Experimental techniques for earth and rockfill dams and their applications

The multifunctional large-scale triaxial experimental system invented by the author and his research team in Nanjing Hydraulic Research Institute (NHRI) is the earliest one in China. It can dynamically capture the volumetric strain during cyclic loadings. Using this system, rockfill materials in more than 70 worldwide earth-rock dams are tested, and a fruitful database is established. On this basis, the particle breakage during static and dynamic loadings as well as the influencing factors, the nonlinear variation of the strength and dilatancy indexes, the evolution of residual strains during dynamic loadings, the creep behaviors of rockfill materials and the liquefaction properties of sand-gravel materials are extensively explored. For the investigation of dynamic responses of high earth-rock dams, experimental techniques for centrifugal shaking table tests and the corresponding method for result interpretation are proposed and successfully applied in studying the failure mechanism of earth-core rockfill dams (ECRD) and concrete face rockfill dams (CFRD), and in verifying the effectiveness of reinforcement measures. The acceleration response and the residual deformation as well as the earthquake failure mechanism of earth-rock dams obtained by centrifugal shaking table tests are found in good agreement with the in-situ observations from Zipingpu CFRD and Bikou ECRD after great Wenchuan Earthquake. The use of a centrifuge effectively solves the problem that the stress within a conventional (ground) shaking table differs too much from that within the prototype, and the proposed experimental and analytical method makes the conditions that the stresses within the model and the prototype are approximately the same unnecessary. Therefore, the centrifugal shaking table can be used to investigate the behaviors of vast masses like high earth-rock dams in spite of the limitation of capacities of the involved equipments. For the breaching mechanism of earth-rock dams, experimental techniques and corresponding analysis method are established. A flow discharge control equipment is devised for the centrifugal model test system so as to maintain a stable transition between the normal and high gravity fields for water flows. Meanwhile, a specific model container for dam breaching experiments that integrates the measurement system with the model arrangement system organically is fabricated, and such an arrangement effectively eliminates the deficiency of using pipeline flowmeters outside the model container under large variation of debris flow discharge.Therefore, an accurate measurement of flood discharge in the whole breaching process is attained by utilizing this measurement system. The above achievements and their engineering applications provide a technological support for improving the level of both the disaster consequence assessment and the safety control of earth-rock dams.