Open-face tunnelling effects on non-displacement piles in clay – part 1: centrifuge modelling techniques

Abstract

A research programme conducted at the University of Cambridge geotechnical centrifuge provided high-quality data on the interaction effects of open-faced tunnelling beneath non-displacement piles in clay. This paper presents details of the novel centrifuge package, including the reinforced composite piles used to measure loads during the centrifuge tests. Attention is particularly drawn to the importance of temperature compensation and the corresponding effect on the model piles. Results from maintained pile load tests conducted in the centrifuge are presented; through photogrammetric techniques, these are compared with data from pile load cells. The results, also compared with analytical t-z power-law modelling of the soil stress-strain behaviour based on triaxial tests, illustrate the importance of modelling the full history of both soil and piles prior to any subsequent tunnellinginduced loading. The experimental results of the simulated tunnelling tests on piles are presented and compared with simple analytical solutions in a companion paper.KEYWORDS: piles & piling; soil/structure interaction; tunnels & tunnelling INTRODUCTIONWith over half of humanity now living in urban areas, the demand on space and new transport infrastructure is unprecedented. The limited availability of surface space in major cities makes the demand for underground infrastructure, which often involves major tunnelling projects, increasingly more compelling. As a result, the construction of new underground railways, sewers and roadways is being undertaken in highly populated urban cities such as London, Amsterdam, Shanghai, Singapore and Hong Kong and many others using various tunnelling techniques.The stress changes from such tunnelling activities result in soil movements that propagate through the soil and are eventually observed as settlement and horizontal displacements at the ground surface. Significant research has gone into the prediction and observation of the effect of these ground movements on buildings supported by shallow foundations (e.g. Burland, 1997;Potts & Addenbrooke, 1997;Franzius et al., 2006;Farrell, 2010;Mair, 2011). However, there has been significantly less research on the effects of tunnelling-induced ground movements on piled foundations and the resulting interaction with the overlying structure(s) that these foundations support.Previous experimental modelling work investigating the effects of tunnelling on piles has mainly focused on the effects of tunnelling on driven piles (Loganathan et al., 2000;Jacobsz et al., 2004;Marshall & Mair, 2011). Driven piles are considered a 'worst-case' scenario, particularly in sands where the stress bulb at the pile toe is subjected to stress relief from tunnelling-induced ground movements that may result in pile failure, as shown by Marshall (2012). However, in order to reduce noise and vibration effects, the majority of piles constructed in major cities in recent years have been non-displacement (bored) piles, rather than driven piles. Field data from well-documented case ...

Tunnel Progression Effects to the Ground Surface and the Adjacent Pile

“…A plenty number of previous researchers focus their studies on the existing adjacent pile to the tunnel rather than the pile above the tunnel [7][10-14]. In doing so, the affected structural integrity of a foundation has been the main interest due to increased lateral loading and bending moment from the pile induced by tunnelling [15].…”

Centrifuge and Real-Time Hybrid Testing of Tunneling beneath Piles and Piled Buildings

“…Physical modeling using a geotechnical centrifuge has been used to investigate many of the mechanisms related to tunnel-pile foundation interaction (Jacobsz et al 2004;Lee and Chiang 2007;Loganathan et al 2000;Marshall and Mair 2011;Ng et al 2013Ng et al , 2014Williamson et al 2017a, b). Conventional centrifuge testing tends to break the problem down into discrete parts (e.g., isolated piles) and/or to use simplified superstructures (e.g., constant loads from the superstructure, rigid connections, and beams).…”