Effect of Changing Plastic Work on Macroscopic Properties

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Introduction'Support fluids' are commonly used for the construction of piles and diaphragm walls to prevent instability and collapse of soil layers into the excavation or to prevent water from permeable layers seeping into the excavation. The most popular support fluid is bentonite which is a largely montmorillonite clay. Polymer support fluids rely on a different mechanism to prevent seepage into the permeable soil layers present in the excavation and therefore in the support of the excavation itself. Polymers rely on high viscosity and significant viscous drag which is exerted on the soil grains, as well as the ability to form a membrane at the soil face, to prevent seepage into the permeable layers of soil. Research (Jefferis & Lam, 2013) conducted on polymers has indicated that there are more benefits in the use of polymers compared with the more widely used bentonite; in terms of economy, performance, and environmental cost.Aims and ObjectivesThe aim of the proposed doctoral research will be to aid and accelerate the transition between unsustainable bentonites to more efficient synthetic polymers. This will involve developing testing techniques for site technicians, design rules to guide application, and to develop the underpinning engineering science. It is important to develop new testing for in-situ circumstances due to the nature of the industry and the mechanics of the support fluid. The current testing procedures used on site are quick and easy to carry out but are inaccurate. Developing design rules for the use of the support fluid will ensure that this research will have a direct impact on industry. Developing design rules will be focused on how the fluid can be used most effectively (in terms of sustainability, cost, and ease of use) and how the use of the fluid may affect the specification of the built structure in the bore.Research MethodologyThe proposed research may be informed by the results of these studies although, following a limited review of recent literature, the approach to the research will be split into three strands: laboratory testing, field testing, and theoretical analysis.During the laboratory phase of the research the focus will be on developing knowledge of polymer behaviour and exploring the various effects polymers have on the surrounding soil and environment. It will be necessary to design and develop bespoke equipment to further understanding of the mechanics of the materials and behaviour exhibited in use.The approach during the field testing will take two different courses; one being to observe the way in which the material is routinely used and how the material behaves in practice, the other being to implement modifications to current practice, informed by the laboratory tests and supported by introduction of on site testing of materials in use.The key focus of the theoretical analysis part of this research will be the interpretation of experimental results to aid development of specifications for use in industry. This could involve controlling rates for mixing, pumping, pile drilling etc.Project TeamThe team involved in this research will consist of Daniel McNamara as the DPhil researcher, Dr Brian Sheil as the main supervisor, Professor Stephan Jefferis as the co-supervisor, and Chris Barker, of Arup, as the industrial supervisor of the project.This project falls within the EPSRC Engineering research areaReferencesJefferis, S., & Lam, C. (2013). Polymer support fluids: use and misuse of innovative fluids in geotechnical works. 18th International Conference on Soil Mechanics and Geotechnical Engineering (pp. 3219-3222). Presse des Ponts.