Browsing by Author "Ibrahim, Mwajuma"

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    Correlation between soil penetrometers test data for analysis and design of foundations under local conditions in Tanzania
    (University of Dar es Salaam., 2010) Ibrahim, Mwajuma
    Both the Standard Penetration Test (SPT) and the Dynamic Cone Penetration Test (DCPT) have been carried out in Tanzania for many years. Data obtained from these tests are used for analysis and design of foundations. While SPT is popular, it involves drilling thereby samples can be recovered for further laboratory testing. The DCPT has the advantage of being less expensive and less time consuming. Besides the advantages, SPT test results are sensitive to test details and procedures and DCPT is not universally standardized. Inspite of the fact that the aforementioned disadvantages are known, consulting firms in Tanzania still design foundations using SPT correlations that are not adjusted to suit the local soil conditions, equipment and test procedure. This research is concerned with formulation of relationship between the penetrometers test data under local Tanzanian practices and soil types. Data from five geotechnical investigation projects performed by experienced consultants were used to formulate correlations where a total of 40 boreholes and 37 DCP tests were involved. Following the analysis, it was observed that SPT values can be correlated with DCPT values, soil bearing resistance and also with vertical overburden stress. Correlations developed in this study are suitable to the specific soil types and equipment used. There is therefore a need of formulating a universal relationship that takes into account the many factors that can influence the penetrometers data and also the relationship that can be useful for any soil type.
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    Geotechnical uncertainties: quantification and consequences in predicting settlement of shallow foundations on sandy soils
    (University of Dar es Salaam, 2016) Ibrahim, Mwajuma
    Geotechnical designs will always be accompanied by uncertainties in form of soilΒ΄s inherent variability, measurement errors and transformation uncertainties. The effects of uncertainties has been traditionally be dealt with by application of experience based factors of safety to virtually reduce the capacity or magnify the applied load for a given design case. Reliability Based Design (RBD) is a relatively new design approach which rationally deals with uncertainties by quantifying and incorporating them to the design process. Due to its relative newness and perceived complexity, to date, RBD is not used in routine geotechnical designs. However, geotechnical practitioners can still benefit from RBD concepts by understanding the effects of different magnitudes of uncertainties in relation to soil testing methods and design models. This research focuses on that aspect of RBD. Geotechnical investigations were performed at different locations in Dar es Salaam and Coastal region using three common in-situ methods and laboratory testing. The data were used to quantify uncertainties using random field theory. Relationships were developed between data from the different investigation methods and respective transformation uncertainties were determined. A range of uncertainties in the form of coefficient of variation (𝐢𝑂𝑉) was applied to determine the consequences in terms of serviceability limit state probabilities of failure (𝑝𝑓) for shallow footings. The results indicate that at a desired limiting settlement, a unique relationship exist between 𝐢𝑂𝑉 and 𝑝𝑓 for each specific settlement prediction model. It is recommended that practitioners should take advantage of RBD concepts by establishing such relationships for different design models and use them as decision making tools.