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 - Thesis"

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    item: Thesis-Abstract
    Behaviour of Sri Lankan peaty soils under surcharging and vacuum loading
    Thavakumar, T; Thilakasiri, HS
    The composition of natural deposits of peaty soil may vary considerably among different sites, as do their engineering properties. Peaty soils have distinctive properties of low shear strength, high compressibility, high secondary compressibility and high initial permeability. This results excessive settlements and may continue for a long period of time due to the dominant creep behaviour. In addition, low shear strength often causes stability problems in peat soils when they are subjected to external loading. This criterion makes construction highway embankments over very soft highly compressible peat layers difficult. Therefore, in order to prevent differential settlements and subsequent potential failures, it is necessary to improve the strength and the stiffness properties of natural peat deposits using appropriate ground-improvement techniques. In this process, it is important to understand and to quantify the consolidation behaviour of peaty soils when employing ground improvement techniques and to predict the short term and long term settlements. Since the consolidation behaviour of the peat may be region-specific, it important to study the index properties and engineering properties of peaty soils. The present research study focuses on the engineering properties and index properties of peaty soils found in Southern Transport Development Project. The first objective of this study is to establish empirical correlations between some important properties such as Ce vs moisture content, C, vs eOt Ca vs Ce, C, vs Ce, C, vs organic matter content and ea vs organic matter content for STDP soils. Thereby update the empirical relationships for Sri Lankan peaty soils developed by Karunawardena (2000) using Southern Transport Development Project peaty soils empirical relationships. Second phase of this research study is to concentrate on consolidation behaviour of peat under surcharges. It is important to identify and separate the components of settlement mainly immediate settlement, primary settlement and secondary settlement. For this purpose graphical methods can be used. The objective of this study is to analyse the applicability of these graphical methods for Sri Lankan peaty soils and thereby predicting the degree of consolidation & hydraulic parameters of peaty soils from field monitoring data obtainedfrom surface settlement plates, subsurface settlement plates, and piezometers. Preloading can be used to improve the engineering properties of the peaty soils due to their high initial permeability. Successfulness of the pre loading depends on the stability of the embankment. This can be achieved by proper control of the pore pressure under embankment and the lateral displacement of foundation soil at the toe of the embankment. Third and final objective of this research study is to study about prediction and control the pore pressure under embankment and the lateral displacement of foundation soil at the toe of the embankment. Vacuum preloading method was applied first time in Sri Lanka at Southern Transport Development Project. The present study focuses on effectiveness of the vacuum pressure in controlling the pore pressures and the lateral displacements during the construction period.
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    item: Thesis-Abstract
    Capacity estimation of piles using dynamic methods
    Jayaweera, MSR; Thilakasiri, HS; Puswewala, UGA
    The foundation is the most important part of any type of structure. Pile foundations are used to transfer very high loads from supper structure to the ground. Therefore, design and construction of piles must be carried out with a high confidence. Engineers are using various methods and equations for testing pile foundations and those methods are improving when new technologies come. Most reliable way of testing of pile is to have a full scale maintain load test on that pile. But this is become critical when large piles encountered. Therefore, application of High Strain Dynamic Test (HSDT) is getting popular. The use of pile foundations is increased and new driving techniques, as well as new sophisticated stress wave measurement equipments have led researchers to look for better understanding of dynamic and static behavior of the hammer-pile-soil system and to develop more reliable methods of pile analysis. The reliability of pile dynamic test is mainly dependent on the accuracy ofthe dynamic soil parameters used in the data analysis. The scope of this study is to find reliable driving equations for different situations by comparing the capacities taken from driving equations and HSDT measurements. Some piles were subject to both HSDT and Static load test to increase the reliability of readings.
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    item: Thesis-Abstract
    Extrapolation of plate load test results to foundations on sand
    Priyantha, S.M.
    Estimation of the settlement of shallow foundations in sand is generally carried out using the settlement estimation equations, empirical correlations based on insitu tests or by extrapolation of plate load test results. Plate load test is a common field test used to estimate allowable bearing capacity, expected settlement and/or the modulus of subgrade reaction of soil. The results obtained from a plate load test are extrapolated to prototype foundation using different extrapolation methods with unknown accuracy levels. There is no standard way to extrapolate the plate load test results and Terzaghi and Peck method is very widely used for most engineering applications. In most practical cases, layered soil mediums are present below foundations. In such situations the effective zone of test plate lies within the top layer whereas that of the prototype foundations is spread to the underlying layers. The behaviour of the plate is based on the properties of the top most layers while the stiffness of the layers below may affect the behaviour of the prototype foundation. In such situations, the reliability of the extrapolation techniques becomes highly questionable. Due to the uncertainties associated with the estimation of the settlement of shallow foundations in sand, this research is aimed at investigation of the settlement estimation methods of shallow foundations in sand using the finite element method. , A special attention is paid to investigate the reliability of the extrapolation of plate load test results. The scope of the study: 1. To investigate the ·reliability of settlement estimation methods in relation to the finite element method. 2. To study the effect of foundation width, foundation depth, elastic parameters (E, 0) and plastic parameters (c, ~) of homogeneous soil on the estimated settlement of shallow foundations. 3. Investigation ofthe accuracy of the extrapolation of the plate load test results in homogeneous and layered soil mediums, compared to the same estimated from the finite element method. 4. To develop a reliable method to estimate the settlement of a foundation .on layered soil using plate load test results.