Influence of free water on dynamic behavior of dam concrete under biaxial compression

The effect of saturation coupled with loading rate on the behavior of dam concrete was investigated under the biaxial compression. Dynamic biaxial compressive experiments on dam concrete cubes with an edge length of 250 mm (dry and saturated) were carried out using a large static and dynamic triaxial electro-hydraulic servo multiaxial testing system. The specimens were loaded in biaxial compressive stress states (with the stress ratios of 0:1, 0.25:1, 0.5:1, 0.75:1 and 1:1 respectively) under static and a series of dynamic loading velocities (with strain rates ranging from 10−5/s to 10−2/s). The ultimate strengths of dry and saturated concretes were found to increase with the increase of strain rate, while the damage pattern and ultimate strength are closely related to the magnitude of lateral pressure exerted on the specimen. In addition, the dynamic failure criterion is proposed to characterize both the effects of strain rate and water content on the ultimate strength of dam concrete under biaxial compressive stress states. By testing dry and saturated specimens, the effect of water content on concrete strength was also examined. The experimental results indicate that the static compressive strengths of saturated concrete are lower than those of concrete in dry state, but on the contrary the dynamic strengths of saturated concrete is higher than those of concrete in dry state. The strain rate effect on strength of saturated concrete is more significant than that of dry concrete in lateral confining pressure, indicating that the saturated concrete is more rate-sensitive than dry concrete. As explained through a basic mechanical analysis, this dissimilarity is mainly attributed to the inertia effect and the viscosity of pore-water inside the saturated concrete during fast (quasi-static or dynamic) loading.