Master of Engineering in Foundation Engineering & Earth Retaining Systems

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Browsing Master of Engineering in Foundation Engineering & Earth Retaining Systems by Subject "CIVIL ENGINEERING-Dissertations"

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    item: Thesis-Full-text
    Application of dynamic and vibro compaction methods for densification of granular fill in reclaimed land in Sri Lanka
    (2019) Samarasinghe AI; De Silva LIN
    In the recent past, Government of Sri Lanka executed a large-scale reclamation project in Sri Lanka to add a brand-new land of 267-hectare to the Capital, Colombo with strategy of converting Colombo as a commercial hub of South Asia. For this project, 72 Million m3 of sea sand which was dredged by Trailing Suction Hopper Dredgers at 10km off from shore of Colombo was placed mainly by hydraulic methods at lower elevation while applying bulldozers at the top. This reclamation material was noted as clean uniform sand and which was under loose to medium dense condition prior to densification. This sand fill was densified using two methods, namely dynamic compaction and vibro compaction. Dynamic compaction, which is generally considered as one of the most economical sand improving methods, was applied in all areas except vibration sensitive areas at the city end and the areas where deep ground improvement was required for stability of earth retaining structures. Since settlement of subsoil in the seabed is not critical, the considered major geotechnical issues were achieving of required bearing capacity, shear strength and avoiding possible liquefaction. To sort out all geotechnical issues, sand densification was the only solution. Though there is a very long history for dynamic and vibro compaction methods, still reclamation projects are not preplanned to utilize the self-compaction achieves during sand placing very effectively, while designs always follow a very conservative approach. Moreover, designs are carried out using pre-defined energy criterions rather than considering existing fill material properties and its pre-compaction condition. Thus, there was a paramount requirement to assess the dynamic and vibro compaction methods for Sri Lankan fill materials and reclamation methods with the intention of optimization of the above compaction methods. In order to optimize dynamic compaction method, the pre-and post-compaction condition (by CPTs) was evaluated by crater depth, net volume changes, influenced depth and related indices, which assess the degree of improvement based on applied iv energy. Similarly, densification by vibro compaction was evaluated with respect to the factor such as point spacing, amperage and compaction holding time. In addition, effect such as age of the compacted fill was considered for both dynamic and vibro compaction in this reclamation fill of clean sand. Finally, verification of densified ground by selecting CPTs at least compacted points with respect to the compaction grids was assessed for both dynamic and vibro compaction to confirm the optimization has no adverse effect on the final design. Based on the finding of this research, fill material’s index properties of Sri Lankan sea sand were determined while being noted that there is no hesitation for applicability of dynamic and vibro compaction for densification. During the analysis it was suggested to modify some correlations derived based on laboratory test data to achieve more realistic output for actual reclamation condition. In addition, design of dynamic and vibro compaction by performance-based method through trial compaction was discussed.
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    item: Thesis-Full-text
    Comparison between empirical, numerical and practical compression capacity of rock socketed bored and cast in-situ pile : a case study
    (2020) Silva HAM; Puswewala UGA
    The development of tall structures as a rapidly developing trend in Colombo-Sri Lanka is evident during the recent past due to the high land prices. These tall structures require to be founded on strong substrata and piling is the most popular method that has been used as the foundation for these tall buildings. In Colombo area having found bed rock at shallow depth around 15m to 20m, always design engineers tend to specify the rock socketed end bearing piles without much considering the load carrying mechanism of the pile. It is evident that Sri Lankan design engineering community has a tendency to disregard the pile shaft skin friction resistance, mostly due to the existence of bentonite slurry within borehole during concreting. Therefore, load carrying capacity of such piles is determined completely based on the end bearing from the bed rock. In addition to that in most standards and codes of practice, the pile load carrying capacity correlations are given for specific soil types i.e. sand, clay, gravel. However in local context it is hard to find such conditions and almost all the soils are residual soils having both 𝑐,∅ values. In this research, different correlations for pile load capacity and its variations are evaluated. A detail comparison is conducted between the compression capacity of piles obtained from different empirical/semi-empirical methods, numerical methods such as FEM and in-situ testing i.e. MLT and HSDLT against the code of practices and local guide lines.
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    item: Thesis-Abstract
    Development of a large-scale shear apparatus for the determination of shear strength properties of municipal solid waste
    (2020) Jayakody SHS; Kulathilaka SAS
    Landfill slope failure became one of the hot topics in Sri Lanka as the infamous Meethotamulla waste fill collapsed, claiming lives of people and infrastructure. Every year all around Sri Lanka, millions of tons of Municipal Solid Waste (MSW) are produced, and no one can predict the variation and heterogeneity of their composition. Although MSW is a difficult material to test, many comprehensive studies have been conducted to determine the likely ranges of waste properties and hence to take them in the design of landfills. In this study, in-situ direct shear test was performed to assess and develop insights about the shear strength properties of MSW. A large-scale direct shear apparatus was fabricated to conduct in-situ test which has dimensions of 300 mm × 300 mm in plan view. The report contains the steps followed to manufacture the large-scale direct shear device. One of the main objectives was to test the MSW at differently aged locations in abandoned Meethotamulla waste fill site. The testing procedure is comprehensively described in the report. Further, density test, moisture content test and composition analysis were also conducted in this study. As stated by many researchers a peak failure state was not observed during in any of the direct shear tests. There was no significant variation in the shear stress parameters of the differently aged samples. However, all the samples are more than 03 years old. The results obtained from the tests were analyzed and compared with the published data in literature. Recommendations were made regarding the further studies needed to develop a relationship between the differently aged MSW and their shear strength properties.
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    item: Thesis-Full-text
    Enhancement of the stability at the site of an ancient landslide in a road cutting with drainage and reinforcement - case history at Ginigathhena
    (2019) Lakruwan SOADM; Kulathilaka SAS
    Engineers involved in infrastructure development projects in the hilly terrain of Sri Lanka encounter ancient landslides which could be triggered by rainfall or construction activities. One such landslide was encountered during the widening of a bridge in the main connecting road between central hill country and capital; Avissavella – Hatton – Nuwaraeliya road at bridge no. 48/2 near Ginigathhena. Extensive mitigation measures had to be designed with detailed attention to construction sequence in order to prevent reactivation of the slide. A valley area had been formed by the previous landslide. Morphology of the area is a sloping land with undulating topography towards upper slope. This has led to the formation of a waterlogged marshy area on a flat land at immediate upper slope and a stream flowing through valley. Water table of the area is quite high. The landslide got activated due to a minor excavation at the toe region for the bridge widening. There had been no rain when the slide was activated. Subsequent rain cause further activation of the landslide. Further widening is necessary according to the new highway design. Ground water regime management and geometry modification are the two primary approaches used in enhancing the safety margins of the site. Surface and subsurface drainage improvement by various methods such as; cutoff drains, berm drains, trench drains and horizontal drains were introduced for lowering the ground water table. The stability of the steep cuts necessary to accommodate the increased road width was enhanced further by the use of soil nailing. Top down approach was adopted to ensure the safety of the slope during construction. Drainage measures were very effective in economizing the soil nailing design. The analysis and design of stabilizing measures were done using GeoStudio Seep/W and Slope/W software. Design outcomes were confirmed by monitoring of ground water table and surface movements of the slope.
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    item: Thesis-Full-text
    Investigation on the equivalent modulus of sub grade reaction of layered soil
    (2019) Mathuwanthy T; Thilakasiri S
    ‘Modulus of subgrade reaction’ is the ratio between the pressure applied on the soil and the corresponding settlement. There is no theoretical relationship found to obtain equivalent subgrade modulus of layered soil. Top dense sand layer thickness, bottom loose sand layer thickness, strip footing width and thickness are changed and equivalent modulus of subgrade reactions are obtained by equivalent spring theory and weighted average method. These, equivalent subgrade modulus are separately applied in Heteryni method equations in order find vertical settlement, bending moment and shearing force along the medium length footings. PLAXIS 3D numerical models are developed for same footing parameters and soil properties to compare the Heteryni method outputs. Equivalent subgrade modulus using equivalent spring method is constant with top soil layer thickness for a given footing width and footing depth. Weighted average method equivalent subgrade module is non linearly increasing with top dense sand layer thickness for a given footing and bottom loose sand layer thickness. Equivalent subgrade module for thinner footing depth is always greater than the thicker footing for a given footing width and soil profile in both spring theory and weighted average method. Settlement along footing obtained by equivalent spring method equivalent subgrade modulus applied in Heteryni method equation is highly varying from weighted average method equivalent subgrade module applied in Heteryni method equation and PLAXIS 3D model settlement output. Equivalent spring method is considered as unsuitable to calculate the equivalent modulus of subgrade reaction for layered soil stratum. Settlement difference between PLAXIS 3D method and weighted average method equivalent subgrade module applied in Heteryni method equation shows up to 45 percentages and this difference cannot be negligible. This study will shed a light in the theoretical relationship of equivalent subgrade module research field as this would be the first attempt to check the behavior and suitability of equivalent subgrade modulus of layered soil stratum.
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    item: Thesis-Full-text
    Investigation on the equivalent modulus of subgrade reaction of layered soil
    (2019) Mathuwanthy T; Thilakasiri S; De Silva LIN
    ‘Modulus of subgrade reaction’ is the ratio between the pressure applied on the soil and the corresponding settlement. There is no theoretical relationship found to obtain equivalent subgrade modulus of layered soil. Top dense sand layer thickness, bottom loose sand layer thickness, strip footing width and thickness are changed and equivalent modulus of subgrade reactions are obtained by equivalent spring theory and weighted average method. These, equivalent subgrade modulus are separately applied in Heteryni method equations in order find vertical settlement, bending moment and shearing force along the medium length footings. PLAXIS 3D numerical models are developed for same footing parameters and soil properties to compare the Heteryni method outputs. Equivalent subgrade modulus using equivalent spring method is constant with top soil layer thickness for a given footing width and footing depth. Weighted average method equivalent subgrade module is non linearly increasing with top dense sand layer thickness for a given footing and bottom loose sand layer thickness. Equivalent subgrade module for thinner footing depth is always greater than the thicker footing for a given footing width and soil profile in both spring theory and weighted average method. Settlement along footing obtained by equivalent spring method equivalent subgrade modulus applied in Heteryni method equation is highly varying from weighted average method equivalent subgrade module applied in Heteryni method equation and PLAXIS 3D model settlement output. Equivalent spring method is considered as unsuitable to calculate the equivalent modulus of subgrade reaction for layered soil stratum. Settlement difference between PLAXIS 3D method and weighted average method equivalent subgrade module applied in Heteryni method equation shows up to 45 percentages and this difference cannot be negligible. This study will shed a light in the theoretical relationship of equivalent subgrade module research field as this would be the first attempt to check the behavior and suitability of equivalent subgrade modulus of layered soil stratum.
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    item: Thesis-Full-text
    Low strain pile integrity testing for rock socketed bored piles in Sri Lanka
    (2020) Kodithuwakku TH; Tilakasiri HS; De Silva LIN
    Low strain pile integrity testing has been available over several decades. It is the widely used method of pile testing to detect serious defects in piles. The transient dynamic response (TDR) method of low strain pile integrity testing needs pile top velocity and pile top force generated by a small handheld hammer hit. The velocity and force details are useful to estimate the pile condition near the top and the stiffness of pile-soil system Researchers have proposed that dynamic stiffness at low frequencies associates to the static stiffness of pile head. The linear region of load-settlement behaviour of a pile is described by the static stiffness. However, little attention has been paid to developing a relationship between static stiffness and dynamic stiffness. The carrying capacity of pile is considered as the most important issue in pile foundations. Load Testing is the most reliable approach to evaluate the carrying capacity of piles. However, load tests are rarely performed as it is costly, labour intensive and time dependent, but all the piles are subjected to low strain integrity tests. Following the testing results, this research proposes a relationship between dynamic stiffness and static stiffness of bored piles. It is intended to evaluate the allowable carrying capacity of piles with results of low strain pile integrity testing and high strength dynamic load testing. Finally, this research presents a simple methodology to estimate the allowable carrying capacity of piles using instrumented low strain pile integrity testing. The developed methodology will be verified using field load testing results. In addition to that, the success of implementing the TDR method on bored piles is proved by case studies.
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    item: Thesis-Full-text
    Systematic approach to integrated mine bench optimization in soil and rock of Sri Lankan open pit mines - a case study
    (2020) De Mel WDM; Puswewala UGA
    Instabilities and failures in rock slopes occur due to numerous factors such as unfavorable slope geometries, geological discontinuities, weak or weathered materials in the slopes, existing weather conditions and environmentally induced external factors such as heavy precipitation, seismic activities and groundwater. Bench optimization is carried out to maintain bench height and dip of the slope within an allowable factor of safety, thus avoiding rock slope failures and instabilities. Therefore, optimum determination of these geometrical features has become a most significant part of soil and rock slope stability analysis in Open Pit Mining where multiple benches of excavation are maintained. Field work related to this research study primarily comprised of observation of structural geological features (dip and strike) and other measurements and observations ( joint spacing, separation, condition of joint) required for analysis work, including Slope Mass Rating analysis, at the selected site of Halbarawa, Sri Lanka. Furthermore, soil and rock samples were collected from the selected site to perform laboratory tests. Proctor compaction test and direct shear test were carried out for selected samples to evaluate the overburden slope stability. Simultaneously, stability of soil and highly weathered rock slope was analyzed by SLOPE W software. In order to analyze rock slopes, initially possible rock failure modes were identified using Georient software. If it indicated some tendency to fail, a detailed analysis of wedge failure was carried out using GEO5 software. Further, Toppling and Planer modes of failure were analyzed via SMR analysis. The study focused on optimizing the bench geometry of mine slopes necessarily consisting soil, highly weathered rock and fractured rock in order to explore ways for safe and economical bench designing. This was achieved by integrating kinematic, empirical and limit equilibrium approaches for slope stability investigation and guidelines were finally developed so that the same methodology can be universally applied for assessing the soil and rock slope stability in similar situations. This procedure was developed through the case study of Halbarawa Mine. Results indicated that the stability is more sensitive to variation in cohesion than variation in friction angle of overburden profile. As far as the bench geometry is considered, multiple benches are seen as the most reliable mining methods for steeply dipping benches. According to RQD of each location, the rocks in the particular area varied from moderately hard rocks to hard rock. The Kinematic analysis disclosed that most of joint planes intersect with each other and produce various potential failure mechanisms. The dip and the dip direction of the slope faces determine the possibility of failure and the mode of failure with respect to the discontinuity plane. For the Halbarawa site, as per the SMR analysis, face 1, 2 and 3 can be categorized into completely unstable (V), partially stable (III) and unstable (IV) rock stability classes respectively. It was also understood that surcharge load is a more critical factor than the static water pressure when a wedge failure is considered. The most successful, economical and rapid remedial measures to enhance the stability of rock slope are reduction of bench height and reduction of bench angle.