Effects of installation and use of polymer support fluids on the load capacity of piles formed in low to medium permeability soils

Installing bored piles in collapsible soils or just drilling a deep hole requires the use of temporary casings or support fluids such as bentonite or polymers to stabilise the shaft. While the impact of these support fluids on the base and shaft resistance capacity of piles has been studied in published literature, such as (Fleming and Sliwinski, 1991; Lam et al., 2010), there is still limited knowledge about their effects on the lateral load capacity and deformation of piles. Currently codes of practice in Europe, the USA, and other regions do not have guidelines on the potential effects of support fluids on geotechnical performance of piled foundations.

The goal of the proposed research is to use laboratory model tests and numerical analysis to simulate different scenarios of piles installed with support fluids of different properties in soils of different properties. The deliverable objectives are to:

·        Assess how different pile installation methods and polymer support fluids affect the lateral load capacity of piled foundations in low to medium permeability soils.

·        Experimentally evaluate the strain distribution and deformation behaviour of piles under lateral loads, considering different support fluids and geometric ratios such as L/Ds (length-to-diameter ratio of the pile), Db/Hb (base diameter-to-height ratio of the pile base), and Db/Ds (base diameter-to-shaft diameter ratio).

·        Investigate the interaction between low to medium permeability soils and polymer support fluids, focusing on soil properties such as shear strength, permeability, and density, and their influence on the effectiveness of the support fluids.

·        Use three-dimensional (3D) finite element numerical simulations to model and analyse the behaviour of piles under lateral loads and develop guidelines and best practices for optimal pile installation and support fluid use based on experimental and simulation findings.

This research will use experimental and numerical methods to develop design recommendations for using different polymer types in piling. A wooden chamber will be filled with soft to firm soil. Piles of different sizes, made of sand-cement mortar with wire mesh reinforcement will be cast in holes bored in the soil, using bentonite/polymer fluids of variable properties. Dial gauges, strain gauges, and transducers will be installed in the piles. Some of the piles will be subjected to incremental lateral loads up to maximum resistance of the soil. Other piles will be subjected to incremental vertical loads to achieve settlement equivalent to 10% of pile diameter. Using finite element programs, simulations will be performed for the load-deformation response of the pile-soil system, for different support fluid properties. This will lead to an improved pile design methodology applicable for polymers and soils of different types.