The Use of Polymer Solutions for Deep Excavations: Lessons from Far Eastern Experience

Solutions of water-soluble polymers have been used to stabilise deep excavations such as pile bores and diaphragm wall trenches since the 1970s. When compared with conventional bentonite slurries, these engineered fluids are recognised as bringing a number of benefits including smaller site footprint, lower environmental impact and lower construction costs. However, despite the years of use too little has been published about their material properties and optimal methods of use so problems still occur. To promote best practice with these engineered fluids, this paper summarises the lessons that may be drawn from a number of published case histories of polymer use in the Far East. It is concluded from the review that the use of biodegradable polymers in deep excavations can be problematic unless a biocide is used. In contrast, synthetic polymers tend not to suffer from microbial degradation but do require the use of special pumping equipment to minimise shear degradation. In coarse soils both types of polymer fluid can show excessive fluid loss. This can be remedied by adding bentonite, superabsorbent gel particles or proprietary fines that are dispersible in polymer fluids. Finally, soft pile bases have been reported which can be linked to the use of low fluid viscosity coupled with long waiting times between end of excavation and concreting. This can be minimised by rigorous fluid and base cleaning. Overall, the case histories show that polymer fluids cannot be managed as if they were simply bentonite slurries. Their use requires different procedures which in turn require different skills and experience from a contractor. This paper concludes with an analysis of future challenges and opportunities with this innovative construction material.