Centrifuge Study on the Influence of Tunnel Excavation on Piles in Sand

Abstract

Tunnelling induced ground movements can affect the equilibrium state of an existing pile, causing uneven settlement among pile groups and damage to connected structures. This paper presents results from five centrifuge tests aimed at evaluating the load redistribution mechanisms that occur within piles located close to tunnel excavation. Two main mechanisms are studied: firstly, those related to ground displacements and stress relief related to tunnelling; and secondly, those related to pile head load changes caused by connected superstructures (accomplished using a hybrid centrifuge-numerical modelling method). A novel fibre Bragg grating sensor system was used to measure shaft shear stresses along model piles. Results are used to quantify the relative impact that these two mechanisms have on pile load redistribution during tunnel volume loss. In addition, post-tunnelling pile loading tests were performed, with results indicating that tunnelling induced ground volumetric strains could influence the post-tunnelling loading response of piles.

Centrifuge application of fibre Bragg gratings: pile axial loads and wall bending moments

“…Note that, during centrifuge spin-up, uneven settlement between the pile and the surrounding soil mobilised some shaft resistance along the piles. Therefore, the initial shear stress prior to pile jacking is not zero; detailed spin-up effects on pile shaft resistance are discussed in Song and Marshall (2020b). Both piles show an increase in average shear stress with pile jacking.…”

“…Figure 10 shows the layout of the testing geometry for two pile jacking tests, referred to as PJ1 and PJ2. Note that the data from test PJ1 was also presented in Song and Marshall (2020b), where it was used within a study on the effect of tunnelling on the load redistribution of nearby piles connected to a framed building (applying the hybrid centrifuge-numerical testing approach from Idinyang et al (2018); Franza and Marshall (2018a)).…”

Tunnel–piled structure interaction: Numerical simulation of hybrid centrifuge tests

“…These tests were previously reported in Song and Marshall (2020b); readers can refer to that paper for a more in-depth description of the equipment and test methodology.…”

“…The approach accurately accounts for vertical pile head load redistribution during tunnel volume loss (which depends on the characteristics of the modelled building), updates the pile head loads applied in the centrifuge as the test progresses, and provides a high-fidelity simulation of the global tunnel-pile-structure interaction problem. Song and Marshall (2020b) used the CCNM application to model the interaction between tunnel volume loss and piles connected to a five-storey steel frame structure and demonstrated the significance of the structure effect on pile resistance.…”

“…In this paper, an advanced hypoplastic constitutive model is employed within the finite element analysis (FEA) software ABAQUS (Hibbitt, 2002) to simulate the tunnel-pile-structure interaction centrifuge tests reported by Song and Marshall (2020b), which used the CCNM application to account for the effect of building stiffness on pile head load redistribution during tunnel volume loss. The displacement controlled method was used in the numerical simulations to replicate the deformed shape of the eccentric rigid boundary mechanical (eRBM) model tunnel used in the centrifuge tests.…”