EXPLANATION AND ASSESSMENT OF GORDON DAM CRACK

摘要

The Gordon dam is a 140 m high, double curvature, arch dam set in a narrow gorge of the Gordon River in the south west of Tasmania. The dam has been in service for 25 years and impounds one of the Hydro Electric Corporation's two major storages. During the initial filling of Gordon, a number of cracks normal to the foundation were noticed on the downstream face of the concrete shell at the foundation contact. The main crack, which is approximately 20 m long, is in block J on the right abutment and runs normal to the foundation approximately 20 m from the base of the dam. Mapping and monitoring of this crack was carried out to better' understand the extent of the crack and its rate of growth. In the 1980's an attempt was made to model the crack using a finite element model, however this met with little success mainly due to the coarseness of the mesh. Modern finite element programs and increased computer power now provide the capability to construct more detailed finite element models. These modern tools provided the capabilities to better model Gordon dam and its crack. A detailed and refined 3-dimensional finite element model was constructed of Gordon dam and its foundations. This model was validated against measured deformations and stresses. Using this model of the dam, a better explanation of the formation of the crack has been developed. The model was also used to assess the effect on the safety of the dam if the crack were to continue to grow and, in effect, isolate the bottom of the dam from the rest of the structure. It was found that the redistribution of stresses, particularly in the horizontal arch direction, was small in magnitude. This makes it unlikely that the failure mechanism would alter from that of an arch dam without a crack. The dam is considered safe.