne, L. C. Kurukulasuriya, B. P. Gonaduwage

      Abstract

      Cohesion and friction angle represents the shear strength parameters of soils. Linear Mohr–Coulomb envelope is the widely used theoretical concept to describe the shear strength of the soils which are related to the geotechnical analysis and designs. However, sand deviates considerably from linear Mohr–Coulomb envelope due to the effects of factors such as confining pressure, relative density, mineralogy, particle crushing, particle size distribution and fines content. The Colombo port city development project, which is in coastal region, reclaimed dredge sand over 13 m depth. This project was proposed to include low rise and high rise buildings all over the reclaimed land where the type of foundation may vary depending upon the structural loads and subsurface conditions. Therefore, determination of shear strength parameters for different loading condition is of utmost importance to determine the bearing capacity and to select the dimensions of foundations. In this study, basic engineering properties of reclaimed sand collected from Colombo port city project were examined. A series of laboratory direct shear tests were conducted to determine the variation of shear stress over different normal stresses. From the analysis of experimental data, it was revealed that shear stress of dredged sand varies linearly with normal stress up to 100 kPa and showed nonlinear behavior thereafter.

   3. Collapsibility Characteristics of a Residual Soil in Matale District, Sri Lanka

      C. J. De Zoysa, A. K. T. Dushan, L. C. Kurukulasuriya

      Abstract

      Collapse is termed as the large volume reduction taken place in partially saturated soils upon wetting under a particular applied pressure, that are otherwise resistant to much larger applied stresses under normal conditions. This phenomenon can be commonly witnessed in Aeolian, alluvial and colluvial type of soils across the globe though not much reported to occur in residual soils. However, a residual soil too can develop into a collapsible soil under certain conditions. In this study, undisturbed soil samples obtained from a construction site in Matale District, Sri Lanka consisting of a residual soil which exhibited unusually low values of dry density was subjected to a series of double oedometer tests to determine the collapse potential and to investigate the variation of collapse potential with the applied normal pressure, relative compaction and degree of saturation. The study revealed that the collapse potential of different locations of the site is directly proportional to the applied normal pressure and inversely proportional to both relative compaction and degree of saturation. Also, it was identified that samples remolded maintaining their in situ dry density can increase the collapse potential of a slightly collapsible soil. A multi-variate regression analysis was performed to develop a relationship for collapse potential in terms of applied normal pressure, relative compaction and degree of saturation.

   4. Hydraulic Characteristics of Ballast Subjected to Particle Degradation and Mud Pumping

      K. D. K. Rupasinghe, L. A. R. L. Weerarathne, L. C. Kurukulasuriya

      Abstract

      Ballast is the primary component of a rail track foundation. Ballast aggregates are composed of crushed and coarse grained hard rock. Main functions of ballast are providing adequate permeability for drainage purposes, support the superstructure by distributing the loads from the moving train and provide lateral resistance to tie movement. Similar to shear strength characteristics, drainage capacity is also one of the most important properties of ballast. When it is degraded and aged, broken and foreign particles accumulate within the voids (ballast fouling) and its drainage capacity is decreased. Ballast degradation is mainly due to internal particle breakage and mud pumping. The aim of this research is to study the effect of particle degradation due to particle breakage and mud pumping on hydraulic characteristics of ballast. Rowe cell apparatus was used to conduct permeability tests. Since the ballast particles are large in size, naturally it was impossible to accommodate sufficient amount of sample within the Rowe cell to achieve a better packing of ballast. Therefore, parallel gradation technique was used and a new sample was prepared according to the parallel gradation technique. Series of constant head hydraulic conductivity tests were done for each of the samples with difference fouling percentages and breaking index values. Variation of hydraulic conductivity due to particle degradation in parallel graded ballast was obtained. This investigation revealed that the hydraulic conductivity decreased significantly with the increase in either the fouling percentage or the breakage index.

   5. The Effect of Fouling Materials on Permeability Behaviour of Large Size Granular Materials

      H. G. S. Mayuranga, S. K. Navaratnarajah, M. M. N. Gimhani, J. M. M. Y. Karunarathne

      Abstract

      Granular materials are discontinuous, highly heterogeneous materials that are randomly assembled. They are widely used in civil engineering constructions such as in highway pavements, rockfill dams, drainage systems, and rail tracks. In this study, the granular type ballast aggregates were used to analyze its permeability behaviour when it is contaminated with fine particles. The ballast provides rapid drainage and supports the heavy loads apply from the trains. However, the accumulation of fines in the ballast layer which is known as fouling causes disturbance in track drainage which is leading for reduced track performance and frequent track maintenance. Therefore, this study focuses on the determination of permeability behavior of fouled ballast with different levels of fouling experienced in Sri Lankan rail tracks and to propose the stage at which track maintenance should be done. A series of constant head permeability tests were conducted by using large-scale permeability apparatus built in the laboratory. Sandy clay was used as the fouling material and the gradation of ballast currently adopted in Sri Lanka was used. Void contamination index (VCI) was selected to indicate the fouling level and the permeability of ballast was measured at different VCI values. A numerical analysis was carried out to simulate two-dimensional flow under actual track geometry in quantifying the drainage capacity of ballast in different degrees of fouling. By using constant head permeability test results as inputs, drainage capacities at different cases were obtained from the numerical analysis and classified according to the drainage capacity criteria. Based on the research outcomes, a relationship between the hydraulic conductivity of ballast and the VCI% was obtained. Also, the critical fouling levels in different layers of ballast were identified to commence the ballast cleaning work at the rail track site.

   6. A Laboratory Investigation on the Advancement of Railway Ballast Behavior Using Artificial Inclusions

      S. Venuja, S. K. Navaratnarajah, T. H. V. P. Wickramasinghe, D. S. A. Wanigasekara

      Abstract

      Ballasted rail tracks are the most popular and conventional rail track foundation system primarily consists of ballast as a major portion by weight and volume. Ballast is a highly angular, coarser material with high bearing capacity, shear strength, and non-water absorbent, which is obtained by crushing rocks. The ballast layer absorbs and widely distributes the moving train loads from sleepers to the ground. With time, the ballast is deteriorated because of frequent cyclic and impact loads from train movements, which ended up with high-cost maintenance. Artificial inclusions are renowned remedial action to the above-mentioned issue. In this laboratory-based study, the effect of rubber pads and geogrids on the shear and deterioration behavior of ballast was evaluated by conducting large-scale direct shear tests under 30, 60, and 90 kPa normal loads with a shearing rate of 4 mm/min. Based on the experimental results, a combination of shock mats and geogrid is suggested which enhanced the stress, dilation, and deterioration behavior of railway ballast.

   7. Numerical Modeling of the Effect of Fine Materials on Shear Behavior of Fouled Railway Ballast

      R. M. D. L. Rathnayake, S. K. Navaratnarajah, M. Daxsan, H. K. K. A. Jayasekara

      Abstract

      Railway network has become the most economical and widely used transportation mode in many countries. This is mainly due to the frequent congestion of major highways which is caused by rapid urbanization. With this increasing demand for railway transportation, the need for heavier and faster trains too has increased. Introducing high-speed trains with heavy axel loads creates high stresses in the track layers and causes excessive settlement and degradation. Therefore, special attention must be given in understanding the behavior of track layers due to vibrations under dynamic loading. The ballast layer plays a crucial part in transmitting and distributing the wheel load from sleepers to the underlying sub-ballast and subgrade. Ballast becomes degraded and fouled by the progressive accumulation of fines between ballast voids due to repeated train loading and various external factors. This phenomenon leads to a change in ballast behavior such as shear and dilation. This study concentrates on analyzing the effect of fine material on the shear behavior of railway ballast material. To achieve this goal a 3D finite element model of ballast during large-scale direct shear test is developed using ABAQUS software. The model is calibrated and validated using data obtained during a previous study. A parametric study is carried on the shear behavior of ballast by varying normal stress and the percentage of fines. This model is then used to predict the effect of fine materials on the shear behavior of ballast.

   8. Potential of Waste Rice Husk Ash to Reduce Propagation of Ground Vibration from Impact Piling: Characteristics of In-Filled Trenches

      G. H. M. J. Subashi De Silva, S. Thoradeniya, K. M. G. C. J. Thilakasiri

      Abstract

      Impact pilling inevitably generates seismic disturbance to the surroundings that can cause discomfort to occupants in nearby buildings, disturbance to the activities undertaken in the buildings, and possible damage to nearby structures. To reduce the disturbances to occupants and damages to structures, the propagation of the impact pilling induced ground vibration needs to be assessed and controlled. The objectives of this study are to investigate the characteristics of ground vibration induced by impact piling, and assess impact pile induced vibration based on the available standards and evaluate the effectiveness of trench characteristics (i.e., shape of the trench, multiple trenches, infilled trenches) in reducing the propagation of ground vibration. The ground vibrations were measured by using a four-channel seismograph and a six-channel seismograph. The measured ground vibrations induced by the impact piling were compared with local and international standards. A damping layer was introduced by using six different types of trenches: Rectangular open single trench, rectangular open double trench, trapezoidal open single trench, trapezoidal open double trench, a single trench filled with RHA, and a double trench filled with rice husk ash (RHA). It was found that the magnitude and frequency of ground vibration induced by impact piling in hard soil was greater than that of soft soil. When the excavations were carried out in hard soil the magnitude of ground vibration exceeded the permissible values recommended in local and international standards, implying a necessity of having a method to reduce the propagation of ground vibration to far-field. It was found that rectangular open double trench reduced ground vibration by 82.9% in the transverse direction and 78.8% in the vertical direction. Double trench filled with waste rice husk ash reduced ground vibration by 76.3% in a longitudinal direction. This study concludes that in-filled trenches with waste RHA, an agricultural by-product, has the potential to reduce the propagation of ground vibration induced by impact pilling.

   9. Investigation of Colloidal Transport in Saturated Porous Media: Experimental and Numerical Study

      B. G. C. Bombuwala, A. M. E. Karunarathna, B. Banithy, T. K. K. Chamindu Deepagoda

      Abstract

      Field and laboratory scale observations conducted during last few decades provided ample evidences to prove colloid-facilitated transport of numerous contaminants in porous media including radionuclides, hydrophobic organic compounds (HOCs), heavy metals, pesticides, pathogens, etc. Therefore, it is vital to investigate colloid and colloid-facilitated contaminant transport in porous media and the soil physico-chemical parameters controlling their subsurface fate and transport processes. This study mainly focused on investigating the effect of flow rate (as a physical perturbation) and ionic strength (as a chemical perturbation) on mobilization and transport colloids in saturated porous media. A series of controlled-laboratory column experiments were conducted using a selected sand as the porous medium and colloids with the Stokes’ diameter <1 μm extracted from an agricultural soil. The ionic strength was controlled by changing the NaCl concentration in the influent colloidal solution while the flow rate changed by varying the hydraulic head of the column. The turbidity of the effluent solution was measured to estimate the colloid concentration and a series of breakthrough curves were obtained for different combinations of ionic strength and flow rates. The experimental results were numerically characterized based the advection–diffusion/dispersion modelling framework coupled with attachment, detachment and straining parameters which were inversely estimated using the HYDRUS 1D software. Estimated attachment coefficients of soil colloids were significantly higher in low flow rates and higher in high ionic strength. Also, the results of numerical analysis identified attachment as the key retention mechanism in saturated porous sand in an ionic solution.

   10. Utilization of Bottom Ash for Clay Mine Rehabilitation

       S. Suloshini, A. S. Ranathunga, S. A. S. Kulathilaka, W. B. Gunawardana, M. M. S. T. M. Mapa

       Abstract

       At the end of mining activities, clay mines were abandoned due to the cost and non-availability of filling materials. These abandoned clay mines cause adverse environmental and social impacts. In addition, large quantities of bottom ash (BA) are generated as a by-product of coal combustion process. This BA is disposed by open dumping in the lands, which creates severe environmental pollution. Therefore, conducted research on utilization of BA for mine rehabilitation is beneficial. The main focus of this research is applicability of BA generated from Lakvijaya power plant, Sri Lanka as a potential backfill material and a soil amendment during the clay mine rehabilitation. Initially tests were conducted to investigate the basic properties of BA. Next, chemical composition of BA was analysed to select the suitable crops for vegetation. Further pH, electrical conductivity and water holding capacity were checked and micro structural morphology of BA was determined through Scanning Electron Microscope. The results showed that BA has good engineering properties and the potential to improve agronomic characteristics of soil. It has better water holding capacity and permeability. BA can adjust soil pH to a desirable plant growth range. As BA has a very porous structure, the root system can easily develop and helps to uptake nutrients by the plant. However, a considerable percentage of trace metals is accumulated in BA which will increase the bioavailability of some trace metals to levels that poses risk to human. Thus, investigations were carried out to identify the heavy metal concentration in leachate of BA using column leaching test. Results showed that leachability potential of trace metals in BA does not exceed the allowable limits.