Installation Effects of Non-Displacement Piles - A study of installation-induced soil displacements from drilled steel tube piles and cast-in-place piles

Abstract

In urban geotechnical design, understanding installation effects of pile foundations is essential, particularly in dense urban areas with challenging soil conditions such as those found in Gothenburg. This thesis explores the installation effects of two types of non-displacement piles; drilled steel tube piles and cast-in-place piles. For drilled steel tube piles, a qualitative interview study was conducted with indus try professionals, supported by numerical simulations in Plaxis 2D to assess the impact of soil volume loss through excessive washout. For cast-in-place piles, soil displacements generated by concrete pressure during casting was evaluated using the analytical cavity expansion method (CEM) and the shallow strain path method (SSPM), along with numerical modeling. Both linear elastic and plastic (Soft soil) constitutive models were used and evaluated for each pile type. Simulations of drilled steel tube piles demonstrated that excessive washout can no tably affect ground settlements. For cast-in-place piles, analytical and numerical models aligned well for both lateral and vertical deformations, depending on the chosen method. Simplified pile group simulations further indicated that significant ground displacements may occur even at considerable distances. Interviews con firmed that excessive washout is a known issue among contractors. Method selection should be project-specific, as no solution is universally superior. The critical role of the drill operator in minimizing installation effects was also highlighted. Diverging views on current contract formulations revealed uncertainty in responsibility alloca tion. Additionally, a tendency to prioritize faster production methods may elevate the risk of installation effects, which can be mitigated by setting limits on allowable ground displacements.