NZSOLD ANCOLD Conference 2025 Christchurch
This technical note describes the design approach used for assessing and accommodating potential liquefaction impacts in foundation pumiceous soils beneath a 12 m high zoned earthfill urban flood detention dam in Rotorua, New Zealand. This technical note focuses on the use of geogrid reinforcement to limit potential embankment deformations and maintain acceptable performance of the embankment element following a large earthquake.
The geological model for the site consists of a sequence of volcanic ash and pumice deposits overlying lake sediments, with reworked volcanic soils as alluvium in the stream bed. The relatively high groundwater levels and discrete loose silt and sand layers/lenses beneath the dam were identified as potentially being susceptible to earthquake-induced liquefaction in both the OBE and SEE events, with the associated loss of foundation strength that could lead to excessive deformations in the embankment. The expected performance of the dam embankment in the design OBE and SEE events was substantially improved by adopting geogrid reinforcement within the embankment to reduce the predicted earthquake-induced lateral displacements.
