3D analysis of the 174-m high Quxue asphalt-core rockfill dam in a narrow canyon

Abstract

The site for the high Quxue Dam has a narrow canyon with very steep abutments and complex geology in Sichuan Province, China. Various types of embankment and concrete dams were considered and an asphalt-core embankment dam (ACED), 174 m high, was selected. The asphalt core is a slender impervious element in an embankment dam and some concerns have been raised about the reliability and safety of the asphalt-core type of dams (ACEDs). This paper presents the case study of the highest asphalt core dam ever built and presents measured and numerical analyses of the core deformations. A 3D non-linear FE analysis has been performed for the Quxue Dam, and the results have been compared with those computed by a 2D analysis to study the effects of the narrow canyon. The computed results are compared with the monitoring data from dam construction and first impoundment. The maximum settlement measured inside the embankment during construction was only about 0.7 m due to the good basaltic rockfill used and the heavy compaction in layers of only 1.0 – 1.2 m thickness. The results of the 3D analysis agree well with the measured downstream displacements and the deflected shape of the thin asphalt core during impoundment, while the 2D analysis overpredicted the maximum displacement by a factor of about two. At a reservoir level 3 m below full supply level, the maximum measured downstream core displacement was only about 80 mm due to the stiff rockfill and the restraining effects of the abutments in the narrow valley.The rockfill behaviour was modelled by the constitutive relationship proposed by Duncan and Chang (1970). The rockfill parameters were determined by laboratory tests prior to construction and were adjusted to better match field observations of vertical settlements during construction. As asphalt concrete exhibits pronounced visco-elastoplastic behaviour, the material modelling was based on long-term triaxial creep tests on samples drilled out of the dam core. The performance monitoring and numerical analysis results for the record-high Quxue ACED document that the concerns expressed about the asphalt core safety and behaviour is not warranted. The asphalt core type of dam is suitable even for high ACEDs in narrow valleys with steep abutments.