Thesis: Carlos Lam

Doctor of Philosophy, St Catherine's College, University of Oxford, Trinity Term 2011

Properties and applications of polymer support fluids in geotechnical engineering

Synthetic polymer fluids have been used as an alternative to conventional bentonite slurries for the excavation of foundation elements over the last two decades. Thus far their use has excited polarised views in the industry -- some construction professionals avoid using them after hearing `horror stories' about past failures whereas others believe that they are the future of support fluids because of the many benefits that they can offer. This situation has been found to be mainly due to a lack of understanding of what polymers really are and their properties. To address this issue, the various polymer products currently available in the market have been categorised based on their intended functions, and the fundamental properties of some of them have been characterised. The research showed that significant difference exists between polymers even of the same chemical family. Based on a series of rheological experiments, it was found that the properties of polymer fluids are highly dependent on the governing shear rate, time, and a range of site dependent factors. The research also showed that the current procedure for the interpretation of viscosity data is incorrect. After an analysis of the properties of currently available polymers, the latter part of the thesis describes a field trial carried out at a site in Stratford, East London. The aims of the trial were twofold: to compare the performance between piles constructed using bentonite and polymer fluids, and to assess the effect of extended pile bore open time for pile bores supported by polymers. From the results, it was found that the polymer piles showed much stiffer load--settlement response than the bentonite pile, and that a pile bore open time of up to 26 h had no adverse effect on the pile performance. The load test results have been carefully back-analysed using a range of methods. It was found that, compared to their bentonite counterparts, polymer fluids can improve the interface shearing resistance with Thanet Sand and the shear modulus of the Lambeth clay.