Implications of grain crushing for tall dams

Sponsor: Start-up fund provided by CUBoulder, Stantec, Inc.

Role: PI

Objectives

Dams are getting taller than ever nowadays. This causes increasingly high stresses inside the dam, risking the breakage of the load bearing granular soils and consequently accelerating creep and pore clogging in the dam. This research theme explores the implications of grain breakage in extremely tall dams.

One specific area of focus is on rockfill water dams. Accurate prediction of the settlement of rockfill dams is hindered by several uncertainties: (a) rockfills used in dam construction are often provided by local, gravelly deposits, rock quarries or excavations that can have a variety of geological origins and grain sizes; (b) the internal stress of high dams can be as high as several megapascals, lasting for its entire service life, during which the time-dependent deformation of rockfills becomes relevant. Both grain size effect and time effect in rockfill mechanics are rooted in the fracture of individual rockfill particles. In a recent study, we leveraged the continuum breakage mechanics theory, fracture mechanics, and subcritical crack growth theories in explaining and modeling this phenomenon. The performance of this model is then evaluated through a case study on the 233m Shuibuya concrete faced rockfill dam (CFRD) (Hubei, China), currently the tallest CFRD in the world.

Another area of focus is on tailings dams. Tailing dams are constructed to impound the byproducts of mining operations and are often built using the coarser fraction of the tailings resulting from gravity separation processes. The high stresses anticipated at the bottom of tall tailings dams can lead to grain crushing, resulting in a reduction in the hydraulic conductivity and, ultimately, long-term performance issues if the water drains at a slower rate than required. Therefore, understanding the evolution of the hydromechanical behavior of the tailings is important for accurate evaluation of the margin of safety in designing tall tailings dams. In collaborating with Stantec, we experimentally studied and modeled the evolution of tailings sand under various vertical stress levels.

3D FE model of the Shuibuya CFRD.

Predicted degree of grain crushing in the dam due to gravity and water load.

Collaborators

Gang Ma, Ph.D., Wuhan University

Sheng Dai, Ph.D., Georgia Institute of Technology

Zygi Zurakowski, Stantec.

Publications

Singh, S., Zurakowski, Z., Dai, S., Zhang, Y. (2021) Effect of grain crushing on hydraulic conductivity of tailings sand. Journal of Geotechnical and Geoenvironmental Engineering 147(12), DOI: 10.1061/(ASCE)GT.1943-5606.0002667.

Kim, J., Zhang, Y., Seol, Y, Dai, S. (2019) Particle crushing in hydrate-bearing sands. Geomechanics for Energy and the Environment 23, 100133, DOI: 10.1016/j.gete.2019.100133.

Zhou, X., Ma, G., Zhang, Y. (2019). Grain size and time effect on the deformation of rockfill dams: a case study on the Shuibuya CFRD. GĂ©otechnique 69(7), 606-619, DOI: 10.1680/jgeot.17.P.299

Ma, G., Zhou, W., Zhang, Y., Wang, Q., Chang, X. (2017). Fractal behavior and shape characteristics of fragments produced by the impact of quasi-brittle spheres. Powder Technology 325, 498-509.

Ma, G., Zhang, Y., Zhou, W., Ng, T.T., Wang, Q., Chen, X. (2017). The effect of different fracture mechanisms on impact fragmentation of brittle heterogeneous solid. International Journal of Impact Engineering 113, 132-143.

Zhou, X., Zhang, Y., Ma, G. (2019). Deformation analysis of the 233 m Shuibuya rockfill dam using breakage mechanics. In Geo-Congress 2019, Philadelphia, PA.

Zhou, X., Ma, G., Zhang, Y. (2018). Settlement analysis of the Shuibuya rockfill dam using breakage mechanics. In 52th US Rock Mechanics/Geomechanics Symposium, Seattle, WA.

Zhang, Y.D., Park J.S., Gao S., Sonta A., Horin B., Buscarnera G. (2017) Effect of grain crushing and grain size on the evolution of water retention curves. In PanAm UNSAT, Dallas, TX.