Real-time data coupling for hybrid testing in a geotechnical centrifuge

Abstract

Geotechnical centrifuge models necessarily involve simplifications compared to the full-scale scenario under investigation. In particular, structural systems (e.g. buildings) generally cannot be replicated such that complex full-scale characteristics are obtained. Hybrid testing offers the ability to combine capabilities from physical and numerical modelling to overcome some of the experimental limitations. In this paper, the development of a coupled centrifuge-numerical model (CCNM) pseudo-dynamic hybrid test for the study of tunnel–building interaction is presented. The methodology takes advantage of the relative merits of centrifuge tests (modelling soil behaviour and soil–pile interactions) and numerical simulations (modelling building deformations and load redistribution), with pile load and displacement data being passed in real time between the two model domains. To appropriately model the full-scale scenario, a challenging force-controlled system was developed (the first of its kind for hybrid testing in a geotechnical centrifuge). The CCNM application can accommodate simple frame analyses as well as more rigorous and non-linear simulations using Abaqus. A novel data-exchange method between Abaqus and LabView is presented, which provides a significant enhancement compared with similar hybrid test developments. Data are provided from preliminary tests which highlight the capabilities of the system to accurately model the tunnel–building interaction problem.

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

“…The coupled centrifuge-numerical modelling (CCNM) technique (Franza et al, 2016;Idinyang et al, 2018) was used to incorporate the effect of the steel frame structure in the centrifuge tests.…”

“…In the TPSI tests, the tunnel, soil and piles are simulated in the centrifuge model (geotechnical domain), and the structure is simulated in a numerical simulation (structural domain). The real-time data interface developed by Idinyang et al (2018) is used to share pile load ( ) and displacement ( ) data between the two domains; the subscripts denote the pile number (refer to Figure 1). The CCNM modelling process can be summarised as follows (illustrated in Figure 2, with numbered stages relating to details given here):…”

“…The central axis of the nearest pile was separated from the tunnel axis by a distance of = 75 mm; the pile tips were at a depth = 140 mm, giving a clear vertical distance to the depth of the tunnel crown of = 75 mm in all tunnelling tests, whereas was 150 mm in the pile jacking test. In the TPSI tests, labelled as test TPSI1, 2 and 3, the same geometric scenario as the TPGI test was considered, except that in these tests the load applied to the piles was adjusted during tunnel volume loss according to the load redistribution of a connected 5-story steel frame structure (accomplished using the CCNM technique (Idinyang et al, 2018;Franza and Marshall, 2018)). The three TPSI tests differed only in terms of final tunnel volume loss , : , =2.2 % for TPSI1, , =3.2 % for TPSI2, and , =2.8 % for TPSI3.…”

Assessment of the Posttunneling Safety Factor of Piles under Drained Soil Conditions

“…The outcomes presented in this paper were all based on tunnel interaction with single piles with constant loads in sands; the outcomes do not account for pile interaction within a group or load redistribution resulting from a connected pile system. Work is ongoing to extend the methods and data sets for clay as well as consider the effect of load redistribution due to a connected superstructure using the hybrid testing method presented in Idinyang et al (2018); . ,0 = Initial average shear stress along the pile shaft (prior to tunnel volume loss)…”

“…Furthermore, the tests presented here applied a constant pile load, which may not accurately reflect reality since a superstructure affected by tunneling induced displacements may be able to redistribute its loads to other foundation elements. This feature is an area of current research by the authors, who are using a novel hybrid testing technique to simulate the tunnel-pile domain in the centrifuge and a finite element model to simulate the superstructure domain, with pile load and displacement data being passed between the domains in order to achieve an accurate simulation of the global tunnel-soil-foundation-building system Idinyang et al, 2018).…”