GeoStudio Sets the Surcharge: Centrifuge Testing of Earthquake Swarm Effects on Dam Foundations Sponsored

Earthquake swarms, clusters of moderate-to-strong seismic events occurring in quick succession, are a growing concern for large dams, whose foundations can suffer cumulative stiffness degradation and progressively rising pore water pressure with each successive shock. A research team from Zhejiang University's College of Civil Engineering and Architecture and its Center for Hypergravity Experimental and Interdisciplinary Research designed a centrifuge testing program to find out exactly how a layered clayey sand foundation responds when repeated aftershocks follow a mainshock, and how the presence of a large dam changes that response.

To make the physical model faithfully represent a real gate dam sitting on the foundation, the team needed the centrifuge model to reproduce the same contact stress distribution the actual dam would impose on its foundation soil. Rather than guess at an equivalent surcharge, the researchers used GeoStudio to compute the foundation contact pressure of the prototype gate dam directly. That calculation showed the dam imposes roughly 375.3 kPa under its centerline and 1189.7 kPa under its edge, numbers the team then used to size a rectangular steel block (400 × 310 × 106.5 mm) placed on top of the centrifuge model's foundation layer, ensuring the stress state inside the small-scale model genuinely matched the stress state beneath the full-size dam.

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With that surcharge block calibrated by the GeoStudio analysis, the team built two 50g centrifuge models, one with the steel block in place, one without, instrumented with accelerometers, pore-pressure transducers, and laser displacement sensors at multiple depths within both the upper and lower soil layers. After a lengthy consolidation phase under centrifugal acceleration, the models were subjected to a sequence of scaled earthquake records: a 0.3g mainshock followed by two successive aftershocks, reproducing the kind of clustered seismicity the study set out to investigate.

The results show that the un-surcharged "free ground" model liquefied readily, accompanied by significant soil dilation. At the same time, consecutive strong-motion events drove a continuous accumulation and escalation of excess pore pressure within the lower clayey layer. Interestingly, the surcharge block representing the dam's weight appeared to suppress pore pressure accumulation during shaking and speed up dissipation afterward, but consecutive seismic events still accelerated the generation of peak excess pore pressure in the foundation overall. Because the surcharge itself was sized using a GeoStudio stress analysis, the researchers can be confident that these observed suppression and acceleration effects reflect the actual loading condition beneath a real dam, rather than an arbitrary approximation, giving the findings direct relevance to seismic design guidance for dam foundations in earthquake-swarm-prone regions.

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