Stress-deformation predictions for the LG 4 main dam

The LG 4 dam, the second largest structure on the La Grande Complex of the James Bay hydroelectric development, is 125 m high, about 4 km long, and is composed of 19 × 106 m3 of fill materials.The design of the dam is characterised by (i) a zoned earth–rockfill section based on a judicious use of the limited quantities of various materials available, (ii) a 70 m high abutment in the river valley with a steep inclination of about 55°, and (iii) a 50 m high section of the dam with its axis curved in the downstream direction.Detailed stress-deformation analyses were carried out in the critical sections of the dam using finite element methods to verify any presence of arching and hydraulic fracturing potentials in the nonplastic till core. An interesting aspect of these analyses was the fact that the material properties were established based on laboratory testing as well as the observed deformation behaviour of the already completed 156 m high LG 2 main dam.The analyses have indicated that the design has adequate reserve of safety against hydraulic fracturing and arching. Nevertheless, the design sections and material placement requirements were optimised, where necessary, to ensure a satisfactory behaviour of the dam. The instrumentation design was also adapted to the findings of this study. Keywords: earth dam, steep abutment, stress-strain, hydraulic fracturing, arching.