Master of Engineering in Foundation Engineering & Earth Retaining Systems

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Browsing Master of Engineering in Foundation Engineering & Earth Retaining Systems by Author "De Silva, LIN"

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    item: Thesis-Full-text
    Estimation of the stability of embankment slopes using field monitoring data
    Nawarathna, THK; De Silva, LIN
    In Sri Lanka lands underlain by soft, weak and problematic soil are being use for various constructions due to rapid development and the lack of suitable lands. Construction of an embankment over soft soil is challenging due to its low shear strength and high compressibility nature. As a result of that embankment can be subjected to a shear failure or excessive settlement. Assessment of the stability of the embankment is vital to ensure a safe embankment and stability can be evaluated by using available analytical methods or field monitoring data. Use of field monitoring data to evaluate the stability is easy and more practicable. In Sri Lanka Matsuo chart which is based on the field monitoring data was used for the prediction of stability of the embankments in the Colombo Katuanayaka highway project. However applicability of Matsuo chart for various embankment conditions is still questionable. This study was carried out to investigate the applicability of Matsuo chart for various embankment conditions using advanced numerical tools. Two test embankments published in the literature and three embankments, which belong to the Colombo - Katunayaka expressway were analyzed by using Finite Element Method, Limit Equilibrium Method and Matsuo chart and compared with the field data. Further, the effect of embankment width, height and the subsoil parameters on the prediction of stability using Matsuo method was investigated. Research finding verify that the Finite Element Method, Limit Equilibrium Method and Matsuo chart can predict the stability of the embankment accurately and Finite Element Method can be used to predict the deformation characteristics. Stability of the embankment is directly proportional to the un-drained shear strength of the sub soil and Factor of Safety values decrease with the increase of the embankment height. However it was found that the embankment width has little influence on the factor of safety.
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    item: Thesis-Abstract
    Evaluation of shansep parameters for Sri Lankan cohesive soils
    (2021) Senewimala EH; Thilakasiri HS; Nawagamuwa UP; De Silva, LIN
    This thesis contains a study on SHANSEP parameters, evaluated for Sri Lankan cohesive soils. In Sri Lanka, various correlations are used for the evaluation of shear strength parameters and the settlement. Most of such correlations are developed in overseas countries, which may not accurately model the behavior of Sri Lankan soils as they are developed from other geological conditions. Though the undrained shear strength is a function of both stress history and stress path, most of the time, they are not considered, which may lead to large errors. The SHANSEP model proposed by Prof. Charles C. Ladd, shows the normalize behavior of the cohesive soils which consider both stress path and stress history in determination of the Undrained Shear Strength of Soils. Therefore, this research is an effort to see the applicability of SHANSEP model for Sri Lankan cohesive soils, using the test data provided by major projects in Sri Lanka. Since CK0U Triaxial testing facilities are not available in Sri Lanka, data from field vane shear test have been used for the estimation of Undrained Shear Strength in this study. Finally, a SHANSEP equation has been proposed in this thesis for selected alluvial clay soils along with two more conservative equations for the estimation of undrained shear strength and over consolidation ratio respectively.
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    item: Thesis-Abstract
    Liquefaction potential in Sri Lanka-preparing a liquefaction hazard map using geotechnical investigation data
    (2014-10-31) Kumarasiri, HC; De Silva, LIN; Abayakoon, SBS
    Soil Liquefaction is a process, where granular soils below the ground water table temporarily lose its strength due to cyclic loading created by an earthquake. Liquefied soil behaves as a viscous fluid rather than a solid. During liquefaction, porewater pressure is suddenly increased, forcing the soil particles to suspend in water. As a result, the buildings, utility services, natural substances and other structures are collapsed causing severe damage to the people and the nature. In some cases, the destruction due to liquefaction is not repairable. Therefore, the mitigation measures are essential to prepare for liquefaction. In Sri Lanka, it is rare to find the historical data of liquefaction or related incidents. Recent studies demonstrated that there is a potential for liquefaction in some places of the island. It could be evaluated by using the basic geotechnical investigation data, according to the simplified procedure proposed by Seed and Idriss (1971). This study is intended to prepare a liquefaction hazard map for Sri Lanka by identifying the hazard zones, using an extensive geotechnical investigation data base. As per the analysis 218 locations were identified as susceptible for liquefaction during an earthquake of magnitude 6.0 out of 3282 locations analyzed. Further, the research has given a special attention to the variation of ground water table and the maximum possible ground acceleration.
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    item: Thesis-Abstract
    A study on ground vibration due to rock blasting at metal quarry: a case study
    (2014-11-01) Madanayaka, TA; De Silva, LIN
    A Study on Ground Vibration Due to Rock Blasting at Metal Quarry Ground vibration, air blast and fly-rock are unavoidable environmental impacts of rock blasting. Despite these, blasting is the widely accepted method of rock breaking in quarrying industry because of cost effectiveness, higher efficiency, convenience and ability to break hard rock. Among the environmental impacts, ground vibration is the most critical since it can cause damages to nearby structures. This study was carried out to compare vertical and horizontal bench blast(s) at a granitic gneiss rock quarry located in Colombo, Sri Lanka and predict the resulting peak particle velocities of ground vibration levels. To achieve these objectives, particle velocities and frequencies of 38 and 35 blasts respectively were measured in three perpendicular directions for horizontal and vertical bench blast(s) with the use of Instantel Blastmate II seismographs. In the blast(s), Ammonium Nitrate (ANFO)(blasting agent) primed by a Gelatin Dynamite primer were electrically initiated. Scaled distance parameters (Maximum charge weight per delay and distance between blasting points to monitoring location) were also recorded. The extensively used equation for seismic law of propagation, proposed by Devine (1962) and Devine and Duvall (1963), was used for the prediction of peak particle velocities. Points were plotted with Peak Particle Velocity (PPV) in Y- axis against Scaled Distance (D/Q0.5) in X- axis. Regression analysis was performed to define the line of best fit. At the end of statistical analysis, an empirical relationship with good correlation was established for prediction of peak particle velocity. Frequency analysis was also done for dominant frequency and zero crossing frequency to identify the effect of frequency of ground vibration to structural damages and identifying the most suitable type of frequency analysis to define the single frequency value for ground vibration. The established relationship, frequency analysis and result obtained are presented.
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    A Study on most suitable slurry cutoff wall material to mitigate seepage in vendrasan dam, Trincomalee
    Wijayawardhana, HMJT; De Silva, LIN
    Earthen dams are constructed to store water for the purposes of human consumption, food production, electricity production, industrial use and flood protection. Failure of Earthen dams may be due to hydraulic failure, structural failure or seepage failure. Hydraulic failure may be due to overtopping, erosion of the upstream/downstream surface/toe and piping. Structural failures can occur in either the embankment or the appurtenances. Failure of a spillway, lake drain, or other appurtenance may lead to failure of the embankment. Cracking, settlement, and slides are the more common signs of structural failure of embankments. Seepage Failure occurs due to the uncontrolled seepage in both velocity and quantity. Water permeating slowly through the dam and progressively erode the soil in the embankment or the foundation toward the reservoir. Eventually with increased seepage flow rate the direct connection is made to the reservoir causing the piping. Piping may occur through the dam or the foundation causing dam failure. Seepage problems in large dams should be addressed in proper way on time to prevent before it becomes a massive disaster. Field investigation and data evaluation reveal the type of seepage and its extent. Then the most appropriate remedial measures can be adopted. Construction of toe filter, toe drain, downstream seepage berm, conducting cement/clay grouting and Cutoff walls construction are more frequently practiced to prevent seepage through and beneath the dam. Cutoff walls make the seepage paths longer, decrease the exit gradient at the toe and reduce the seepage quantities. Compacted impervious trench cutoffs, concrete cutoff walls, sheet piles, slurry trenches/cutoff walls are some different types of cutoff walls currently being utilized.
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    Study on the effect of dredging on existing sheet pile retaining structures
    Senarathne, DEN; De Silva, LIN
    Sheet pile retaining structures are widely used in many purposes in engineering designs. Most common applications are shoring, stabilize excavations, harbor quay wall structures, canal bank protection structures.. etc. This research is mainly focused on the issue of stability of harbor quay wall structure when deepening the harbor basin to cater larger vessels. Most of the quay wall structures in Srilanka are anchored sheet pile walls. So the effect of dredging on the sheet pile structure is studied. If the same method can be applied for the cantilever sheet pile walls which could be used in drainage improving projects. The study is extended to both anchored and cantilever sheet pile structures to increase the stability while reducing the depth of embedment. Another improvement sheet pile wall is proposed from the passive side of the existing sheet pile structure to provide an additional support to the main structure. The finite element analysis is used to estimate the effect of the improvement wall on the stability and the deflection of the wall in cohesion less soils. The effect of the distance between the existing structure and the improvement wall and the effect of increasing the depth of embedment of the improvement structure are analyzed through the finite element models. The models are tested for 22 to 38 degrees wide range of friction angles of cohesion less soils The results of the finite element model are verified by a physical model conducted in a laboratory. The results of the analysis shows that the improvement wall can significantly increase the stability of the existing structure. Compared to anchored sheet pile walls higher improvement can be achieved for cantilever sheet pile walls from this method. Rather than replacing the entire structure , applying a this sort of improvement method will be highly economical as well as less damages to the other structures close to the existing sheet pile wall.