Influence of pile installation techniques on ground heave in clays M.D. Larisch 1, 2 , D.J. Williams 1 and A. Scheuermann 1 1 Geotechnical Engineering Centre, School of Civil Engineering, The University of Queensland, Brisbane QLD 4072, Australia 2 Piling Contractors Pty Ltd, PO Box 346, Lawnton Qld 4501, Australia ABSTRACT The installation of driven displacement piles in clays creates vertical soil movement that is commonly known as heave. Numerous researchers have developed theoretical models to calculate the expected volume of soil heave due to pile driving.Screw auger displacement piles are a relatively new and, due to their cost-effectiveness, increasingly popular piling technique that has been used successfully in Australia and New Zealand over the past two decades. Soil heave in clays during the installation of screw auger displacement piles has not been investigated in detail, even though the effects are commonly known throughout the industry. The authors introduce some of the most popular general soil heave theories and compare their validity to screw auger displacement pile applications. The paper presents the measured ground heave results of three screw auger displacement piles during a field test in hard clay and correlates the results with the well-established SSPM heave theory.The installation process of driven and screw auger displacement piles is fundamentally different and the paper investigates and discusses whether or not common heave models for driven piles can be applied to screw auger displacement piles where the soil at the auger tip is physically cut, sheared and disturbed by the action of the auger. Keywords: clay, driven piles, heave, pile installation, screw auger displacement piles, soil movement 1 INTRODUCTION The installation of closed end driven and drilled displacement piles in clay formations results in horizontal and vertical soil movements of the ground surface. The soilarounda pilethat is installed using such displacement techniques, tend to move upwards during the installation process, because this direction is the only one that is unrestrained.Thisphenomenon is known as ground heave and has been investigated by numerous authors researching this topicover the last 40 years (Adams and Hanna 1971, Hagerty and Peck 1971). Whereas closed end driven piles have been successfully used worldwide for centuries as structural elements, drilled displacement piles are a relatively new technology that has gained increased popularity over the past two decades. The system was invented in Europe in the 1990s and is based on the installation of a purpose-built displacement tool (typically 360 to 450 mm in diameter), which ispushed and rotated into the groundby hydraulic piling rigs, causing soil displacement. Once the design depth is reached the hollow stem of the displacement tool is used to place concrete under pressure to form the pile shaft.The process is described in detail byBottiau et al. (1998). 2 GROUND HEAVE DURING THE INSTALLATION OF DRIVEN CAST IN SITUDISPLACEMENT PILES Ground heave refers to the vertical soil movement at the ground surface surrounding a pile and may lead to the uplift of neighbouring pilesthat have already been installed (Gue, 1984). Healy et al. (1981) concluded that ground heave andupliftas a result of pile driving can cause several problems which include but are not limited to: (i) squeezing, necking or cracking of the piles, (ii) pile shaft lifting from its base; (iii) loss of load capacity in end-bearing, (iv) the separation of pile segments or units due to cracking; and (v) additional tensile forces on pile joints for pre-fabricated piles. However, while the damage caused by ground heave is often permanent, ground heave itself can be a temporary phenomenon. An investigation conducted by Cummings, Kerkhoff, and Peck (1950) indicated that ground heave of a magnitude of 330mm at the centre of a group of timber piles driven to