Innovative design methodology for secant pile walls

Abstract

Many infrastructure projects in New Zealand require deep excavations in unstable granular, soft or liquefiable soil below the water table. The use of secant piles to form temporary or permanent retaining walls supporting the ground during excavation and reducing ground water inflows is becoming very common in New Zealand urban projects. Secant pile walls can also be used as permanent structural foundation systems. Recent developments in drilling equipment and construction procedures allow cost-effective construction of secant pile walls to tight tolerances. Optimal design of the secant pile walls increases efficiency, reduces construction costs and carbon footprint. Simplified secant pile wall design methods do not adequately capture the complex stress-strain state of secant pile walls and cannot be used for design optimisation. An innovative design methodology for secant pile walls has been developed and applied on a major wastewater project in Wellington. Non-linear steel, concrete and soil models were used in a 3D finite element analysis of the secant pile walls under static and seismic loads. The design methodology, material models and results of the 3D analysis as well as design optimisation process are described.