Abstract: Conventional internal settlement monitoring instruments are difficult to meet the requirements of a 300-meter-high rockfill dam in terms of water-pressure resistance, high accuracy, large measurement range, and digital intelligence. To address the technical challenge, this study improves the traditional flexible inclinometer in the measurement principle and performance, and develops a high-accuracy method for measuring distributed internal deformation in high rockfill dams based on a flexible intelligent displacement meter. We first discuss its system configuration and installation scheme, and then derive its measurement principle, incorporating correction methods for the systematic errors induced by its flexible hose bending and stretching and the gauge point sliding. For this novel device, laboratory tests are conducted to verify its water-pressure resistance, angular measurement accuracy, and displacement measurement accuracy. The method achieved a success in its application to the Shuangjiangkou central core rockfill dam in Aba Prefecture, Sichuan, China. The results show the device withstands water pressure up to 4.5 MPa and achieves an angular accuracy higher than 0.005°. Over a 50 m long gauge line, the elevation profiles measured agree well with the electronic level measurements across the full measurement range, both fully consistent in deformation trends. At elevation 2370 m of this dam, two flexible intelligent displacement meters are installed along the cross-river direction, for mutual verification in the overlapping zone. By the measurements, MAE is in the range of 5.74 - 12.96 mm, RMSE in 6.75 - 13.76 mm, and MAPE does not exceed 2%, indicating negligible relative deviation between the two meters. Further comparison with three adjacent electromagnetic settlement rings confirms both following consistent deformation trends. This study demonstrates that the deformation measurement method based on the flexible intelligent displacement meter is an effective monitoring of the internal settlement in high rockfill dams, and it represents a distributed deformation monitoring technology with promising application prospect.

Key words: rockfill dam, settlement, deformation, triaxial accelerometer, error correction