Determination of Soil Plasticity Developing Manafi Method and Apparatus

Abstract

Soil plasticity is one of the essential index properties required for classifying soils in geotechnical engineering practice. Determination of plasticity properties of soils is also critical for correlation with their engineering properties such as shear strength, permeability, and compressibility. However, present standard test methods for soil plasticity suffer, to different extents, from operator-dependency and inconsistency. This research aims to further develop and establish a recently introduced determination method, named the Manafi Method and Apparatus in the author's MPhil project, and obtain more precise and accurate soil plasticity determinations than from the current standard methods. This thesis by publication document presents the research outcomes. The document comprises six chapters. Except Chapters 1 and 6, Chapters 2 to 4 were written in the format of research articles. These articles have been published, accepted for publication, or submitted to journals for possible publications by the time of thesis lodgement. The Introduction chapter presents the aims and objectives of the research project and outlines the thesis structure. Chapter 2, entitled “A New Approach to Soil Consistency Determination”, presents research outcomes related to theory and implementation of the new testing approach. The contents reviewed and discussed the conventional quantitative methodology for soil consistency determination using standard tests. It also proposed a novel combined qualitative and quantitative research methodology for a behavioural study on soil consistency determination. A new parameter, called ‘workability’, was introduced and formulated for quantifying soil consistency. This study lays the theoretical basis for developing the novel methodology and proposed solutions to issues related to standard tests. Chapter 3, entitled “Utilisation of Extrusion Method in Geotechnical Tests: Conception and Theoretical Analysis”, evaluates the capability of the extrusion method for soil property determinations and proposes the development of a closed-form solution for the determination of extrusion pressure using this technique. This study presents the theoretical basis underpinning the extrusion process by extending the conventional slab analysis method to the modelling of soil extruding. In addition, the described extrusion mechanics explained reasons for some discrepancies observed in various geotechnical parameters due to the different soil deformation mechanisms among the test methods. Chapter 4 presents the third paper, entitled “Determining Soil Plasticity Utilising Manafi Method and Apparatus”. This paper demonstrates the utilisation of the new combined qualitative and quantitative approach for soil property determinations, namely the Manafi Method and Apparatus. The proposed technique is instrumented with a new soil extrusion device to quantify the workability of soils and is calibrated to translate the workability to their liquid and plastic limits. The method is applied to seven soil samples of varying particle sizes and plasticity to determine the liquid and plastic limits, and the results are compared with those obtained by conventional methods. The outcomes suggest that the new technique provides a more precise and reliable means of soil plasticity determination in the tested samples. Chapter 5 is the fourth paper, entitled “Effect of Particle Size on Soil Plasticity and Soil Classification”. Although the full range of particle sizes affects soil consistency, the conventional test methods and apparatuses only study the unrepresentative sub-samples containing medium sand particles of less than 425 microns. However, the novel Manafi Method and Apparatus can enhance the consistency determination method by exploring a more comprehensive range of soils containing coarser particles. Therefore, several soil samples containing various portions of coarse grains are studied. The results show that the coarse grains significantly affect soil plasticity and classification. As a result, a revision to the Unified Soil Classification System is proposed. Chapter 6, “Conclusions and Recommendations”, summarises the research results, discusses the limitations of the study, and recommends future investigations pertinent to soil plasticity determination. The articles presented in the thesis were prepared in collaboration with two more international experts in the research field, Professor Mark B. Jaksa and Professor Nagaraj HB, forming a high standard authorship team. In addition, the research seeks to demonstrate a well-defined paradigm in favour of using the proposed method in broader soil property determinations.