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Permanent ground deformation is arguably the most severe hazard for continuous buried pipelines. This paper presents results from two pairs of centrifuge tests designed to investigate the differences in behavior of buried high-density polyethylene pipelines subjected to normal and strike-slip faulting. The tests results show that, as expected, the pipeline behavior is asymmetric under normal faulting and symmetric under strike-slip faulting. In the case of strike-slip faulting, the soil–pipe interaction pressure distribution is symmetric with respect to the fault. However, in the case of normal faulting, there is a pressure concentration close to the fault trace on the up-thrown side, with much lower soil–pipe interaction pressures at other locations on the pipe. The soil–pipe interaction force versus deformation relationship (i.e., the p–y relationship) was obtained based on the experimental data. The p–y relationships for both the strike-slip and normal faulting cases were also compared with the relationships defined within the American Society of Civil Engineers (ASCE) guidelines. It was found that, for the case of strike-slip faulting, the experimental p–y relationship is generally consistent with the ASCE guidelines. In contrast, the experimental p–y relationship is much softer than that defined by the ASCE guidelines for the normal faulting scenario.

Dynamic soil–structure interaction analyses were carried out for the seismic retrofit design of the immersed George Massey Tunnel, both to predict and study soil liquefaction and related tunnel movements and to design ground improvement. The proposed ground improvement included ground densification using vibroreplacement stone columns along both sides of the tunnel and seismic gravel drains adjacent to the outer edge of the densified zones. The den sification and drainage were proposed to locally mitigate soil liquefaction and reduce displacements of the tunnel to tolerable levels. Centrifuge model tests with base shaking to simulate earthquake effects were conducted to verify and calibrate the numerical models. This included simulating the effects of ground densification and drainage on reme diating tunnel movements. This paper presents the principal results from the dynamic analyses, the centrifuge model design and testing procedure, the class A predictions of the centrifuge tests, and discussions of the centrifuge test results and numerical model calibrations.Key words: immersed tunnel, seismic retrofit, soil liquefaction, design verification, centrifuge testing, numerical calibration.

The prediction of liquefaction and resulting displacements is a major concern for earth structures located in regions of moderate to high seismicity. Conventional procedures used to assess liquefaction commonly predict the triggering of liquefaction to depths of 50 m or more. Remediation to prevent or curtail liquefaction at these depths can be very expensive. Field experience during past earthquakes indicates that liquefaction has mainly occurred at depths less than about 15 m, and some recent dynamic centrifuge model testing initially appeared to confirm a depth or confining-stress limitation on the occurrence of liquefaction. Such a limitation on liquefaction could greatly reduce remediation costs. In this paper an effective stress numerical modeling procedure is used to assess these centrifuge tests. The results indicate that a lack of complete saturation and densification at depth arising from the application of the high-acceleration field are largely responsible for the apparent limitation on liquefaction at depth observed in some centrifuge tests.Key words: liquefaction, dynamic centrifuge modeling, numerical modeling, depth limitation.